We have studied the influence of the geometrical interaction of different detectors with the impinging optical/laser received beam for a wide range of laser sensing applications. Although different techniques apply, it is found that similar aspects of geometrical physics plays a role in direct detection of a range-resolved large M2 OPO atmospheric Lidar, heterodyne multi-detector reception of atmospheric turbulence distorted coherent lidar type laser sensing, and the distribution and summation of laser induced fluorescence signals after being spectrally resolved with a spectrometer and detected by a column summing CCD detector. In each of these systems, the focused received light is spatially and spectrally distributed due to several factors including Fieldof- View considerations, laser beam quality/divergence, multi-detector aspects, and hardware and software summation (coherent and non-coherent) of multi-element or spatially integrated signals. This invited talk will present some of our recent results in these areas and show the similarities in tho detector spatial and temporal summation techniques of these different laser sensing systems.

We applied the laser-induced fluorescence (LIF) method to the monitoring of plant disease caused by environmental changes. An LIF spectrum measurement system and an LIF lifetime measurement system were developed for this purpose. The former one was constructed with a 6 ns, 355-nm Nd: YAG laser and a multiwavelength spectroscopic detection system. The later one was constructed with a 300 fs, 660-nm laser and a streak scope with a time resolution of 25 ps. Morning glory and Zelkova were prepared to investigate disease process monitoring by the LIF measurement system. The LIF spectra of the stressed leaves showed that the spectral intensities at 460 nm and 530 nm rapidly increased for 3 hours and then decreased for 20 hours, while the spectra at 685 nm and 740 nm decreasing constantly. In the LIF lifetime measurement, the chlorophyll fluorescence lifetime of Zelkova leaves was measured at 685 nm and 740 nm. It was found that the lifetime was composed of a fast component of about 100 ps and a slow one of about 600 ps and after UV-B irradiation the lifetime varied sinusoidally among the lifetime of normal leaves. Through these experiments the performance of the systems was checked and their potential for plant disease process monitoring was confirmed.

Various kinds of nonlinear Raman spectroscopy, such as coherent anti-Stokes Raman spectroscopy (CARS), stimulated Raman gain spectroscopy (SRGS), photo-acoustic Raman spectroscopy (PARS), and thermal-lens Raman spectroscopy (TLRS), can be applied for the detection of molecules in the atmosphere. In traditional nonlinear Raman spectroscopy, two lasers whose frequency difference was tuned to the Raman shift frequency had to be prepared. We proposed a new configuration using a Nd:YAG laser and a Raman shifter. The Raman shifter contained the same kind of gas to be measured, so that efficient Raman-shifted beam was automatically generated in this simple configuration. We demonstrated sensitive detection of H2 and CH4 in the atmosphere by various kinds of nonlinear Raman spectroscopy as mentioned above. The detection limit was approximately 1-30 ppm level in every method using a sample gas cell. In the case of SRGS, remote sensing is possible, and the detection sensitivity can be increased using long optical pass as in the absorption spectroscopy, because the signal is obtained by a coherent light beam and there is no limitation caused by phase-matching condition. Using the Mie scattering in the atmosphere as a distributed mirror, a new type of nonlinear Raman lidar can be constructed. In this paper, we discussed on the feasibility of long-pass and lidar measurement for the detection of CH4, H2 and CO2 by SRGS using a pulsed Nd:YAG laser.

High-power, femtosecond light filaments, also termed light strings, are experimentally observed to propagate over distances which substantially exceed the diffraction lengths that would correspond to their transverse dimensions. Thus, they provide a way to deliver high powers of focused light over long distance, and may potentially serve as light probes in remote sensing. We concentrate on a theoretical understanding of the underlying physics. In this talk, we review the results of our computer simulations providing insight into the rich spatio-temporal dynamics of this interesting phenomenon.

Most of lidar systems are being manually operated on site, therefore, a frequency of observations is limited due to a manpower etc if the lidar site is geographically far away from a laboratory. In such a case, an unattended automatic lidar system or a remote controllable one is expected as for increasing the frequencies. On the other hand, as well known, a computer is linked to the other through the Internet, and remotely operated each other. We have proposed the Internet LIdar System (named ILIS) as the unattended operational lidar. A concept of the ILIS is controllable through the Internet, anytime and anywhere. The ILIS proposed here has been successfully operating every night without any difficulty of the geographical distance of 1,000km.

The design of an unusually compact and rugged backscatter lidar system is described in detail. This lidar system, called AROL- 2, was designed for routine monitoring of the boundary layer, tropospheric aerosols, and clouds. In order to support the maximum possible range of observations with minimum investment of labor, the system was specifically designed to be mobile, rugged, and easy to set up and deploy. The lidar system is housed in a weatherproof enclosure, in order to allow operation at sites without sophisticated laboratory facilities. In order to provide maximum flexibiliity and sensitivity in a relatively small package, the lidar system is equipped with both analog and photon counting channels, with two polarization channels to allow for quantitative measurementsof depolarization behavior. Substantial effort has been expended to produce a lidar that is flexible, easy to use, and robust in the field environment.

Results of two lidar measurement campaigns are presented, HOLO-1 (Utah, March 1999) and HOLO-2 (New Hampshire, June 1999). These tests demonstrate the ability of lidars utilizing holographic optical elements (HOEs) to determine tropospheric wind velocity and direction at cloud altitude. Several instruments were employed. HOLO-1 used the 1.064 mm transmission-HOE lidar (HARLIE, Goddard Space Flight Center), a zenith-staring 532 nm lidar (AROL-2, Utah State University), and a wide-field video camera (SkyCam) for imagery of clouds overhead. HOLO-2 included these instruments plus the 532 nm reflection-HOE lidar (PHASERS, St. Anselm College). HARLIE and PHASERS scan the sky at constant cone angles of 45° and 42° from normal, respectively. The progress of clouds and entire cloud fields across the sky is tracked by the repetitive conical scans of the HOE lidars. AROL-2 provides the altitude information enabling the SkyCam cloud images to be analyzed for independent data on cloud motion. Data from the HOE lidars are reduced by means of correlations, visualization by animation techniques, and kinematic diagrams of cloud feature motion. Excellent agreement is observed between the HOE lidar results and those obtained with video imagery and lidar ranging.

Solid-state 2-?m laser has been receiving considerable interest because of its eye-safe property and efficient diode pump operation. It has potential for multiple lidar applications to detect water vapor, carbon dioxide and winds. In this paper, we describe a 2-?m double pulsed Ho:Tm:YLF laser and end-pumped amplifier system. A comprehensive theoretical model has been developed to aid the design and optimization of the laser performance. In a single Q-switched pulse operation, the residual energy stored in the Tm atoms will be wasted. However, in a double pulses operation mode, the residual energy stored in the Tm atoms will repopulate the Ho atoms that were depleted by the extraction ofthe first Q-switched pulse. Thus, the Tm sensitized Ho:YLF laser provides a unique advantage in applications that require double pulse operation, such as DIfferential Absorption Lidar (DIAL). A total output energy of 146 nil per pulse pair under Q-switch operation is achieved with as high as 4.8 % optical to optical efficiency. Compared to a single pulse laser, 70% higher laser efficiency is realized. To obtain high energy while maintaining the high beam quality, a master-oscillator-power-amplifier 2-tim system is designed. We developed an end-pumped Ho:Tm:YLF disk amplifier. This amplifier uses two diode arrays as pump source. A non-imaging lens duct is used to couple the radiation from the laser diode arrays to the laser disk. Preliminary result shows that the efficiency of this laser can be as high as 3 %, a factor of three increases over side-pump configuration. This high energy, highly efficient and high beam quality laser is a promising candidate for use in an efficient, multiple lidar applications.

An innovative approach to obtaining high energy at 946 nm has yielded 101 mJ of laser energy with an optical-to-optical slope efficiency of 24.5%. A single gain module resonator was evaluated, yielding a maximum output energy of 50 mJ. In order to obtain higher energy a second gain module was incorporated into the resonator. This innovative approach produced unsurpassed output energy of 101 mJ. This is of utmost importance since it demonstrates that the laser output energy scales directly with the number of gain modules. Therefore, higher energies can be realized by simply increasing the number of gain modules within the laser oscillator. The laser resonator incorporates two gain modules into a folded “M-shaped” resonator, allowing a quadruple pass gain within each rod. Each of these modules consists of a diode (stack of 30 microlensed 100 Watt diode array bars, each with its own fiber lens) end-pumping a Nd:YAG laser rod. The diode output is collected by a lens duct, which focuses the energy into a 2 mm diameter flat to flat octagonal pump area of the laser crystal. Special coatings have been developed to mitigate energy storage problems, including parasitic lasing and amplified spontaneous emission (ASE), and encourage the resonator to operate at the lower gain transition at 946 nm.

A coherent Doppler lidar is a useful sensor for wind velocity detection in clear air condition. A stable single frequency and relatively long Q-switched pulse width (~200 nsec order) in eye-safe wavelength range (>1.4 ?m) is required for a composed pulsed laser. For these requirements, we have developed an injection-seeded diode-pumped Q-switched Er,Yb:glass laser which oscillates at 1.54 ?m. The maximum laser output energy of 10.9 mJ and the pulse width of 228 nsec were obtained. A stability of the pulsed laser output frequency was less than +/-1.9 MHz standard deviation from the seeded light frequency.

Advances in coherent lidar using eyesafe solid state lasers in recent years have driven the development of increasingly compact, high performance single frequency CW lasers for use as master oscillator and local oscillator sources. In addition to highly stable single-frequency operation for coherent detection, many applications require agile frequency tuning capability. Examples include space-based coherent lidar where the local oscillator must be tunable in order to compensate for the fast platform motion. For a 45 degree conical scan about nadir the 7.5 km/s platform velocity introduces a ± 5.3 GHz Doppler shift. We have recently developed a Tm;Ho:YLF master oscillator producing over 50mW of single frequency power that can quickly tune over 25 GHz in frequency using a PZT. Over 50 GHz of continuous mode-hop-free single frequency tuning has been demonstrated by temperature tuning. In this paper we review the status of master/local oscillator work at CTI. We also describe the application of this 2.05 ?m laser to column content measurements of atmospheric CO2 and water vapor using a direct detection colunm content DIAL technique.

New submount technology is essential for the development of conductively cooled high power diode laser. The simulation and experimental results indicate that thermal conductivity of submount for high power laser-diode must be at least 600 W/mlk or higher for stable operation. We have simulated several theoretical thermal model based on new submount designs and characterized high power diode lasers to determine temperature effects on the performances of laser diodes. The characterization system measures the beam power, output beam profile, temperature distribution, and spectroscopic property ofhigh power diode laser. The characterization system is composed of four main parts: an infrared imaging camera, a CCD camera, a monochromator, and a power meter. Thermal characteristics of two commercial-grade CW 20-W diode laser bars with open heat-sink type were determined with respect to the line shift of emission spectra and beam power stability. The center wavelength of laser emission has a tendency to shift toward longer wavelength as the driving current and heat sink temperature are increased. The increase of heat sink temperature decreases the output power of the laser bar too. Such results lay the guidelines for the design of new submount for high power laser-diodes.

We report on fmdings from ongoing polarization lidar research at the University of Utah Facility for Atmospheric Remote Sensing (FARS). This facility was established in 1987, and the current total of lidar and radiometric measurements is ~2,9OO-h. Research at FARS has been applied to the climatological investigation of cirrus cloud properties for basic research and satellite measurement validation (currently in its 1 3th year), and studies of contrails, mixed phase clouds, and volcanic and Asian dust aerosols. Among the techniques utilized for monitoring cloud and aerosol properties are triple-wavelength linear depolarization measurements, and high (1 .5-rn by 10-Hz) resolution scanning observations. The usefulness of extended time lidar studies for atmospheric and climate research is illustrated.

Asian dust have been measured by Multiwavelength lidar which supplied with three wavelengths (355, 532 and 1064 nm) laser and multimode receiver system. The system provides three modes of receiving system of Aerosol (355, 532 and 1064 nm), Raman (387, 408 and 355 nm) and Polarization (532 am) measurements. Six cases of Asian dust profiles from 5 km upto 12 km are achieved in spring of 2000. As the results, we can see the backscattering ratio of aerosol and Asian dust shows similar value that is in the range of 1.2 to 3, but the values of depolarization ratio is large that over 15% of Asian dust than below 10% of aerosol. Also, the concentration of large particle size over O.7O7tm is increased when in cases of Asian dust.

A multi-wavelength Mie lidar is a powerful tool to investigate the optical properties of aerosol particles along with their vertical profile information. In the usual analysis with the Fernald method, however, it is required to assume both the lidar ratio S1 and the extinction coefficients at the far end boundary. For a multi-wavelength lidar, appropriate choices of these parameters are indispensable to derive consistent profiles from the actual data. In this work, we propose two algorithms for the analysis of four-wavelength lidar data. The first algorithm is more comprehensive in that it adopts the direct fitting of the lidar A-scopes to the theoretical curves that are based on a look-up table: the table is pre-calculated for various combinations of the extinction coefficient, S1 parameter, complex refractive index, and aerosol size distribution. As a result, the vertical profiles of these parameters are determined along with the extinction profile. The second approach is a pragmatic one, and it relies on the sun photometer data simultaneously measured with the lidar data. By assuming a constant S1 value for each wavelength in the lower troposphere, a consistent set of S1 is determined by fitting the observed profiles to reference profiles that are relevant to the aerosol optical thicknesses from the sun photometer measurement.

The climatology of tropospheric clouds and aerosol layer are studied with the results of observation by Compact Mie- scattering Lidar (CML) located at Tsukuba, Japan. The operation of CML is fully automated and the data have been collected constantly every 15 minutes regardless of weather conditions. Therefore the results of the observation by CML are devoted to statistical analyses of characteristics of aerosols and clouds. Range-corrected signal intensity from the zenith during June 1996 and August 2000 was analyzed to detect the cloud base and the top of aerosol layer. Multi-modal distribution of clouds were detected and the annual and year-to-year variation of them were confirmed. Though the distribution of the top of aerosol layer also indicated temporal variations, the characteristics were little complicated and general tendency was obscure. Backscattering coefficients in the lower troposphere were also inferred using Fernald's method when there was no cloud in the lower layer. The annual and diurnal variations were examined and characteristics of profiles of backscattering coefficients were dependent on the seasons.

Long-term global radiation programs, such as AERONET and BSRN, have shown success in monitoring column averaged cloud and aerosol optical properties. Little attention has been focused on global measurements of vertically resolved optical properties. Lidar systems are the preferred instrument for such measurements. However, global usage of lidar systems has not been achieved because of limits imposed by older systems that were large, expensive, and logistically difficult to use in the field. Small, eye-safe, and autonomous lidar systems are now currently available and overcome problems associated with older systems. The first such lidar to be developed is the Micro-pulse lidar System (MPL). The MPL has proven to be useful in the field because it can be automated, runs continuously (day and night), is eye-safe, can easily be transported and set up, and has a small field-of-view which removes multiple scattering concerns. We have developed successful protocols to operate and calibrate MPL systems. We have also developed a data analysis algorithm that produces data products such as cloud and aerosol layer heights, optical depths, extinction profiles, and the extinction-backscatter ratio. The algorithm minimizes the use of a priori assumptions and also produces error bars for all data products. Here we present an overview of our MPL protocols and data analysis techniques. We also discuss the ongoing construction of a global MPL network in conjunction with the AERONET program. Finally, we present some early results from the MPL network.

On the windward side of Oahu, a multi-wavelength Mie-Rayleigh (MR) scanning lidar is used on a regular basis for measuring aerosol attenuation in the marine boundaiy layer. The lidar data are being used for investigathg dynamic effects of marine aerosol fields on electro-optical (EO) properties. The lidar has been operated mostly at 532 and 1064 nm, and recently at 355 nm. We have observed that the vertical aerosol distribution can be very non-uniform. Under certain atmospheric conditions, ascending and descending streaks of aerosols with high extinction (2x 1O-4 per meter) have been observed, indicating that both the surface and cloud drizzle effects are important. Horizontal lidar scans at 6 meters above the sea surface indicate that aerosol is fairly uniform on a large scale but can exhibit significant variability on small scales particularly close to protruding reefs and shorelines. Above the reefthe enhanced aerosol fields have been observed to rise as high as 100 meters. As expected there is a strong correlation between wind speed and sea salt extinction values. The temporal and spatial distribution ofthese aerosol fields and their dependence meteorological parameters and wave height are discussed.

Lidars are ideal for mapping the spatial distribution ofaerosol concentrations, however efforts to convertthe lidar measurements into estimates of the aerosol extinction or scattering coefficient are usually complicated. The difficulties arise from the uncertainty in the aerosol backscatter-to-extinction ratio and the lidar calibration. In marine conditions with little absorption, the aerosol backscatter-to-extinction ratio is identical to the aerosol phase function/4? at 1 80 degrees (backscatter) . Uncertainty in the lidar calibration is another source ofuncertainty, which can change with time depending on the state ofthe optics (clean or dirty). Here we investigate several techniques to obtain calibrated aerosol extinction coefficient values. The first approach uses horizontal lidar measurements over the open ocean where the atmosphere is horizontally homogeneous. The lidar calibration or aerosol phase function is adjusted until the derived aerosol extinction coefficients are flat with distance. Modeling shows that this provides correct aerosol extinction values. A second approach uses a target to reflect the lidar beam at different distances. The aerosol extinction is derived from the differential transmission measurements. As an independent measurement, the aerosol phase function and scattering coefficients can be measured with a polar nephelometer.

The altitude profile of the effective radius, reff, of atmospheric boundary layer aerosols was retrieved from simultaneous twowavelength lidar measurement near Manila Bay. The effective radius was retrieved using a simple method that makes use of the angstrom coefficient, ?, obtained from the extinction coefficients at the two wavelengths. The altitude profiles of the extinction coefficients at 532-nm and 1064-nm lidar wavelengths were obtained using Femald's inversion algorithm combined with Klett's boundary value algoritlun. used to obtain the aerosol extinction coefficient at the reference height. Assuming a lognonnal size distribution. with a geometric standard deviation of 1 .54, for atmospheric boundary layer aerosols. and a constant refractive index of 1.45 - Oi, the angstrom coefficient is determined at different mode radius, rg, using Mie Scattering Theory. A curve fitting analysis using the method-of-least-squares is done on the theoretical value of ? to obtain a sixth-order polynomial equation that gives the dependence of ? with rg. The altitude profile of reff is retrieved by using the measured value of ? into the equation. This method was applied to actual lidar experiments and the effective radius of the atmospheric boundary layer aerosols was observed to vary between 0.26 ?m to 0.29 ?m within the layer.

We present a new method of the rotational Raman lidar using an absorption cell of metallic vapor. The conventional rotational Raman lidar can hardly measure the temperature profiles in the atmosphere containing a lot of aerosol particles like in the lower troposphere. In this paper, it is shown by the computer simulation that the aerosol scattering contamination disturbing the measurement can be easily eliminated by using a metallic vapor filter in addition to the interference filters. Moreover, the interference filters of which the characteristics affect decisively the measurement accuracy can be designed more suitably. We design and fabricate the lidar system with a Na vapor cell and a narrowband dye laser to prove the usefulness of this method experimentally.

Vertical profiles of aerosols are observed in Jakarta, Indonesia with a Mie scattering lidar network system. It is consisting of three lidars located in the coastal, central, and inland areas. The structure of the planetary boundary layer was observed during dry season and wet season from 1998 to 2000. Radiometer measurement was performed in Jakarta in a period and we used this data in analyzing lidar data. In comparison, the boundary layer and their structure were different in daytime and nighttime. We found also different structure between dry and wet season. In some periods in dry season, the diurnal variation of the boundary layer structures were clearly observed. The mixed layer sometimes reach to maximum of approximately 2.5 km in thytime. The sea-land breeze circulation was observed in this observation. Low concentration of aerosol was brought by a sea breeze, and a layer of aerosols was formed at the top of the boundary layer by the reverse flow. In wet season, the boundary layer was not clearly observed. Aerosol distribution was complicated and also observed above the boundary layer at altitudes of 2 to 5 km. While there were much cloud in altitude of 5 to 8 km. mixed layers were still lower below 1 km The mixed layer height have close relationship to the air pollution condition.

As lidar technology is able to provide fast data collection at a resolution of meters in an atmospheric volume, it is imperative to promote a modeling counterpart of the lidar capability. This paper describes an integrated capability based on data from a scanning water vapor lidar and a high-resoiution hydrodynamic model (HIGRAD) equipped with a visualization routine (VIEWER) that simulates the lidar scanning. The purpose is to better understand the spatial and temporal representativeness of the lidar measurements and, in turn, to extend their utility in studying turbulence fields in the atmospheric boundary layer. Raman lidar water vapor data collected over the Pacific warm pool and the simulations with the HIGRAD code are used for identifying the underlying physics and potential aliasing effects of spatially resolved lidar measurements. This capability also helps improve the trade-offbetween spatial-temporal resolution and coverage ofthe lidar measurements.

Laser multiple scattering phenomena occurring inside a cloud were experimentally confirmed by showing the spread of the scattered laser light as a two-dimensional spatial distribution image. By changing the gate delay time of a CCD camera, range-resolved scattering images were obtained with a gate time width of 100 ns, which corresponds to a resolution of 15 m cloud depth. The size of the scattering area enlarged just after the laser pulse hit the cloud, and gradually decreased as the beam went deeper inside the cloud where extinction overcame the multiple scattering. An extinction coefficient of 3.62x102 [ m-1] was calculated from the laser beam transmission. The particle size distribution of the cloud was derived to fit the obtained extinction coefficient. A Monte Carlo simulation using the new distribution function reproduced the experimental scattering image very well. This new experimental and simulation method to show the multiple scattering as a spread image will provide informative knowledge for cloud lidar observations.

We sometimes observed ice clouds (cirrus) that coexisted with an Asian-dust layer in the upper troposphere by a polarization lidar during Asian dust events over Tokyo, Japan in the springs of 1998 to 2000. Here we present such lidar observations during spring 2000. We discussed qualitatively a mechanism of the formation of the cirrus clouds combined with imageries of Geostationally Meteorological Satellite 5 (GMS-5) and the nearest radiosonde data. The water-vapor channel imagery indicates that the cirms was formed or enhanced over a high mountain area in the middle of Japan. The cirrus that we observed over Tokyo was a part of the cirrus flowed by the westerly wind. Asian dust particle seems to act as ice nuclei in the upper troposphere if the air mass merged with a humid air mass during the transportation.

Tropospheric aerosols effects on climate in directly through various cloud formation, the lidar has been used to study the composition of many particles mixing in the atmosphere including to study the aerosol and cloud. Currently, it has many types of lidar systems depending on the purpose of measurements. In this report, the ground-based lidar system was established at King Mongkut's Institute of Technology Ladkrabang (KMITL), THAILAND to study and measure the aerosol in boundary layer and cirrus clouds in the tropopause region. The aerosol measurement is in the form of scattering ratio whereas the signal depolarization has been applied to identify layers of cirrus clouds. The lidar system consists of laser source (Nd:YAG) with second harmonic wavelength, 28 cm Schmidt-Cassegrain telescope, photomultiplier tube (PMT) and data acquisition system.

Observations of aerosols and clouds have been conducted in the Pacific with a ship-board Mie scattering lidar using the research vessel Mirai. The purpose of the observations is to obtain global distribution of aerosols and clouds over the Pacific Ocean for climatology and studies of radiative processes and ocean-atmosphere interaction. The data are used also in the study of data reduction and utilization methods for the space-borne lidars. The lidar for R/V Mirai is a two-wavelength Miescattering lidar (532 nm and 1064 nm) using a flashlamp pumped Nd:YAG laser. It has a depolarization receiver at 532 nm. We have performed observations in six cruises of R/V Mirai since 1999. Cloud distribution, cloud phase, vertical distribution of aerosol, wavelength dependence of aerosol backscatter, etc. have been analyzed. The parameters measured with the lidar, i.e. backscatter at two wavelengths and depolarization, are similar to space-borne lidars such as PICASSO and the Japanese "A-lidar". The results of the observations demonstrate the usefulness of a two-wavelength polarization lidar.

A mobile volume scanning Mie Lidar has been integrated to take slant angle scan of aerosol distribution over 120 degree within 10 minutes. The Lidar system is a bi-axial design with operating wavelength of 532nm. The receiver is a compact Schmidt-Cassegrain telescope. Since the system is designed to be compact and lightweight, it could be readily fitted into a small van for field observations. This system has been deployed to study the correlation between the spatial distribution of aerosols over the urban area in Hong Kong and the conditions of local traffic congestion. The scans covered approximately a range from 1 to 4 km. From the data obtained, spatial variations were clearly observed, and the location of enhanced aerosol density correlated with areas of high traffic congestion very well. From the data, a vertical dispersion model can be verified. With the time series analysis of the distributions, one would be able to compute the time scale of the dispersion. With routine observations, the cause of aerosol variations can be better understood in the future. Thus it would lead to good suggestions in improvement of the air pollution problem in an urban city with dense population. Other potential studies that can be carried from this Lidar include the aerosol variations over a sea-land system and the internal boundary height over a complex terrain.

Monitoring of urban atmospheric aerosols and trace gases using the lidar techniques has been in progress at the Indian Institute of Tropical Meteorology (IITM), Pune (18°32'N, 73°51'E, 559 m AMSL), India since 1985. The Argon-ion lidar facility, being fully computer-controlled, offers all the benefits of on-line acquisition and processing of data while retaining the very valuable graphical representation in the familiar two- and three-dimensional views of aerosol and trace gas characteristics. Over 1000 lidar-derived profiles (covering the altitude range between 20 m and 1380 m) of aerosol number density obtained during night clear-sky conditions over the 12-year period (October 1986 through September 1998) have been used to build the climatology of mixing depth, stable layer, and associated ventilation coefficients and aerosol layer structures in the atmospheric boundary layer. The analysis of long-term data indicates variations in mixing depth from about 200 m to 550 m, and the associated ventilation coefficients reveal relatively higher values during the pre-monsoon (March-May) indicating better air quality due to larger mixing depths and stronger transport winds, and lower values during the south-west monsoon (June-September) and winter (December-February) seasons indicating low dispersal of pollutants or poorer air quality over the experimental station. Though the ventilation coefficients are low during the monsoon months, the effect of air pollution is considered to be negligible due to the effects of cloud scavenging and rain washout. But the low coefficients during the winter late evenings exhibit higher pollution potential at the station. Thus, the above results emphasize the importance of lidar for air quality measurements and pollution potential forecast in urban regions in general, and industrial regions in particular.

A lidar system was installed at Ny-Ålesund, Svalbard in January 1994 to observe polar stratospheric clouds (PSCs). Observation campaigns were performed in the following seven winter seasons. The backscattering at 1064 and 532 nm, and the depolarization at 532 nm were observed by the lidar system. The results of observations in each winter season are summarized. A vertical sandwich structure of type I PSCs, in which layers of depolarization are above and below a scattering layer, has frequently been observed when the stratospheric temperature decreases to near the frost point of ice. An enhancement in scattering was observed at the altitude of the liquid PSC layer, but not at the altitudes of the solid layers. There tended to be a negative correlation between scattering ratio and depolarization ratio. The small increase in the scattering ratio over time at the altitude of the depolarization maximum implies a slow nucleation of solid particles. The lidar observations including temperature histories suggest that the sandwich structure arises from the external mixing of two different types of particles.

Observation of mesospheric temperature profiles with a new sodium lidar has started at Syowa Station (69° 00'S, 390° 3 5'E) since February, 2000. The transmitter is composed from injection seeded Nd:YAG lasers of 1064 nm and 1 3 1 9 nm, producing sodium resonance line at 589 nm by sum frequency generation. The advantage of this instrument is the transmitter is simple thus transportable, and a reliable solid state system requiring less maintenance compared with ordinary type of dye laser transmitters. The 589 nm laser bandwidth is well narrowed less than 100 MHz, pulse width is 40 nsec, and the energy is 40 mJ/pulse. The 589 nm wavelength is controlled by a personal computer with monitoring a seed laser wavelength using a wavemeter with an accuracy of 0. 1 pm. Temperature structures were measured by two frequency technique and by sodium D2 Doppler profile filling. Both results were in good agreement and consistent with model temperature structure.

The Center for Atmospheric and Space Sciences (CASS) at Utah State University (USU) operates the ALO for studying the middle atmosphere from the stratosphere to the lower thermosphere. ALO's mid-latitude location (41.74°N, 1 1 1.81°W, 1466 m) is very unique in that it is in the middle of an extensive set of rugged mountains, the Rocky Mountains, which are a major orographic source of gravity waves that may give rise to a longitudinal variation in the mesospheric structure. Mesospheric observations between approximately 45 and 90 km have been carried out on many clear nights with the ALO Rayleighscatter lidar since late 1993. They have been carried out, mostly, with a frequency-doubled Nd:YAG laser producing 18 W at 532 nm and a 44-cm zenith-pointing telescope. To obtain better and more complete observations in the future, a considerably bigger steerable telescope, an alexandrite ring laser for resonance scatter, and an expanded data-acquisition system are being developed. The observations in the extensive existing database have been reduced to provide absolute temperature profiles, which provide important information for understanding the physics and chemistry of the middle atmosphere and for examining global change. They have been used to make a mesospheric temperature climatology that has been and is being used to examine secular, annual, seasonal, and tidal variations, to compare with other temperature observations and with modeled temperatures, and to study mesospheric inversion layers. Day-to-day changes in the temperature profiles are also being compared to meteorological parameters to see if mesospheric changes can be related to low-altitude sources. Temporal and spatial fluctuations in the density profiles have also been examined to provide more direct information on gravity wave activity. And, on 24 June 1999 UT, the lidar probed the first known noctilucent cloud to penetrate to this low latitude, approximately 10° equatorward of previously reported sightings and detections.

A compact and high-pulse-energy Ti:Sapphire laser with its Third Harmonic Generation (THG) has been developed for an airborne ozone differential absorption lidar (DIAL) to study the distributions and concentrations of the ozone throughout the troposphere. The Ti:Sapphire laser, pumped by a frequency-doubled Nd:YAG laser and seeded by a single mode diode laser, is operated either at 867 nm or at 900 nm with a pulse repetition frequency of 20 Hz. High energy laser pulses (more than 110 mJ/pulse) at 867 nm or 900 nm with a desired beam quality have been achieved and utilized to generate its third harmonic at 289nm or 300nm, which are on-line and off-line wavelengths of an airborne ozone DIAL. After being experimentally compared with Beta-Barium Borate (?-BaB2O4 or BBO) nonlinear crystals, two Lithium Triborate (LBO) crystals (5×5×20 mm3) are selected for the Third Harmonic Generation (THG). In this paper, we report the Ti:Sapphire laser at 900nm and its third harmonic at 300nm. The desired high ultraviolet (UV) output pulse energy is more than 30mJ at 300nm and the energy conversion efficiency from 900nm to 300nm is 30%.

The NASA Langley Research Center's airborne UV Differential Absorption Lidar (DIAL) system measures vertical profiles of ozone and aerosols above and below the aircraft along its flight track. This system has been used in over 20 airborne field missions designed to study the troposphere and stratosphere since 1980. Four of these missions involved tropospheric measurement programs in the Pacific Ocean with two in the western North Pacific and two in the South Pacific. The UV DIAL system has been used in these missions to study such things as pollution oufflow, long-range transport, and stratospheric intrusions; categorize the air masses encountered; and to guide the aircraft to altitudes where interesting features can be studied using the in situ instruments. This paper will highlight the findings with the UVDIAL system in the Pacific Ocean field programs and introduce the mission planned for the western North Pacific for February-April 2001. This will be an excellent opportunity for collaboration between the NASA airborne mission and those with ground-based lidar systems in Asia Pacific Rim countries to make a more complete determination ofthe transport ofair from Asia to the western Pacific.

A multiwavelength differential absorption lidar (DIAL) system for measurement of trace atmospheric substances was developed. Vertical concentration profiles of SO2 in the lower troposphere were measured by three wavelength dual-DIAL (on wavelength=300.05 nm, off wavelengths=299.35 nm, 300.90 nm, with null profiles obtained at 300.05 nm) . The measurement wavelengths were chosen to minimize the effect of O3 . Measurement results showed an average SO2 concentration of 0.6 ppb for height 2000-4000 m, and the SO2 measurement error was estimated to be about 1 ppb for 150 m range resolution. Although the measured SO2 concentration was below the resolution of our system, the results show that the system is capable of measuring trace SO2 with approximately 0.15 ppm-m resolution. In addition, vertical O3 concentration profiles in the lower troposphere were measured using two identical DIAL pairs (on wavelength=285.0 nm, off wavelength=290.1 nm), from which two null profiles and two DIAL profiles were obtained simultaneously. The DIAL profiles, which showed an average O3 concentration of 42 ppb for height 1000-4000 m, agree with simultaneous O3 sonde measurements. The effect of backscatter gradients was shown to be small. The O3 measurement error was estimated to be 3.4 ppb for 150 m range resolution, or about 0.5 ppm-m.

The measurement of various minor constituents in the atmosphere is of great significance to understand physics, Chemistry and dynamics of the atmosphere. Ozone in the troposphere is one of the most important trace species as it is a greenhouse gas trapping the longwave radiation in 9.6 ?m band affecting the energy budget of the earthatmosphere system. It is also a pollutant produced as a result of anthropogenic activities such as fossil fuel burning and has potential to affect human health and vegetation if it is allowed to attain high concentrations. Water vapour also plays a significant role in climate studies and the chemistry of the atmosphere. Ethylene is an urban pollutant and its concentration as low as 10 ppb is toxic to plants. A differential absorption lidar system using a tunable CO2 laser has been designed and developed at National Physical Laboratory, New Delhi, to monitor various minor constituents in the atmosphere. Some times ethylene concentration was found to be more than 20 ppb while that of surface ozone was more than 140 ppb which is a health hazard. In this paper salient features of experimental set up and results obtained will be presented in detail.

GLOW (Goddard Lidar Observatory for Winds) is a mobile Doppler lidar system which uses direct detection Doppler lidar techniques to measure wind profiles from the surface intO the lower stratosphere. The system is contained in a modified van to allow deployment in field operations. The lidar system uses a Nd:YAG laser transmitter to measure winds using either aerosol backscatter at 1064 nm or molecular backscatter at 355 nm. The receiver telescope is a 45 cm Dall-Kirkham which is fiber coupled to separate Doppler receivers, one optimized for the aerosol backscatter wind measurement and another optimized for the molecular backscatter wind measurement. The receivers are implementations of the 'double edge' technique and use high spectral resolution Fabry-Perot etalons to measure the Doppler shift. A 45 cm aperture azimuth-overelevation scanner is mounted on the roof of the van to allow full sky access and a variety of scanning options. GLOW is intended to be used as a deployable field system for studying atmospheric dynamics and transport and can also serve as a testbed to evaluate candidate technologies developed for use in future spaceborne systems. In addition, it can be used for calibration/validation activities following launch of spaceborne wind lidar systems. A description of the mobile system is presented along with the examples of lidar wind profiles obtained with the system.

A coherent lidar is an attractive sensor for atmospheric observation because it enables the wind velocity measurement in clear air conditions. A 1.5-?m eye-safe coherent lidar is more attractive than a 2-?m eye-safe coherent lidar. The wavelength of 1.5-?m provides a ten times higher maximum permissible exposure for human eyes than the wavelength of 2-?m. In addition, optical fiber components and devices developed for optical fiber communications are easily available. We have already reported first 1.5-?m coherent lidar system for wind velocity measurement, and recently completed the full system. The system has the Er,Yb:Glass pulsed laser with the output energy 10.9-mJ and the telescope with effective aperture of 100-mm. The system provides the available measurement range of 5-km (SNR>+1-dB), the detectable wind velocity range of between -50- m/sec and +50-m/sec and the range resolution of 30-m. The velocity accuracy of 0.14-m/sec (standard deviation) is obtained by measuring velocity of a nonmoving hard target.

In this paper, a new signal processing method named SCCI (Self- Compensated Coherent Integration) which enables a coherent integration over a longer time, compared to a coherence time of a back-scattered signal, is proposed. A back-scattered signal is gated by a constant time gate of which a gate time is set to be shorter than a coherence time. Each gated signal is sampled as a former and a latter part. A gated signal in each part is integrated coherently by FFT. A cross spectrum of two parts is calculated in each time gate. Since a phase of a cross spectrum in each time gate is constant, this process is identified to a self-phase-compensation. A cross spectrum is integrated over all time gates. This process is identified to a coherent integration of a back-scattered signal over a signal length which is longer than a coherence time, since a phase of a cross spectrum in each time gate is constant. The signal to noise ratio (SNR) for SCCI is theoretically higher than that for PDI (Post Detection Integration) in the case of N>16/SNRP2 (N: Gate number, SNRp: SNR of a time gate for PDI) at low SNR. SCCI is superior to PDI in every case at low SNR if a required SNR in a system is up to 6dB and a Doppler frequency of a back-scattered signal is constant in a signal length. Furthermore, if SNRP becomes lower and lower, and a required SNR is higher and higher compared to 6dB, the effect of using SCCI appears more and more distinctly. We confirm the effect experimentally using a 1.5-µm wind sensing lidar system. Keywords: Coherent lidar, Coherent integration, Coherence time, Signal division, Self-compensation, Doppler frequency, Wind sensing, SNR, SCCI, PDI

A compact direct-detection Doppler lidar system has been developed for tropospheric wind measurements. ALD-pumped Nd:YAG Q-switched laser with frequency stabilized and two-frequency oscillation was realized for the differential Doppler wind measurements. Basic principle of system performance and system parameters are shown as well as the experimental results.

A new incoherent Doppler lidar technique for atmospheric wind measurement is presented. This direct detection Doppler lidar is realized by the transmitting laser with two wavelengths and the receiving system with only one bandpass or absorption filter. We fabricated actually the Doppler lidar system using the frequency doubled Nd:YAG laser which was alternately tuned to the both slopes of one absorption line of the molecular iodine with an AO wavelength shifter, and performed simultaneous measurements of the eastward and northward wind components from 8 to 25km altitude with 500m vertical resolution. This Doppler lidar system is very useful to measure the wind profiles between lower troposphere and stratosphere by one effort.

Development of a UV laser transmitter capable of operating from a space platform is a critical step in enabling global earth observations of aerosols and ozone at resolutions greater than current passive instrument capabilities. Tropospheric chemistry is well recognized as the next frontier for global atmospheric measurement. NASA Langley Research Center (LaRC) and the Canadian Space Agency (CSA) have jointly studied the requirements for a satellite based, global ozone monitoring instrument. The study, called Ozone Research using Advanced Cooperative Lidar Experiment (ORACLE) has defined the Differential Absorption Lidar (DIAL) instrument performance, weight and power, and configuration requirements for a space based measurement. In order to achieve the measurement resolution and acceptable signal-to-noise from lidar returns, 500mJ/pulse (5 Watts average power) is required at both 305-308nm and 315-320nm wavelengths. These are consecutive pulses, in a 10 Hz, double-pulsed format. The two wavelengths are used as the on- and off-lines for the ozone DIAL measurement. NASA Langley is currently developing technology for a UV laser transmitter capable of meeting the ORACLE requirements. Experimental efforts to date have shown that the UV generation scheme is viable, and that energies greater than 100mJ/pulse are possible. I n this paper, we will briefly discuss the down select process for the proposed laser design, the study effort to date and the laser system design, including both primary and alternate approaches. We will describe UV laser technology that minimizes the total number of optical components (for enhanced reliability) as well as the number of UV coated optics required to transmit the light from the laser (for enhanced optical damage resistance). While the goal is to develop a laser that will produce 500 mJ of energy, we will describe an optional design that will produce output energies between 100- 200mJ/unit and techniques for combining multiple laser modules in order to transmit a minimum of 500mJ of UV energy in each pulse of the on- and off-line pulse pairs. This modular laser approach provides redundancy and significantly reduces development time, risk and cost when compared to the development of a single, 500mJ double-pulsed laser subsystem. Finally, we will summarize the laser development effort to date, including results that include the highest known UV energy (130 mJ @ 320nm) ever produced by a solid-state laser operating in this wavelength region.

NASA is intent on exploiting the unique perspective of space-based remote optical instruments to observe and study largescale environmental processes. Emphasis on smaller and more affordable missions continues to force the remote sensing instruments to find innovative ways to reduce the size, weight, and cost of the sensor package. This is a challenge because many of the proposed instruments incorporate a high quality meter-class telescope that can be a significant driver of total instrument costs. While various methods for telescope weight reduction have been achieved, many of the current approaches rely on exotic materials and specialized manufacturing techniques that limit availability or substantially increase costs. A competitive lightweight telescope technology that is especially well suited to space-based coherent Doppler wind lidar has been developed through a collaborative effort involving NASA Marshall Space Flight Center (MSFC) through the Global Hydrology and Climate Center (GHCC) and the University of Alabama in Huntsville (UAH) at the Center for Applied Optics (CAO). The new lightweight optics using metal alloy shells and surfaces (LOMASS) fabrication approach is suitable for high quality metal mirrors and meter-class telescopes. Compared to alternative materials and fabrication methods the new approach promises to reduce the areal density of a meter-class telescope to less than 15-kg/m2; deliver a minimum ?/1O-RMS surface optical quality; while using commercial materials and equipment to lower procurement costs. The final optical figure and finish is put into the mirrors through conventional diamond turning and polishing techniques. This approach is especially advantageous for a coherent lidar instrument because the reduced telescope weight permits the rotation of the telescope to scan the beam without requiring heavy wedges or additional large mirrors. Ongoing investigations and preliminary results show promise for the LOMASS approach to be successful in demonstrating a novel alternative approach to fabricating lightweight mirrors with performance parameters comparable with the Space Readiness Coherent Lidar Experiment (SPARCLE). Development and process characterization is continuing with the design and fabrication of mirrors for a 25-cm telescope suitable for a lidar instrument.

Global observations oftropospheric wind profiles represent a significant potential for advancing weather research and operational forecasting. Space-based Doppler lidar is considered to be one ofthe best candidates for providing vertical wind profiles over the entire globe. The traditional issues of accuracy, spatial resolution and global coverage are currently being formulated within the context of modem 4-D data assimilation. However, this is being done without the benefit of space heritage for active Doppler lidars in space. Considerable resources are being directed at developing "roadmaps" that will guide investments in the technologies that will eventually deliver the data products usable by tomorrow's ever more demanding numerical models. Coherent detection and direct detection offer two very different lidar approaches to making wind observations. In some quarters, the issue is which system to choose over the other. However, given that the two detection techniques have complimentary attributes, it may be more cost effective to employ both. This paper describes the merits of a Wind Observing Satellite using Hybrid (WOSIH) Doppler lidar technologies which would involve (1) a conically scanned 2 micron coherent Doppler lidar for cloud and PBL aerosol wind observations and (2) a 4 point conical-step-stare direct detection tripled YAG (.355?m for obtaining mid and upper tropospheric winds from the Rayleigh returns.

This paper discusses the design and development of a 2J, 10Hz coherent Doppler wind lidar transmitter for global wind sensing from the International Space Station. This work is being performed in support of a proposal to operate such a lidar from the Japanese Experimental Module. The conceptual lidar transmitter design is complete and risk reduction measurements are currently underway to demonstrate the 2J, 10Hz operation using a 2 micron laser transmitter with a MOPA (master oscillator – power amplifier) configuration. The paper discusses the lidar performance requirements for global wind sensing from the Space Station, general design characteristics of the two micron lidar transmitter, and the current status of the risk reduction measurements.

A collection of issues is discussed that are potential pitfalls, if handled incorrectly, for earth-orbiting lidar remote sensing instruments. These issues arise due to the long target ranges, high lidar-to-target relative velocities, low signal levels, use of laser scanners, and other unique aspects of using lasers in earth orbit. Consequences of misunderstanding these topics range from minor inconvenience to improper calibration to total failure. We will focus on wind measurement using coherent detection Doppler lidar, but many of the potential pitfalls apply also to noncoherent lidar wind measurement, and to measurement of parameters other than wind.

Coherent Doppler Lidar (CDL), which has a capability of 3-D wind velocity measurements, can realize a global measurement of the wind profile in the troposphere from space. ISS(International Space Station) has been constructing from last year, and JEM(Japanese Experimental Module) attached to ISS is scheduled to be provided as a laboratory in space. We have been making a feasibility study for ISS-JEM/2-micrometer CDL. We expect that the ISS might give some technical problems because of a large scale and a man attended station. On the other hand, a measurement accuracy of 1m/s is required from the atmospheric science. We have to analyze the systematic error with considering the error factors to meet this requirement. There are two factors of the wind measurement errors caused by the nutation of ISS’s attitude. One of them is a change of receiving power, since it should change distances between CDL and a observing point. In this case, we have already shown that the wind error estimated was only ±0.05m/s (assumed width of pitching angle ; ±3deg). The other factor is a change of orbital Doppler shift. The accuracy of 1m/s is corresopnding to 1MHz. We calculated a frequency of orbital Doppler shift in case of non conical scanning one when ISS has the nutation of attitude with ±3deg,as a pitching angle and a rolling angle,respectively. The results obtained in this syudy are very useful to design a frequency agile CW laser as a local oscillator.In this paper, we describe more details for our analysis.

A new multi-FOV space-borne lidar named "A-lidar" is being studied by the National Space Development Agency of Japan (NASDA) for the earth radiation mission proposed as a joint program with the European Space Agency (ESA). The mission is named "EarthCARE". It was formerly called ATMOS-B1 or ERM. The lidar has a two-wavelength transmitter (1064 nm and 532 nm), a dual polarization receiver at 1064 nm, and a multi-field-of-view (multi-FOV) receiver at 532 nm. The multi- FOV feature of A-lidar will enable us to solve the multiple scattering problems with space lidar measurements of profiles of clouds and aerosols. The multi-FOV feature can also be used for characterization of aerosols.

Measurement error is discussed in a wavefront sensor consisting of lenslets and CCD. It is supposed that the center of gravity in a binary image, obtained through binarization from an analog image on the detection plane of the CCD, is used for estimation of the positions of focused spots on the detection plane. The standard deviation of the estimation error is analyzed for two kinds of focused spot shapes; circular and square. It is shown that the standard deviation of the estimation error is smaller in the case of the circular shape than that in the case of the square shape and also that the standard deviation in the case of the circular shape decreases significantly as the diameter of the circular increases.

We are developing a new remote-operational lidar system, with multimedia technology. This system reduces the necessity to go to the remote place. The system is located in Rikubetsu (43.3N, 143.5E), in north portion of Japan, which is a famous place for a fair weather all the year round. We use SHG of Nd:YAG laser and receive P, S components of Mie back scatter with photon counter. All necessary controling of instruments such as the roof of the housing, tilt mirror, laser, photon counters, oscilloscope, and so on, are done by personal computers. Operator uses a web browser from a remote site to operate the lidar system, with monitoring the weather and the total state of the system. There is another workstation which runs a newly developed desktop video conference system. With these system, several persons can simultaneously observe and watch the data, discuss with each other. We can now observe the aerosols more frequently than ever. This will let us to get precise information about the aerosols in north regions of Japan.

Tunable single-frequency sources in the 2-4 micron wavelength region are useful for remote DIAL measurements of chemicals and pollutants. We are developing tunable single-frequency transmitters and receivers for both direct and coherent detection lidar measurement applications. We have demonstrated a direct-diode-pumped PPLN-based OPO that operates single frequency, produces greater than 10 mW cw and is tunable over the 2.5 —3.9 micron wavelength region. This laser has been used to injection seed a pulsed PPLN OPO, pumped by a 1.064 micron Nd:YAG laser, producing 50-100 microJoule single-frequency pulses at 100 Hz PRF near 3.6 micron wavelength. In addition, we have demonstrated a cw Cr:ZnSe laser that is tunable over the 2.1 —2.8 micron wavelength region. This laser is pumped by a cw diode-pumped Tm:YALO laser and has produced over 1.8 W cw. Tm- and Tm,Ho-doped single-frequency solid-state lasers that produce over 50 mW cw and are tunable over approximately 10 nm in the 2 —2.1 micron band with fast PZT tuning have also been demonstrated. A fast PZT-tunable Tm,Ho:YLF laser was used for a direct-detection column content DIAL measurement of atmospheric CO2. Modeling shows that that all these cw and pulsed sources are useful for column-content coherent DIAL measurements at several km range using topographic targets.

We have performed a basic experiment on a diode laser pumped Tm:Ho:YLF laser with the purpose of developing a light source for a JEM-borne coherent Doppler lidar. This laser oscillator has 8-figure type ring cavity and its cavity length is 2.9m. Unidirectional operation was performed with a Faraday rotator and a polarizer in the cavity. A composite crystal is used for the oscillator. Doped YLF is clad with undoped YLF and had undoped YLF at both ends. The crystal is supported its both ends with copper, and is cooled to a temperature of 205K in a vacuum chamber. Doped part of the crystal is pumped by four diode lasers with total pumping energy of 700mJ. We have obtained Q-switched pulses of 5.OmJ at pulse repetition rate of 10 Hz, with a wavelength of 2.05 micrometer and a pulse width of 326ns, and an optical to optical efficiency of 0.7%. In the injection seeding for a single mode operation, a computer controls cavity lengths by way of moving one of mirrors so that pulse buildup time keeps minimum value. We have also obtained a spectrum width of 1 .5MHz, and this value is almost same as Fourier transform limited width.

MUSES-C is a sample return mission of a near-earth asteroid. The MUSES-C spacecraft rendezvous and touches down an asteroid. In order to approach safely, it has a LIDAR system with the range covering from 50 m to 50 km. The range accuracy at 50 km was less than 10 m. The LIDAR uses a diode pumped Nd:YAG laser with l2mJ output energy for ranging. The prototype-model of the LIDAR was developed and it has been testing to prove performance for MUSES-C. The prototype-model of the laser satisfied all of the required specifications for MUSES-C. Also, the laser realized the weight fewer than 300g with Mg alloy for frame and glue fixation of optics.

In the present work, a sensing system for methane gas leakage monitoring based on a differential absorption lidar with a high temporal resolution is proposed and a spectrally narrowed light source at 1.67 ?m is developed for the same. To realize a compact light source, an injection seeded optical parametric oscillator (OPO) combined with two-stage optical parametric amplifiers (OPAs) is considered. Both OPO and OPAs were pumped by a compact frequency doubled Nd:YAG laser, and a single—mode diode laser (781.6 nm) was employed for injection seeding of the OPO. The output energy of around 5 mJ corresponding to a pump input of 85 mJ was obtained using Ce doped KTP (Ce:KTiOPO4) crystals. The spectral width of the source was measured as 0.5 cm-1 with a beam divergence angle of less than 2 mrad. These output characteristics are satisfactorily meeting the requirements to detect the methane leakage in a short range.

We have developed the resonance scattering lidar system for measurements of mesospheric metallic species such as Na, K, Fe atoms and Ca ions and mesospheric temperature and wind. The flashlamp pumped Ti:sapphire laser injected by the seeder that consists of an external cavity laser diode is applied for measurements of the K and Fe atoms and the Ca ions. The sophisticated lidar system which consists of a pulsed dye oscillator and an amplifier system injection-seeded by a stabilized cw ring dye laser is also applied for Na atoms, temperature and wind measurements. Its injection-seeder consists of the single mode ring dye laser locked to the Na fluorescence line using the wavemeter and the Na vapor cell. The most characteristic of this laser system is to generate the comparatively high pulse energy ( more than 100mJ/pulse ) keeping up the narrow bandwidth ( about 0.1pm ). In this paper, the details of the laser design and the results observed by these lidar system are shown.

Lidar and Optical Particle Counter (OPC) measurements were performed in the Canadian Arctic and in the Indonesian Tropical region. The observations yielded very interesting and important results about the features of the latitudinal difference in the stratospheric aerosols. Besides the latitudinal difference, the aerosol distributions and their time variation showed unique characteristics in each of the regions. In Arctic winter, the aerosol concentration varies frequently day-today. In the Tropical region, the aerosol distribution and the vertical transport is, probably, controlled by the variation of the circulation pattern in the lower stratosphere related to the QBO in the tropical stratosphere. Based on the results of the simultaneous measurements by lidar and OPCs, we estimated surface area density, volume density, S-parameter (extinction to backscatter ratio), backscatter to surface area conversion factor, and backscatter to volume conversion factor of the stratospheric aerosols at 20km-altitude in the Arctic and Tropical regions.

For the study of stratospheric aerosol over the Tropics, balloon-borne OPC measurements have been made six times from April 1997 to March 2000 at Bandung, Indonesia (6.9?S, 107.6?E) where Lidar measurements have also been made since early 1997. Correlative measurements of Lidar and OPC were conducted on March 25,1998 and August 23, 1999. Results of the latter measurement were compared in this paper. The profile of back scattering ratio measured by Lidar almost represents a vertical distribution of small particles having radii smaller than O.4?m. We calculated back scattering coefficients from the results of OPC measurement. The calculated and measured back scattering coefficients were not consistent completely but not so unreasonable.

Height profiles of temperatures and winds of the middle atmosphere between 30km to 60km are observable only by Rayleigh lidar and Rayleigh Doppler lidar except for rocket sounding which is expensive and not suitable for continuous measurements. We developed a Rayleigh lidar system and it is now working well for temperature observations of the Arctic middle atmosphere at Poker Flat Research Range near Fairbanks, Alaska (65.1N, 147.5W). A comparison of lidar data and balloon sonde data showed good agreement in overlapped altitudes. A Rayleigh Doppler lidar for wind measurements of the middle atmosphere is under the phase of development. The expected accuracy in measurements of horizontal winds up to an altitude of 60km is smaller than 6m/s in 2hours observation. The system will be also operated at Poker Hat. The combination of these lidars and radars installed at Poker Flat give us chances of simultaneous observations of the structure and dynamics of the atmosphere in broad range of altitudes. Here, we give descriptions of the Rayleigh lidar and the Rayleigh Doppler lidar for the observations of the Arctic middle atmosphere at Poker Flat.

Variation of stratospheric aerosol affects atmospheric minor constituents and climate through changes in the radiation field as well as by dynamic and chemical processes. In order to estimate the impact quantitatively, it is very important to observe stratospheric aerosol vertical distribution and their lime variation To obtain stratospheric aerosol especially in equatorial region a lidar was installed in Bandung (6.9° S; 107.7° E) Indonesia under collaboration between National Institute of Aeronautic and Space (LAPAN), Communication Research Laboratory of Japan and Meteorological Research Institute of Japan. The Lidar transmitter system employ fundamental (1064 nm), second harmonic (532 nm) and third harmonic (355 am) wavelengths ofNd: YAG laser are transmitted. The second harmonic backscatter light and its N2 ranian backscatter light (607 am) are collected by a 28 cm and a 35 cm diameter telescope. In 35 cm telescope system, upper troposphere and stratosphere are observed by photon counting. 532 am light component polarized parallel and perpendicular to the laser light are separately observed to get information about shape of aerosol. Bandung is located at around 750 m above mean sea level and it is surrounded by mountains, therefore clouds are easily formed especially between 10 and 17 km height. Stratospheric aerosol over Bandung are spreaded between 18 and 35 km in altitude and form more than 1 sub layer, below 30 km and upper 30 km. The maximum aerosol concentration is obtained around 22.5 km height. To understand the seasonal variation of stratospheric aerosol we integrated the backscattering coefficients for altitude range 18-35 km and it was obtained that the stratospheric aerosol concentration in 1997 was higher than in 1999. The integrated backscattering coefficient in June was higher than in August. But seems the seasonal variation of integrated backscattering coefficient in Bandung does not so clear determined yet.

Owing to understanding the transportation and chemical reaction of the aerosols, it is important to observe the aerosol density, depolarization ratio, wind profiles, temperature profiles and water vapor density simultaneously. We have prepared several lidar systems for simultaneous measurement of these constituents and parameters. The polarization lidar consists of the frequency-doubled Nd:YAG laser and polarizer for measurement of density and non-sphericity of the aerosol. The wind lidar consists of the incoherent Doppler lidar using the frequency-doubled Nd:YAG and the iodine vapor filter for measurement of the wind profiles. The temperature lidar is realized by the rotational Raman lidar with the Mie scatter blocking filter. And water vapor profiles are measured by a vibrational Raman lidar using the frequency doubled Nd:YAG laser. We got preliminary results of these parameters in the aerosol layer.

Simultaneous two wavelength LIDAR measurements of clouds and boundary layer aerosols were performed near Manila Bay. Philippines. The two-wavelength LIDAR system employs the simultaneous outputs at 1064-nm (420 mJ) and 532-nm (175 rnJ) of a Q-Switched, 20-Hz Nd:YAG laser and a 203 .20-mm diameter Schmidt Cassegrain telescope set for 1-mrad field-of-view. The vertically-pointing, biaxial Mie LIDAR facilily became operational early last year and is in the STRC building (14.339°N, 120.595°E) of De La Salle University (DLSU), Taft Avenue, Manila. LIDAR measurements were obtained in 1-minute intervals from 0812-0830 hours (local time) on December 20, 1999 and 0650-0930 hours (local time) on March 23. 2000. Extinction coefficients for these boundary layer aerosols and clouds were computed using Klett's modified inversion algorithm. The extinction coefficients for the clouds observed on December 20 were 20 —100 km-1 (1064 nm) and 5 — 40 km-1 (532 am). Boundary layer aerosols found on the same day had extinctions of 10 km-1 for both wavelengths and reached up to 300 m above the site. The March 23 data show mostly boundary layer aerosols from 200 — 600 in above the LIDAR having extinction values of 6 —8 km-1 for both wavelengths.

The observation of atmosphere dust in China's desert show that there is a continuous dust layer always existed in lower atmosphere under the height of 5 km. The dust concentration in the layer is changed with altitude and season. According to the Lidar data analysis the backscattering ratio value changes in the range of 2.5-5.5 in clear weather. The higher value ofthe ratio can be extended to the height about the height of3.5 km. The dust concentration is reduced sharply over 3.5 km. In the range of 15-20 km height, an aerosol layer is often observed in Shapotou region. The maximum backscattering ratio usually appears in 1 5- 1 8 km. The value is approximately 1.2.

A comparative measurement of the free tropospheric aerosol particles using a ground-based Raman lidar and in-situ sampling instruments on board an aircraft was made over central part of Japan (35-36?N, 136-137?E) in the Asian dust period on April 23, 1996. We compared the aerosol properties measured with the lidar (aerosol backscattering coefficients and the depolarization ratio at the wavelength of 532 nm) and those obtained with the aircraft-based instruments (aerosol shape and surface feature, number size distribution, and chemical composition). The aerosol backscattering coefficients calculated from the aerosol size distribution obtained with the airborne optical particle counters (OPCs) showed good agreements (mean relative difference of 22%) with those measured with the lidar above the altitude of 3.1 km and showed large difference (mean relative of 50%) below 3.1 km. The aerosol depolarization ratios correlated well with the fractions of the backscattering coefficient of the coarse mode particles (radius>0.5 ?m) in the total aerosol backscattering coefficient calculated from the OPCs data above 3.4 km. This suggests that the coarse mode particles that considered mainly of nonspherical mineral dust particles predominantly contributed the depolarized signals in this altitude region. The aerosol depolarization ration of the coarse mode particles was estimated to be 16?4% at 5.3 km.

A Mie lidar system was built at Okayama University in 1998. The system is featured by the ability of discriminating depolarization of received signals with a spatial resolution of 15m. Examinations were conducted on the received rangenormalized signal and the depolarization ratio from Asian dust. Intense Asian dust occurred in springs of 1998-2000. Vertical distribution of Asian dust was found to be inhomogeneous contrary to the homogeneity assumption employed in preceding works. Multiple scattering in the layers of Asian dust also observed. Complicated structure of Asian dust wrapped by liquid or water droplets were also conjectured from the sudden changes of depolarization ratio in Asian dust layers.

The polarization lidar measurements were carried out to investigate the optical properties of ice crystals. The cloud height, extinction-to-backscattering ratio, optical depth, and depolarization ratio for cirrus clouds in the height range of 10-17 km were analyzed. We found the cloud optical depth has a clear height dependence, with high clouds optically thin. There is an increasing trend of depolarization ratio with height between 12-16 km. There is a clear relationship between the depolarization ratio and the optical depth. For cirrus clouds at heights between 13 and 16 km region, the clouds with optical depths smaller than 0.1 have depolarization ratios about 0.3. Large depolarization ratio (0.6) was found for subvisual clouds of optical depthabout 0.02. Thick clouds with optical depth larger than 0.1 have an average depolarization ratio about 0.2.

We analyze lidar backscattering enhancement for pristine hexagonal ice crystals by using Fraunhofer diffraction based on Kirchhoff's diffraction theory (KD). Our numerical computations show that received power Pr(Z) at the altitude Z in lidar equation is proportional to Z-?, where ? is a function of Z, size and shape of particles. Pr(Z) is proportional to Z-1.5 for hexagonal plate and column randomly oriented in horizontal plane at Z=200 m where its aspect ratios are 1/3 and 3 and mode radiuses are 100,um. Our calculations suggest hexagonal ice crystals that have mode radiuses of 100 ?m and 30 ?m with perfectly oriented in horizontal plane have anomalous backscattering enhancement compared with a sphere at even high altitude. This might explain the phenomena reported by Platt et. al. (1978).1,2

We have developed the bistatic imaging lidar for measuring the lower atmosphere at the daytime as well as at nighttime. The lidar has composed of a transmitting system of a Nd: YAG laser (532nm, 10Hz, and 5OmJ) and a receiving system of a cooled high-sensitive CCD camera with an image intensifier as a high-speed shutter. Vertical profiles could be obtained every one minute and indicated in a real time monitor with color contoured time-height indication. We have been making regularly the 24 hours observations of the atmospheric boundary layer once a week at the inland district capital, Nagano City, closed in by the high mountains since August 1999. Some interested results have been obtained from the temporal and seasonal variations of the boundary layer. We describe the oscillatory rising motion of the top height of the boundary layer in the morning, the diffusion of aerosols due to car fumes during the rush hours both in the morning and in the evening and the downward motion of the cloud base height just before rain or snow. Moreover, it is reported about the difference of boundary layer activities between in summer and in winter under an inland climate.

The first polarization lidar was developed in Manila in early 1997 and it has been operating regularly to the present time. The regular observations aim to monitor and characterize the urban air ofManila and to study tropical clouds as well. The fixed, vertically pointing lidar transmits l5OmJ, 532 nm polarized pulses at 20Hz. The backscatter that is collected by the 27.9 cm, 0.358 nirad telescope is transmitted through a narrow bandpass filter and polarizing beamsplitter, to a two-channel receiver with PMTs operated in analog mode. Lidar signals are averaged for 2 minutes by an 8-bit digitizing storage oscilloscope and transferred to a PC. In this paper, combined measurements on suspended aerosols and boundary layer with lidar and filter-sampling of particles will be presented. These measurements, together with the meteorological data from radiosonde soundings of the weather bureau, on particular cold and hot months will be analyzed and compared. Measurements on an episodic event such as New Year's celebrations will also be discussed. The discussions in this paper will focus on the following: a) characterization of suspended aerosols and boundary layer by lidar depolarization ratio and extinction coefficient measurements and by filter-sampling method, and b) seasonal and diurnal changes ofthe above items.

For the future spaceborne water vapor DIAL system, an airborne differential absorption lidar (DIAL) system in the near infrared has been developed. An injection seeded triple pulse Ti:sapphire laser is used for the transmitter and an LD pumped conductive-cooled Nd:YLF laser is employed for the pump laser of the Ti:sapphire laser. The entire system including the receiving telescope, receiving optics, an APD detector and signal processing system are developed. The system was onboard the Beechcraft B200 aircraft and flight tests of the system were conducted at three nights of November 1999.

Vertical NO2 concentration profiles, which are important in studies of atmospheric chemistry and urban pollution, were measured by a differential absorption lidar (DIAL) based on a pair ofNd: YAG pumped dye lasers. In the experiment, 448.1 nm and 446.8 am were used for the "on "and "off' wavelengths, respectively. NO2 concentration profiles of 0-40 ppb were obtained for altitude 900 —2250 m with 150 m range resolution. Null error, which was estimated by the deviation ofthe null profile from zero, was <2ppb. The statistical error, systematic error from aerosols, and error due to uncertainty of absorbtion cross section were ?3.35 ppb, <3 ppb and <1 ppb, respectively. The total error was about 5 ppb. The estimation of aerosol backscatter and extinction error in NO2 measurement due to inhomogeneous aerosol distribution is treated in detail.

A major component of the hydrologic cycle is river discharge. Within the continental USA, the USGS operates nearly 7000 streamgaging stations. For much of the rest of the world major river discharge is poorly, sparsely or not monitored at all. In preparation for a shuttle demonstration of coherent Doppler lidar wind observing, it was determined that the assumption of a zero velocity for the surface return was probably not valid for a large fraction ofthe globe. Ocean currents, river currents, blowing sand or dust near the surface, or even swaying trees violate that assumption. However, what appeared as a confounder for shot to shot velocity calibration may actually be useful information to oceanographers and those involved with river flow. This paper describes the current status of efforts to determine both the usefulness of an observation of the river surface velocity and the feasibility of obtaining such information from a space-based Doppler lidar.

This paper studies the wind measurement accuracy of two kinds of incoherent UV Doppler lidars, which use two transmission slopes of one etalon filter and those of one atomic vapor filter. The third harmonic wavelength of the injection seeded Nd:YAG laser is made to change alternately to near the midpoint of one slope and near the midpoint of the another slope using the AO wavelength shifters. The signals that pass through the two edges are synchronously received and the Doppler shift component is derived from the ratio of these signals. It is desirable to use the eye safe wavelengths for the high power lidar or the space borne lidar, and this technique is available to apply to the eye safe wavelength. In this paper, simulation results of the wind measurement accuracy of the space borne Doppler lidar using an etalon filter and a silver atomic vapor filter are shown. They show accuracy of ~5m/s below 35km altitude and ~10m/s below 48km altitude using the etalon filter and accuracy of ~1m/s below 22km altitude and ~10m/s below 54km altitude using the silver vapor filter with 500m range resolution, respectively. The measurement accuracy of the etalon filter method is not so good as the silver filter method, because the thermal stability of the etalon filter is worse than that of the silver filter.

Spaceborne lidar systems yield the unique possibility to collect observation data with good horizontal and vertical resolution. However, due to the special geometry of space lidar measurements the return signals are much stronger influenced by multiple scattering effects. The amount of multiple scattering depends partly on system parameters. We show that the system characteristics have negligible influence on multiple scattering in observations of cirrus clouds. On the other hand for layers with stronger sideward scattering we found a considerable dependence of multiple scattering on the configuration of the lidar system.

Over the past 7 years, NASA Marshall Space Flight Center (MSFC) through the Global Hydrology and Climate Center (GHCC) has been working; in collaboration with the University of Alabama in Huntsville (UAH) Center for Applied Optics (CAO), and others; towards demonstrating a solid state coherent Doppler lidar instrument for space-based global measurement of atmospheric winds. The Space Readiness Coherent Lidar Experiment (SPARCLE) was selected by NASA's New Millennium Program to demonstrate the feasibility and technology readiness of space-based coherent wind lidar. The CAO was responsible for the design, development, integration, and testing of the SPARCLE optical system. Operating at 2-micron wavelength, SPARCLE system performance is dominated by the optical quality of the transmitter/receiver optical system. The stringent optical performance requirements coupled with the demanding physical and environmental constraints of a space-based instrument necessitate extensive characterization of the telescope optical performance that is critical to predicting the lidar system efficiency and operation in space. Individual components have been measured prior to assembly and compared to the designed specifications. Based on the individual components, the telescope design was optimized to produce a suitable telescope. Once the telescope is completed, it will be tested and evaluated and the data shall be used to anchor computer based models of the optical system. Commercial optical modeling codes were used to evaluate the performance of the telescope under a variety of anticipated on-orbit environments and will eventually be compared to environmental tests conducted in the course of qualifying the telescope for flight. Detailed analysis using the "as built" data will help to reduce uncertainties within the lidar system model and will increase the accuracy of the lidar performance predictions.

We studied data reduction algorithms for the retrievals of optical properties of cloud and aerosols for a two-wavelength (1053 nm and 527 nm) spaceborne lidar which has been developed in the frame of the Japanese spaceborne lidar project. We simulated cloud and aerosol observations with this lidar for prelaunch characterizations and investigation of the retrieval of cloud and aerosol optical properties. In the simulations, first, lidar return signals were generated for a two-dimensional artificial model atmosphere taking into account all possible noise sources as detector, background radiation, etc. and simulated realistically both the digitized data sampling process and the saturation behavior of the photon counting system. Then, the developed data reduction algorithms were tested with these simulated two-wavelength lidar signals to retrieve cloud and aerosol optical scattering parameters. The results showed that this lidar will provide not only qualitative information of cloud and aerosol distributions but also allows for the quantitative retrieval of optical properties of some aerosol layers and optically thin clouds. Recently, we applied the data reduction methods to the analysis of the data observed by the Lidar In-space Technology Experiment (LITE) in September 1994. The applicability of these methods to retrievals of optical properties of aerosols and optically thin clouds such as cirrus have been demonstrated. Moreover, comparisons of the simulated results for ELISE with the LITE observation were conducted to verify the developed simulation method. In this paper after a brief review of the data reduction algorithms, we present a three-component solution of the lidar equation for data analysis of high level thin clouds with volcanic aerosols and apply it to the LITE data of orbit 125.

It is now believed that the global wind observation from space is crucially important for both Numerical Weather Prediction and the studies on the global climate model since the global data of the wind profile are not enough. The global tropospheric wind profiles with the sufficient accuracy for the NWP and the climate model can be measureed only by the space-borne coherent Doppler lidar. A program of Japan for development of the coherent Doppler lidar in space was started by CR1 from 1997 FY under the support of the Phase II studies of the Ground Research Announcement of NASDA. Objective of the program is to make a feasibility study on the coherent Doppler lidar for the Japanese Exposure Module (JEM) of the International Space Station (155). The ISS/JEM-borne cohrent Doppler lidar can measure tropospheric line-of-sight (LOS) winds from space in an accuracy to 1-2 m/s of the vertical resolution of about 1 km and the horizontal resolution 100kmx100km.

Since the beginning of space remote sensing of the earth, there has been a natural progression widening the range of electromagnetic radiation used to sense the earth, and slowly, steadily increasing the spatial, spectral, and radiometric resolution of the measurements. There has also been a somewhat slower trend toward active measurements across the electromagnetic spectrum, motivated in part by increased resolution, but also by the ability to make new measurements. Active microwave instruments have been used to measure ocean topography, to study the land surface, and to study rainfall from space. Future NASA active microwave missions may add detail to the topographical studies, sense soil moisture, and better characterize the cryosphere. Only recently have active optical instruments been flown in space by NASA; however, there are currently several missions in development which will sense the earth with lasers and many more conceptual active optical missions which address the priorities of NASA's earth science program. Missions are under development to investigate the structure of the terrestrial vegetation canopy, to characterize the earth's ice caps, and to study clouds and aerosols. Future NASA missions may measure tropospheric vector winds and make vastly improved measurements of the chemical components of the earth's atmosphere.

A method of wave-front tilt sensing (sensing wave-front fluctuations) that uses two quadrant detectors (QD) is described in this paper. The error in the detection of wave-front tilt that is caused by dispersion of the intensity distribution at the aperture of the receiving telescope can be reduced. The tilt can be detected more accurately than when the conventional single focal plane QD method is used. when the intensity distribution is not uniform. A function to extracting the variation in a wave-front tilt was confirmed by observation of a fixed star.

The application of a charge coupled device (CCD) based detection system to Raman lidar is described, experimental details and initials results are presented for rotational Raman studies of tropospheric temperature. The band envelopes of the Stokes and anti-Stokes rotational lines of N2 and O2 were measured simultaneously at a spectral resolution of 0. 1 8 nm and a Marquardt-Levenberg fitting method used to construct atmospheric temperature profiles from the ground. The system's potential as an altitude resolved atmospheric probe of temperature is discussed.

Progress of Japanese lidar or laser radar technology is reviewed briefly. Recent and future activities of the research and development of the lidars are outlined for environmental research and industrial monitoring applications.