China has conducted radar remote sensing technology and application for more than 20 years. In 1979, the first synthetic aperture radar (SAR) sample system in China was successfully developed by the Chinese Academy of Sciences. Since then a single channel with single polarization SAR and a multi-channel with multi-polarization SAR systems were produced in 1983 and 1987 respectively. Since 1988 the Hi- Tech Research and Development Program of China has organized and conducted a research titled 'Spaceborne SAR and Image Processing Technique', and has accomplished a real time digital SAR imaging processor.An airborne SAR with L-band and HH polarization was flown experimentally in 1997, acquiring imagery with 3 X 3 m spatial resolution. All these progresses have laid good foundations for the development of spaceborne SAR in China. At the same time, China has carried out extensive international cooperation in radar remote sensing, and has participated in SIR-C/X-SAR, Radarsat, ERS-1/2, JERS-2 SAR and GlobeSAR research programs for earth observations. The remote sensing satellite ground station in China can receive Radarsat and other spaceborne SAR data. Using these SAR data, significant application results have been achieved in the detection of ecology, hydrology, geology and oceanography, and monitoring of natural hazards.

Because of the ability to provide data of the earth's surface independent from sun illumination and cloud coverage, SAR has become a valuable complement to optical remote sensors, such as SPOT HRV, MOMS-2 etc. In this paper, the equivalent scan-line projection geometry is adopted to carry out the stereoscopic intersection of satellite SAR data. According to this geometry, the collinearity equations can be written to express relations between the image points and the corresponding ground points. Then the collinearity equations are used to compute the orbital parameters for each image of the stereopair, respectively, which is called the backward space intersection. By using the collinearity equations combined with the computer orbital parameters and the measured image coordinates, the forward space intersection is carried out, from which the slant distances R₁, and R₂ from an unknown ground point to the left and right antennas are computed, followed by the computation of the range difference dR; and then the relevant relations between the unknown ground coordinates and the distance difference dR are used to compute the unknown ground coordinates.

Spaceborne microwave (MW) remote sensing of rainfall distribution with multi-channel radiometers has been proved as a powerful tool in past decade, in particular with DMSP's SSM/I data. Similar instruments but with different channel combinations, such as ADEOS-II/AMSR are being developed. Although there have been several retrieval schemes used for research and operational application, improvement of retrieval accuracy is still an important subject. As part of a NASDA project for ADEOS-II/AMSR retrieval algorithm development and Chinese National High-Tech R and D Program for Space Development, we proposed two kinds of retrieval algorithms for rainfall rate over ocean with SSM/I data. The first kind of algorithm is based on the probability pairing method, in which three different retrieval rain indices composed with different combination of SSM/I's channels are used as pairing indices with surface rainfall rate data provided by NASDA, Japan. Three different empirical rainfall rate--rain index relationship are produced. The second kind of algorithm is based on the method of self organization feature mapping (SOM), a kind of artificial neural network. SSM/I data and co-located surface rainfall data are put into SOM and clustering procedure is self-trained. After training, 154 clustering centers are formed and for each cluster a regressive relationship between retrieved rainfall rate and SSM/I data is established. In this paper, these two kinds of algorithm are briefly reviewed with their developments and validation. Their respective advantages and limitations are discussed.

China is one of the largest oceanic countries in the world. China Seas, particularly southern CHina sea areas, is often dominated by rainy, foggy and cloudy weather that it is difficult to detect the near-real time, continuous marine environmental conditions, such as wind fields, surface waves, surface current and tidies, meso-scale eddies, fronts and coastal dynamic changes etc. SAR becomes a powerful tool for observing oceanic phenomena. In the paper, SAR, imaging, remote sensing methods and information extraction of oceanographic features are presented and analyzed in detail. The end of the paper, the potential of SAR images in marine applications is summarized.

In this paper, research progress in Fudan WSRSC during recent four years on theoretical modeling and data validation is reported. A theoretical model of multi-level, non-spherical scatterers is developed for completely polarized scattering in SAR remote sensing image. The Mueller matrix, coherency matrix and its eigen-analysis are discussed. Comprehensive vector radiative transfer theory and numerical approaches for multi-level, non-spherical and densely clustered scatterers are developed for the earth surfaces such as snowpack, vegetation canopy, sea surface, etc. Numerical results simulate the observations of DMSP SSM/I, ERS and other microwave remote sensing sensors. The algorithm and retrieval method of data calibration/validation for satellite-borne microwave remote sensing are discussed with theoretical simulations. Correlation of active and passive remote sensing such as ERS and SSM/I and are simulated and discussed.

Taking the Tu-Ha basin as an example, JERS-2 SAR data processing and integration with TM, airborne radioactive and magnetic survey data have been elaborated and image effects have been described in the paper. By means of the analyses of the processed images, the stratigraphy, structures, and ore-controlling factor in the study area have successfully been interpreted; the underground water mobile characteristics have been discussed; and the metallogenic environment and condition have been summarized. Based on above research results, the prospecting criteria have been proved and favorable sections have been suggested. The practice has indicated that the application of spaceborne SAR data to uranium reconnaissance and exploration has potential prospects.

The application of SAR images in remote sensing is a new subject. In this paper, the theory and method of monitoring floods by use of spaceborne SAR images are present. The image matching method based on network-feature is derived. At last, we introduce an example of using spaceborne SAR images for monitoring flood in Poyang lake which is the biggest fresh water lake in China.

In China, detailed flood maps are produced in near real time using an airborne SAR and data transmission system. Water bodies are extracted and the information is integrated with other thematic data to facilitate the rapid response to economic and humanitarian relief. One problem has been that terrain shadow on SAR images is classified as water and this proves difficult to eliminate without detailed elevation data. However interferometric processing of ERS Tandem Mission data has been used to produce a digital elevation model for a test area in China. This has been used to mask areas of terrain shadow on SAR images therefore improving the automatic classification of water bodies. The result is promising compared with the previously used method that relied on manual elimination of shadow areas.

The nonseismic geophysical exploration with its portability and low cost is the focus on geophysical exploration. The ultralong electromagnetic wave remote sensing is the one of the low cost, portable, sensitive and rapid geophysical exploration methods. The detector receiving the natural ultralong electromagnetic wave is composed of three parts: main engine with portable computer, antenna with amplifier and external power. The detector operation is always stable and repeated at the same spot but the different time. The detector with high sensitivity and high signal-to-noise ratio can reveal the geological and lithologic interfaces, strata and related mineral sources. For two-year-experiment and application, the detector resolved, a lot of problems in the geological exploration, which can be applied in finding the paleoweathering crust, mafic lave, hydrocarbon reservoir, water and oil reservoir, and sea ooze. The technology is an economic and rapid method to explorate the area under water, with cover, varied topography, human disruption and lava shields.

Rain area discrimination and rain-rate estimation are two key problems of the rain retrieval by the satellite data. First, five categories of the earth surface are divided by the cluster analysis method, i.e. convective rain, stratus rain, wet soil, dry soil and ocean. The rain area then ca be discriminated by the special sensor microwave/imager (SSM/I) data. Secondly, a mixed scattering index is defined on the basis of the conceptions of the polarization-corrected temperature and the scattering index, which are functionally related with the rain-rate. A nonlinear mixing scattering- based algorithm to retrieval rain-rate with an accuracy less than 4mm/hr is presented by integrating the linear and nonlinear relationships between the scattering index and the rain-rate. Finally, rain in Huai River Basin area of China in the Meiyu season of 1991 is studied using SSM/I data. The results show that the classification and rain-rate algorithm can give reasonably good estimates of the rain area and the rain-rate.

Rainfall distribution over global and regional scales pays important role in research and application for climate change and global water cycle within the ocean-land- atmosphere system. Satellite-borne microwave (MW) radiometry, such as DMSP's SSM/I has been proved as a powerful tool for global rainfall estimation. Although its success in revealing global pattern and annual variation of global rainfall distribution, there is still big discrepancy in the accuracy and correlation of retrieval rainfall to real rainfall. For the improvement of retrieval accuracy, we still need to investigate the relationship between MW radiometry and rainfall rate through basic radiative transfer simulation of different precipitating cloud models. In this paper the primary analysis of the simulation is given, emphasizing the difference of the simulation results and their function to the remote sensing accuracy.

A ground-based microwave heterodyne spectrometer for detection of middle atmospheric ozone has been developed at Max-Planck-Institut fuer Aeronomie, Germany. It was in operation from October 1995, until May 1996 at the Arctic Lidar Observatory for Middle Atmospheric Research near Andenes, Norway. The microwave system provided ozone profiles in the altitude range from 15 to 80km. During this period, a lidar system has been operated at the same location. The ozone profiles from the lidar covered the altitude range from 10 to 44 km. An intercomparison of 60 ozone profiles between the two instruments shows a good agreement. The mean microwave data were lower than the convolved mean lidar data by only 3 percent at 24-38 km, and higher by only 5 percent at 20-24 km. Above 38 km the lidar measurements become more and more noise dominated, resulting in increasing errors and disagreement with the microwave measurements. The intercomparison suggests that the ozone profiles, provided by the microwave instrument, are not modulated by tropospheric transmission variations and that the other systematic error sources like residual baselines are properly modeled.

The effects of the hydrometeor spectra and water-coated ice spheres in a precipitating cloud on radiation transfer has been studied in a numerical experiment with an algorithm for analytical solution to microwave radiance based on the Eddington approximation. The results have shown that radiant fluxes at some levels in the cloud would change if either the size spectrum changes or some of the ice spheres are coated with liquid water. Nevertheless, whether the variation can be reflected in out-going brightness temperatures at the earth's surface and cloud top depends on rainfall rate, wavelength, size spectrum of water-coated ice spheres, and the thickness of the coat. Radiation transfer and out-going brightness temperatures at 6.6, 10.7 and 18 GHz are influenced more than at higher frequencies.

A practical method is provided, which is used for forecasting lower atmospheric refractivity profile in short time. For an experiment which sounding the profile at sunrise and sunset when the refractivity varies violently, it is used to forecasting the profile. With time various parameters measured by microwave refractometer it can forecast the lower profile in 2-3 hours, the forecasted profile agreed with the sounded profile very well.

In this paper the recent decades, radar remote has played a more and more important role in atmospheric research. In this paper we discuss the 915MHz microwave Doppler radar, which obtain the mean wind profiles in the Atmospheric Boundary Layer. The radar receives backscatter from clear- air's refractive-index fluctuations. It can provide vertical profiles of horizontal wind speed and direction and vertical wind velocity. It can also provide virtual temperature profiles with a Radio Acoustic Sounding System. In this paper, we discussed the radar parameters and some atmospheric factors that can affect the result of the radar. We also discussed the result of radar under different meteorology condition. The refractive index structure function parameter, C_n², can also be taken from Doppler velocity spectra measured by the radar.

The Atmosphere Boundary Layer is the most accessible layer of earth's atmosphere. It is also the most important layer to the atmospheric research. We measure the wind and turbulence profile in the ABL with a Doppler Sodar which can cover from 30m up to 300 500m, and a boundary microwave wind profiler, which can cover from 100m up to 3000m. With all these experimental sets, we can get the continuous profiles of wind, refractive index structure function parameter, C_n² and the wind structure C_v² from the ground up to 3000m. From the result of these sets, we can obtain the characteristics of profiles and diurnal variations.

It is given in the paper the method to study the static models which can be used according to surface meteorological data, to calculate the radiation received by antenna side lobes of round base radiometer. The statistic models for radiometer operation in frequency about water vapor absorbing lines are presented. Some actual experimental observations demonstrate the method workable.

In the research of using HF ground wave radar to detect sea environment, we adopt symmetrical Yagi antenna array, correct the influence on antenna beam direction by platform on-sea and sea surface, optimize the schemes in the post- processing, which include multiple correlation, Bragg- Doppler spectrum identification and reconstruction processing. During the signal gathering, the statistical character of slow sea-state variation is utilized. It facilitates the multiple correlation integration and satisfy the requirement for reconstruction processing. So the reliability of extracting sea echo data and articulation of Bragg-Doppler spectrum are greatly improved. We simulate how platform on-sea and sea surface influence beam direction with scale model. And under varied conditions the rise degree of main beam is measured. These data can help us correct the direction of vertical antenna during practical erecting. With these data, we do the inversion of sea surface flow field and wave field parameters. The result agrees with what the standard scaling machine measure.

Measurements of electromagnetic backscattering from sea surface at L band have been done with airborne side-looking radar system. Several flights are made for various sea states. Coherent radar data ta HH polarization and some truth data such as wave height, wind velocity and direction, temperature of sea water are recorded. Corner reflectors and active backscattering coefficient can be derived from the radar data and the cinematic data. The result presented in this paper include scattering coefficient and statistical analysis of radar echo with typical probability distribution functions such as Rayleigh, Weibull, Log-normal and K distribution.

In this paper, the statistical analytical results are introduced. The data of radio sounding had been obtained at Xiamen and Dongshan in Fujian in October 1995 and 1997. The emphases are on the horizontal and vertical distribution of atmospheric refractivity and vapor density in this area. The atmospheric model for correction of tropospheric radio refraction and its parameters have been given in charts and tables. The parameters include the refractivity at sea level, on the ground, above 1km and elevation of 9km and other latitude. It also includes the horizontal and vertical gradient of the refractivity and vapor density. The statistical results provide the basic environmental data for the correction and prediction of the refractive effect of radio wave system and of communication system signal loss.

This paper presents the theory of remote sensing of sea state by high frequency ground wave over-the-horizon radar. The mathematical models for extracting surface current, surface wind and key sea wave parameters from high frequency ground wave radar sea echo Doppler spectrum are derived. By these models, sea wave parameters within Bohai sea gulf area are extracted by radar first time in China and the experimental derivations are also reported.

Based on the nearly coincided and collocated SSM/I and radiosonde data provided by NASDA (Japan), a self-organizing map (SOM) network-based model is developed for retrieving the oceanic total precipitable water (PW) from the SSM/I brightness temperature measurements. The model was firstly trained with the 5/6th of the data and then tested by the rest data. Comparisons of retrieved results with other algorithms show that the SOM model is significantly better than the classical statistically-based algorithms, especially in the low PW regime. The consuming time for PW retrievals with the SOM model is also acceptable in the operational applications.

The purpose of this paper is to evaluate JERS-1/SAR data for determining vegetation types in arid regions. First, a noise speckle filter was applied to the original JERS-1/SAR image data using a Map Filter with an adaptive 7*7 window. Second, a small part of the study area was extracted for the full scene image for further analysis. The NRCS values of each extracted image data were computed with the known Calibration Factor for the NASDA supplied JERS-1/SAR data. Each image was assigned to one of the three categories with two selected threshold levels. These two threshold levels can be obtained by Otsu's Automatic threshold selection method.In order to generate color composite images, multi- temporal SAR images were registered with the JERS-1/OPS image using a second-order polynomial function. The accuracy of registration was within 0.5 pixel RMS error. Following this color composite an image based on above three scenes was generated to identify the training samples. Finally, the color composite image was evaluated for vegetation type discrimination in the study area. A test site along the Tarim River in the Tarim Basin, China, was selected for this purpose.

This paper presented an inverse method of moisture and roughness of wet soil, which is based upon the small perturbation scattering model, the Kirchhoff model, integral equation model and the model of wet soil. Analysis and inversion examples show that this inverse method is feasible and effective.

Expressions for calculating the attenuation cross sections of poly-disperse, small spheroids, whose rotatory axes are in specific status, have been derived from a universal formula for calculating the attenuation cross section of a particle of arbitrary shape. Attenuation cross sections of liquid, ice, and spongy spheroidal droplets in different size and eccentricity at different wave lengths have been computed and analyzed.

In this paper, a time-varying band-limited fractal model is proposed for modeling dynamic evolution of sea surface. A new method for scattering from fractally rough perfectly conducting or dielectric surfaces is formulated with use of the T-matrix analysis and the extended boundary condition method. We expand the field through generalized Floquet modes and obtain the analytical formula of the expression of matrix elements in the term of the Bessel functions. We obtain analytical closed-form expression for the scattering amplitudes for both horizontal and vertical polarization of the incident electromagnetic waves. The validity of this method is checked through the energy-balance parameter and comparison with approximate method. Backscattering energy pattern versus incident angle, fractal dimension have also been discussed. We also calculate the scattering coefficient as function of time using this method. Finally, numerical scattering results from fractal surfaces are provided.

In this paper, a scheme of microwave interferometric radiometer for earth observation is proposed. The movement of the interferometer will produce a u-v plane coverage of the visibility function, which can be used for imaging of the brightness temperature distribution. The coverage is analyzed and some comparisons of this interferometer with that for space observation are made. The inversion method is proposed and simulation results are presented to show the possibility. Some open problems are drawn out for further researchers.

A X-band ground-based radiometer-scatterometer system (RASAM) is designed for a ground-based microwave remote sensing. By measuring backscattering coefficient (sigma) ⁰, brightness temperature T_Bp and emissivity e_p, active and passive microwave characteristics of ground objects can be obtained. This system operational model uses a combination of two references digital demodulated radiometer with noise scatterometer. This paper describes RASAM design, instrument structure and experiment results.

In microwave remote sensing, if we want to acquire active and passive remote sensing information of an object simultaneously, we usually measure it with a scatterometer and a radiometer at the same time. Because two remote sensors are used, the experiment is very complicated. A scattero-radiometer is developed in order to reduce remote sensor cost and experiment difficulty. This scattero- radiometer consists of a continuous wave scatterometer and a digital gain compensation radiometer. In this paper, the block diagram and the timing program of this scattero- radiometer are detailed submitted. Performance test show that the scattero-radiometer not only remains original performance of a scatterometer and a radiometer, but also is able to measure backscattering coefficient and brightness temperature simultaneously. It is more fit for acquiring active and passive microwave remote sensing information simultaneously.

The types and technology performance of multi-frequency microwave radiometers designed and developed from 1973 are briefly introduced. Some images and data for land and sea surface by our multi-frequency microwave radiometers are given. Technology foundation of developing spaceborne microwave radiometers and space systems for monitoring natural disasters in China is discussed.

A dual channel Airborne Microwave Radiometric Imaging system (AMRI) was designed and constructed for regional environment mapping. The system operates at 35GHz, which collects radiation at horizontal and vertical polarized. It runs at mechanical conical scanning with 45 degrees incidence angle. Two Cassegrain antennas with 1.5 degrees 3 dB beamwidth scan the scene alternately and two pseudo-color images of two channels are displayed on the screen of PC in real time. Simultaneously all parameters of flight and radiometric data are stored in hard disk for postprocessing. The sensitivity of the radiometers of flight and radiometric data are stored in hard disk for postprocessing. The sensitivity of the radiometers (Delta) T equals 0.16K. A new display method, unequal size element arc displaying method, is used in image displaying. Several experiments on mobile tower were carried out and the images demonstrate the AMRI is available to work steadily and accurately.

Microwave radiometer is a kind of passive microwave remote sensor. Generally microwave radiometer is considered passively receiving radiation from the object and no energy radiate from the antenna to the outside. In the practical system, the components of radiometer really have thermal noise and radiate energy in the reverse direction. In another case, the reverse radiation comes for the mismatch of the components between the antenna to the receiver system. The energy radiates to the outside through antenna, and reflected back by the objects and received by antenna again. The value of reverse radiative temperature is related to the noise of the receiver and components of the receiver front-end. The reverse radiative temperature in the system will affect the accuracy of the calibration of microwave radiometer and the ground-based microwave radiative measurements near nadir angle.

Microwave radiometer, as one of the most useful tools in remote sensing of earth resources and environment, has been developed rapidly. The recent research in this area is to concentrate how to improve spatial resolution. But the methods, which depend on increasing antenna aperture or decreasing carrier wavelength to obtain high spatial resolution, are inapplicable to aerospace engineering. The synthetic aperture technique needs the coherence effect of active microwave transmitted signal, so it cannot be used by passive radiometer. In this paper, a new approach is introduced. Firstly, the radiation of far-field target is received by 2D linear antenna array. The incident signals received by all array elements have an amount of delay among them. These coherent signals of same wave front are amplified individually and applied to piezoelectric transducers of a multi-channel Bragg cell. The electronic signals are converted into traveling acoustic waves in acousto-optic cell. The refractive index of crystal is changed proportionally to the input voltages. When collimated laser is incident upon the crystal, Bragg diffraction occurs. Fourier transform lens produces optically a 2D Fourier transform of the signals in a charge- coupled device plane. The direction and radiation intensity of arrival signal can be obtained simultaneously. Since the radiation signal of some far field target in the antenna coverage can be detected individually, that means the spatial resolution of radiometer can be improved. Theoretical derivation will be given in detail in this paper.

Spaceborne microwave radiometer is an important remote sensor in acquiring information of the earth's surface. That its behavior is good or bad affects directly the success or failure of the whole satellite. Because analysis and test directly in real system will take very large risk and price digital simulation becomes an effective measure. This paper advances a basic idea and goals of digital simulation study of spaceborne microwave radiometer. The mathematical models of all sections in total-power microwave radiometer are built. And the simulation study of total-power microwave radiometer has been done. In simulation test discrete fast Fourier transform is used in signal processing. The simulation results prove that the models are accurate and effective. Also the result lay a foundation for the advancement of realizing spaceborne environment simulation test.

In this study, we develop an independent method to derive global temperature trend from Microwave Sounding Unit (MSU) radiometer observations in Ch 2, made from sequential, sun- synchronous, polar-orbiting NOAA operational satellites. Also, a detailed examination of the systematic errors in these data is performed with the objective to improve this method. Partitioning these data from 75 N to 75 S into global land and ocean sets, and further subdividing them into AM and PM subsets with the help of the LECT, enables us to perform this examination. The systematic errors in the MSU Ch 2 data are mainly related to differences in the MSU instrument calibration and the Local Equatorial Crossing Times (LECT) of successive satellites. They can be removed from these data with the help of the overlapping observations made by successive satellites. Errors in the MSU Ch 2 data are also introduced by orbital drift, which is the progressive change in the LECT of a satellite. Changes of the AM and PM observation times due to orbital drift causes Ch 2 brightness temperatures from each satellite to be affected by the diurnal cycle. In addition, orbital drift alters satellite illumination by sun, and thereby the instrument calibration. These errors introduced by orbital drift cannot be eliminated objectively. However, in this study, the uncertainty in the global temperature trend resulting from the cumulative error generated by drifts of all the satellites is inferred with an indirect approach. Based on our method of analysis of the MSU Ch 2 data, we find a global temperature trend from 1980 to 1996 of 0.11 K decade ^-1 with an uncertainty of 0.06 K decade ^-1.

Satellite measurements from the Special Sensor Microwave Water Vapor Sounder are used to study the scattering effects of cirrus clouds at 183 GHz. These measurements are used in conjunction with near-coincident Geostationary Operational Environmental Satellite imager observations of visible optical depth and effective particle size. For a case of extensive cold front cirrus off the eastern US coast, the 183 GHz brightness temperature depression relative to clear skies averaged about 3 K, but sometimes exceeded 6 K. The mean effective radius of the ice particles was 141 +/- 14 micrometers . These results show promise for the estimation of ice water path form combined (Delta) T_b and effective particle size observations.

The advanced microwave sounding unit (AMSU), launched on May 13 1998, is a twenty-channel passive microwave radiometer deisgned to provide information on atmospheric temperature and humidity structure in clear and cloudy conditions, complementing existing IR radiometers which provide information only in clear areas. AMSU has some channels similar to those flown on existing missions and others which are new. Observed radiances from the special sensor microwave imager and the microwave sounding unit are compared with radiances calculated from numerical weather prediction model profiles, and the differences discussed. A processing method for ATOVS radiances is described, and differences from previous techniques are highlighted. An initial evaluation of AMSU data is given. Finally the impact of passive microwave observations on the skill of numerical weather forecasts is discussed.

In recent year san increasingly diverse range of passive microwave satellite data has become available for applications in numerical weather forecasting, climate studies and environmental monitoring. Top of atmosphere radiance is measured, which as originated from both the surface and the atmosphere. When retrieving atmospheric quantities such as temperature, humidity or cloud liquid water content near the surface it is necessary to account correctly for the contribution to the measured radiance from the surface. This depends on the surface emissivity, which varies widely with surface type, roughness and temperature. For real time applications such as numerical weather forecasting, it is necessary to be able to model the surface emissivity very quickly. There is therefore a need for a fast surface emissivity model has therefore been developed. This is a semi-empirical mode. Some aspects are physically based, for example many surface scan be assumed to be di- electric media. Other aspects such as geometric roughness have been parameterized for speed. For some complex or poorly understood aspects of the electromagnetic interaction empirical adjustments are made to fit observed values. The model has been compared with emissivities derived from aircraft radiometer measurements at 24, 50, 89 and 157 GHz. It is also intended to compare with data from the special sensor microwave imager and advanced microwave sounding unit instruments. For the ocean surface the fast model fits estimated emissivities from airborne radiometers two within 1-2 percent, and it fits the unparameterized model to within 0.1-3 percent.

This paper presents an algorithm for calculating wind profiles form profiler Doppler spectra. Our algorithm produces hourly averaged winds by consensus averaging of the spectral peak power densities. The peak power method, applied separately on each height and on each antenna beam, can detect the atmospheric echo in each spectrum which results in the calculation of radial velocities in all antenna beams. The consensus algorithm is then applied to average over one-hour intervals using 12 radial velocities over each hour. A resultant 24-hour profile of horizontal winds is given to illustrate the effectiveness of the algorithm.

This paper proposes an efficient way to retrieve the microwave emissivity from advanced microwave sounder unit (AMSU) brightness temperature measurements. In the first step, the atmospheric temperature profile, moisture profile and surface skin temperature are determined using AMSU channel 5 to 14, 18 and 19 which are less sensitive to surface radiation. In the second step, the microwave emissivity is then determined using the AMSU window channel 3. Finally, the atmospheric profile and the microwave emissivity are retrieved simultaneously based on a non- linear iteration algorithm using all AMSU and high resolution IR radiation sounder measurements. Simulation results have shown this algorithm is practical in solving for the microwave emissivity. This algorithm will be part of the International ATOVS Processing Package developed by Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin-Madison.

Several methods are proposed in this study to retrieve some cloud physical parameters from ground-based simultaneous observations with a microwave radiometer and other instruments. When cloud is thin, liquid water path and columnar water vapor amount can be retrieved to be consistent with measured intensities of two frequencies around 20 GHz and around 30 GHz under the assumption of homogeneous cloud temperature. In this retrieval procedure, cloud temperature, which affects the calculated value of liquid water path seriously, is given form measurement with an IR radiative thermometer. The effective radius of cloud particles is also derived from comparing the measured downward solar flux on the ground surface to calculated one. For the thick cloud, which is expected that the temperature difference between top and bottom of cloud is large, cloud top temperature is also retrieved from narrow view angle measurements of transmitted radiance of solar radiation at two wavelengths in addition to microwave measurements. The liquid water path is deduced from the comparison of measured radiances at the two wavelengths to the calculated values, thus the appropriate cloud top temperature can be retrieved to be consistent with the measured microwave intensity at two frequencies. Practices suggested that the observation with a microwave radiometer and a pyrnometer enables to derive the detail of cloud structure.

The Institute of Applied Physics has developed a new model, called BEAM, for the simulation of microwave propagation in the atmosphere. The model is very flexible and can be used for simulations as well as operational retrievals. Microwave spectra are calculated using data from the JPL and HITRAN spectroscopic databases as well as the millimeter wave propagation model MPM-93. An new automatic frequency selection algorithm can increase the speed of the calculations by a factor of 10-100 under certain conditions.

The objective of the European project EMCOR was the development of a heterodyne receiver for the frequency range of 201 to 210 GHz for the measurement of the amounts of various minor constituents of the stratosphere involved in ozone chemistry. In order to be able to measure even very faint spectral lines a superconducting tunnel junction has been chosen as mixer element. Additionally, special care has been taken in developing the calibration unit of the system. Besides the classical hot-cold calibration three different balancing methods can be employed: a beam-switch technique with an atmospheric reference signal, a beam switch technique with a reference signal from a variable reference load or a frequency switch technique. The system has been integrated and is currently under testing. It will be installed at the International Scientific Station Jungfraujoch in he Swiss Alps and operated within the framework of the European Alpine stations of the Network for the Detection of Stratospheric Change.

The 268-280 GHz radiometer MIRA2 was constructed for ground- based monitoring of vertical profiles of minor stratospheric constituents and has been optimized especially for the observation of the extremely weak chlorine monoxide signature at 278 GHz and its diurnal variation. For calibration an adjustable internal load was developed, which provides any required brightness temperature from cryogenic to ambient temperatures, dependent on mechanical adjustment. In comparison to the well established external beam switching method this new technique result in a higher contrast in particular under critical conditions of the troposphere, For inversion of the measured spectra the modified Constrained Linear Inversion and the Optimal Estimation Method were used alternatively. The extensions of these well established methods include the fit of standing waves within the inversion process itself an the joint retrieval of several spectral lines. The advances in calibration and inversion techniques became obvious during the evaluation of the data measured at Kiruna, Sweden, 1996 and 1998, and Ny-Alesund, Svalbard, 1997. Profiles of the trace gases Ozone, N₂O, HNO₃ and ClO could be retrieved. From the data measured in Ny-Alesund a unique time series of ClO- and Ozone has been achieved which shows diurnal and long term variations of ClO and Ozone, respectively.

A rain-rate range-profiling algorithm has been developed for 'standard' data processing of TRMM Precipitation Radar (PR). Major challenges in the algorithm include the corrections for the effects of rain attenuation and non-uniform beam filling (NUBF) and in the rejection of surface clutter. A combination of the Hitschfield-Bordan and surface reference methods is used to correct radar returns for the rain attenuation. The NUBF effects are estimated from the spatial variations of the estimated total path integral of attenuation from the top of rain to the surface in the vicinity of the radar beam concerned. In this paper, we first outline the range profiling algorithm. Next we show two examples of PR observation; a typhoon over Pacific and a squall line over Florida. In the Florida case, we compare the PR and ground-based radar measurements. The results indicate that this algorithm is basically working well. Further studies are needed to statistically evaluate the performance.

The power density spectra of wind profile are usually contaminated by persistent ground clutter. The radial wind speed estimated in such spectral data can produce a considerable error if each spectrum is processed independently. For the clutter-elimination purpose, we propose an algorithm for estimating radial wind speed that takes into account a spatial relationship within range-gated spectra. The candidates for the atmospheric echo in each spectrum are firstly determined by detecting all local power density maxima in the smoothed and normalized spectra. The spatial relationship is then exploited by linking those local maxima across gates, with respect to a continuity criterion. A number of features can be extracted from each candidate and a neural network is subsequently used to identify the local maximum most likely reflecting the radial atmospheric velocity.

Snow water equivalence, which is the product of snow density and depth, is the most important parameter in snow hydrology. This paper demonstrates the algorithms for estimating dry snow density, depth, grain size, under-ground dielectric constant and surface RMS height using multi- frequency and -polarization SAR measurements. The algorithms were developed based on the numerically simulated backscattering coefficients. We use L-band VV and HH to estimate snow density and the underground surface parameters: dielectric constant and roughness RMS height. The underground surface can be either soil or rock. Then, C- band VV, HH and X-band VV are used to estimate snow depth and grain size. The validation from the field snow density measurements averaged from the top and bottom snow layers indicate that an absolute and relative accuracy of 0.042 gcm^-3 and 13.15 percent can be expected. The comparison with the ground scatterometer measurements showed RMSE of 4.1 percent by volume for solid moisture estimation and 0.42 cm for the surface RMS height with this newly developed algorithms. The validation by using three SIR-C/X- SAR image data indicated that this algorithm performed well for incidence angle greater than 30 degrees with RMES 34 cm and 0.27 mm for estimation of snow depth and ice optical equivalent particle radius, respectively.

The mirror image rain echo, received through the double reflection of the radar from the surface, may provide useful information in estimating the rainfall rate form airborne and spaceborne weather radars. As the TRMM spaceborne weather radar has been successfully launched recently, issues regarding the utility of this measurement are pertinent and timely. In this study, having described a mirror image model, which yields the co- and cross-polarized components of the mirror image nd bistatic returns as a function of the radar parameters and the scattering properties of the rain and surface, several algorithms to estimate the path attenuation based on the mirror image returns are constructed. These methods generally use a difference between the direct and mirror image radar returns where the returns are taken at equally distant ranges above and 'below' the surface. In some implementations of the algorithm the return power from the surface is used as well. To test the accuracy of these algorithms, the first, mirror image and surface return powers are generated from measured raindrop size distributions, a surface scattering model and a mirror-image scattering model. These models can be used to control the characteristics of the rain profiles as well as the surface scattering characteristics. Comparisons between the mirror-image and the surface reference techniques are made for various rain intensities, vertical rain profiles and surface scattering characteristics. In the final part of the paper, some preliminary results of comparisons of the mirror image algorithms with the surface reference technique are given using data for the TRMM precipitation radar.

The polarization corrected temperature (PCT) derived from SSM/I 85 GHz data is used for the retrieval of rainfall rate over South China in the summer season. The 85 GHz PCT observed from space is strongly dependent on the emission and scattering by cloud and rain droplet particles. Hourly rain gauge measurement data were used to relate PCT with surface rainfall rate. Since the rainfall phenomena have large variabilities in time and space, a direct comparison between rain gauge measurement and satellite measurement is not adequate. On the other hand the rainfall rate distribution in a wide area does not change even if the measurement time is slightly different. Therefore the rainfall rate distribution measured with rain gauge and PCT change distribution were compared and a relationship between them is constructed. By applying it to SSM/I data, rainfall properties over the South China during periods from June to August of 1991-1995 were investigated.

Regression method, look-up table technique, neural network, and physical inversion method are discussed in this study. Results from model calculations and measurements show that all retrieval algorithms achieve the similar accuracy for total precipitable water and sea surface wind. However, in contrast to the regression method physical inversion method, look-up table technique, and neural network yield a better accuracy for the cloud liquid water path. Instantaneous comparisons between ship-based radiosonding and the estimate from Special Sensor Microwave/Imager give rms errors of 2.9 Wm^-2 and 2.7 ms^-1 for the total column water vapor and sea surface wind, respectively. Due to the limit of data source comparison for cloud liquid water path is only performed for different data sets. Comparison for precipitation is only carried out with different algorithms.

It is shown that geophysical inversion problems can be solved by usage of a hybrid algorithm, which combines optimal estimation with further optimization techniques. We employ a Bayesian approach to nonlinear inversion and discuss several extensions of this method. Especially, a sensible guess of a priori information, the shape of the probability density functions, the utility of Monte Carlo methods, and the advantages of simulated annealing have been investigated. All these techniques furnish capability of retrieving state vectors, which depend on the data in a highly nonlinear manner. A combination of these powerful tools can provide solutions to questions that cannot be tackled with standard inversion methods properly. As a moderately nonlinear optimization problem, profiling of water vapor based on downlooking microwave sounder data is a typical geophysical problem that could not be treated with standard inversion algebra adequately. Based on synthetic state vector data, we show the potential and the characteristics features of all of the hybrid algorithm's components contributing to the retrieval of the state. The hybrid algorithm has been employed in a way that it is able to provide humidity profiles in a numerically stable and computationally efficient manner. Using this example application, the benefit of a hybrid approach is demonstrated.

The feasibility of retrieving water vapor profiles from SSM/T-2 data is demonstrated by usage of an extended Bayesian inversion algorithm. The SSM/T-2 downlooking sounder data consisting of brightness temperature measurements in five microwave bands sensitive to water vapor absorption can be used, together with total water vapor content data, in order to compute water vapor profiles of about 3-5 km vertical resolution. The corresponding radiative transfer equation yields a nonlinear mapping of state space into measurement space. This is reflected in a significant nonlinearity in the cost functional which has to be minimized, and necessitates several extensions of the well known optimal estimation inversion. We supplemented the optimal estimation by simulated annealing and iterative a priori lightweighting. The resulting a hybrid algorithm furnishes capability for acting as an important source of height-resolved meteorological information. Retrievals based on SSM/T-2 data were compared to atmospheric analyses of the European Centre for Medium-range Weather Forecasts. A statistical validation for the retrieved profiles is presented. The comparisons indicate an approximate accuracy of about 15 to 20 percent for relative humidity. The developed algorithm can be readily extended to include all sensible sources of additional information, on the state as well as from additional measurements.

Precipitation radar (PR) on-board the Tropical Rainfall measuring Mission (TRMM) satellite is the first rain radar to measure precipitation from space. After the successful launch of the TRMM satellite in last November, initial on- orbit test and calibration of the PR were conducted for about two months. From these tests, it was confirmed that on-orbit performances of the PR are fundamentally coincident with those verified at ground test and satisfy the specifications.

The NOAA-K polar-orbiting satellite was launched on 13th May 1998. On board are a number of new instruments, including the microwave sounders AMSU-A and AMSU-B. The UK Met Office were responsible for the procurement and characterization of AMSU-B and have a continuing role in supporting the program. The first AMSU-B flight model was activated in orbit on 20th May 1998. This paper describes the initial test that were conducted on the instrument and gives some preliminary results. Functionally, the instrument appeared to work well, but major discrepancies were apparent for two channels between measured and predicted brightness temperatures. The problem has been traced to RF interference from spacecraft transmitters; characterization of the errors is still in progress. Finally, a technique is outlined, and preliminary results presented, for measuring the co-channel alignment between the 89 GHz channels on AMSU-A and AMSU-B.

A new algorithms is developed whereby the cloud liquid water path (LWP) and the total precipitable water (TPW) may be determined from microwave radiometric data. A large meteorological database obtained from the European Centre for Medium-Range Weather Forecasts forecast model is used to simulate, with a radiative transfer model, brightness temperatures (T_B) at the top of the atmosphere for the special sensor microwave imagery frequencies. A single- hidden-layer ANN was used. An error backpropagation training algorithm was applied to train the ANN. A first comparison with a log-linear regression algorithm, shows that the ANN can represent more accurately the underlying relationship between T_B and, TPW and LWP. The ANN seems to be able to give a better fit at large values of LWP. Furthermore in the case of TPW, a validation is made with radiosonde data, with another new algorithm.

Passive radiometers at 100-700 GHz offer great potential for remote sensing of cirrus clouds and upper-tropospheric water vapor from space because radiation at these frequencies can penetrate and interact with cirrus clouds without being cut off at/near cloud surface. This paper focuses mostly on satellite microwave observations from UARS MLS at 186.5 and 203.2 GHz. Advantages of limb-viewing geometry include better vertical resolution and less contamination of Earth's surface conditions since the limb background radiance depends only on pointing and water vapor abundance. MLS radiance measurements show that water vapor and cloud signals are separable with frequencies of different sensitivities to water vapor. The cloud-induced radiances can be used to directly retrieve ice water content at 14- 18km altitudes if the ice particles are smaller than 100 microns. Model simulations at these frequencies are also presented for various cloud types and heights. With the modified MLS radiative transfer mode, we are able to simulate limb and nadir radiances at all frequencies between 10 and 1000GHz for both cloudy and clear atmospheres. Our sensitivity studies show that brightness temperature depression at the lowest MLS tangent height can be used to infer cloud height and ice content in the upper troposphere. With more channels near 122, 240, and 640 GHz, we find that the chance of separating cirrus cloud and water vapor is greatly enhanced, and these radiometers are to be flown as the future MLS on board NASA CHEM-1 spacecraft.