Validation experiments for the EarthCARE ATLID JAXA Level 2a data products using the ground-based lidar network, the Asian Dust and aerosol lidar observation Network (AD-Net) are described. The ATLID JAXA level 2a standard data product consists of the feature mask, target mask, and optical parameters for aerosols and clouds, and planetary boundary layer height. The ATLID JAXA L2a research data product provides extinction coefficients for aerosol components (water soluble, mineral dust, sea salt, black carbon). Direct comparison with the ground-based 355-nm HSRLs and Raman lidars in AD-Net is the basic method for validating the standard data products for aerosol. A data matching method considering the trajectory of air mass is employed. Statistical comparison in the suitable temporal and spatial regions is employed in the validation of feature mask, target mask and cloud optical parameters, because the spatial distribution scale is small for clouds. In the validation of the research data product (extinction coefficients of aerosol components), multi-wavelength HSR and Raman lidars are employed because the aerosol components can be better estimated with more measurement parameters.
We have developed algorithms to produce JAXA ATLID level two products using data measured by the lidar ATLID and imager MSI onboard the EarthCARE satellite. The algorithms estimate particle optical properties such as extinction, backscatter, and depolarization ratio as well as layer identifier, particle type identifier, and planetary boundary layer height. Furthermore, the algorithm estimates extinction coefficient of four aerosol components, dust, sea-salt, carbonaceous, and water-soluble particles using ATLID data; the other algorithm uses both ATLID and MSI data to estimate the extinction coefficient of the four aerosol components and column-mean mode-radii of fine-mode and coarse-mode aerosols. Prior to the ATLID algorithm development, we have developed a similar aerosol component retrieval algorithm using CALIOP and MODIS data; this technique was introduced into the ATLID algorithm. These algorithms were applied to the CALIOP long-term data, and the estimates have been used for evaluating aerosol radiation effects and data assimilation.
Atmospheric High Spectral Resolution Lidars (HSRLs) are unable to perform measurements close to the emission source because, apart from being blind in the first hundredths of meters (overlap problem), their spatiotemporal resolution is insufficient since they use low repetition rate and ultranarrow band (and thus long-pulse) lasers. In this work, we present the proof-of-concept of a compact short-range HSRL (SR-HSRL), closing the gap of aerosol characterization in the short-range. The system and laser were characterized, and the right balance between spectral performance (laser linewidth) and range resolution (pulse duration) was found. Then, the SR-HSRL concept was tested, measuring water droplets under controlled conditions. We demonstrate that it is feasible to implement the HSRL technique in the short range to characterize aerosols near the source without making assumptions.
In the southern South America, various types of aerosols have been observed including biomass burning aerosols from the Amazon region, flying ashes from the volcanic eruptions coming from the Andean Volcanic Belt, mineral dust from the Patagonian Desert, and air pollution aerosols from urban areas. To monitor such aerosols continuously, we developed a lidar observation network in Argentina and Chile. Eight lidars were installed in Argentina and one in Punta Arenas, Chile. Backscattering signals are measured at three wavelengths: 355, 532, and 1064 nm. Eight of those instruments are measuring depolarization ratio at 355 and 532 nm to detect non-spherical aerosols. In addition, four lidars are equipped Ramans channels and two high-spectral-resolution channels to measure backscattering and extinction coefficients quantitatively. Lidar operation, data analysis, and products release are implemented within the South American Environmental Risk Management Network (SAVER-Net) system, which was developed by a trinational project among Japan, Argentina, and Chile. Using lidar data, hazard information on the aerosol type and extinction coefficient at low altitude is provided for public in a near real time. In addition, plume height and qualitatively concentration for volcanic ashes are estimated. The information on volcanic ashes may be effectively used for advising aircraft landing and departing when volcanic eruptions occurs.
Aerosol observations with ceilometers have been made worldwide recently. To use ceilometer data to retrieve aerosol profiles, raw signals should be accurately converted to the attenuated backscattering coefficient. Hence, the calibration coefficient for the system constant has to be determined correctly. We conducted a ceilometer–lidar comparative experiment to evaluate the Lufft CHM15k Nimbus product. The attenuated backscattering coefficient using CHM15k was smaller by a factor of 1.48 compared to that of lidar. The calibration coefficient should be periodically corrected using the ceilometer signal itself since lidar data are generally unavailable in the field observations. We recalibrated the product using both Rayleigh fitting and cloud attenuation methods. The correction factor, determined from the recalibration, was 15% (9%) smaller when using the Rayleigh fitting (cloud attenuation) method than the factor determined from lidar. Uncertainties from backscattering ratios at the reference height and the lidar ratio can cause systematic errors in the correction factor determined from the Rayleigh fitting method. Uncertainties due to the multiple scattering factor contribute to systematic errors for the cloud attenuation method. We propose a calibration method using depolarization ratios for future polarization-sensitive ceilometers, which can estimate the calibration coefficient without multiple scattering factors.
A regional elastic-scattering lidar network called Asian dust and aerosol lidar observation network (AD-Net) has operated for 15 years (since 2001) in East Asia. In this network, the extinction coefficient of aerosols below an altitude of 9 km is continuously obtained when conditions are clear; the coefficient is divided into two parts: dust extinction and spherical extinction coefficients. The dust extinction coefficient has been compared with several parameters measured by other instruments and utilized by various studies, including studies on the epidemiology of Asian dust. Recent expansion of the lidar system at some observatories allows more optical parameters to be retrieved at those observatories. All AD-Net products are used for monitoring global environmental change as an activity of global atmospheric watch lidar observation network.
Continuous monitoring of aerosol profiles using lidar is helpful for a quasi-real-time indication of aerosol concentration. For instance, volcanic ash concentration and its height distribution are essential information for plane flights. Depolarization ratio and multi-wavelength measurements are useful for characterizing aerosol types such as volcanic ash, smoke, dust, sea-salt, and air pollution aerosols. High spectral resolution lidar (HSRL) and Raman scattering lidar can contribute to such aerosol characterization significantly since extinction coefficients can be measured independently from backscattering coefficients. In particular, HSRL can measure aerosol extinction during daytime and nighttime with a high sensitivity. We developed an HSRL with the iodine filter method for continuous observation of aerosols at 532nm in the northern region of Argentina in the framework of the South American Environmental Atmospheric Risk Management Network (SAVER.Net)/SATREPS project. The laser wavelength of the HSRL was controlled by a feedback system to tune the laser wavelength to the center of an iodine absorption line. The stability of the laser wavelength with the system satisfied the requirement showing very small systematic errors in the retrieval of extinction and backscatter.
Atmospheric monitoring stations are being developed in Argentina. The most important targets are volcanic ashes, desert aerosols in particular Patagonian dust and biomass burning aerosols. Six stations deployed in the Patagonian Region and Buenos Aires have lidar systems, sun photometers integrated to the AERONET/NASA monitoring network, in situ optical particle analyzers, four solar radiation sensors (pyranometer, UVA, UVB and GUV), and meteorological equipment. The stations are in the main international airports of the Regions (San Carlos de Bariloche, Comodoro Rivadavia, Neuquén, Rio Gallegos) and in Buenos Aires (Aeroparque Jorge Newbery and at CEILAP/CITEDEF). CEILAP and the National Institute of Environmental Studies (NIES) at Tsukuba, Japan developed the first iodine cell-based high spectral resolution lidar (HSRL) in Argentina to add in the lidar network. We upgraded the standard CEILAP multi-wavelength Raman lidar adding the laser frequency tuning system and the 532 iodine-filtered channel at the reception to built the HSRL. HSRL will provide daytime and nighttime direct observation of the aerosol and cloud optical properties (backscatter and extinction) without the pre-assumption of the lidar ratio. This work shows the design and construction of the first Argentinean HSRL. We also show the first lidar observations done in the country with this kind of lidar.
Continuous observations of aerosols are being conducted with the Asian Dust and aerosol lidar observation Network
(AD-Net). Currently, two-wavelength (1064 nm and 532 nm) polarization-sensitive (532 nm) lidars are operated at 20
stations in East Asia. At the primary stations (6 stations), nitrogen vibrational Raman scattering is also measured to
obtain the extinction coefficient at 532 nm. Recently, continuous observations with a three-wavelength (1064 nm, 532
nm and 355 nm) lidar having a high-spectral-resolution receiver at 532 nm and a Raman receiver at 355 nm and
polarization-sensitive receivers at 532 nm and 355 nm) was started in Tsukuba. Also, continuous observations with
multi-wavelength Raman lidars are being prepared in Fukuoka, Okinawa Hedo, and Toyama. A data analysis method for
deriving distributions of aerosol components (weak absorption fine (such as sulfate), weak absorption coarse (sea salt),
strong absorption fine (black carbon), non-spherical (dust)) has been developed for these multi-parameter lidars. Major
subjects of the current studies with AD-Net include data assimilation of multi-parameter lidars, mixing states of Asian
dust with air pollution particulate matter, and validation of EarthCARE ATLID based on the aerosol component analysis
method.
Ceilometer instruments are simple backscatter lidar systems and are usually set in airports for detecting the
base of clouds. The instrument can also measure aerosol vertical distribution. Since ceilometers barely detect
the molecular backscatter signals, retrieval of aerosol optical properties is an issue. This study investigates
applicability of ceilometers to retrieval of optical properties. We make an idealized signal profile with the lidar
ratio of 50 sr and calculate the retrieval errors caused by 30% errors of lidar ratio. In the forward inversion,
useable (small error) optical properties are backscattering coefficients and the retrieval errors are less than 15% if
the aerosol optical depth (AOD) is less than 0.2. The initial backscattering coefficients must be determined from
other instruments (e.g., multi-wavelength lidar). Whereas in the backward inversion, if the AOD of idealized
signals is larger than 1.5, extinction coefficients converge to the true value (within 5% errors), regardless of lidar
ratios and initial conditions. Since there is no need for the system constant or molecular backscatter in this
method, ceilometers can be an effective tool for retrieving extinction coefficients of dense aerosols in East Asia.
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