PARASOL/GRASP at ICARE

This page provides a summary documentation of the PARASOL/GRASP products available at ICARE and how to access the data.

ICARE is responsible for the processing of the POLDER/PARASOL products derived from the GRASP science algorithms provided by the French science team at LOA, and streamlined to run in the ICARE production environment. ICARE is also in charge of the archiving and distribution of the science products to the GRASP community (online archive, FTP, SSH).

    The following PARASOL/GRASP products over ocean and land are currently available:
    • PARASOL/GRASP "high precision" (slow processing)
    • PARASOL/GRASP "optimized" (fast processing)
    All products are openly distributed from ICARE (see Data Access section below).

    GRASP algorithm Description

    GRASP (Generalized Retrieval of Aerosol and Surface Properties) algorithm is designed to retrieve complete aerosol and surface properties globally. In order to achieve reliable retrieval from satellites observations even over very reflective desert surfaces, the algorithm performs retrieval as elaborated statistically optimised fitting of all available POLDER observation (i.e. at all wavelengths and using all viewing directions). In addition, GRASP is designed as simultaneous inversion of a large group of pixels within one or several images. Such multi-pixel retrieval regime takes advantage of known limitations on spatial and temporal variability in both aerosol and surface properties. Specifically the variations of the retrieved parameters horizontally from pixel-to-pixel and/or temporary from day-to-day are enforced to be smooth by additional appropriately set a priori constraints. This concept provides a satellite retrieval of higher consistency. The retrieval is conducted both over land and ocean. The details of GRASP algorithm can be found in the articles by Dubovik et al., 2011, 2014. GRASP is an open source software.

    The source code and additional documentation can be obtained at https://www.grasp-open.com/.

    The POLDER/PARASOL instruments

    Here is a brief summary of the POLDER/PARASOL missions and characteristics of the instruments. ICARE is the scientific ground segment for the missions and provides full documentation on instruments, data and services on the POLDER/PARASOL pages.
    The POLDER instruments consist of a digital camera with a 274×242-pixel CCD detector array, wide-field telecentric optics and a rotating filter wheel enabling measurements in 9 spectral channels with bandwidths between 20nm and 40nm. Because it acquires a sequence of images every 20 seconds, the instrument can observe ground targets from different view directions. The POLDER-I and POLDER-II instruments onboard ADEOS-1 and 2 are identical while PARASOL onboard a CNES/Myriade microsatellite has been turned 90 degrees to favor multidirectional viewing (maximum of 16 directions compared to 14) over daily global coverage (swath of 2400 km compared to 1600 km). Depending on the altitude of the platforms, the size of the images varies from 2400 x 1800 km2 to 1600 x 2100 km2 with a corresponding ground resolution of 7×6 km2 and 5.3×6.2 km2 at nadir. The PARASOL platform is part of the A-Train and takes advantage of the other instruments in the constellation. The 3 instrument spectral coverage ranges from blue (443µm) through near-infrared (0.91µm) with 3 polarized spectral bands. For POLDER/PARASOL, the bluest polarized channel has been moved from 0.443µm to 0.490µm and a 1.02 µm waveband has been added.

    PARASOL/GRASP aerosol and surface data products

    Input parameters and retrieval specifications

    This data sets includes the aerosol and surface reflectance retrieval product obtained from the POLDER/PARASOL data processed by GRASP code. The POLDER/PARASOL data including measurements of all angular measurements intensity at 0.443, 0.490, 0.565 , 0,670, 0, 765, 0.865 and a 1.02 µm and Q and U polarization component at 0.490, 0,670 and 0.865 at the instrument native resolution were inverted in cloud-free conditions as determined by original cloud-mask algorithm developed by Laboratoire d’Optique Atmosphérique. The data at polar regions at latitudes higher than 70 degrees north and south were not processed. The observations with less than 10 viewing directions were ignored.

    The retrieval were performed using one aerosol component model with 5 size bin size distribution and spectrally dependent complex refractive index. The aerosol vertical distribution was modeled using exponential profile and scale height was retrieved. The “high-precision” settings were used in RT modeling of multiple-scattering in the atmosphere in producing the data.

    Output parameters

    The full list of the retrieved parameters, as well as additional characteristics derived from retrieved parameters can be found in the POLDER/PARASOL Products section, in the table of all POLDER/PARASOL Level-3 science products, or from here: PARASOL/GRASP product file description.

    Further details of the retrieval setting can be provided on request (See contact information below).

    Data Access

    Access to the data is subject to the Data Policy below. All users must register beforehand. Registered users can access the data through the Archive Web Interface and the FTP server:

    Data Policy

    The products provided on the ICARE server are openly and freely available. No warranty is given by their providers. Users must acknowledge the GRASP project and ICARE as the service provider. We encourage interaction with the service providers on proper use of the products and would like to receive a copy of all reports and publications using the datasets. An offer of co-­authorship should be considered, if the GRASP datasets constitute a major component of a scientific publication.
    Credits for science products
    Publications using data from GRASP/ICARE must include the following sentence:
    "POLDER/PARASOL Level-1 data originally provided by CNES. Products from PARASOL/GRASP versatile algorithm for characterizing the atmosphere. Products obtained from AERIS/ICARE Data and Services Center (http://www.icare.univ-lille1.fr)"
    Short credit: "Credit: CNES/GRASP/LOA/ICARE"

    Contact and Links

    For more information regarding product access, registration, or any technical information, please contact contact@icare.univ-lille1.fr
    For science questions about the GRASP products, please contact Oleg Dubovik.

    The source code and additional information can be obtained on the grasp-open web site: https://www.grasp-open.com/
    More information on POLDER and PARASOL can be found on ICARE specific web pages: http://www.icare.univ-lille1.fr/parasol


    References

    Dubovik, O., M. Herman, A. Holdak, T. Lapyonok, D. Tanré, J. L. Deuzé, F. Ducos, A. Sinyuk, and A. Lopatin, “Statistically optimized inversion algorithm for enhanced retrieval of aerosol properties from spectral multi-angle polarimetric satellite observations”, Atmos. Meas. Tech., 4, 975-1018, 2011.

    Dubovik, O., T. Lapyonok, P. Litvinov, M. Herman, D. Fuertes, F. Ducos, A. Lopatin, A. Chaikovsky, B. Torres, Y. Derimian, X. Huang, M. Aspetsberger, and C. Federspiel “GRASP: a versatile algorithm for characterizing the atmosphere”, SPIE: Newsroom, DOI:10.1117/2.1201408.005558, Published Online: September 19, 2014. http://spie.org/x109993.xml