******************************************************************************* * * * Readme file for the MODIS_CLAMS_L2_AEROSOL_PRODUCTS Data Set * * * ******************************************************************************* 1.0 Introduction: This readme file contains information about the aerosol data products provided by the Moderate Resolution Imaging Spectroradiometer (MODIS) for the Chesapeake Lighthouse Aircraft Measurements for Satellite (CLAMS) field campaign. The CLAMS campaign was designed to validate and improve EOS Terra satellite data products produced from the CERES, MISR, and MODIS sensors onboard Terra. This data set is available at the Atmospheric Sciences Data Center as: MODIS_CLAMS_L2_AEROSOL_PRODUCTS The MODIS_CLAMS_L2_AEROSOL_PRODUCTS are stored in the Hierarchical Data Format (HDF). The Aerosol Product monitors aerosol type, aerosol optical thickness, particle size distribution, aerosol mass concentration, optical properties and radiative forcing. A list of the 53 gridded parameters is given in section 4.0 below and a detailed description of each of the parameters is available at: http://modis-atmos.gsfc.nasa.gov/MOD04_L2/format.html. This readme file includes the following sections: Section 2.0 - Data Set Description Section 3.0 - Format and Packaging Section 4.0 - Science Parameters Information Section 5.0 - Description of Sample Read Software Section 6.0 - Implementing Sample Read Software Section 7.0 - Sample Output Section 8.0 - Additional Data Information If you have any questions, please contact the Langley Atmospheric Sciences Data Center (ASDC) Science, Users and Data Services Office at: Atmospheric Sciences Data Center Science, Users and Data Services Office Mail Stop 157D 2 South Wright Street NASA Langley Research Center Hampton, Virginia 23681-2199 U.S.A. E-mail: larc@eos.nasa.gov Phone: (757)864-8656 FAX: (757)864-8807 URL: http://eosweb.larc.nasa.gov 2.0 Data Set Description: The MODIS_CLAMS_L2_AEROSOL_PRODUCTS data set available from the CLAMS archive at the Langley ASDC are from the Moderate Resolution Imaging Spectroradiometer (MODIS) Aerosol Products. These MODIS aerosol data products are for the time period of the CLAMS field campaign, and give the ambient aerosol optical thickness over the oceans and over a portion of the continents. The aerosol size distribution is derived over the oceans, and the aerosol type is derived over the continents. Daily Level 2 data were produced at the spatial resolution of a 10×10 1-km (at nadir)-pixel array. The MODIS_CLAMS_L2_AEROSOL_PRODUCTS cover the time period from July 10, 2001 (Julian day 191) to August 2, 2001 (Julian day 214) over the spatial region nomally from -106 degree longitude to -42 degree longitude and from 57 degree N latitude to 18 degree N latitude. A more detailed description of the MODIS Aerosol Products is available at http://modis-atmos.gsfc.nasa.gov/MOD04_L2/index.html, and of the CLAMS field campaign at http://www-clams.larc.nasa.gov/clams/. 2.1 Instrumentation Description: The MODIS instrument provides high radiometric sensitivity (12 bit) in 36 spectral bands ranging in wavelength from 0.4 µm to 14.4 µm. Two bands are imaged at a nominal resolution of 250 m at nadir, with five bands at 500 m and the remaining 29 bands at 1,000 m. A ±55-degree scanning pattern at the EOS orbit of 705 km achieves a 2,330-km swath and provides global coverage approcimately every two days. Additional information on the MODIS instrument is available from: http://modis.gsfc.nasa.gov/about/index.html 2.2 Data Quality: There are no known anomalies in these data. 2.3 Science Contact: Questions pertaining to the data values contained within these files should be directed to: Name: Robert Levy Address: SSAI/ NASA GSFC Code 913 Greenbelt, MD 20771 Telephone: (301) 614-6123 Fax: (301) 614-6307 Internet Address: levy@climate.gsfc.nasa.gov 3.0 Format and Packaging: MOD04_L2 Aerosol Product files are stored in Hierarchical Data Format (HDF-Version 4). The MOD04_L2 Aerosol Product files associated with the CLAMS field campaign have been bundled in zipped files for each campaign day. To read the files, first unzip them with Info-Zip software or other appropriate software. Information about downloading and using the freeware software, Info-Zip, is available at the following URL: http://www.cdrom.com/pub/infozip/ The following files are available from the CLAMS data archive in Langley's Atmospheric Sciences Data Center: Filename Description ---------------------------------------------------------------------------- readme_MODIS_CLAMS.txt This readme file. CLAMS_MODIS_MODO4_L2_A2001191.zip These zipped files contain the CLAMS_MODIS_MODO4_L2_A2001192.zip MOD04_L2 Aerosol Product files. CLAMS_MODIS_MODO4_L2_A2001193.zip There is one zip file for the CLAMS_MODIS_MODO4_L2_A2001194.zip time period from Julian day 191 CLAMS_MODIS_MODO4_L2_A2001195.zip to 214, 2001. CLAMS_MODIS_MODO4_L2_A2001196.zip CLAMS_MODIS_MODO4_L2_A2001197.zip CLAMS_MODIS_MODO4_L2_A2001198.zip CLAMS_MODIS_MODO4_L2_A2001199.zip CLAMS_MODIS_MODO4_L2_A2001200.zip CLAMS_MODIS_MODO4_L2_A2001201.zip CLAMS_MODIS_MODO4_L2_A2001202.zip CLAMS_MODIS_MODO4_L2_A2001203.zip CLAMS_MODIS_MODO4_L2_A2001204.zip CLAMS_MODIS_MODO4_L2_A2001205.zip CLAMS_MODIS_MODO4_L2_A2001206.zip CLAMS_MODIS_MODO4_L2_A2001207.zip CLAMS_MODIS_MODO4_L2_A2001208.zip CLAMS_MODIS_MODO4_L2_A2001209.zip CLAMS_MODIS_MODO4_L2_A2001210.zip CLAMS_MODIS_MODO4_L2_A2001211.zip CLAMS_MODIS_MODO4_L2_A2001212.zip CLAMS_MODIS_MODO4_L2_A2001213.zip CLAMS_MODIS_MODO4_L2_A2001214.zip The file naming convention used for the zipped files is: CLAMS_MODIS_MODO4_L2_AYYYYDDD.zip where YYYY - Year DDD - Juilan Day A - The platform code (A=Terra) Each zipped file contains a browse image of the combined ocean/land optical depth at 550 nm and several hdf files containing the MODIS_L2 Aerosol Products and their accompanying text metadata (*.hdf.met) files. For example the data file CLAMS_MODIS_MODO4_L2_A2001192.zip contains the image files: AOT0550.2001.192.1605.jpg AOT0550.2001.192.1645.jpg the hdf files: MOD04_L2.A2001192.1510.003.2001308220953.hdf MOD04_L2.A2001192.1645.003.2001309005011.hdf and the test metadata files: MOD04_L2.A2001192.1510.003.2001308220953.hdf.met MOD04_L2.A2001192.1645.003.2001309005011.hdf.met The MODIS Level-2 Atmosphere Aerosol Product HDF files have the following standardized filename convention: MOD04_L2.AYYYYDDD.HHMM.VVV.YYYYDDDHHMMSS.hdf where: MOD04_L2 is the Earth Science Data Type Name A is the Platform Code (A=Terra) first YYYYDDD is the Data Year and Julian Date first HHMM is the Data Hour and Minute Start Time VVV is the 3 Digit Version Number final YYYYDDHHMMSS is the Processing Date and Time (All times are UTC time) 4.0 Science Parameters Information: The parameters provided in the MOD04_L2 Aerosol Product files are: Geolocation and Time Parameters (1) Geodetic Longitude (2) Geodetic Latitude (3) International Atomic Time at Start of Scan replicated across the Swath Solar and Viewing Geometry Parameters (4) Solar Zenith Angle, Cell to Sun (5) Solar Azimuth Angle, Cell to Sun (6) Sensor Zenith Angle, Cell to Sensor (7) Sensor Azimuth Angle, Cell to Sensor Combined Land and Ocean (8) Scattering Angle (9) Aerosol Optical Thickness at 0.55 micron for both Ocean (best) and Land (corrected) Land Only: (10) Aerosol Type (11) Continental Optical Thickness at 0.47 and 0.66 microns (12) Corrected Optical Thickness at 0.47, 0.55, and 0.66 microns (13) Uncertainty of Optical Thickness at 0.47 and 0.66 microns (14) Mass Concentration over Land (15) Angstrom Exponent at 0.47 and 0.67 microns (16) Normalized Reflected Flux at 0.47 and 0.66 microns (17) Normalized Transmitted Flux at 0.47 and 0.66 microns (18) Cloud Fraction (%) (19) Dust Aerosol Weighting Factor (20) Number of Pixels in Desired Percentile (21) Mean Reflectance at 5 bands (22) Standard Deviation of Reflectance at 5 bands Ocean Only: (23) Solution Number Index for Small Particles (24) Solution Number Index for Large Particles (25) Aerosol Optical Thickness for Best Solution at 7 bands (26) Aerosol Optical Thickness for Average Solution at 7 bands (27) Aerosol Optical Thickness for Small Mode of Best Solution at 7 bands (28) Aerosol Optical Thickness for Small Mode of Average Solution at 7 bands (29) Aerosol Optical Thickness for Large Mode of Best Solution at 7 bands (30) Aerosol Optical Thickness at 7 bands for large mode of average solution (31) Mass Concentration for Best and Average Solutions (32) Effective Radius of Both Solutions at 0.55 microns (33) Column Number of CCN of Both Solutions at 0.55 microns (34) Asymmetry Factor for Best Solution at 7 bands (35) Asymmetry Factor for Average Solution at 7 bands (36) Backscattering Ratio of Best Solution at 7 bands (37) Backscattering Ratio of Average Solution at 7 bands (38) Angstrom Exponent for 0.550 and 0.865 microns (39) Angstrom Exponent for 0.865 and 2.130 microns (40) Normalized Reflected Flux of Best Solution at 7 bands (41) Normalized Reflected Flux of Average Solution at 7 bands (42) Normalized Transmitted Flux of Best Solution at 7 bands (43) Normalized Transmitted Flux of Average Solution at 7 bands (44) Least Square Error Estimate (45) Small Mode Weighting Factor (46) Ratio of Optical Depth of Small Mode vs. Effective Optical Depth at .55 microns (47) Cloud Fraction in Percentage (48) Number of Pixels used for 0.55 micron solution (49) Mean Reflectance’s at 7 bands (50) Standard Deviation of Reflectance’s at 7 bands Cloud Mask and QA Parameters: (51) Cloud Mask QA at 10x10 km resolution (52) Run-Time QA Flags for Land (53) Run-Time QA Flags for Ocean 5.0 Description of Sample Read Software: MOD04_L2 product files are stored in Hierarchical Data Format (HDF-Version 4). HDF is a multi-object file format for sharing scientific data in multi-platform distributed environments. HDF files should only be accessed through HDF library subroutine and function calls, which can be downloaded from the HDF web site (http://hdf.ncsa.uiuc.edu/). Each of the 53 gridded parameters listed in section 4.0 above is stored as a Scientific Data Set (SDS) within the HDF file. Additional information on software and tools for working with MODIS data is available at http://modis-atmos.gsfc.nasa.gov/tools.html and HDFLOOK software is available at http://www-loa.univ-lille1.fr/Hdflook/hdflook_gb.html. 6.0 Implementing Sample Read Software: Please refer to http://modis-atmos.gsfc.nasa.gov/tools.html and http://daac.gsfc.nasa.gov/MODIS/software.shtml for information on software and tools for working with MODIS data. 7.0 Sample Output: See http://modis-atmos.gsfc.nasa.gov/MOD04_L2/acquiring.html for a sample MOD04_L2 HDF file. 8.0 Additional Data Information: The following is a list of publications that provide additional information on the MOD04_L2 Aerosol Products: References: http://modis-atmos.gsfc.nasa.gov/MOD04_L2/atbd.html Kaufman & Tanre, 1998: Algorithm for Remote Sensing of Tropospheric Aerosol from MODIS. Products: MOD04_L2, MOD08_D3, MOD08_E3, MOD08_M3. ATBD Reference Number: ATBD-MOD-02. Kaufman, Y. J., Tanre, D., Gordon, H. R., Nakajima, T., Lenoble, J., Frouin, R., Grassl, H., Herman, B. M., King, M. D., & Teillet, P. M. (1997). Passive remote sensing of tropospheric aerosol and atmospheric correction for the aerosol effect. Journal of Geophysical Research-Atmospheres, 102(D14), 16815-16830. [Full Text*] Kaufman, Y. J., Tanre, D., Remer, L., Vermote, E. F., Chu, A., & Holben, B. N. (1997). Operational remote sensing of tropospheric aerosol over the land from EOS-MODIS. Journal of Geophysical Research, 102(14), 17051-17068. [Full Text*] Tanre, D., Kaufman, Y. J., Herman, M., & Mattoo, S. (1997). Remote sensing of aerosol properties over oceans using the MODIS/EOS spectral radiances. Journal of Geophysical Research-Atmospheres, 102(D14), 16971-16988. Validation: Chu, D. A., Y. J. Kaufman, C. Ichoku, L. A. Remer, D. Tanre and B. N. Holben, Validation of MODIS aerosol optical depth retrieval over land. Geophys. Res. Lett., 29, 10.1029/2001GL013205, 2002. Ichoku, C., D. A. Chu, S. Mattoo, Y. J. Kaufman, L. A. Remer, D. Tanre, I. Slutsker and B. N. Holben, A spatio-temporal approach for global validation and analysis of MODIS aerosol products. Geophys. Res. Lett., 29, 10.1029/2001GL013206, 2002. Martins, J. V., D. Tanre, L. A. Remer, Y. J. Kaufman, S. Mattoo and R. Levy, MODIS Cloud screening for remote sensing of aerosol over oceans using spatial variability. Geophys. Res. Lett.,29, 10.1029/2001GL013252, 2002. Remer, L. A., D. Tanre, Y. J. Kaufman, C. Ichoku, S. Mattoo, R. Levy, D. A. Chu, B. N. Holben, O. Dubovik, A. Smirnov, J. V. Martins, R.-R. Li and Z. Ahmad, Validation of MODIS aerosol retrieval over ocean. Geophys. Res. Lett.,29, 10.1029/2001GL013204, 2002.