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ASTER Image of AST_07SD

EDG Data Set Name
ASTER On-Demand L2 Surface Reflectance VNIR

Granule Shortname
AST_07

Data Set Characteristics
Area: ~60 km x 60 km
Image Dimensions: 4200 rows x 4980 columns
File Size: ~180 Megabytes
Spatial Resolution: VNIR 15 m
Projection: Universal Transverse Mercator (UTM)
Data Format: HDF-EOS
GeoTIFF
Vgroup Data Fields: 3

The ASTER On-Demand L2 Surface Reflectance is a multi-file product that contains atmospherically corrected data for both the Visible Near-Infrared (VNIR) and Shortwave Infrared (SWIR) sensors. Each product delivery includes two hdf files: one for the VNIR, and the other for the SWIR. They are distinguished from one another by a one-second difference in the production time that appears as part of the file name. The more obvious distinguishing feature is the file size. VNIR is always the bigger of the two. The ASTER On-Demand L2 Surface Reflectance product description is presented individually for each sensor. This document describes the VNIR reflectance product, which is distributed as part of the same package.

Product Description
The ASTER On-Demand L2 Surface Reflectance (VNIR) is a higher-level product that contains atmospherically corrected visible and near-infrared data. It is generated using the three VNIR bands (between 0.52 and 0.86 µm) from an ASTER Level-1B image. Atmospheric correction involves deriving a relationship between the surface radiance/reflectance and the top of the atmosphere (TOA) radiance from information on the scattering and absorbing characteristics of the atmosphere. Once this relationship is established, it is used to convert ASTER VNIR's original radiance values to atmospherically corrected surface radiance and reflectance values. The atmospheric correction algorithm for VNIR is based on a Look-Up Table (LUT) approach that uses results from a Gauss-Seidel iteration of the Radiative Transfer Code (RTC). This methodology derives from the reflectance-based, vicarious calibration approach of the Remote Sensing Group (RSG) at the University of Arizona. The algorithm is based on the relationship between the angular distribution of radiance, scattering and absorption in the atmosphere, and the surface properties. The RTC used to generate the LUT for the atmospheric correction is based on the following parameters: solar zenith angle, satellite view angle, relative azimuth angle between the satellite and sun, molecular scattering optical depth, aerosol scattering optical depth, aerosol scatter albedo, aerosol size distribution parameter, and surface reflectance. The size distributions for aerosol are based on either a Junge size distribution or on the set of aerosol types used in the atmospheric correction of Multi-angle Imaging Spectroradiometer (MISR) data. The initial versions of the algorithm rely on external climatological sources for information on atmospheric absorption and scattering parameters. Eventually, this information is likely to come from other Terra sensors like MISR and the Moderate-Resolution Imaging Spectroradiometer (MODIS). A digital elevation model provides the slope and elevation information for accurate modeling of surface reflectance.

Vgroup Data Fields/
Spectral Range (µm)		 Units Data Type Valid Range Band Scale Factor

VNIR (15 Meters)
Band 1 (0.52 - 0.60) None 16-bit unsigned integer 0 - 1000 0.001
Band 2 (0.63 - 0.69) None 16-bit unsigned integer 0 - 1000 0.001
Band 3N (0.78 - 0.86) None 16-bit unsigned integer 0 - 1000 0.001


There are 3 groups of ancillary data inputs used in the atmospheric correction of ASTER radiance and reflectance:

  • Ozone data input: The NCEP/TOVS (National Centers for Environmental Prediction/TIROS (Television & Infrared Observation Satellite) Operational Vertical Sounder) data are acquired from a NOAA satellite, and provides the ancillary column ozone data twice daily. This was the default option with the alternative Naval Research Laboratory’s (NRL) Ozone Climatology data set. Starting on April 18, 2005, NOAA’s TOVS developed an irreversible instrument problem, and therefore, the use of the NCEP/TOVS ancillary data was discontinued for ASTER Level-1 data acquired from April 18, 2005 onward. This ancillary data source is available for ASTER data acquired prior to April 18, 2005. Currently, the only alternative in use for column ozone is NRL’s Ozone Climatology data set.
  • Aerosol data input: Presently, NRL’s Aerosol Climatology ancillary data are the only available input.
  • Temperature, Atmospheric pressure, and Moisture Profile data inputs: The source of these data are the NCEP-GDAS (Global Data Assimilation System) available at every 6 hours temporal frequency. The alternative is the NRL Climatology data set. These data sets are based on modeling, simulation, and prediction, and therefore, they are static, monthly, averaged data sets used only as a last resort.

    • View a Version Formatted for Printing

    Ordering ASTER On-Demand L2 Surface Reflectance
    The ASTER On-Demand L2 Surface Reflectance product can be ordered through the EOS Data Gateway. The process and procedures for ordering this product are described in the http://lpdaac.usgs.gov/tutorial/. As part of that process, it is necessary to first select an ASTER Level 1B granule from the EOS Data Gateway.

    Product Information
    Release Notes
    (http://asterweb.jpl.nasa.gov/content/03_data/01_Data_Products/release_aster_surface_reflectance.htm)
    ASTER Level-1 Data Products Specification
    (http://asterweb.jpl.nasa.gov/content/03_data/04_Documents/ASTER_L1_Product_Spec_Ver_1.3_July01.pdf)
    ASTER User Handbook
    (http://asterweb.jpl.nasa.gov/content/03_data/04_Documents/aster_user_guide_v2.pdf)
    ASTER Level-1 Users Guide
    (http://www.science.aster.ersdac.or.jp/en/documnts/users_guide/index.html)
    ASTER Higher-Level Product User Guide
    (http://asterweb.jpl.nasa.gov/content/03_data/04_Documents/ASTERHigherLevelUserGuideVer2May01.pdf)
    Algorithm Theoretical Basis Document (ATBD)
    (http://eospso.gsfc.nasa.gov/eos_homepage/for_scientists/atbd/docs/ASTER/atbd-ast-07-09.pdf)
    ASTER JPL Web Page
    (http://asterweb.jpl.nasa.gov/data_products.asp)
    EOS Data Products Handbook (Volume 1, Revised 2004)
    (http://eospso.gsfc.nasa.gov/ftp_docs/data_products_1.pdf)

    Contact Information
    LP DAAC User Services
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    Last Update: Tuesday, July 01, 2008
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