ASTER On-Demand L2 Surface Reflectance VNIR


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ASTER Image for AST_06VD

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

Granule Shortname
AST_07XT

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 data files in Hierarchical Data Format (HDF), one for VNIR, one for SWIR. The ASTER On-Demand L2 Surface Reflectance product description is presented individually for each sensor. This document describes the VNIR reflectance product, which is not affected by the SWIR crosstalk problem but 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 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 is derived from the reflectance-based, vicarious calibration approach of the Remote Sensing Group 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.

Product Output Information

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

Three groups of ancillary data inputs are 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; as a result, use of the NCEP/TOVS ancillary data was discontinued for ASTER Level-1 data acquired April 18, 2005. 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 is the NCEP-GDAS (Global Data Assimilation System), which are available every 6 hours. The alternative is the NRL Climatology data set. These data sets are based on modeling, simulation, and prediction; they are static, monthly, averaged data sets that are used only as a last resort.

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

Product Information

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
U.S. Geological Survey (USGS)
Earth Resources Observation and Science Center (EROS)
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Phone: 605-594-6116

Toll Free: 866-573-3222

866-LPE-DAAC

Fax: 605-594-6963

Email: LPDAAC@eos.nasa.gov

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URL: http://LPDAAC.usgs.gov/aster/ast_07xtv.asp
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Last Update: Tuesday, July 01, 2008
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