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Activiities of ASTER Working Groups |
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AIST
Isao Sato |
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The Advance Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on board the TERRA spacecraft* (originally called EOS-AM1) consists of three separate subsystems: a Visible and Near Infrared Radiometer (VNIR: with a resolution of 15m, 6 bands), a Short Wave Infrared Radiometer (SWIR: 30m, 6 bands), and a Thermal Infrared Radiometer (TIR: 90m, 5 bands), thereby enabling observation of the Earth's surface over a wide spectral range from the visible through to the thermal infrared.
The products derived from ASTER data (Data Product: DP) are divided into three categories: Standard DP, Semi-standard DP, and Special DP.
The standard DPs are Level 1A (LA1), Level 1B (L1B), decorrelation stretch (for each sensor), brightness temperature, surface radiance (two types; for TIR and for the other two), surface reflectance, surface kinetic temperature, surface emissivity, polar surface and cloud classification, and digital elevation model (DEM). The difference between L1A and L1B is that L1B data are radiometrically calibrated and geometrically coregistered, while L1A data are unprocessed digital data. Polar surface and cloud classification and DEM are generated in the U.S.
Semi-standard DP (Relative DEM and Orthogonal projection image) are uniquely prepared for Japan. Special DPs are generated at the Earth Remote Sensing Data Analysis Center (ERSDAC), Japan. The following are among those under consideration by the Japan ASTER Science Team for the potential Special DP: tectonic mapping, volcano mapping, minerals and rocks distribution mapping, water surface temperature charting, turbidity charting, and aquatic plant distribution mapping.
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The standard format is HDP-EOS. This is an additional format especially developed for NASA's Earth Observing System (EOS), built on the Hierarchical Data Format (HDF), so that a variety of data formats such as images and points can be handled. [The HDF was originally developed by the National Computer Society Association (NCSA) in the U.S.A.] A conventional Super Structural Format format is also planned for DP distribution in Japan, where the HDF is not common. |
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A general header and specific header are created for each DP. The General Header provides basic information shared that is shared in common and is used in data retrieval or data archiving, while the Specific Header varies product by product and describes each one's unique parameters. |
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QA Plane - pixel-level quality data - is attached to each DP for a quality assessment. The data quality is classified into Bad, Suspect, Good, and Dummy, judged from first four-bit information of the first plane (eight bits). The next two bits describe whether or not clouds exist, and the last two represent information on adjacent effects by clouds. The reason why the Dummy class was established is to pinpoint pixels for which no data existed. (Those pixels are derived from the earth's rotation and should be distinguished from general data error.) The second plane (some DP's miss this) and the following planes provide quality information specific to each DP. Data users can use this information to assess the results from data processing and analyses. |
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The o-oriented objection method for L1B is adopted for each ASTER DP. This is to keep spectral data error to a minimum and to eliminate the need for multiple resampling. For that reason, users wanting a map-oriented DP on which north is upwards have to rotate the image by means of suitable software. |
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(Higher Level Data Products WG ) |
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