ASTER User's Guide - NASA

ASTER Users Handbook3.1 ASTER Level-1A DataThe ASTER Level-1A raw data are reconstructed from Level-0, and are unprocessed instrumentdigital counts. This product contains depacketized, demultiplexed and realigned instrumentimage data with geometric correction coefficients and radiometric calibration coefficientsappended but not applied. These coefficients include correcting for SWIR parallax as well asinter- and intra-telescope registration. (The SWIR parallax error is caused by the offset indetector alignment in the along-track direction and depends on the distance between thespacecraft and the observed earth surface. For SWIR bands the parallax corrections are carriedout with the image matching technique or the coarse DEM data base, depending on cloud cover).The spacecraft ancillary and instrument engineering data are also included. The radiometriccalibration coefficients, consisting of offset and sensitivity information, are generated from adatabase for all detectors, and are updated periodically. The geometric correction is thecoordinate transformation for band-to-band co-registration. The VNIR and SWIR data are 8-bitand have variable gain settings. The TIR data are 12-bit with a single gain. The structure of thedata inside a Level-1A product is illustrated in Figure 7. This is in HDF-EOS format.3.1.1 ASTER Level-1A BrowseThe ASTER Level-1A also contains browse images for each of the three sensors. The browseproduct contains 1-scene of image data generated based on the Level-1A data with similarradiometric corrections and mis-registration corrections applied to Level-1B data. All imagedata (VNIR, SWIR, TIR) are 24-bit JPEG compressed images stored in an HDF file in RIS24objects. The following table (Table 2) provides the main characteristics of the Level-1A browseimages:Telescope Dimensions Compression Quality Blue Green Red(pixel x line) Method FactorVNIR 224x208 JPEG 50 Band 1 Band 2 Band 3NSWIR 224x208 JPEG 50 Band 4 Band 5 Band 9TIR 224x208 JPEG 50 Band 10 Band 12 Band 14Table 2: Specifications of the ASTER Level-1A Browse Product.19