ASTER User's Guide - Aster - NASA

ASTER Users Handbook
3.1 ASTER Level-1A Data
The ASTER Level-1A raw data are reconstructed from Level-0, and are unprocessed instrument
digital counts. This product contains depacketized, demultiplexed and realigned instrument
image data with geometric correction coefficients and radiometric calibration coefficients
appended but not applied. These coefficients include correcting for SWIR parallax as well as
inter- and intra-telescope registration. (The SWIR parallax error is caused by the offset in
detector alignment in the along-track direction and depends on the distance between the
spacecraft and the observed earth surface. For SWIR bands the parallax corrections are carried
out 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 radiometric
calibration coefficients, consisting of offset and sensitivity information, are generated from a
database for all detectors, and are updated periodically. The geometric correction is the
coordinate transformation for band-to-band co-registration. The VNIR and SWIR data are 8-bit
and have variable gain settings. The TIR data are 12-bit with a single gain. The structure of the
data inside a Level-1A product is illustrated in Figure 7. This is in HDF-EOS format.
3.1.1 ASTER Level-1A Browse
The ASTER Level-1A also contains browse images for each of the three sensors. The browse
product contains 1-scene of image data generated based on the Level-1A data with similar
radiometric corrections and mis-registration corrections applied to Level-1B data. All image
data (VNIR, SWIR, TIR) are 24-bit JPEG compressed images stored in an HDF file in RIS24
objects. The following table (Table 2) provides the main characteristics of the Level-1A browse
images:
Telescope Dimensions Compression Quality Blue Green Red
(pixel x line) Method Factor
VNIR 224x208 JPEG 50 Band 1 Band 2 Band 3N
SWIR 224x208 JPEG 50 Band 4 Band 5 Band 9
TIR 224x208 JPEG 50 Band 10 Band 12 Band 14
Table 2: Specifications of the ASTER Level-1A Browse Product.
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