ASTER User's Guide - Aster - NASA

ASTER Users Handbook
6.0 ASTER Geometry
ASTER’s geometric system correction primarily involves the rotation and the coordinate
transformation of the line of sight vectors of the detectors to the coordinate system of the Earth.
This is done as part of ASTER Level-1 processing at GDS using engineering data from the
instrument (called supplementary data) and similar data from the spacecraft platform (called
ancillary data). The geometric correction of ASTER data has evolved through elaborate
processes of both pre-flight and post-launch calibration.
Pre-Flight Calibration
This is an off-line process to generate geometric parameters such as Line of Sight (LOS) vectors
of the detectors and pointing axes information evaluated toward the Navigation Base Reference
(NBR) of the spacecraft deemed to reflect on the instrument accuracy & stability. These data are
stored in the geometric system correction database.
Post-Launch Calibration
Following launch of ASTER, these parameters are being corrected through validation using
Ground Control Points (GCPs) and inter-band image matching techniques. Geometric system
correction in the post-launch phase entails the following processes:
• Pointing correction
• Coordinate transformation from spacecraft coordinates to the orbital coordinates
• Coordinate transformation from orbital coordinates to the earth’s inertial coordinates
• Coordinate transformation from earth’s inertial coordinates to Greenwich coordinates
• Improving Band-to-Band registration accuracy through image-matching involves 2
processes:
o SWIR parallax correction
o Inter-telescope registration process
Based on current knowledge, the geometric performance parameters of ASTER are summarized
in Table 6.
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