ASTER User's Guide - NASA

ASTER Users Handbook6.0 ASTER GeometryASTER’s geometric system correction primarily involves the rotation and the coordinatetransformation 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 theinstrument (called supplementary data) and similar data from the spacecraft platform (calledancillary data). The geometric correction of ASTER data has evolved through elaborateprocesses of both pre-flight and post-launch calibration.Pre-Flight CalibrationThis is an off-line process to generate geometric parameters such as Line of Sight (LOS) vectorsof 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 arestored in the geometric system correction database.Post-Launch CalibrationFollowing launch of ASTER, these parameters are being corrected through validation usingGround Control Points (GCPs) and inter-band image matching techniques. Geometric systemcorrection 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 2processes:o SWIR parallax correctiono Inter-telescope registration processBased on current knowledge, the geometric performance parameters of ASTER are summarizedin Table 6.27