Evidence Of Post-Measurement Geoid Undulation Integration In SAR, Airborne Radar, And Related Systems: Implications For Geometric Assumptions In Remote Sensing

Abstract

THIS PAPER COMPILES AND ANALYZES EVIDENCE FROM SYNTHETIC APERTURE RADAR (SAR), AIRBORNE RADAR, AND RELATED REMOTE SENSING SYSTEMS DEMONSTRATING THAT GEOID UNDULATION CORRECTIONS—OFTEN REFERRED TO AS "BAKE-IN"—ARE APPLIED DURING POST-PROCESSING RATHER THAN INHERENT IN RAW MEASUREMENTS. DRAWING FROM DECLASSIFIED DOCUMENTS, TECHNICAL MANUALS, PEER-REVIEWED STUDIES, AND THESES ON SYSTEMS SUCH AS THE AN/APG-68 (F-16), ASARS-1 (SR-71), AN/APQ-181 (B-2), TERRASAR-X/TANDEM-X, SENTINEL-1, LANDSAT ETM, AND GRAVIMETRIC GEOID MODELS (E.G., OVER ZAMBIA AND SUDAN), WE SHOW THAT RAW DATA ACQUISITION ASSUMES LOCAL FLAT GEOMETRY (SLANT-RANGE OR SIMPLIFIED 2D MODELS). GEOID MODELS (E.G., EGM2008, GEOID18) AND ELLIPSOID REFERENCES (E.G., WGS84) ARE INTRODUCED LATER VIA SOFTWARE TOOLS LIKE PARGE, ATCOR, SNAP, AND GAMMA TO ENFORCE GLOBAL CURVATURE ALIGNMENT. THIS "PATCH" PROCESS SUPPORTS THE HYPOTHESIS THAT OBSERVED CURVATURE IS MODEL-DEPENDENT, NOT EMPIRICAL, ALIGNING WITH PLANAR BASELINE ASSUMPTIONS IN ENGINEERING APPLICATIONS. WE INTEGRATE FINDINGS FROM PROVIDED DOCUMENTS AND RELATED SOURCES TO PROVIDE AN IRONCLAD COMPILATION, WITH IMPLICATIONS FOR GEODESY, PHILOSOPHY OF MODELING, AND ALTERNATIVE COSMOLOGIES.