The SAR Passband Problem: Analytical Model and Possible Practical Solutions

Abstract

Recently equivalent radar cross section (ERCS) was introduced as a new radiometric measurement quantity for synthetic aperture radar (SAR) systems. The focus of this paper is the dependence of a point target's ERCS (which is proportional to the pixel intensity) on the passband of the measuring SAR system. The SAR passband is mostly defined by the range and azimuth apodization functions used for side-lobe control during processing. The core of the problem is that different SAR passbands lead to different radiometric measurement results despite radiometric calibration, a so far neglected fact. The problem is especially pronounced for high-resolution SAR systems, which become more and more available. To quantify the effect of the passband problem, an analytical model is developed and numerically verified with different examples. Finally, several approaches for resolving the SAR passband problem in the future are proposed, where passband standardization across SAR missions is favored from a point of view of accurate radiometric measurements. Tackling and resolving the passband problem will enable truly consistent and reproducible radiometric measurements across SAR beams, modes, and systems.