Microlocal analysis of Doppler Synthetic Aperture Radar

TL;DR

This paper applies microlocal analysis to Doppler Synthetic Aperture Radar (DSAR) to understand and mitigate artifacts in imaging, demonstrating how flight path geometry affects image quality and artifact suppression techniques.

Contribution

It provides a microlocal analysis framework for DSAR, revealing how flight path geometry influences artifacts and proposing filtering methods for artifact reduction.

Findings

Straight flight path causes left-right ambiguity artifacts

Circular flight path allows artifact-free imaging with filtering

Results are robust under more realistic approximations

Abstract

We study the existence and suppression of artifacts for a Doppler-based Synthetic Aperture Radar (DSAR) system. The idealized air- or space-borne system transmits a continuous wave at a fixed frequency and a co-located receiver measures the resulting scattered waves; a windowed Fourier transform then converts the raw data into a function of two variables: slow time and frequency. Under simplifying assumptions, we analyze the linearized forward scattering map and the feasibility of inverting it via filtered backprojection, using techniques of microlocal analysis which robustly describe how sharp features in the target appear in the data. For DSAR with a straight flight path, there is, as with conventional SAR, a left-right ambiguity artifact in the DSAR image, which can be avoided via beam forming to the left or right. For a circular flight path, the artifact has a more complicated structure, but filtering out echoes coming from straight ahead or behind the transceiver, as well as those outside a critical range, allows one to obtain an artifact-free image. Initially derived under a start-stop approximation widely used in range-based SAR, we show that some of these results are robust and hold under a more realistic approximation.