Abstract
The Ka-Band Radar Interferometer (KaRIn) instrument on the Surface Water and Ocean Topography (SWOT) mission is a single-pass synthetic aperture radar (SAR) interferometer tasked with, among others, measuring ocean topography to within a few centimeters over kilometer scale resolutions. A SAR interferometer relies on very precise phase difference measurements between two spatially distant antennas to estimate topography. Multipath phase caused by unintended scattering off the spacecraft structure is a known error source for radar interferometers and takes up a significant portion of the KaRIn error budget. This paper outlines some analytical multipath models that were used for instrument design, performance analysis and mitigation of the multipath signal.
Highlights
Multipath is caused by the transmit or receive signal bouncing off different parts of the spacecraft structure and coherently adding with the intended direct-path signal used for estimating topographic height, while switch leakage broadly refers to any signal leakage inside the radar electronics between the two interferometric channels
The simplified analytical models for multipath and leakage for single-pass synthetic aperture radar (SAR) interferometers presented here are intended to provide insight into the observed interferometric phase that usually includes a combination of the undesired, albeit unavoidable error sources. These models are useful for interpreting interferometric data as well as guiding instrument design by outlining the type of signatures expected from each source
For instance, there is a single dominant specular reflection point on the spacecraft structure, it will show up as a sinusoid in the interferometric phase. This was borne out during extensive analysis of the Surface Water and Ocean Topography (SWOT) multipath issue, where edges of the modeled mast structure behaved as specular scatterers and the simulated multipath matched predictions of the analytical models summarized here
Summary
Multipath is caused by the transmit or receive signal bouncing off different parts of the spacecraft structure and coherently adding with the intended direct-path signal used for estimating topographic height, while switch leakage broadly refers to any signal leakage inside the radar electronics between the two interferometric channels. Provided these effects remain stable, they are typically calibrated out using a phase screen estimated during instrument calibration [24,26]. While specific details of that study are outside the scope of this article and of limited use to the general community, the authors hope that analytical models of φs presented in this article for various scenarios applicable to SWOT are generic enough to be of broader use
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