Abstract
The estimation of Signal-to-Clutter Ratio (SCR) of a radar point target, such as a corner reflector, is an essential step for synthetic aperture radar (SAR) interferometry and positioning, as it influences the phase measurement variance as well as the absolute positioning precision. The standard method to estimate the SCR of a point target relies on the debatable assumption of spatial ergodicity, using the clutter of the surrounding as representative of the clutter at the point target. Here, we estimate the SCR of a corner reflector using a time series of SAR measurements, i.e., assuming temporal ergodicity. This assumption is often more realistic, particularly in a complex environment, in the presence of other point scatterers, and for small-sized reflectors. Empirical results on a corner reflector network, using Sentinel-1 SAR measurements, show that the temporal method yields a less biased and more precise estimate of the average SCR. A second experiment shows that the InSAR phase variance as well as positioning precision, predicted using SCR estimated by the temporal estimation method, is closer to the truth.
Highlights
C ORNER reflectors are commonly used for radiometric and geometric synthetic aperture radar (SAR) sensor calibration and validation, [1]–[3], SAR interferometry (InSAR) applications over areas with few natural coherent reflectors [4], and for InSAR datum connection and geodetic integration [5].These methods require a precise and unbiased estimation of the Signal-to-Clutter Ratio (SCR): the ratio of the Radar-Cross section (RCS) of the reflector and the power of its background clutter
In the context of point scatterers (PSs), digital number (DN) is converted to RCS, which describes the ability of a PS to intercept incident energy with an effective cross-sectional area and reflect it in the direction of a radar receiver [1]
As the impulse response function (IRF) is finitely sampled by the SAR image pixels, oversampling and numerical integration is employed within the estimation process
Summary
C ORNER reflectors are commonly used for radiometric and geometric synthetic aperture radar (SAR) sensor calibration and validation, [1]–[3], SAR interferometry (InSAR) applications over areas with few natural coherent reflectors [4], and for InSAR datum connection and geodetic integration [5] These methods require a precise and unbiased estimation of the Signal-to-Clutter Ratio (SCR): the ratio of the Radar-Cross section (RCS) of the reflector and the power of its background clutter. The standard method for estimating RCS and SCR of point targets involves spatial numerical integration of pixel intensity values in square-law detected SAR images [8], [9] It assumes that the background clutter over the integrated area exhibits the same statistical properties as its surroundings, i.e., spatial ergodicity. A secondary objective of the proposed method is to utilize the time series of RCS to track the reflector performance, and identify possible outliers due to damage, debris accumulation, or other external factors
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