Abstract
Synthetic aperture radar systems perform signal acquisition under varying incidence angles and register an implicit intensity decay from near to far range. Owing to the geometrical interaction between microwaves and the imaged targets, the rates at which intensities decay depend on the nature of the targets, thus rendering single-rate image correction approaches only partially successful. The decay, also known as the incidence angle effect, impacts the segmentation of wide-swath images performed on absolute intensity values. We propose to integrate the target-specific intensity decay rates into a nonstationary statistical model, for use in a fully automatic and unsupervised segmentation algorithm. We demonstrate this concept by assuming Gaussian distributed log-intensities and linear decay rates, a fitting approximation for the smooth systematic decay observed for extended flat targets. The segmentation is performed on Sentinel-1, Radarsat-2, and UAVSAR wide-swath scenes containing open water, sea ice, and oil slicks. As a result, we obtain segments connected throughout the entire incidence angle range, thus overcoming the limitations of modeling that does not account for different per-target decays. The model simplicity also allows for short execution times and presents the segmentation approach as a potential operational algorithm. In addition, we estimate the log-linear decay rates and examine their potential for a physical interpretation of the segments.
Highlights
S YNTHETIC aperture radar (SAR) is used for a broad scope of observations, both from satellite and airborne platforms
The application of a singlerate correction followed by Gaussian-mixture-based segmentation resulted in fewer bands and less overlap compared to the first case, but the segments were still not connected throughout the entire range [see Fig. 4(c)]
This article presents a new approach for the automatic segmentation of wide-swath SAR images
Summary
S YNTHETIC aperture radar (SAR) is used for a broad scope of observations, both from satellite and airborne platforms. The SAR imaging modality involves side-looking geometry and the acquisition of backscattered signals under varying incidence angles. As a result of the incidence angle-dependent interaction between microwaves and the imaged targets, the amount of backscattered energy decreases from near to far range, a phenomenon known as the incidence angle effect. The backscatter gradient becomes noticeable in the case of wideswath scenes, which cover hundreds of kilometers over large ranges of incidence angles (> 20◦). Owing to differences in the Manuscript received July 15, 2019; revised December 19, 2019; accepted April 20, 2020. Date of publication May 28, 2020; date of current version June 16, 2020.
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