Abstract
Recently, it was demonstrated that low-frequency wavelength-resolution synthetic aperture radar (SAR) images could be considered to follow an additive mixing model due to their backscatter characteristics. This simplification allows for the use of source separation methods, such as robust principal component analysis (RPCA) via principal component pursuit (PCP), for detecting changes in those images. In this manuscript, a change detection method for wavelength-resolution SAR images based on image stack through RPCA is proposed. The method aims to explore both the temporal and flight heading diversity of a set of wavelength-resolution multitemporal SAR images in order to detect concealed targets in forestry areas. A heuristic based on three rules for better exploring the RPCA results is introduced, and a new configurable parameter for false alarm reduction based on the analysis of image windows is proposed. The method is evaluated using real data obtained from measurements of the ultrawideband (UWB) very high-frequency (VHF) SAR system CARABAS-II. Experiments for stacks of four and seven reference images are conducted, and the use of reference images acquired with different flight headings is explored. The results indicate that a gain in performance can be achieved by using large image stacks containing, at least, one image of each possible flight heading of the data set, which can result in a probability of detection (PD) above 99% for a false alarm rate (FAR) as low as one false alarm per three square kilometers. Furthermore, it is demonstrated that high PD and low FAR can be achieved, also considering images from similar flight headings as reference images.
Highlights
The materials and tools used for the method evaluation can be summarized as follows: (a) the CARABAS-II data set and (b) an robust principal component analysis (RPCA) via principal component pursuit (PCP) algorithm implementation
Considering that the data set is limited to 24 images and that, for N = 7, one entire mission is used as reference images (6 images), the images from Missions 3–5 are individually used as surveillance images when Mission 2 is used as the reference image
It is possible to observe that the best performance is achieved when the reference images of the stacks are acquired with all three possible flight headings (“all F.H”), achieving probability of detection (PD) = 0.968 for false alarm rate (FAR) = 0.897 false alarms (FA)/km2
Summary
Wavelength-resolution SAR can be characterized by a large fractional bandwidth, such as the ones achieved by ultrawideband (UWB) SAR, and a wide antenna bandwidth. The backscattering phenomenology for wavelength-resolution SAR systems differs from traditional microwave SAR. For wavelength-resolution systems, small objects tend to follow the characteristic of a Rayleigh scattering regime whereas large target-size elements present a resonance scattering regime [1]. The scattering process is mainly related to the contribution of scatterers with dimensions in the order of the signal wavelengths, mitigating the contribution of small objects. A resolution cell may only contain one scatter
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