Abstract
This paper presents a new approach for the discrimination of ship responses using polarimetric SAR (PolSAR) data. The PolSAR multidimensional information is analyzed using a linear Time-Frequency (TF) decomposition approach, which permits to describe the polarimetric behavior of a ship and its background area for different azimuthal angles of observation and frequencies of illumination. This paper proposes to discriminate ships from their background by using characteristics of their polarimetric TF responses, which may be associated with the intrinsic nature of the observed natural or artificial scattering structures. A statistical descriptor related to polarimetric coherence of the signal in the TF domain is proposed for detecting ships in different complex backgrounds, including SAR azimuth ambiguities, artifacts, and small natural islands, which may induce numerous false alarms. Choices of the TF analysis direction, i.e., along separate azimuth or range axis, or simultaneously in both directions, are investigated and evaluated. TF decomposition modes including range direction perform better in terms of discriminating ships from range focusing artifacts. In comparison with original full-resolution polarimetric indicators, the proposed TF polarimetric coherence descriptor is shown to qualitatively enhance the ship/background contrast and improve discrimination capabilities. Using polarimetric RADARSAT-2 data acquired over complex scenes, experimental results demonstrate the efficiency of this approach in terms of ship location retrieval and response characterization.
Highlights
Ship detection and discrimination using Synthetic Aperture Radar (SAR) has been a topic of considerable interest in the recent years, and the increasing availability of multi-polarimetric high resolution SAR data has favored the emergence of new techniques for this application [1,2,3,4,5]
This paper proposes a new approach for discriminating ships lying in complex backgrounds, based on the coherent Time-Frequency (TF) analysis of polarimetric SAR data, introduced in [6] and [7] for the study of anisotropic scattering behaviors, and in [8] and [9] for the characterization of complex urban environments using intermediate resolution PolSAR images
One of the main achievements of the TF coherence-based ship discrimination presented in this work lies on its ability to effectively mitigate energetic ghost echoes induced by SAR azimuth ambiguities, range artifacts or potential false alarms related to sidelobe patterns
Summary
Ship detection and discrimination using Synthetic Aperture Radar (SAR) has been a topic of considerable interest in the recent years, and the increasing availability of multi-polarimetric high resolution SAR data has favored the emergence of new techniques for this application [1,2,3,4,5]. The main application novelties introduced in this study are as follows: One of the main achievements of the TF coherence-based ship discrimination presented in this work lies on its ability to effectively mitigate energetic ghost echoes induced by SAR azimuth ambiguities, range artifacts or potential false alarms related to sidelobe patterns. This ghost filtering is not performed by comparing the cross-polarized HV and VH channels as proposed in [18,19], but rather by the TF coherence indicator itself: real target echoes remain coherent over different spectral locations, whereas ambiguous or sidelobe ones do not.
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