David J. Crisp

Comparison of ship detectors for polarimetric SAR imagery

This paper examines the benefits of using fully polarimetric SAR imagery for ship detection. There are three related aspects to the work. First, RadarSat-2 quad-pol stripmap imagery is used to compare the performance of various ship detection algorithms/methods. The comparison is based on the use of ROC curves. Second, circular spotlight SAR imagery is used to examine how detector performance varies with the azimuth angle. Owing to the small number of available ship samples, this analysis has limitations. Third, again using the circular spotlight SAR imagery, the variation, with respect to azimuth angle, of the elements of the polarimetric covariance matrix of both the ship and the ocean are analysed. The results are as follows. Using the stripmap imagery, it is found that exploiting both polarimetry and spatial correlations greatly improves detection performance. Using the circular spotlight imagery, it is found that detection performance is variable with respect to azimuth angle and trends are hard to discern. Moreover, the performance of the Pauli double bounce detector is generally poor. It is conjectured that ship pitching motion degrades the polarimetric backscatter response in the circular spotlight imagery. Finally, the covariance matrix analysis confirms known trends for the ocean backscatter. The implication of these trends is that the polarimetric covariance matrix is sensitive to changes in azimuth angle and hence detectors based on them are also. The data indicate the extent to which this is the case.

Characterisation of low-PRF X-band sea-clutter doppler spectra

Understanding the characteristics of the sea is critical in forming a picture of the sea-clutter as seen by a radar. Current research at the DSTO is interested in the properties of sea-clutter at medium grazing angles, over all azimuth directions, with full polarisation and differing weather conditions. This paper builds on previous work which studied the Doppler spectrum over all azimuth directions using the three component Walker scattering model. An improved model is presented here which includes the aliasing present in low pulse repetition frequency (PRF) data collected using Ingara - the DSTOpsilas X-band synthetic aperture radar (SAR). This enables a large number of data sets to be analysed with differing grazing angles and weather conditions. The goal of this work is to characterise the sea-clutter and improve the fidelity of future analysis into the performance of medium grazing angle target detection algorithms in the maritime environment.

Mathematical Analysis of An Extended Mumford-Shah Model for Image Segmentation

Morel and Solimini have established proofs of important properties of segmentations which can be seen as locally optimal for the simplest Mumford-Shah model in the continuous domain. A weakness of the latter is that it is not suitable for handling noisy images. We propose a Bayesian model to overcome these problems. We demonstrate that this Bayesian model indeed generalizes the original Mumford-Shah model, and we prove it has the same desirable properties as shown by Morel and Solimini.