Classification of low backscatter ocean regions using log-cumulants

Paper presented at ‘PolInSAR 2015, Frascati, Italy 26–30 January 2015 (ESA SP-729, April 2015)In a synthetic aperture radar image, low backscatter regions of various origin can be observed in ocean areas. Operational oil spill detection services work to discriminate anthropogenic oil spills from natural phenomena such as seeps, low wind fields, thin ice and biogenic slicks. In this paper, we investigate the potential of using matrix log-cumulants for this purpose

An alternative approach for calculating the SAR damping ratio of verified oil slicks

Source: https://ieeexplore.ieee.org/xpl/conhome/1000307/all-proceedings.The damping ratio is a calculated feature that measures the contrast between oil-slicked water and the open ocean in SAR data. To implement the damping ratio, the current literature suggests estimating the open water backscatter by taking strips of undefined width across the range direction, obtaining the damping ratio as a function of incidence angle. We show in this paper that the method proposed in the literature can be improved by instead sampling open water pixels randomly. The method is tested on RADARSAT-2 quad-polarimetric SAR imagery of a verified oil slick acquired during the 2013 NOFO oilon-water exercise conducted in the North Sea. The results suggest that deviations in the derived damping ratio encountered by implementing the method proposed in the literature can be reduced from of order 100 – 10-1 to 10-3

A Sensitivity Study of L-Band Synthetic Aperture Radar Measurements to the Internal Variations and Evolving Nature of Oil Slicks

This thesis focuses on the use of multi-polarization synthetic aperture radar (SAR) for characterization of marine oil spills. In particular, the potential of detecting internal zones within oil slicks in SAR scenes are investigated by a direct within-slick segmentation scheme, along with a sensitivity study of SAR measurements to the evolving nature of oil slicks. A simple, k-means clustering algorithm, along with a Gaussian Mixture Model are separately applied, giving rise to a comparative study of the internal class structures obtained by both strategies. As no optical imagery is available for verification, the within-slick segmentations are evaluated with respect to the behavior of a set of selected polarimetric features, the prevailing wind conditions and weathering processes. In addition, a fake zone detection scheme is established to help determine if the class structures obtained potentially reflect actual internal variations within the slicks. Further, the evolving nature of oil slicks is studied based on the temporal development of a set of selected geometric region descriptors. Two data sets are available for the investigation presented in this thesis, both captured by a full-polarization L-band airborne SAR system with high spatial- and temporal resolution. The results obtained with respect to the zone detection scheme developed supports the hypothesis of the existence of detectable zones within oil spills in SAR scenes. Additionally, the method established for studying the evolving nature of oil slicks is found convenient for accessing the general behavior of the slicks, and simplifies interpretation

Characterization of Low Backscatter Regions in the Marine Environment by Multipolarization C- and X-band Synthetic Aperture Radar Data

The focus of this thesis is the application of multipolarization SAR data for characterization of marine oil spills and other low backscatter ocean phenomena. A variety of SAR descriptors are investigated for the purpose of discriminating between oil spills and look-alikes. The effects of various parameters on the imaging, including sensor frequency, imaging geometry and oil properties, are addressed. The analysis is performed on a unique data set collected during annual oil spill exercises in the North Sea. Cross-polarization channels are found to be severely contaminated by noise, and only copolarization channels are used in this study. Coherent systems, in which the relative phase between polarization channels is preserved, are found preferable to sensors where only intensity information is useful. A number of dual-copolarization features are compared in terms of their discrimination ability. The two most promising features are selected and used as basis for image classification. The results show that the feature pair can distinguish between a simulated biogenic slick and mineral oil spills. A comparison between C- and X-band data is conducted, including analysis of near coincident acquisitions by Radarsat-2 (C-band) and TerraSAR-X (X-band). Multipolarization features here show enhanced detection and characterization abilities in the Radarsat-2 data compared to TerraSAR-X data. No clear difference in terms of data quality is found. The presence of a non-Bragg scattering component in the data is revealed for both sensors. Some differences in the statistical and scattering properties are identified between the two sensors and among low backscatter regions of various origins. A potential for using log-cumulants for discrimination between mineral oil spills and other marine low backscatter regions are demonstrated. This is shown for both Radarsat-2 and TerraSAR-X, and for both single-polarization and multipolarization data. The proposed method has a potential for classification of low backscatter ocean regions of unknown origin