During the oil spills response actions, the rapid location and mapping of the oil slicks at sea surface is needed, as well as the characterization of different types of oils, avoiding false alarms whenever possible. In this way, all information provided by remote sensors can be useful to improve the strategies to cleanup oceanic regions and to protect the vulnerable coastal areas, minimizing possible environmental damages.
Synthetic Aperture Radars (SAR) are widely used for this purpose, due to their potential for systematic data acquisition covering large areas with near real time delivery capability, offering different spectral and spatial resolutions, swaths, incidence angles and polarization channels.
Since the nineties automatic and semiautomatic algorithms have been developed to detect low backscatter regions related with oil slicks aiming to assist large scale monitoring initiatives. Traditionally, the majority of the SAR data used have commonly been acquired with wide swaths in single or dual-pol channels. However during the emergency situations, where the position of the oil spills are known, polarimetric SAR data (Pol SAR) can be used to provide detailed information about the occurrences, as well as to minimize the false alarms interference. Recent studies, using several polarimetric attributes, have been investigating the potential of dual, quad and compact polarization modes to detect different backscatter mechanisms in biogenic and mineral oil slicks, probably related with different chemical properties and thicknesses variations.
The objective of this paper is to evaluate the potential and the trade-offs provided by single, dual and quad-polarized data to detect oil slicks at sea surface. To accomplish this, a set of SAR data acquired by RADARSAT-2 [quad-polarized] and Sentinel-1 [dual-polarized] were processed and classified using a region classifier named Pol Class based on stochastic distances.
The Pol Class was used because of its potential to use proper statistical modeling to process SAR data in different formats. This work uses the Intensity and the Polarimetric modules to classify the SAR data. The Polarimetric module is used to evaluate all complex information contained in the Pol SAR data, and the Intensity module provides the dual and single-polarized channels assessment, making feasible to compare the advantages of using all possible polarimetric combinations.
The expectation is to contribute with the scientific community evaluation about the trade-offs provided by the single, dual and quad-polarized SAR data applied to oil detection, considering as reference the needs of the operational use during both, routine monitoring and emergency situations.
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