Fully Polarimetric SAR data for Oil Slick Observation
Ferdinando Nunziata(1), Attilio Gambardella(1) and Maurizio Migliaccio(1)
(1) Università di Napoli Parthenope, Centro Direzionale, Isola C4, 80143 Napoli, Italy
Synthetic Aperture Radar (SAR), due to its all-weather day and night capabilities, is the key sensor for oil spill monitoring. However, SAR oil spill observation is not an easy task due to speckle noise which affects SAR images and due to other natural phenomena (biogenic films, rain cells, low wind areas...) which look like oil spills in SAR images (look-alikes). Several approaches have been proposed in literature for oil spill observation which are generally based on the use either of texture, radiometric and geometrical features or ancillary external data, such as optical data .
However, it is well-known that a single polarization SAR, employing a single polarization antenna for both transmission and reception of the signal, measures the field scattered by the observed scene, a vector quantity, as a scalar quantity. As a matter of fact, any additional information about the scattering mechanism, inherently burned in the polarization properties of the scattered signal, is lost. On the other hand, a polarimetric SAR, performing a vectorial measurement, can provide such additional information which can be employed for gaining better understanding of the scattering mechanism. Although SAR polarimetry has been widely employed for terrain-type and land-cover classification, only few studies have been accomplished for oil spill observation purposes -.
In this paper, polarimetric sea surface scattering mechanism is analyzed with and without surface slicks, under low to moderate wind conditions, by using the Mueller matrix. A simple model which relates the co-polarized and cross-polarized terms of the Mueller matrix to the presence of a surface slick is proposed. Such relationship, under low to moderate wind condition, is shown to exhibit a different sensitivity with respect to oil and biogenic slicks. Following the above mentioned rationale a simple an very effective filtering technique has been developed for SAR oil spill observation.
The filtering technique has been tested on fully polarimetric C- and L-band SAR data. Experiments shown the usefulness of the proposed technique for both observing oil spills and distinguishing between oil spills and biogenic films. Moreover, the filtering technique, unlike classical oil spill observation procedures, which are generally based on thersholding techniques, does not need any threshold.
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