Transport characteristics of oil slicks are reported from a controlled release experiment conducted in the North Sea in June 2015, during which mineral oil emulsions of different volumetric oil fractions and a look‐alike biogenic oil were released and allowed to develop naturally. The experiment used the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) to track slick location, size, and shape for ∼8 h following release. Wind conditions during the exercise were at the high end of the range considered suitable for radar‐based slick detection, but the slicks were easily detectable in all images acquired by the low noise, L‐band imaging radar. The measurements are used to constrain the entrainment length and representative droplet radii for oil elements in simulations generated using the OpenOil advanced oil drift model. Simultaneously released drifters provide near‐surface current estimates for the single biogenic release and one emulsion release, and are used to test model sensitivity to upper ocean currents and mixing. Results of the modeling reveal a distinct difference between the transport of the biogenic oil and the mineral oil emulsion, in particular in the vertical direction, with faster and deeper entrainment of significantly smaller droplets of the biogenic oil. The difference in depth profiles for the two types of oils is substantial, with most of the biogenic oil residing below depths of 10 m, compared to the majority of the emulsion remaining above 10 m depth. This difference was key to fitting the observed evolution of the two different types of slicks.

Abstract-Oil spill detection using a time series of images acquired off Norway in June 2015 with the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) is examined. The relative performance of a set of features derived from quadpolarization vs. hybrid-polarity modes in detection of various types of slicks as they evolve on a high wind driven sea surface is evaluated. It is shown that the hybrid-polarity mode is comparable to the full-polarimetric mode in its ability to distinguish the various slicks from open water for challenging conditions of high winds (9-12 m/s), small release volumes (0.2 -0.5m3 ), and during the period 0-9 hours following release. The features that contain the cross-polarization component are better for distinguishing the various slicks from open water at later and more developed stages. Although these features are not available in the hybrid-polarity mode, we identify alternative features to achieve similar results. In addition, a clear correlation between the results of individual features and their dependence on particular components within the two-scale Bragg scattering theory is identified. The features that show poor detectability of the oil slicks are those that are independent of the small-scale roughness, while the features resulting in good separability were dependent on several factors in the two-scale Bragg scattering model. We conclude that the hybrid-polarity mode is a viable alternative for SAR-based oil spill detection and monitoring that provides comparable results to those from quad-polarimetric SAR.

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The effects of both system additive and multiplicative noise on X-, C-, and L-band Synthetic Aperture Radar (SAR) data covering oil slicks are examined. Prior studies have attempted to characterize such oil slicks, primarily through analysis of polarimetric SAR data. Here we factor in system noise that is added to the backscattered signal, introducing artifacts that can easily be confused with random and volume scattering. This confusion occurs when additive and/or multiplicative system noise dominates the measured backscattered signal. Polarimetric features used in this study are shown to be affected by both additive and multiplicative system noise, some more than others. This study highlights the importance of considering specifically multiplicative noise in the estimation of the signal-to-noise ratio (SNR). The SNR based on additive noise should at least be above 10dB. The SNR involving both additive and multiplicative noise should at least be above 0dB. The SNR from TerraSAR-X and Radarsat-2 is below 0dB for the majority of the oil slick pixels when considering both the additive and multiplicative noise, rendering these data unsuitable for any analysis of the scattering properties and characterization. These results are in contrast to the reduced impact of noise on oil slicks detected by the Lband UAVSAR system. In particular, we find there is no need to invoke exotic scattering mechanisms to explain characteristics of the data. We also recommend a noise subtraction for any polarimetric scattering analysis.