Abstract
In this feasibility study discriminating oil slicks and newly formed sea ice using synthetic aperture radar (SAR) imagery is investigated, using imagery from the L-band high-resolution uninhabited aerial vehicle synthetic aperture radar (UAVSAR) airborne and the satellite C-band RADARSAT-2 (RS-2) systems. To determine the separability of these two varying but similar appearing low backscatter ocean surfaces, multipolarization features are utilized from both SAR datasets. The discrimination is evaluated using the Kolmogorov–Smirnov separability test. All imagery was obtained during several sea ice campaigns in the Arctic Ocean and separate oil spill campaigns in Norway and the Gulf of Mexico, with each campaign collecting in situ observations. We observe that the polarization difference (VV-HH) reliably separates the mineral oil slicks and newly formed sea ice areas using UAVSAR images, due to the low noise floor and subsequent high signal-to-noise ratio (SNR) radiometric performance of the airborne system. The comparably higher noise floor and related lower SNR hampers the separability in the RS-2 images. Simulated noise floors were generated by adding white Gaussian noise to the UAVSAR data, which show that discrimination between the two low backscatter phenomena using multipolarization features is possible, provided that both datasets are still well above the noise floor. The pixel resolution has a limited effect on the separability. The results of this study provide an approach to distinguish oil slicks from newly formed sea ice, which might be of special interest should an oil spill occur within the marginal ice zone.
Highlights
T HE thinning of sea ice and the reduced sea ice cover in the Arctic [1] over the last decade has led to an increase in maritime traffic and petroleum-related activities, activities thatManuscript received March 31, 2020; revised June 12, 2020 and August 12, 2020; accepted August 13, 2020
We examine fully polarimetric (FP) SAR images from spaceborne C-band RADARSAT-2 (RS-2) SAR images as well as airborne L-band SAR images acquired onboard the National Aeronautics and Space Administration (NASA) uninhabited aerial vehicle synthetic aperture radar (UAVSAR) sensor, to identify multipolarization features that can separate oil slicks from newly formed sea ice types over a range of incidence angles (IA)
And (b) we observe that there is a good oil–sea contrast in both σV V and polarization difference (P D) for the UAVSAR data. This high oil–sea contrast for P D was observed for three mineral oil emulsions (40%, 60%, and 80% volumetric oil fraction) in [34], and P D has a reduced dependence on IA for the oil slick compared to the open water
Summary
T HE thinning of sea ice and the reduced sea ice cover in the Arctic [1] over the last decade has led to an increase in maritime traffic and petroleum-related activities, activities thatManuscript received March 31, 2020; revised June 12, 2020 and August 12, 2020; accepted August 13, 2020. An oil spill within or near newly formed sea ice has not yet been known to occur nor captured on radar imagery In this feasibility study we examine the situation in radar imagery when sea ice appears most similar to an oil spill in an otherwise clean ocean, using both fully polarimetric (FP) and multifrequency data, in order to investigate the possibilities of discriminating between new ice formation and oil spills using uniform datasets. FP (HH/HV/VH/VV) satellite images have a small areal coverage and are not suitable for regular monitoring of the vast Arctic region These images can be used to investigate whether various sea ice types and ocean conditions, including oil slicks and the similar-appearing sea ice can be discriminated using all three operationally available dual-polarimetric modes provided by presently operational satellite sensors such as Sentinel-1 (C-band), the RADARSAT Constellation Mission (C-band) and ALOS-2 (L-band). In [19] newly formed sea ice was reported to have backscatter values of −25 dB
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