Evaluation of SAR Polarimetric data for Study Oil Spills and Natural Slicks Parameters
Ivonin, Dmitry1; Ivanov, Andrei1; Dostovalov, Mikhail2; Sineva, Anastasia1; Khalikov, Zaur1; Zakharov, Alexander3
1P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences, RUSSIAN FEDERATION; 2Research Institute of Precision Instruments, Moscow, RUSSIAN FEDERATION; 3Kotelnikov Institute of Radio Engineering and Electronics, Russian Academy of Sciences, RUSSIAN FEDERATION
Recently ìany efforts have been made to apply dual (VV & VH) and quad-polarization (HH, HV, VH & VV) SAR data to improve oil spill detection and classification. For this reason two experiments with Radarsat-2 (R-2) and TerraSAR-X (TSX) synthetic aperture radars (SAR) have been carried out over the Oil Stones (Neftyanye Kamni, Azerbaijan) oil production site in the Caspian Sea. Based on processing and analysis of the R-2 quad-polarization SAR images acquired in 2009, and R-2 and TSX dual-polarization SAR images acquired in 2012, it was shown that HH and VV components are reliable for obtaining information on extent and area of oil slicks. Meantime, signal of VH components of R-2 and TSX dual-pol images are affected by noise floors, which are -27 and -25 dB respectively. This makes VH images acquired in dual-pol mode unusable for slick parameters extraction. Fortunately, VH component of the R-2 quad-pol image has noise floor of about -36 dB that enables contrast (σ_0) estimation between oil covered and clean water surfaces. Typical contrast for R-2 VV, HH and VH components for the oil slicks at wind 6 m/s are about 2.0 dB. These values are in a good agreement with predictions by Kudryavtsev et al. (2008) who used Jenkins & Jacobs (1997) model for the oil film with thickness of 0.01-0.1 mm and film pressure of 4 mN/m.
It is possible to exclude the signal from wave breaking, which feels slicks slightly, from the sigma0 and distinguish resonant backscattered signal by using component defined as: σ_P=σ_VV - σ_HH. The latter had 3.0 dB contrast over the oil slick area. We took into account that sigmaVH is proportional to the curvature spectrum of capillary-gravity waves B(k) multiplied by the wave slopes dispersion, while sigmaP is proportional to B(k) plus some strong dependence on the 2nd derivative of B(k) [Kudryavtsev et. al. 2003]. We proposed a way how to estimate B(k) and the 2nd derivative of B(k) changes over oil slicks from sigmaP and sigmaVH. The 2nd derivative of B(k) together with B(k) itself seem to provide better estimates of oil film thickness. We extended the previous results for the case of natural monomolecular films with pressure >12 mN/m, and showed that the latter could be theoretically distinguished from the oil slicks with pressure of 4 mN/m using sigmaP and sigmaVH from R-2 quad-pol images. Finally we conclude that VH cross-polarization channel despite commonplace opinion can be used for oil spill characterization. These findings should be considered preliminary and need to be studied deeper.
This work was funded by Russian Government (Grant No.11.G34.31.0078) for research under supervision of the leading scientist at Russian State Hydrometeorological University, Program of the Presidium RAS N 23 ''Sea wave dynamics in remote sensing of the sea surface problems at near-shore zone'', RFBR grants N 12-05-31498, N 12-05-92004-HHC_a.
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