Oil Spill Detection by means of Dual-polarized SAR data/Analysis of the sea surface scattering with and without surface slicks

Ferdinando Nunziata⁽¹⁾, Attilio Gambardella⁽¹⁾ and Maurizio Migliaccio⁽¹⁾

⁽¹⁾ Università di Napoli Parthenope, Centro Direzionale, Isola C4., 80100 Napoli, Italy

Abstract

Oil Spill Detection by means of Dual-polarized SAR Data

Ferdinando Nunziata⁽¹⁾, Attilio Gambardella⁽¹⁾ and Maurizio Migliaccio⁽¹⁾

⁽¹⁾ Università di Napoli Parthenope, Centro Direzionale, Isola C4., 80100 Napoli, Italy

Abstract

Airborne and space-borne remote sensing cover a key role in supporting law enforcement and minimising the ecosystem impact of sea oil pollution, especially by means of all-weather day and night Synthetic Aperture Radar (SAR) sensor. SAR oil spill detection is possible because oil slicks damp the short waves responsible of the signal backscattered to the SAR antenna and generate a low backscattering area which result in dark areas over SAR images. However, over the SAR image the reliability of observation needs to be enhanced. In fact, since other physical phenomena (known as look-alikes) can generate dark areas in SAR images, SAR oil spill detection is not an easy task. Classical oil spill detection proced ures are generally based on filtering technique accomplished on multi-look single-polarization SAR data. In last years it was shown that radar polarimetry is able to provide additional information to environmental applications, and recent studies have been shown that fully polarimetric features can be used for distinguishing between oil spills and biogenic look-alikes. However, although a fully polarimetric SAR is to be desired, there may be hardware and budget considerations that can suggest to implement a simpler polarimetric configuration such those utilised by the SARs on board of ENVISAT and COSMO SKYMED missions, which can operate only in single or in dual polarization modes. As the matter of fact, the use of dual-polarised SAR sensors for oil spill observation is operational interesting.

In this study the co-polarised phase difference (CPD), i.e. the phase difference between the HH and VV channels, is modelled and employed to characterize the scattering return from oil spills and biogenic look-alikes. The developed model predicts, under low to moderate sea conditions, a different CPD sensitivity with respect to oil spills and biogenic look-alikes, since their different damping effects. Following the model guidelines a new and very effective filtering technique has been conceived an implemented.

Experiments accomplished over a large data-set consisting of multi-look complex (MLC) C- and L-Bands SAR data confirm that the C-band is to be preferred to the L one for oil spill detection and show the capability of the CPD both to assist oil spill observation and to distinguish between oil spill a nd biogenic look-alikes.

Analysis of the Sea Surface Scattering With and Without Surface Slicks

Ferdinando Nunziata⁽¹⁾, Piotr Sobieski⁽²⁾, and Maurizio Migliaccio⁽¹⁾

(1) Dipartimento per le Tecnologie, Università degli Studi di Napoli Parthenope, Centro Direzionale, Isola C4, 80100 Napoli, Italy.

(2) Laboratoire de Télécommunications et Télédétection, Université Catholique de Louvain, place du Levant, 2, B-1348 Louvain-la-Neuve, Belgium.

Abstract

The observation of sea oil pollution from radar images is a rather difficult task as there are several physical phenomena that influence the darkening of sea areas in radar images (look-alike) due to the wave damping phenomenon which complexity is not yet completely well understood. The radar backscattering from a sea surface with slicks is often described by means of the Small Perturbation Model (SPM) which takes into account the short waves part of the sea surface elevation spectrum only. Actually, the presence of oil slicks, reducing the wind energy input to the surface waves, firstly damps the short wave part of the sea surface elevation spectrum, then, through complex and non-linear wave-wave interaction also affects the long wave part. The whole range of the spectrum has thus to be taken into account for a complete description of the damping phenomena.

In this study the behaviour of the sea surface backscattering coefficient with and without surface slicks has been investigated by using the Université catholique de Louvain (UCL) sea surface scattering model. In this model the scattering by the rough sea surface is simulated, for different radar configurations, by means of the two-scale Boundary Perturbation Model (BPM), which allows to take into account the whole sea surface elevation spectrum. Therefore, the contrast of radar signals scattered from a slick-free and from a slick covered surface is evaluated considering both fully and non fully developed sea conditions.

An experimental validation of this approach is under way considering numerical simulations based on the mentioned models for chosen sea surface areas with and with surface slicks along with the corresponding L and C-band SAR images. For the comparison, co-located environmental data are taken from ECMWF data base for the areas under investigation.

Workshop presentation

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry