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. The occurrence of oil seeps on the sea surface from active petroleum systems has been extensively documented by radar imaging using SAR (Synthetic Aperture Radar). Polarimetry is consolidating in the oil industry as a sophisticated technique for the study of marine seeps. The Cantarell Complex, located in the Gulf of Mexico, is currently the most prolific natural seep site in the world. This paper aims to add to the discussion on the physical properties of seepage slicks from full polarimetric data (quad-pol) from RADARSAT-2 satellite. The fact that the research was based on two images (ID#02 and ID#04) acquired at the same place and with the same mode of operation but with a time lapse between acquisitions and different incidence angles allowed to evaluate the influence of the imaging geometry on target signatures. To this end, samples of four classes (sea, offshore platform, oil and false targets) were collected. The data of the samples were afterwards shown in graphs and plotted in the classification plan of Cloude & Pottier – entropy (H) vs. alpha angle (¯α) – for backscattering mechanism analysis. Such elements made it possible to certify that (i) the sea is a Bragg-type surface regardless the incidence angle, (ii) platforms have double-bounce scattering, but small incidence angles are inadequate for their characterization, (iii) false targets (associated in ID#02 to regions of little wind) are moderately random/quasi deterministic surfaces, and (iv) oil behaves either as a Bragg (19.0◦–22.7◦ incidence angle range) or as a random/anisotropic surface (33.7◦–36.7◦ incidence angle range). Keywords : H-¯α diagram, incidence angle, radar imaging, marine seeps. RESUMO. A ocorrencia de exsudacoes de oleo na superficie do mar a partir de sistemas petroliferos ativos vem sendo extensivamente documentada por imageamento utilizando sistemas SAR ( Synthetic Aperture Radar ). A polarimetria esta se consolidando na industria do petroleo como uma tecnica sofisticada para o estudo de seeps marinhos. O Complexo de Cantarell, situado no Golfo do Mexico, e atualmente o local de exsudacao natural de oleo mais prolifico do globo terrestre. Este trabalho visou contribuir com a discussao acerca das propriedades fisicas de escapes de oleo a partir dos dados polarimetricos completos ( quad-pol ) do satelite RADARSAT-2. O fato da pesquisa valer-se de duas imagens (ID#02 e ID#04) adquiridas no mesmo local e modo de operacao, mas com intervalo entre as aquisicoes e diferentes ângulos de incidencia, possibilitou avaliar a influencia da geometria de imageamento na assinatura dos alvos. Com esse proposito, foram geradas amostras de quatro classes (mar, plataforma, oleo e falso alvo), que tiveram os dados posteriormente relacionados em graficos e no plano de classificacao de Cloude & Pottier – entropia (H) vs. ângulo alfa (¯α) – para analise do mecanismo de espalhamento. Tais elementos permitiram atestar que (i) o mar e uma superficie do tipo Bragg independente do ângulo de incidencia, (ii) as plataformas tem espalhamento double-bounce , mas baixos ângulos sao inadequados para sua caracterizacao, (iii) falsos alvos (associados em ID#02 a regioes de baixo vento) sao superficies moderadamente aleatorias/quase deterministicas, e (iv) o oleo comporta-se ou como Bragg (19,0◦–22,7◦), ou como uma superficie aleatoria/anisotropica (33,7◦–36,7◦). Palavras-chave : Diagrama H-¯α, ângulo de incidencia, imagem de radar, seeps marinhos.

DETECTION OF SEEPAGE SLICKS IN CANTARELL COMPLEX (GULF OF MEXICO) USING POLARIMETRIC SAR DATA OF RADARSAT-2