Application of remote sensing data for oil spill monitoring in the Guanabara Bay, Rio de Janeiro, Brazil

Abstract

The rupture of a pipeline transporting hydrocarbons at high temperature caused the spill of 1,300 m3 of fuel oil near the Guanabara Bay shoreline, on January 18, 2000. Immediately after the accident, an emergency effort was undertaken to obtain satellite images in order to monitor the spill's location and movement. One Landsat-5/TM (Thematic Mapper) and 15 Radarsat-1 images were acquired. This paper describes the results obtained with the interpretation of the first three images acquired after the spill. The low frequency of acquisition and the prevailing cloud cover limited the use of visible and infrared spaceborne sensors. Image processing techniques were applied to highlight oil-covered areas on the water surface. Ambiguities in the oil detection were resolved with the aid of ancillary information such as location of knows sources of pollution; aerial inspection information and OPS controlled aerial photos taken from helicopters. The RADARSAT-1 images show clearly the area affected by the spill accident allowing the differentiation of oil-free water areas, fluvial discharge or effluents areas, and oil-covered water areas. One limitation to oil detection using the Landsat-5/TM image was the presence of clouds and haze near the spilled area. In order to improve the visual discrimination of patterns on the water surface related to oil, many RGB combinations of the seven TM bands were evaluated. A supervised classification procedure was applied resulting in the following classes: oil-free water, fluvial discharge, bay areas affected by haze and oil-covered water. The CIS integration of the classification results with ancillary information, such as location of knows sources of pollution; aerial inspection information and GPS controlled aerial photos acquired simultaneously with image acquisition, allowed the final selection of oil-covered areas. The results obtained helped PETROBRAS to optimize the emergency response procedures and subsequent cleaning efforts.