Ocean surface monitoring, especially oil slick detection, has become mandatory due to its importance for oil exploration and risk prevention on ecosystems. For years, the detection task has been performed manually by photo-interpreters using Synthetic Aperture Radar (SAR) images with the help of contextual data such as wind. This tedious manual work cannot handle the increasing amount of data collected by the available sensors and thus requires automation. Literature reports conventional and semi-automated detection methods that generally focus either on oil slicks originating from anthropogenic (spills) or natural (seeps) sources on limited data collections. As an extension, this paper presents the automation of offshore oil slicks on an extensive database with both kinds of slicks. It builds upon the slick annotations of specialized photo-interpreters on Sentinel-1 SAR data for 6 years over 3 exploration and monitoring areas worldwide. All the considered SAR images and related annotation relate to real oil slick monitoring scenarios. Further, wind estimation is systematically computed to enrich the data collection. Paper contributions are the following : (i) a performance comparison of two deep learning approaches: semantic segmentation using FC-DenseNet and instance segmentation using Mask-RCNN. (ii) the introduction of meteorological information (wind speed) is deemed valuable for oil slick detection in the performance evaluation. The main results of this study show the effectiveness of slick detection by deep learning approaches, in particular FC-DenseNet, which captures more than 92% of oil instances in our test set. Furthermore, a strong correlation between model performances and contextual information such as slick size and wind speed is demonstrated in the performance evaluation. This work opens perspectives to design models that can fuse SAR and wind information to reduce the false alarm rate.
Recent studies aim to exploit vegetation hyperspectral signature as an indicator of pipeline leakages and natural oil seepages by detecting changes in reflectance induced by oil exposure. In order to assess the feasibility of the method at larger spatial scale, a study has been carried out in a greenhouse on two tropical (Cenchrus alopecuroides and Panicum virgatum) and a temperate (Rubus fruticosus) species. Plants were grown on contaminated soil during 130 days, with concentrations up to 4.5 and 36 g.kg-1 for heavy metals and C10-C40 hydrocarbons respectively. Reflectance data (350-2500 nm) were acquired under artificial light from 1 to 60 days. All species showed an increase of reflectance in the visible (VIS, 400-750 nm) and short-wave infrared (SWIR, 1300-2500 nm) under experimental contaminants exposure. However, the responses were contrasted in the near-infrared (NIR, 750-1300 nm). 47 normalized vegetation indices were compared between treatments, and the most sensitive to contamination were retained. Same indices showed significant differences between treatments at leaf and plant scales. Indices related to plant pigments, plant water content and red-edge reflectance were particularly sensitive to soil contamination. In order to validate the selection of indices, hyperspectral measurements were performed outdoor at plant scale at the end of the experiment (130 days). Leaf samples were also collected for pigment analysis. Index selected at day 60 were still sensitive to soil contamination after 130 days. Significant changes in plant pigment composition were also observed. This study demonstrates the interest of hyperspectral data for oil exploration and environmental diagnosis.
On-shore, hyperspectral imagery is currently used to detect and measure remotely oil spill extension for environmental purpose and hydrocarbon seepage for petroleum exploration. In this study, variations of hyperspectral signatures of vegetal species have been analyzed at the laboratory scale to detect indirectly the potential impacts on the plants of crude oil seepage and spills in the soil. Experimental study has been performed under greenhouse to simulate the exposure of two species of plants to a co-contamination of hydrocarbons and heavy metals contained in sludge from mud pit. Maize and bramble have been selected for this study since they are cultivated and spontaneous species respectively located in the region of interest. Five levels of exposure were performed over a period of 100 days. Reflectance evolution of each plant was measured with a spectroradiometer from 350 nm to 2500 nm with a dedicated leaf clip. Net morphological impacts were observed for maize with a global reduction of plants and leaves sizes correlated to the level of cocontamination. Hyperspectral measurement on maize revealed a higher reflectance in the absorption wavelength of water at 1450 and 1900 nm due to contamination and water stress. Reflectance in the visible increased at 600 nm (red interval) for bramble plants exposed to co-contamination. Then, the level of reflectance in the NIR decreased between 700 and 800 nm (red-edge) and absorption of water also decreased at 1450 and 1900 nm as described previously for the maize.
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