Dataset for: "Hindcast modeling of oil slick persistence from natural seeps"

This study was conducted on the basis of the open archive for Synthetic Aperture Radar (SAR) images collected over the lease block Green Canyon 600 (GC600) and its surrounding region from January 2003 to November 2011. The objective of this work was to estimate the surface residence-time of the oil slicks, and to determine the importance of wind and surface currents on the trajectory and fate of the released oil. SAR imagery was collected by eight SAR satellites: Cosmo-Skymed-1, -2, and -3; RADARSAT-1 and -2; ENVISAT ASAR, ALOS PALSAR, and ERS-2. Image sources included European Space Agency (ESA), National Aeronautics and Space Administration (NASA) with support from the Alaska Satellite Facility, and the Center for Spatial Technologies and Remote Sensing (CSTARS). We matched the location of the GC600 against the coverage of the SAR images and determined whether the oil slicks were visible in archived SAR images. Some of the image scenes were un-usable due to poor image quality, or did not contain oil. After preliminary screening, a Texture Classifying Neural Network Algorithm (TCNNA) was used to delineate georectified polygons for oil slicks from 41 SAR images. Trajectories of these oil slicks were investigated by employing a two-dimensional Lagrangian particle-tracking surface oil drift model. The evolution of each oil slick on the surface of the ocean was simulated by computing the two-dimensional trajectories of 100 particles every 15 minutes. The initial positions of the particles were randomly distributed near the Oil Slick Origin (OSO) point within the seeding radius. The seeding radius was defined as 1/3 width of the oil slick at the OSO estimated from SAR image. The trajectories of the particles were computed within a time-varying velocity field that is some combination of ocean surface currents derived from the HYbrid Coordinate Ocean Model (HYCOM) and 10-m winds derived from Cross-Calibrated Multi-Platform Ocean Surface Wind Vectors (CCMP). A set of numerical simulations was performed by increasing hindcast interval in reverse time order from the image collection time in order to obtain the closest resemblance between the simulated oil pathways and the length and shape of the oil slicks observed in SAR images. A surface residence-time estimate for an observed oil slick was the hindcast interval that best reproduced the length and shape of that oil slick in the simulated representation. The wind scaling coefficient of 0.035 and the wind deflection angle of 20° to the right of the wind direction yielded the most accurate trajectory of the oil particles compared to SAR data. To study the effect of wind and surface currents on the trajectory and fate of the natural oil slicks, the following simulations with the surface oil drift model were performed: 1) wind and surface currents combined; 2) surface currents alone (wind scaling coefficient was set to 0), and 3) wind alone (ocean currents were set to 0). In addition, a wind-powered autonomous surface vehicle (SailDrone) deployment provided in-situ observations at the lease block Green Canyon 574 (GC574) and its surrounding region to verify the importance of wind and surface currents in deriving the trajectory of oil slicks on the sea surface.