1769 / 2019-08-29 10:42:05

Sun glint thresholds for the remote detection of oil films on the ocean surface

7、地理与地理信息科学 > 专题6：海洋、湖泊与河流先进监测技术

It has been known that the presence of sun glint can enhance oil-water spatial contrast and thus facilitating oil slick detection in optical imagery. However, the strength of sun glint required to detect thin oil films has never been quantified objectively. Natural oil slicks in the western Gulf of Mexico are used to determine the sun glint threshold required for optical remote sensing of oil films. Thin oil films from the natural seeps are used here to minimize reflectance signal from oil optical properties (absorption and scattering). The threshold is determined using the same-day image pairs collected by Moderate Resolution Imaging Spectroradiometer (MODIS) Terra, MODIS Aqua, and Visible Infrared Imaging Radiometer Suite (VIIRS) (N = 2297 images) over the same oil slick locations where at least one of the sensors captures the oil slicks. For each sensor, statistics of sun glint strengths, represented by the normalized glint reflectance (LGN, sr-1), when oil slicks can and cannot be observed are generated. The LGN threshold for oil film detections is determined to be 10-5–10-6 sr-1 for MODIS Terra and MODIS Aqua, and 10-6–10-7 sr-1 for VIIRS. Below these thresholds, no oil films can be detected, while above these thresholds, oil films can always be detected except near the critical-angle zone where oil slicks reverse their contrast against the background water. The sun glint thresholds determined here will provide critical information on which images (or which portions of an image) can be used to search for oil, thus reducing false negative detection.