Optical discrimination of emulsified oil in optically complex estuarine waters.

Coastal estuaries, characterized by highly varying waters with complex optical properties, pose challenges for effective oil discrimination via optical remote sensing. In this study, an object-based spectra comparison (OBSC) approach was proposed to extract emulsified oil slicks from Balikpapan Bay, Indonesia, using optical imagery from Sentinel-2 Multispectral Instrument (MSI) and PlanetScope. The OBSC approach utilizes the spectral signatures of oil emulsion to develop emulsified oil index and normalized emulsified oil index to identify potentially emulsified oil objects from MSI and PlanetScope, respectively. Reflectance spectra of the potential objects were compared with those from dynamically-selected nearby waters to rule out false-positive detections, accounting for the varying water optical properties in the estuary. This OBSC approach performed well in extracting emulsified oil slicks from optical images. Moreover, multiple sensor capabilities for oil detection were compared, and requirements for detection and discrimination of oil spills in the coastal estuary environment were further discussed.