Modelling of seawater polluted by light and heavy crude oil droplets

Significant amounts of crude oil transported from offshore fields to the refineries using tankers or pipelines, demand increased control of seawater pollution. Tanker accidents resulting in oil spills drive much attention, as they influence local marine life and coastal industry. However, the most significant annual amount of crude oil enters the sea in the form of oilin- water emulsion as a result of standard tanker operations, offshore oil extraction and daily work of refineries. Many branches of science are challenged to provide new methods for oil detection, less expensive, more sensitive and more accurate. Remote satellite or airborne detection of large oil spills is possible using joint techniques as microwave radars, ultraviolet laser fluorosensors and infrared radars. Some methods are capable to deal with oil streaks detection and estimation of oil thickness. Although there is currently, no method to detect small concentration of oil droplets dispersed in seawater. Oil droplets become additional absorbents and attenuators in water body. They significantly change seawater inherent optical properties, which imply the change of apparent optical properties, detectable using remote sensing techniques. To enable remote optical detection of oil-in-water emulsion, a study of optical properties of two types of crude oil was conducted. Radiative transfer theory was applied to quantify the contribution of oil emulsion to remote sensing reflectance (Rrs). Spectra of Rrs from in situ measurements in Baltic Sea were compared to Rrs spectra of seawater polluted by 1 ppm of crude oil emulsion, collected using radiative transfer simulation. The light crude oil caused a 9-10% increase of Rrs while the heavy one reduced Rrs up to 30% (model accuracy stayed within 5% for considered spectral range). Results are discussed concerning their application to shipboard and offshore oil content detection.