Visual observations and the Bonn Agreement

The challenges facing environmental scientists regarding response to an oil spill were discussed. As oil interacts with the environment, its properties change. The size of the response depends on the volume released, but often the quantity is not known. As such, attempts have been made in the past 4 decades to develop technology or operating procedures that can quantify the spill by the size and visible appearance of the slick. Systems based on the visible spectrum are the most common remote sensing technique for estimating spill thickness. However, to date, there is no recognized method or equipment that can reliably provide the response team with an accurate answer. This paper reviewed the theoretical and practical challenges that have prevented the advancement in this area. Several formulas have been built to link slick appearance with spill thickness. The Bonn Agreement Aerial Surveillance Handbook uses an appearance code based on published scientific literature, laboratory and outdoor experiments and field trials. The limitations of estimating thickness and volume using such visual appearance methods include atmospheric visibility constraints; spatial and temporal inhomogeneity of the oil; irregularity of the water surface; and optical characteristics of the oil. The paper also presented a potential modification involving separation into simple thick oil and sheen areas. 22 refs., 1 tab., 2 figs.