An Evaluation Algorithm for Thick Oil Film on Sea Surface Based on Fluorescence Signal

Oil film thickness is a significant index to evaluate oil spill pollution at sea surface. Laser-induced fluorescence (LIF) is one of the most effective oil spill detection technologies at present. Nowadays, based on the LIF detection technology, the effective evaluation of the thickness of thin oil film on the sea surface has been implemented. However, the studies on the evaluation of thick oil film on the sea surface are relatively few. Furthermore, the existing inversion algorithm for thick oil film is not applicable to the evaluation of oil film thickness under various detection angles except vertical sea surface. In view of this, a new evaluation algorithm for thick oil film based on fluorescence signal is put forward in this article. The transport mechanism of photons in oil film medium is regarded as the basis. Simultaneously, the influence factors, such as detection mode and detection angle, are comprehensively considered in the LIF detection process. In this way, the function relationship between the fluorescence signal intensity of the oil film, and its thickness is established. Afterward, the algorithm is experimentally verified by selecting the mixture of crude oil and white oil as the experimental oil. The results show that the algorithm is suitable for evaluating the thickness of thick oil film in a certain thickness range (i.e., the fluorescence intensity of oil film is not saturated). The effective evaluation of thick oil film on the sea at any detection angle under noncoaxial transmit–receive form and coaxial transmit–receive form can be realized by this algorithm.