A Comparative Detection Probability Analysis of the Water Surface Oil-Product Films by Laser Reflection Method for the Eye-Safe Sounding Wavelengths

Abstract

Among the remote-sensing techniques the most efficient ones to detect oil films on the water surface are laser refection methods based on the record of reflected radiation from the water surface and fluorescent methods based on the record of laser-induced fluorescence radiation of the water surface. Laser equipment, for example, installed on the delivery aircraft, can be used regardless of the time of day in a fairly wide range of optical states of the Earth's atmosphere and detect pollution of the small-size oil-products. Laser reflection metods based on the record of reflected radiation from the water surface allow detection of oil films at high altitude of delivery aircraft (and, respectively, at the wideband spatial scanning on the surface of the water). The paper is concerned with development of the laser reflection method to detect the oil-product films on the sea surface, which uses eye-safe laser radiation wavelengths. The eyes safety requirement makes it necessary to choose between ultraviolet (0.18 - 0.38 μm) and near-infrared (over 1.4 μm) spectral ranges. The choice between these two options should be based on the efficient use of ultraviolet (0.18 - 0.38 μm) and near infrared (over 1.4 μm) ranges for detection of oil films on the water surface. The results of mathematical modeling show that for the oil film thickness more than 20 μm the detection probability is 100% for the sounding wavelength both of 0.355 μm and of 1.54 μm . However, for the thinner films of oil (a thickness of the oil films may be of units of μm or less) the situation is different. In laser sounding at a wavelength of 0.355 μm, the laser reflection method allows reliable detection of the oil film, which have a thickness of 2 μm, at least, with an appropriate probability of the proper detection (more than 0.9) and the false alarm rate (less than 0.002) for the relative noise of measurement being no more than 5%. At the same time, in laser sounding at a wavelength of 1.54 μm a probability of the proper detection of the oil films with a thickness of 2 μm can have any value within the range 0 ... 1 (depending on the random thickness of the film in sounding point).