Teledetection of the thickness of oil films on polluted water based on the oil fluorescence properties

Review of oil spill remote sensing

Remote-sensing for oil spills is reviewed. The use of visible techniques is ubiquitous, however it gives only the same results as visual monitoring. Oil has no particular spectral features that would allow for identification among the many possible background interferences. Cameras are only useful to provide documentation. In daytime oil absorbs light and remits this as thermal energy at temperatures 3-8K above ambient, this is detectable by infrared (IR) cameras. Laser fluorosensors are useful instruments because of their unique capability to identify oil on backgrounds that include water, soil, weeds, ice and snow. They are the only sensor that can positively discriminate oil on most backgrounds. Radar detects oil on water by the fact that oil will dampen water-surface capillary waves under low to moderate wave/wind conditions. Radar offers the only potential for large area searches, day/night and foul weather remote sensing.

Oil UV extinction coefficient measurement using a standard spectrophotometer

This paper investigates the possible techniques for measurement of the extinction coefficient of oils in the near UV. Results show that the best technique, in precision and ease of use, is the unknown thickness method. This method, never proposed up to now as far as we know, allows the use of a standard spectrophotometer. Beer's law is also validated for oils and a simple function is proposed for fitting the extinction coefficient spectra.

Lidar fluorosensing of mineral oil spills on the sea surface

Airborne fluorosensor measurements over maritime oil spills show that this method enables a sensitive classification and quantification of surface films having a thickness in the 1-microm range. However, significant changes of the optical signature of oil occur in the presence of submicrometer films which are not yet fully understood. Possible reasons for this effect are discussed and the limitations of laser fluorosensing of small oil discharges are outlined.

Measurement of fluorescence decay of crude oil: a potential technique to identify oil slicks

The single photon counting technique has been used to measure the decay time for several Kuwaiti crude and refined oils. Fluorescent characteristics of two different bunker oils from widely separate geographic areas have been studied. Laser induced fluorescent data for the crude oil samples are compared with the decay time results to evaluate the potential of these techniques for the identification of oil sticks in the marine environment. Response of the oil film thickness to various excitation wavelengths from a CW Ar ion laser and a pulsed xenon lamp has been investigated.

Laser measurement of the spectral extinction coefficients of fluorescent, highly absorbing liquids

A conceptual method has been developed to deduce rapidly the spectral extinction coefficient of fluorescent, highly absorbing liquids such as crude or refined petroleum oils. The technique has the advantage of only requiring one laser wavelength and a single experimental assembly and execution for any specific fluorescent liquid. The liquid is inserted into a very thin wedge-shaped cavity for stimulation by a laser from one side and fluorescence measurement on the other side by a monochromator system. For each arbitrarily chosen extinction wavelength the wedge is driven slowly to increasing thicknesses until the fluorescence extinguishes. The fluorescence as a function of wedge thickness allows the determination of the extinction coefficient using an included theoretical model. When the monochromator is set to the laser emission wavelength, the extinction coefficient is determined with the usual on-wavelength signal extinction procedure. For all other wavelengths, the technique is limited to those spectral regions possessing fluorescence.

Oil film thickness measurement using airborne laser-induced water Raman backscatter

The use of laser-induced water Raman backscatter for remote thin oil film detection and thickness measurement is reported here for the first time. A 337.1-nm nitrogen laser was used to excite the 3400-cm(-1) OH stretch band of natural ocean water beneath the oil slick from an altitude of 150 m. The signal strength of the 381-nm water Raman backscatter was always observed to depress when the oil was encountered and then return to its original undepressed value after complete aircraft traversal of the floating slick. After removal of background and oil fluorescence contributions, the ratio of the depressed-to-undepressed airborne water Raman signal intensities, together with laboratory measured oil extinction coefficients, is used to calculate the oil film thickness.

Laser measurement of extinction coefficients of highly absorbing liquids

A coaxial dual-channel laser system has been developed for the measurement of extinction coefficients of highly absorbing liquids. An empty wedge-shaped sample cell is first translated laterally through a He-Ne laser beam to measure the differential thickness using interference fringes in reflection. The wedge cell is carefully filled with the oil sample and translated through the coaxially positioned dye laser beam for the differential attenuation or extinction measurement. Optional use of the instrumentation as a single-channel extinction measurement system and also as a refractometer is detailed. The system and calibration techniques were applied to the measurement of two crude oils whose extinction values were required to complete the analysis of airborne laser data gathered over four controlled spills.