3.3 Oil film thickness
If data of extinction coefficient of the medium were known, the oil thickness can be estimated by the depression of the signal in the region, where the water Raman scattering or the fluorescence of chlorophyll is blocked by the oil film. According to Hoge's discussion the oil thickness may be written by following equation,
where, d is the thickness of the oil film, ke , kr are the extinction coefficients of the oil film at laser wavelength, and at the water Raman wavelength, respectively. R' is the water Raman component through the oil film, R is the water Raman component without the oil film. R' should be a net emission of the water Raman scattering from which the fluorescence contribution of the oil film and background are subtracted. In the bright mode, the oil thickness can be estimated by fluorescence signal strength.
4. FIELD EXPERIMENIS
In order to confirm the basic function of the system and find out problems in field measurements, the feasibility tests were conducted at a basin, on a ship and on an airplane. The gate operation of the systems have worked effectively to eliminate back scatter by only receiving a return signal from the layer being probed for day time measurements, and also can measure the distance to the target. A reduced gate width will contribute to improve the signal to noise ratio (SNR), by greatly decreasing the effective area from which back scatter can occur. In cleaner mediums increasing the gate width will aid in increasing vertical search area without a major decrease in operational efficiency.
4.1 Test at a basin
The first test was conducted at the basin about 77m from our lidar laboratory to observe oil floating on the water. After examined various sets of gate operation and band pass filter, we confirmed that the laser induced fluorescence of light fuel oil was clearly identified in the wide view of image even in daytime. Fluorescence of oil by the sun light is also monitored using narrow band filter.
