Abstract
ABSTRACT A new fiber optical transmittance meter has been designed to measure oil concentrations in water. No electronic components are placed in the underwater sensor housings which are made relatively small to avoid influence on the surroundings. Both the light emitting diode and the receiver are synchroned demodulated. This together with AC-linked amplifiers in both the sender and receiver electronics give appropriate noise reduction. A transmittance meter was calibrated in a 1,0000:1 laboratory tank. Results from this calibration with mechanically dispersed Ekofisk crude oil and Reginol SAE 30 water-in-oil emulsion are presented. It was found that the beam attenuation increased almost exponentially up to a certain oil concentration which was a function of the particle size distribution and length of the waterpath of the light beam. The time changes in the concentration of dispersed oil under breaking waves in a wave tank in the laboratory have been measured at different depths below the surface. It was found that the oil concentrations decreased almost exponentially below the surface down to a depth approximately equal to the height of the breaking wave. During a full scale field experiment with oil in the North Sea in May 1982 the oil leakage under two different oil booms was measured with a beam transmittance meter at 1.5 m depth about 5 m behind the oil booms. Two-minute mean values of the beam transmittance were recorded. The measurements showed large variations in the oil concentrations behind the oil booms. Transmittance meter measurements also were carried out during offshore full scale tests with different chemical dispersants. The instruments have been towed at different depths from small boats passing through the slicks, measuring oil concentrations continuously at different levels simultaneously under the slicks. At Frigg in June 1984, the concentration of dispersed oil at 1, 2, and 3 m depth varied from (approximately) 0 to 60 ppm under one slick.
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