A robust, compact dual-wavelength optical beam attenuation meter termed the SAM (Scattering Attenuation Meter) is under development. The sensor is designed for observing platforms that require very small form factors such as the REMUS AUV and SLOCUM glider.The device will have a flat sensing face exposed to the water that can accommodate mechanical wipers to prevent biofouling. The device will measure beam attenuation using a novel approach made possible by recent technological advances in the measurement of backscattering in water. Beam attenuation is derived from the ratio of scattered fluxes measured by two detectors. Resolving power is directly linked to the magnitude of the pathlength differential between the two source-detector pairs. An advantage of the method is that attenuation is obtained ratiometrically—thus, the method is self-calibrating, independent of fluctuations in source intensity, the relative sensitivities of the detectors, and the magnitude of backscattering.This approach seeks to solve the paradox of making high-resolution attenuation measurements over long pathlengths with a very compact sensor (dimensions on the order of several centimeters).
