A novel dual wavelength optical beam attenuation meter for automated underwater vehicles

"The development of a robust, compact dual-wavelength optical beamattenuation meter termed the SAM (Scattering Attenuation Meter)is proposed. The sensor is designed for observing platforms thatrequire very small form factors such as the REMUS AUV. The devicewill have a flat sensing face exposed to the water with a coppershutter to avoid biofouling. No cleaning or maintenance will berequired for this sensor over periods of months. The device willmeasure beam attenuation using a novel approach made possible byrecent technological advances in the measurement ofbackscattering in water. Beam attenuation is derived from theratio of scattered fluxes measured by two detectors. Resolvingpower is directly linked to the magnitude of the pathlengthdifferential between the two source-detector pairs. An advantageof the method is that attenuation is obtained ratiometrically -thus, the method is self-calibrating, independent of fluctuationsin source intensity, the relative sensitivities of the detectors,and the magnitude of backscattering. This approach solves theparadox of making high-resolution attenuation measurements overlong pathlengths with a very compact sensor (dimensions on theorder of centimeters).BENEFITS: The SAM sensor will have immediate applicability for military operations requiring 4-D (space and time) knowledge of beam attenuation within the battle space environment. These include optics-based mine and submarinecountermeasur