Proceedings PaperUnderwater Illumination & Imaging Measurements
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Modulation transfer function measurements were carried out in relatively clear fresh water using separated narrow-beam transmitter and receiver and diffuse flectance bar and edge targets. The source was a mercury arc lamp. The detector was a multiplier phototube. The results show useful spatial frequency responses up to angular frequencies of 1000 to 2000 cycles per radian at target ranges up to 4 water attenuation lengths. The measured attenuation length for collimated light was 15 feet. With the narrow-beam apparatus, back-scatter was small and was reduced proportionally to the separation between the transmitter and the receiver. The relative backscatter was also reduced as the transmitter beam width was reduced. It was shown that from an examination of the signal response when a target edge was scanned, it was possible to deduce the relative amounts of unscattered and forward scattered light.