This paper describes and experimental technique for measuring the attenuation of sound in marine sediments at low frequencies. The method makes use of the signals from sub-bottom reflectors that are received on a vertical hydrophone array at close ranges in shallow water environments. The signal path geometry is determined from an inversion of the travel time differences of the sea bottom and sub-bottom reflected paths to estimate the sediment sound speed and the depth of the sub-bottom reflector. The method is applied to data from experiments carried out at a site on the New Jersey continental shelf in the Shallow Water 06 experiment. The sediment type and the structure of the sediment column were ground truthed by independent measurements at the site. The chirp signal was transmitted in two frequency bands, from 100-900 and 1500-4500 Hz, and the data were match filtered to obtain the multipath signals at the array. A prominant signal from a sub-bottom interface known as the R-reflector was resolved in the data for each frequency band. Results are presented for the average attenuation over the depth to the reflector. [Work supported by ONR Ocean Acoustics.]

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