Measurements of Acoustic Backscatter of the Deep Sea Floor Using a Deeply Towed Vehicle.

摘要

An area of Cu-Ni rich manganese nodules at 14 deg 40 min N, 126 deg 25 min W (site 'E') was intensively studied with the deep-tow of the Scripps Inst. of Oceanography, and 16 box cores were collected. Deep-tow studies of the Thirtymile-Bank off the California Coast and the deep sea at the foot of the Patton Escarpment followed. Nodule coverage at site 'E' varies from 0% to 80%. Nodule sizes vary between 1 and 13 cm. The nodule size distributions are best modeled by a Gaussian distribution. The three main nodule axes are related to each other at 1:0.8:0.5. Average density of individual nodules is 2.0 + or - 0.04 g/cc and the volumes increase on the average with the 2.8 power of the third root of the product of the three radii. Changes of the thickness of the upper acoustic unit of the sediment column correlate with changes in nodule coverage and concentration. Acoustic backscatter was measured for frequencies of 4.5, 9, 15, 28.60, 112 and 63 kHz and grazing angles from normal incidence to 5 deg. Backscatter of deep sea sediments at the foot of the Patton escarpment exceeds the backscatter of the sediments at site 'E' by several dB (depending on frequency and on grazing angle). Backscatter from manganese nodules depends on nodule coverage and on frequency and exceeds that of sedimens, but is less than that from the Thirtymile-Bank phosphorites.