Vibration of Echo Amplitude from Sea-Bed due to Ship's Motion-I

Abstract

On an echo survey under streaming, the echo amplitude from sea-bed showed some variations. HASLETT [1] reported that the observed variation of echo amplitude may be attributed, mainly, to: (a) the geometric effects of the beam patterns, due to rolling and pitching, (b) the variation in coupling between the transducers and the water, and, (c) variations in the reflectivity of sea bed. It is interesting to note the variation of echo emplitude from seabed due to ship's motion. Some field observations for this study were made with an echo-sounder operating at a frequency of 200kHz on board the bull trawler, Tokai-Maru, No.1, on a steady course of beam wind at a speed of 4m per min near the Socotra Rock in the East Sea in October 20th 1968. The sea-bed was very flat and consisted, mainly, of fine sand. Recording of the echo, pitching angle of the trawler and also rolling angle were made on a magnetic tape recorder (TEAC, R-200). Individual echoes and angles of pitching and rolling corresponding in time to the respective echo were later analized for 700 series of the data in the laboratory. We found on the results that there were hardly direct relation between the echo amplitude and ship's motions but also with some relationship on the phase consideration.