A pulse-compression echo sounder for ocean bottom surveys

Abstract

A pulse-compression echo sounder (PCES) has been developed and used in two ocean bottom surveys. The PCES transmitted a chirp signal, i.e., a frequency-modulated signal, instead of a gated sine wave. The returned echo was correlated with the stored replica of the transmitted signal in the polarity coincidence Deltic correlator. The bandwidth of the chirp signal was 1.6 kc/s centered at 12 kc/s. The chirp duration was 20 msec, the peak power during the pulse was 800 watts, and the pulse-compression ratio was 32:1. The results show that the system provides (1) a fine resolution of closely spaced bottom and sub-bottom surfaces in the deep ocean, (2) improvement in signal-to-noise ratio over the conventional echo sounders, and (3) sub-bottom penetration of up to 30 meters and a qualitative indication of the bottom surface roughness. Typical sections of the data are given.