Field Test of Buried Ocean‐Wave Directional Spectrometer System

Abstract

This paper presents a new and unique method of measuring the directional spectra of ocean surface waves with a buried instrument containing horizontally oriented seismometers and a pressure sensor. Based upon the assumption that the seabed responds in an elastic, incompressible, and linear manner to ocean‐wave‐induced pressure fluctuations, the directional spectrum of the sediment motion has been found using the maximum entropy method. This motion is converted to a surface‐wave directional spectrum using linear wave theory and the differential pressure gauge's frequency spectrum. This system was incorporated into the Office of Naval Research (ONR) sponsored Sources of Ambient Micro‐Seismic Ocean Noise (SAMSON) experiment for three months off the Army Corps of Engineers' Field Research Facility (FRF) near Duck, North Carolina, in the fall of 1990. Four working sensors produced directional spectra results from nearly 22 gigabytes of recorded data that were collected 2 km offshore of the FRF under 12–13 m of water and approximately 1 m of sediment. Comparisons to the FRF's 12‐point array of bottom‐mounted pressure sensors, which was located 1 km inshore and in 8 m water depth, are made with favorable results.