Measurements of the Directional Spectra of Shallow Water Waves Using the Maximum Entropy Principle and a Single Ocean Bottom Seismometer

Abstract

A new method for measurement of the directional spectra of surface gravity (water) waves is presented here. Measurements are made at a single point by orthogonally mounted seismometers buried 0.5 meters below the seabed surface and a pressure sensor resting on the seafloor. The maximum entropy principle, which uses entropy as an index of uncertainty in the directional distribution, is used to find the directional distribution function for the waves traveling through the sediments as measured by the seismometers. This function is combined with the frequency spectra of the ocean surface waves to form the directional spectra of the surface gravity waves. Single point measurements are advantageous due to the relative case of implementation and expense compared to arrays, as well as for measurement of non-uniform wave fields. Due to attenuation of shorter wavelengths with depth, this procedure is limited to shallow or intermediate depths. Field data was collected on the New Jersey Shelf and the results show that the method produced high directional resolution for instruments that were adequately coupled with the seabed.