Estimation of significant wave height using reflected digital communication signals

This paper presents a semi-empirical relationship between the coherence time of ocean-reflected digital satellite radio signals and significant wave height (SWH). An experiment was conducted on Platform Harvest, a petrochemical exploration platform located in the Pacific Ocean off the coast of Southern California. Raw data were recorded from both directly-received and ocean-reflected signals from the XMradio (S-bandwith center frequency 2.342 GHz), and DirecTV (Ku-Band with center frequency 12.239 GHz) from antennas located at an approximate altitude of 27 meters above the ocean surface. Using a technique first developed for Global Navigation Satellite Systems (GNSS) signals, the coherence time of the Interferometric Complex Field (ICF) is computed by cross-correlating the direct and reflected signals. A relationship is developed between the ICF and SWH. This is done by first developing a model showing a relationship between ICF, correlation time of the sea surface and SWH. A Monte Carlo simulation of the ocean surface is used to show that empirical relationship between correlation time of the sea surface and SWH takes a quadratic form. The coefficients of this empirical model are finally determined from fitting experimental data of S-band signals and a limited amount of Ku-band signals, from the XM radio and DirecTV transmission, respectively. The retrievals of SWH from experimental data through inverting this relationship are then compared to the in-situ recordings from the nearest buoy (8 km away). S-band measurements are found to have a standard deviation of 0.51 meters over a range of SWH from 1 to 5.6 meters.