Application of the ICF Coherence Time Method for Ocean Remote Sensing Using Digital Communication Satellite Signals

This paper applies an ocean remote sensing method, first developed for reflected Global Navigation Satellite System (GNSS-R) signals, to reflected digital communication satellite signals. The fundamental observation is the time series of the Interferometric Complex Field (ICF) of the reflected signal. A relationship is derived between the coherence time of the ICF time series and the significant wave height (SWH) and mean wave period (MWP) of the ocean. Direct and reflected signals from the S-band satellite transmissions providing the commercial XM radio service were recorded at Platform Harvest over a 65-day period. In situ measurements from a nearby buoy were used to calibrate this measurement by determining coefficients of a semi-empirical model. SWH retrievals using this model on 1 min of reflected signal observations were found to have a standard deviation of 0.38 m over the range from 1 to 4.5 m. An error analysis was done to show that the primary contribution to this error was uncertainty in the relationship between MWP and SWH, and to quantify the retrieval error from different forward models.

I. Introduction

Remote sensing of the ocean is an important tool for atmospheric and weather modeling. Several methods for remotely sensing ocean topography using microwave frequencies have been developed including altimetry, scatterometry, and radiometry. One of the methods developed in the last two decades is bistatic radar using Global Navigation Satellite System (GNSS) signals. The concept of GNSS reflectometry (GNSS-R) was first proposed in 1993 for satellite altimetry [1]. Since then there has been tremendous development of GNSS-R techniques for ocean remote sensing, including methods for retrieval of wind speed and significant wave height (SWH) from various platforms [2]–[6]. Recently, this technique has also been extended to imaging of ocean surface for oil slick detection [7].