Ocean wave imaging using an airborne single pass across-track interferometric SAR

An airborne single pass across-track interferometric synthetic aperture radar (InSAR) is used to image ocean waves. A theoretical model explaining the imaging mechanisms is developed, and simulations of the interferogram as well as the conventional SAR intensity image are presented for given ocean wave spectra. Distortions of digital elevation models (DEM) derived from InSAR data are explained by the motion of the sea surface. A Monte Carlo method based on forward simulations is used to estimate variance spectra of the distorted elevation models. It is shown that a straightforward estimation of wave height using the distorted InSAR elevation model is in good agreement with true wave height for low amplitude swell with about 10% error depending on propagation direction and coherence time. However, severe underestimation of wave height is found for wind seas propagating in flight direction. Forward simulations show that the distorted InSAR DEM is less dependent an the model chosen for the real aperture radar mechanism than conventional SAR images. Data acquired during an experiment over the North Sea by a high precision InSAR system are compared with simulations.

I. Introduction

SO FAR, synthetic aperture radar (SAR) is the only all- weather system providing directional information on ocean waves on a continuous and global basis. For this reason, SAR data have become a valuable source of information for both wave researchers and mariners. SAR imaging of the sea surface has been investigated in many studies [1]–[4]. A major step in understanding the SAR ocean wave imaging process was the derivation of a nonlinear integral transform describing the mapping of a two dimensional ocean wave spectrum into the corresponding SAR image spectrum [1]. Based on this imaging model, algorithms were developed to derive ocean wave spectra from spacebome SAR observations, using additional information from ocean wave models or buoy measurements [5].