How well can wave height and nonlinear wave statistics be determined from grazing incidence remote sensing

Abstract

The motivation of writing this thesis arises in connection with the interpretation of wave measurements: How can the wave height be determined from a grazing incidence radar image? How well can nonlinearity of the ocean surface be distinguished from grazing incidence RADAR images given the fact that the imaging mechanism itself is highly nonlinear? Wave height estimation from RADAR images has traditionally been considered a difficult task. Several fundamentally different approaches have been described for the extraction of wave height. The approach chosen by WAMOS II is based on an empirical formula proposed for marine RADAR by Nieto Borge(1997,1998) building on established theory for Synthetic Aperture Radar imaging. However, recent theoretical work by Krogstad and Trulsen (2010) suggests that for a nonlinear wave field, the linear dispersion relation may not be revealed by direct Fourier analysis of spatiotemporal data. This may have implications regarding the correct identification of “signal” and “noise” in the signal-to-noise ratio . In this thesis, numerical simulations of linear and nonlinear wave fields are carried out and used as a basis to generate synthetic radar imaging with grazing incidence. By studying the differences of the remote sensing image-spectra for the linear and nonlinear ocean wave fields, I come to the following conclusion: The signal-to-noise ratio becomes more and more inaccurate as the actual wave height increases. The numerical simulations of nonlinear wave fields are essentially a repetition of recent work by Krogstad & Trulsen.