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SIMULATION OF SAR OCEAN WAVE IMAGERY FROM SPACEBORNE PLATFORMS 
D.R. Lyzenga 
Radar Science Laboratory 
Environmental Research Institute of Michigan 
Ann Arbor, MI 48107 
ABSTRACT 
A numerical model for predicting the synthetic aperture radar (SAR) 
image of a moving ocean surface is described, and results are presented to 
illustrate the effects of surface motions on the SAR imaging process. The 
relationship between the SAR image spectrum and the wave height and wave 
slope spectrum is examined using this model, and the possibility of invert- 
ing this relationship is discussed. 
1. INTRODUCTION 
The ability of synthetic aperture radar systems to image ocean waves 
is dependent on system parameters as well as environmental conditions. 
This dependence has been extensively investigated over the past decade, 
and although there are still areas of disagreement regarding the theoreti- 
cal basis for this imaging, models have been developed which appear to 
explain most of the trends observable in the experimental data base. 
In the present paper, a conceptually simple model for the SAR imaging 
process is discussed and the numerical implementation of this model is 
described. Predictions of the SAR image spectra for various environmental 
conditions and SAR system parameters are presented, some comparisons with 
actual SAR data are discussed, and the possibility of inverting the process 
to obtain wave height or slope spectra is evaluated on the basis of this 
model. 
2. MODEL DESCRIPTION 
The microwave scattering properties of the ocean surface, including 
the phase changes due to surface motions, may be described in terms of a 
complex reflectivity r(x, t). The signal received by a synthetic aperture 
radar within a given range cell may then be written as 
-2jkR(x". t) 
s(t) - frs, t)a, (x' - Vt) e dx' (1) 
where aj(x' - Vt) represents the antenna gain pattern, k is the electro- 
magnetic wavenumber, and R(x', t) is the instantaneous range distance from 
the scattering surface to the SAR platform, which is located at x' = Vt. 
Assuming that the antenna pattern limits the illumination to an along-track 
distance interval which is much smaller than the range distance, this range 
distance may be approximated by 
: 2 
R(x!, 8) = gt UE (2) 
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