TRACKING OCEAN WAVE SPECTRA FROM SAR IMAGES 
A. D. Goldfinger 
R. C. Beal 
F. M. Monaldo 
D. G. Tilley 
The Johns Hopkins University/Applied Physics Laboratory 
Johns Hopkins Road, Laurel, Maryland 20707, USA 
Commission II/5 
ABSTRACT 
For several years we have been working on an end-to-end algo- 
rithm for recovery of ocean wave spectral peaks from SAR 
images. We report on the progress that has ‘Deen made, and 
show that current approaches ars allowing precision of i 
percent in wave number, and 0.6 deg in direction. 
l. "INTRODUCTION 
A SAR image spectrum is a complex product of the actual ocean 
wave spectrum, the physics of the scattering process, the SAR 
instrument, the processing algorithms, and many other effects 
and parameters. From one or more of these spectra, we seek to 
either recover the actual ocean wave energy spectrum or to 
estimate other derived parameters of interest, such as the 
locations: of storm sources, 
An overall model is shown in Fig. 1l. The left side shows the 
effects that occur in the production of a- SAR spectrum. The 
right side shows the steps we are undertaking in recovery of 
information from such a spectrum. 
Starting from the actual ocean surface, the physics of the 
microwave scattering process determines a distribution of 
Scattering cross-section on the sea surface, the so-called "go 
map". The physics of this process was the subject of a work- 
shop held at APL. in October 1982. We will not discuss this 
further here but instead refer the interested reader to Beal 
(1982). 
The og map is viewed by the SAR instrument and three types of 
corruption occur: 
1. Dynamic effects: due to motion of the sea surface, scat- 
tered energy is defocused and/or displaced in the SAR 
image. Both effects serve to decrease azimuth (along- 
track) resolution, creating a roll-off in the system 
transfer function for energy with high azimuth wave 
number. This is described by Monaldo (1983) and Beal, et 
ai. (1983). 
2. -SAR instrument: the impulse response of the SAR 
instrument determines a modulation transfer function 
(MTP), which may vary with time, and certainly is à 
function of the SAR processor employed. 
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