the 16-millimeter film may permit improvement in the original settings 

 of some of the console controls and may facilitate automatic data anal- 

 ysis routines. 



The CERC radar is being tested at the CERC Field Research Facility 

 (FRF) at Duck, North Carolina, where wave height spectra are available 

 from a number of other sensors (including a waverider buoy) within the 

 radar field of view. Windspeeds and wave spectra at FRF present an 

 opportunity to better define the minimum conditions to obtain wave 

 images. A study of the quality of wave images for various wave heights, 

 wave periods, and windspeeds is needed. Since the radar-scattering 

 capillary waves are enhanced due to the curvature of the gravity waves, 

 a stronger return would be expected from the steeper waves. Thus, the 

 minimum conditions for wave imagery would probably be a function of wave 

 height and wavelength. Antenna height also has an impact on whether par- 

 ticular wave conditions can be imaged. Although images have been ob- 

 tained for wave heights of 1 meter or greater for most conditions and 

 often for waves of smaller height, these future tests should provide 

 the quantities of data necessary to precisely establish limits on the 

 conditions suitable for radar wave imagery. 



These tests at FRF will also present an opportunity to study the 

 relationship between radar return and wave height. An "A-scope" display 

 will be inserted into the radar system to show the return along a partic- 

 ular azimuth where the display is similar to that of an oscilloscope with 

 the vertical axis representing the magnitude of the radar return and the 

 horizontal giving the range to the targets. In the CERC system the re- 

 turn along a particular azimuth will be gated to the A-scope, and will 

 likely be a type of storage oscilloscope. Radar return strength as 

 measured from the A-scope will be compared with the wave spectra for 

 a variety of sea states and wind conditions. 



The CERC radar system has been used at Channel Islands Harbor, 

 California, in support of a sediment study and to obtain wave imagery 

 as part of the West Coast Experiment. This system has been moved to 

 Duck, North Carolina, to further develop the system's capabilities and 

 to support research projects at the FRF. The unit will also be available 

 to support CERC or U.S. Army Engineer Districts in projects involving 

 wave imagery. 



VIII. SUMMARY 



This report has shown that images of the most prominent waves on the 

 sea surface can often be obtained with the aid of commercially available 

 marine navigational radar. Images of the wave field are collected by 

 photographing the display scope of the radar. Records may be obtained 

 in an unattended mode by a programing device which activates the system 

 and collects a sequence of photos at fixed-time intervals. Wave direc- 

 tion at a fixed point or the prevailing wave direction for a designated 

 area may be determined by inspecting the photos. 



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