A SYSTEM FOR USING RADAR TO RECORD WAVE DIRECTION 



by 

 M.G. Mattie and D.L. Harris 



I . INTRODUCTION 



The Coastal Engineering Research Center (CERC) and the Beach Erosion 

 Board (BEB) (predecessor to CERC) have collected wave data along the U.S. 

 coasts for nearly 30 years. Although a wealth of statistics on wave 

 height and period and thousands of wave spectra have been obtained, few 

 measurements of wave direction have been made. Information on wave direc- 

 tion is needed for the estimation of longshore sand transport, harbor 

 design, and the solution of other coastal engineering problems. Many 

 techniques for recording wave direction have been proposed and tested 

 but none have been entirely satisfactory. 



This report discusses a technique for recording wave direction, based 

 on the use of imaging radar. Ijima, Takahashi, and Sasaki (1964) and 

 Wright (1965) were probably among the first to report the use of radar 

 for imaging ocean waves. Oudshoorn (1960), Wills and Beaumont (1971), 

 Evmenov, et al. (1973), and others have reported wave images obtained 

 with radars similar to those used in the experiments described in this 

 report. However, it is not known whether any of these authors attempted 

 to develop imaging radar as an operational tool for collecting wave 

 information. 



Radar may be used to image the prominent wave crests in a wave field 

 (when conditions are suitable) by photographing the display scope (see 

 Fig. 1). Figure 2 is an aerial photo of the same area shown in Figure 1. 

 In general, radar images show many of the same characteristics as aerial 

 photos and several distinct wave trains can often be identified. Although 

 radar images are not as clear as aerial photos, they have the distinct 

 advantage of being obtainable at night and during storms; an expensive 

 platform (aircraft) is also unnecessary. Interpretation of the radar 

 image is often as simple as that of a good aerial photo. The interpre- 

 tation of aerial photos has been examined by McClenan and Harris (1975) . 



The CERC radar system is described in Section II as a wave data col- 

 lection device. Samples of radar wave imagery and a data analysis system 

 are presented in Section III. The essentials of radar theory and opera- 

 tion, needed for an understanding of the engineering characteristics of 

 a wave data collection system, are discussed in Section IV. Section V 

 compares the data on wave direction and length obtained by radar with 

 that obtained by other methods. 



Other procedures for using radar in the collection of wave data, 

 including several proposed procedures for obtaining these data without 

 radar are presented in Section VI. Section VII discusses additional 

 capabilities of radar and future plans for its use. A summary high- 

 lighting the advantages and disadvantages of obtaining wave information 

 with an X-band shore radar is presented in Section VIII. 



