surface imaging radar, and coastal HF radar (CODAR) . An intercomparison of these 

 sensors was performed during the Atlantic Remote Sensing Land Ocean Experiment 

 (ARSLOE) and has heen reported by Grosskopf, et al. ^ Several offshore wave 

 measurement systems were also compared during ARSLOE. These systems included wave 

 buoys and airborne radars. The pitch-roll-heave buoys used were the MET buoy, 

 Cloverleaf , XERB and the ENDECO Wave-Track. The Surface Contouring Radar (SCR) 

 measured wave height, frequency and direction from the air. Two systems that did 

 not measure all three characteristics were also present. The Datawell Waverider 

 Buoy was deployed as a standard for wave height and frequency, while the Side 

 Looking Airborne Radar (SLAR) determined only wave direction, not height and fre- 

 quency. The preliminary comparisons have been published by Szabados . 



A hull mounted radar has also been developed to measure wave height, frequency, 

 and direction. This radar, developed at the Naval Research Lab (NRL) , has shown 

 some potential in the measurement of high frequency wind waves, as reported by 

 Schuler, et al. 15 



CHOICE OF SENSOR 



Given the wide variety of sensors available, it was difficult to select a 

 system that would best validate the Spectral Ocean Wave Model and provide more 

 appropriate wave data during ship motion trials. It was clear from the outset that 

 onshore and bottom mounted/moored sensors were impractical to operate in the deep 

 open ocean. Airborne mounted radars would be prohibitively expensive to maintain 

 lengthy on-station times for the many flights necessary over a period of time. 

 Hull mounted radars may provide quality data in limited fetch areas, but require 

 considerable time and expertise to set up and operate. This leaves deployable wave 

 buoys as the optimum instrument to be used from naval ships of opportunity where 

 there may be little deck handling area. Also, there may not be the usual cranes 

 and A-frames found on most oceanographic research ships. At most, a davit may be 

 available. This restriction points to the selection of a small, lightweight pitch- 

 roll-heave buoy which would survive rough sea conditions and provide a sufficient 

 first order measurement of wave directionality. 



Therefore, an ENDECO Wave Track Buoy was selected (see Figure 3). This buoy 

 relies on a different concept to measure the wave directionality than does a con- 

 ventional slope following buoy (see Figure k) . Subsequently, the analysis of the 

 data requires a modification to the conventional slope analysis. 



