3. Meteorological Instruments . 



a. Anemometer. Winds were measured using a National Weather Service 

 (NWS) Model F420C anemometer, which consisted of a cup rotor and spread-tail 

 wind vane. The anemometer was located 58 meters behind the dune with the cups 

 6.4 meters above NGVD (Fig. 2). The accuracy of the speed transmitter and 

 indicator assemblies is 0.05 meter per second up to 5 meters per second and 

 0.1 meter per second from 5 to 10 meters per second. The wind direction 

 transmitter and indicator assemblies are accurate to ±5° at an airspeed of 

 0.26 meter per second or greater. 



b. Microbarograph . This recording instrument is an aneroid sensor used 

 to measure atmospheric pressure and responds to pressure changes on the order 

 of 0.169 millibar. The microbarograph, which is manufactured by the Belfort 

 Instrument Company, Baltimore, Maryland, was located inside the office 

 trailer, 8.5 meters above NGVD (Fig. 2). 



c. Maximum-Minimum Thermometers. These thermometers were housed in the 

 instrument shelter and were used to determine the daily extreme temperatures. 



d. Rain Gage. A 30-centimeter weighing rain gage manufactured by the 

 Belfort Instrument Company was used to measure the daily amount of precipita- 

 tion. The gage was located near the instrument shelter 87 meters behind the 

 dune (Fig. 2). The manufacturer's specifications indicate that the instrument 

 accuracy is ±0.5 percent for precipitation amounts less than 15 centimeters, 

 and ±1.0 percent for amounts above 15 centimeters. 



e. Sling Psychrometer. A sling psychrometer was used to measure "wet" 

 and "dry" bulb temperatures for determining relative humidity and dewpoint. 

 The psychrometer has two thermometers mounted in a frame which is rotated 

 rapidly. A moistened muslin wick is attached to the bulb (which is then the 

 wet bulb) of one of the thermometers and the device is whirled to ventilate 

 both thermometers. The wet and dry bulb temperature readings and a set of NWS 

 tables are used to determine the dewpoint. 



f. Pyranograph . A mechanical pyranograph, manufactured by the Weather 

 Measure Corporation, Sacramento, California, was located on the top of the 

 weather instrument shelter and provided a record of the duration and intensity 

 of solar radiation. 



IV. DATA COLLECTION AND ANALYSIS 



This section discusses the FRF data collection techniques, data acqui- 

 sition systems, and data analysis procedures, as well as quality control 

 measures. 



1. Digital Wave Data . 



a. Recorders and Signal Conditioning . Two different recording systems 

 were used to collect digital wave data. The primary system transmitted ana- 

 log data signals via telephone lines from the FRF to CERC at Fort Belvoir, 

 Virginia. Data were recorded in digital form on a Modcomp 11/25 minicomputer. 

 The backup system recorded data at the FRF using a Lockheed Store 7 (FM) 

 recorder. A second FM recorder, which was located at CERC (Fort Belvoir), was 



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