the dynamic response, including single-frequency sinusoids, broad band 

 random noise, and asymetrical (ramp) functions, all with various amplitude- 

 frequency combinations. No net flow rate was present in the basin during 

 the tests. 



The results were somewhat disconcerting as shown in Figure 16 (from 

 Cunningham, Guza, and Lowe (1979). For the broad band response, the gain 

 was found to be dependent upon both the frequency present and the spectral 

 content. A random-noise generator running in three different modes was 

 employed (curves I, II, and III) to vary the spectrums (Fig. 16). The 

 black dots in the figure show results for the single-frequency tests where 

 it was learned that the gain was also amplitude dependent. Recognizing 

 these limitations and based on further experience gleaned from the Santa 

 Barbara experiments for NSTS, Guza (Scripps Institute of Oceanography, La 

 Jolla, California, personal communication, February 1981 stated that the 

 uncertainty associated when using a single gain factor (d.c.) for all 

 frequencies is roughly ±10 percent or ±5 centimeters per second, whichever 

 is larger. Air bubbles in the water did not seem to alter this conclusion 

 as stated by E.B. Thornton (Scripps Institute of Oceanography, La Jolla, 

 California, personal communications, February 1981). Further research ia 

 needed to improve this accuracy, especially if velocity spectra are of 

 interest. 



.BOO 

 .650 

 900 

 950 

 1.000 

 1.050 



• Singlt Frtquwcf Pit. 

 « DC CoHttolitn (tomtdl 



.25 .50 .75 1.0 1.25 1.5 1.75 2.0 2.25 

 FREQUENCY, Hz 



2.5 



Figure 16. Gain response of flow meters for pseudorandom noise runs, 

 single-frequency runs, and towed (d.c.) values (after 

 Cunningham, Guza, and Lowe, 1979). 



Because of these difficulties other meters for continuously record- 

 ing current components in the surf zone are being developed and tested. 

 These included the use of radar to track reflectors, doppler radar, and 

 acoustic current meters (e.g., see Appell, 1978) such as the Neil Brown 



57 



