TM No. 377 



Kishi (195^) and Majfrlo (1957) also report on wave particle tracing techniques 

 using high speed cinema cameras, 



Mee (1963) reports on an investigation of wave surface particle velocities usin£ 

 a 3.2 cm wavelength doppler raaar system. Observations of waves generated in 

 a wave tank showed that the frequency spectra of microwave radiation back- 

 scattered from simple surface wave systems correlated with the orbital velo- 

 city spectra of surface water particles. An analytic description was devel- 

 oped for the observed trochoidal wave shapes and the non-circular orbital 

 motions of the water particles. The stream-lines of the water particles 

 were again found to have a geometry resembling a prolate cycloid, with an 

 eccentricity increasing as a function of the wave steepness. The derived 

 equations describe an orbital motion wherein the particles do not move 

 with a constant angular velocity, but move faster on the wave crests than 

 at the troughs. This effect was substantiated by actual estimates of 

 particle velocities using the radar system. This noted effect of non- 

 constant angular velocity of wave particles is important because it pro- 

 vides a simple momentum transfer mechanism. Further discussion of this 

 is found in chapter V. 



This method could well be used in observations of wind waves from a 

 fixed platform. Certainly this method lends itself to measuring waves in 

 a standard fashion, whereby the doppler radar signatures of various sea 

 states could be obtained with the standard system at a fixed angle of 

 sight and at a fixed height above the water. 



Eagleson, and Van de Watering (1963) import on experiments using a 

 thermistor probe to measure particle orbital speeds in water waves . They 

 describe development and testing of a thermistor probe and its associated 



electronic circuitry. The probe was used to make one -dimensional measure- 

 ments of laboratory generated water waves. 



This system utilizes the temperature measuring concept of a thermistor 

 inversely j i.e., its function is similar to the hot wire anemometer in that 

 the temperature variations in the fluid are neglected and the cooling effect 

 of the thermistor bridge element is a known function of the fluid velocity. 

 The system was towed in a tank at various speeds to provide a steady flow 

 calibration. The response of the system was estimated up to 0.5 cps. The 

 device was used to provide continuous values of velocity, and gave results 

 comparing well with the theory of Stokes waves. 



The preceding experiments are merely a sampling of laboratory work 



which could provide many innovations in the methods used to measure 

 particle motions in ocean waves. Unfortunately, most of these techniques 

 have never been applied in the real ocean. Certainly, here lies a store- 

 house of potential for making dynamic records of the complex motions of 

 the wind wave regime. 



In summary, there have been more than a few attempts to measure 

 fluctuating motions both in the sea and in the laboratory. However, 



