u velocity component at that same point and time of observation. 
Lines for future research 
All of the things suggested above on the autocorrelation 
functions and the cross correlation functions cannot be treated here 
in detail because they recuire very extensive mathematical abilities 
and they are sidelights on the main problem of wave analysis, wave 
propagation, and wave refraction. Their importance is obvious, 
and they suggest many avenues for future research and investigation. 
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