heights are the only way to obtain wave data. They are also, in many 

 cases, the only way to verify a wave forecast. A visual observation 

 can never yield more than a crude estimate of the wave spectrum. 

 However, it can be taken in a way which will yield an estimate of the 

 average wave height, a verification of the distribution given by equation 

 (1), and an estimate of the reliability of the observed values. 



The results to be described are applicable to the type of observation 

 made on ships at sea such as the sea state conditions reported by 

 Atlantic Weather Patrol personnel and seamen on naval vessels. If 

 these results are applied to such observations, the utility of the 

 observations can be expected to increase greatly. The procedures to 

 be described have been tested by Atlcintic Weather Patrol personnel, 

 and they do work. 



2. Applicability of Theory 



The theory discussed above has established the following points. 



1. The waves must be observed at a fixed point or at a moving 

 point because scatter- shot observations cannot be treated 

 theoretically. 



2. The p.d.f. of the amplitudes is very nearly given by equation 

 (1) and the p.d.f. of the heights may well be approximated by 

 doubling the values given in equation (1) and in the tables. 



3. The successive waves are not independent occurrences and 

 there is a correlation between successive amplitude values 

 (and successive height values). 



From these results, an attempt will be made to deterinine the 

 reliability of wave height observations. 



The wave observer is assumed to be keeping his eye on a fixed point 

 on the sea surface (or on a point fixed relative to the moving vessel on 

 which he is stationed). He sees a series of waves pass this point. He 

 does not know the level of the sea surface and therefore he must estimate 

 crest-to-trough wave heights. Waves with heights ranging from near 

 zero to very large values will be passing the point at which the observers 

 attention is fixed. It is assumed that the observer is estimating the 

 heights as carefully as possible and that a tabulation of the observed 

 heights is made. 



A wave height is defined to be the difference between the height of 

 the highest part of a mound above sea level and the deepest part of the 



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