I. INTRODUCTION 



Sea waves are irregular, confused, and sometimes mountainous. 

 They are short-crested in that a given crest can be followed by- 

 eye along the crest for at most a distance of three or four times 

 the distance between successive crests. Even the apparently more 

 regular swell is still irregular in that there are considerable lengths 

 of time during which the swell is very low in height. Swell is also 

 short- crested, although swell crests are longer than sea wave crests. 

 The visual observation of such an irregular pattern is a difficult 

 and complicated procedure which needs to be described and interpreted 

 precisely. 



The main purpose of this paper is to describe wave irregularity 

 and to present techniques for the visual observation of wave heights, 

 "periods," "wave lengths," and "speeds." These techniques will make 

 the values obtained by observation more useful because they will 

 be more precise. A second purpose of this paper is to give the theo- 

 retical justification for the procedures given in the wave forecasting 

 manual prepared by Pier son, Neumann, and James (1955). 



Visual height observations w^ill never be as precise as instrumental 

 observations of adequate duration as made by the various wave- pole 

 techniques which have been developed for both deep and shallow water. 

 The data obtained by the Hydrographic Office with instruments developed 

 by the Beach Erosion Board will yield information which covild never 

 be obtained visually. However, visual observations will always be 

 needed to supplement instrumental observations. 



II. THEORETICAL AND PRACTICAL ASPECTS OF WAVE HEIGHT 

 OBSERVATIONS 



A. Techniques for Wave Height Observation 



The mathematical representation of ocean waves as a short-crested 

 Gaussian sea surface, as proposed by Pierson (1952, 1954), appears to 

 represent the sea surface and its mathematical properties in a realistic 

 way. This paper will be based on the results of this theory, but the 

 practical aspects of the problem will be emphasized instead of the 

 theoretical aspects. 



Consider figure 1. It shows the irregular pattern of the sea surface 

 as observed from an aircraft flying at a height of about 4,000 feet. 

 One way to observe the wave heights would be to estimate or measure 

 the crest- to- trough heights of the highest part of each short-crested 



