A. B. Wood 191 
250 CMS 
(a) Computed Chart (for Range 200-250 cms)(Hand Plott ing) 
CMS 
Fig. 10.31. Comparison of 
computed record with 
measured record. Water is 
5.0 cm deep, the bottom is 
plate glass, and the fre- 
quency is 560 kcps. 
150 225 CMS 
(b)Computed Chart(for Range 150-225 cms Automatic Plotting) 
50 450 CMS. 
{c) Record made in Model Tank (for Range 50-450 cms ) 
problem and employing Hankel functions has derived expressions for the spatial 
distribution of sound intensity ina shallow water layer. Using Weale's theoretical 
results, K. W. Harrison has, by means of computer techniques, plotted the sound 
field in a part of a record actually made in the course of the experiments here 
described. The actual record and computed sound fields are shown in Fig. 10.31. 
In (a) the theoretical sound field is plotted by hand in the range from 200 to 245 
cm while in (b) the theoretical sound field is plotted automatically in the ranges 
from 150 to 225 cm. The actual record obtained under the conditions assumed in 
the theoretical computation is shown in (c), covering the range from 50 to 450 
cm. The diamond and V structure of the recorded sound field is observable 
in all the records, and the slope of the V lines is approximately the same in 
the computed and recorded records when allowance is made for the relative 
scales of the X and Y axes in the various cases, In this record the bottom was 
plate glass partly covered by rubber (to remove some of the higher modes), the 
water was 5 cm deep, the frequency of the sound 560 kcps, and the transmitter 
situated about 2 mm above the bottom. 
As a first attempt, this theoretical computation is very encouraging. It has, 
however, taken a long time and much effort to obtain, and there is clearly much 
more to do. 
Full-scale trials are in preparation to try out the scanning technique in the 
sea. For this purpose suitable transducers and scanning equipment have to be 
designed and a suitable area chosen for the experiments. All this is taking much 
time and manpower, not to mention expense, all of which tends to emphasize the 
advantages of small-scale model experiments. 
