A. B. Wood 173 
Cee ee Oe Oat at 
— 50 
-- 49 DEpTH oF BOTTOM 
8 WATER (a) 
“yo FROM OTOSem RUBBER 
(FREQ. 430 kc/s) 
a 
-0 
CO OO 
Cie 8! 
! ' ' | 
fo) ! 2 3 DEPTH 4 CMS 5 
4@@@02OZHOHHO88OHO8OOD 
db 
- 40 
- 30 (b) 
- 20 SOFT 
HN oh - 10 
ll i} 0 
we ee te ee eee 
0 5CM 
@enaeaeeaeeneoeae 2ee0ea2020 C04 
db 
40 
30 (c) 
a HARD 
| | 10 
ep eee seer ccoccccece. (0) 
0 5CM 
Fig. 10.11. Records of sound transmission over different bottoms (frequency constant 
at 430 kcps) as the ‘water depth is varied. (a) Absorbent (rubber) bottom, 430 kcps, 
(b) soft bottom, and (c) hard bottom. 
sound intensity with very small increases in depth have an important bearing on 
sound observations in tidal water where the sea level may vary over a range of 
10 to 15 ft with the tidal changes. As we have seen, on the model scale a change 
of depth of the order ofa millimeter, corresponding to a meter at full scale, may 
result in a change of 30 db in sound intensity at a receiver. 
10.3. VISUAL OBSERVATION OF SOUND DISTRIBUTION ON THE BOTTOM AND SURFACE 
The small-scale observations made so far can only be regarded as pre- 
liminary and qualitative. A few general pointers have been established regarding 
the nature of the bottom and depth of water relative to wavelength. The one out- 
standing feature, however, is the great difficulty of forming a mental image of 
the general sound distribution in the water. It has become obvious that a very 
large number of bottom-to-surface records taken at very short range intervals 
