marine detection is greatly increased when the refraction pat- 
tern is known. Near the coast during the summer months downward 
refraction generally prevails; in such regions, sediment charts 
indicate in which areas echo ranging and listening may possibly 
be improved by bottom reflections. Whenever possible, however, 
the sediment charts should be used in conjunction with a bathy- 
thermograph. 
Other Uses of Sediment Charts 
As has been briefly explained, sediment charts, es- 
pecially when used in conjunction with a bathythermograph, allow 
a qualitative prediction of the range at which a submarine can 
be detected in shallow water. In addition the charts may be 
useful in the following ways: 
1. ROCK areas are shown in which one may expect strong 
reverberations, which at times can be mistaken for echoes from 
a submarine. 
2. In so far as mine laying operations are concerned with 
‘tthe type of bottom, these charts are of interest in this context 
also, for they show the sediments in a more reliable manner than 
do the navigation charts. 
3. In the same way sediment charts may be of some help to 
a submarine which is searching for a place to rest on the bot- 
tom. 
< 
4. Finally the charts indicate areas of SAND sediments, 
where acoustic devices installed on the bottom are most likely 
to provide long-range detection under conditions of downward 
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