P.M. Kendig 239 
PRESSURE LEVEL IN I-CPS BAND (db vs | dyne/cm*) 
PRESSURE LEVEL IN I-CPS BAND (db vs | dyne/cm?) 
CROAKERS (late May and early June) 
IF CROAKERS 
(early July) 
AVERAGE SNAPPING SHRIMP NOISE 
KNUDSEN CURVES, 
~~Z_ SEA STATE 6 
/ 
| 
@ 
(e) 
1 
Xo) 
(e) 
-50F a = 
-60F De oe 
-70- ar 
—~___,SEA STATE 0 
ee ee ee eee) 
Ol | 10 100 
FREQUENCY (kc) 
Fig. 13.2, Ambient noise levels produced by croakers and snapping shrimp. 
HIGH-NOISE AREA (entrance to New York harbor in daytime) 
AVERAGE-NOISE AREA (upper Long Island Sound near ship lane) 
DEEP-WATER NOISE FOR 
-50- A NO. 2 SEA STATE 
-60- ge 
-7ob 
-gol 
Cansei  ee 1 it 1 Ht To eel 1 1 TREE TICS 
FREQUENCY (kc) 
Fig. 13.3. Ambient noise levels in the presence of ship sounds. 
all observed sounds with the particular marine animals that make them. Two 
types of marine animals, snapping shrimp and croakers, are known to produce 
a chorus of sound that can maskdesired signals. Shrimp are common in shallow, 
