1. Why the Southern California Operating Area?
The Northeastern portion of the operating area offers: Shallow Water, Steep Bathymetry, Underwater Ridges, and the Instrumented Underwater Range
California
Duplicates anticipated deployment environments.
Southern California provides ships the ability to conduct complicated/Integrated ASW training in conditions that are similar to many of those Strike Groups would expect to see on deployment: shallow water, steep bathymetry, and underwater ridges.
No other area is available to U.S. forces that offers the combination of air warfare (Fallon, China Lake), a shallow water undersea warfare range (San Clemente Island (SCI)), instrumented undersea warfare ranges (SCI), bombing ranges (SCI, Pendleton, El Centro), radars (various), air targets (Point Mugu), surface and underwater targets and support (SCI, others), amphibious landing areas (Camp Pendleton, SCI), training support, and emergency divert fields such as those that have been developed or are readily available in the SOCAL area.
Instrumented range allows accurate reconstruction of events (ground truth) allowing in-depth evaluation of performance against measures of effectiveness. Also allows real-world ability to validate/verify current and advanced tactics, techniques and procedures.

2. Why the Southern California Operating Area?
Provides Strike Groups the ability to conduct complicated/Integrated SONAR training in the environmental conditions that are similar to those where they would expect to fight.
Duplicates anticipated deployment environments.
Southern California provides ships the ability to conduct complicated/Integrated ASW training in conditions that are similar to many of those Strike Groups would expect to see on deployment: shallow water, steep bathymetry, and underwater ridges.
No other area is available to U.S. forces that offers the combination of air warfare (Fallon, China Lake), a shallow water undersea warfare range (San Clemente Island (SCI)), instrumented undersea warfare ranges (SCI), bombing ranges (SCI, Pendleton, El Centro), radars (various), air targets (Point Mugu), surface and underwater targets and support (SCI, others), amphibious landing areas (Camp Pendleton, SCI), training support, and emergency divert fields such as those that have been developed or are readily available in the SOCAL area.
Instrumented range allows accurate reconstruction of events (ground truth) allowing in-depth evaluation of performance against measures of effectiveness. Also allows real-world ability to validate/verify current and advanced tactics, techniques and procedures.

3. Navy Active SONAR Mitigation Efforts
Nominal source level of 235dB (measured 1 meter from transmitter)
Marine Mammals emit up to 228dB
SONAR Operation w/o Powerdown
189dB
181dB
179dB
0dB
200 meters
175dB
500 meters
175dB
171dB
1,000 meters
175dB
169dB
Reduced SONAR Operation
As whales get closer, crew reduces SONAR output
Temporary Threshold Shift (TTS) ~ 195dB (est)
Non-injurious
Can produce behavioral effects
Evaluated on Bottlenose Dolphins and Beluga Whales in San Diego Harbor. Essentially a captive sample and may not corrolate to open ocean.
215 dB for permanent psychological effects is based on extrapolating the 195 dB data.
Ambient noise of 40dB
IAW NWP 76-1:
Spherical Spreading ( yds): Spreading Loss = 20 Log (R2/R1)
200 yds – 189 dB
200 meters – 188 dB
500 yds – 181 dB
500 meters – 180 dB
1000 yds – 175 dB
1000 meters – 174 dB
Cylindrical Spreading (>1000 yds): Spreading Loss = 10 Log (R2/R1)