An article in the Honolulu Advertiser about the upcoming RIMPAC exercise and concerns about sonar use contains the same misinformation about relative sonar noise levels that I discussed last October. From the article:
"The Defense Council described active military sonar as acting like a floodlight, emitting sound waves, or pings, that sweep across tens or even hundreds of miles of ocean, and revealing objects in that path from the bounceback. Passive sonar listens for sound.
"The environmental group said the Navy's low-frequency system can generate 215 decibels — sound as intense as a twin-engine jetfighter at takeoff.
"Some mid-frequency systems produce 235 decibels, as loud as a Saturn V rocket at launch, it said."
As I discussed, airborne and waterborne reference levels are completely different, so the comparisons are worthless. Given that humpback whale song runs about 190 dB, which is the new Navy proposed limit, I'm not sure that there's as big a need for concern about marine mammals as the conservationists would have us believe.
Update 0027 30 March: From Navy NewsStand, an analysis of the likelihood that active sonar contributed to the whale stranding off North Carolina in January 2005. Their conclusion, based on the fact that the sonar use was 2-3 days before the beaching, among other things, was that it was unlikely that sonar played a role.