Marine mammals won a significant victory today in the US District Court, Northern California. Magistrate Elizabeth Laporte ruled that the US Navy, which has been trying to increase its use of high-tech active sonar in the open oceans, must establish sonar-free zones in sensitive ocean habitats around the world. The Bahamas, the Great Barrier Reef, the Galapagos Islands, Davison Seamount off Monterey Bay, and several other spots around the world were mentioned.
A week ago, a related decision was handed down by a federal judge in Los Angeles, who refused to exempt the Navy’s active sonar tests from environmental laws.
The issue is profound and usually mortal injuries that whales and dolphins, and likely other types of marine life, suffer, directly or indirectly, from exposure to intense bursts of artificial sound such as active sonar pings. Mass strandings of cetaceans have been documented after sonar tests in the Bahamas, the Mediterranean, and elsewhere. On her blog Cocktail Party Physics, Jennifer Ouellette has posted one of the best summaries of the issue I’ve seen, discussing the political and scientific angles.
The sonar tests at issue involve mid-frequency sounds, from about 1 to 10 kHz, a bit more than a three octave range, with the low end pitched about here:
and the high end here:
A few years back the Navy was going through similar court battles regarding Low-Frequency Active Sonar, which uses sounds of about 250-300 hertz, about like this:
Keep in mind that those sound samples are almost unbelievably quiet compared to the sonar pulses we’re talking about. How loud they are when you play them depends on your machine and its settings, but let’s assume you have it turned up to about as loud as a typical conversation in a quiet room. That’s about 60 decibels or so. Decibels (dB) are defined logarithmically, remember: an increase of ten dB means a tenfold increase in volume, so that 70dB is ten times louder than 60, 80dB is 100 times louder than 60, and so forth. A noise of 160dB, a billion times louder than 60dB, will destroy your eardrums instantly.
The midlevel active sonar pings being discussed range around 230dB. Water conducts sound much more readily than does air, and 300 nautical miles away from the test zone, the ping may only have attenuated to about 140dB, about like standing next to a military jet taking off. That’s also the level the Navy has set, after study, as the loudest underwater sound to which one of its divers can be safely exposed. Cetaceans, with senses of hearing unimaginably more sensitive than humans’ — humpbacks have been observed carrying on conversations across distances of hundreds of miles — get a whole lot louder sounds than that “safe level” if they venture within 300 miles of a test.
So why is the Navy carrying on these tests at all? As Jennifer Ouellette puts it:
From the Navy’s perspective, sonar training exercises are critical to US national security interests: smaller diesel submarines can’t be detected with passive sonar, for example, and over 40 nations deploy these kinds of subs. Ultimately, it’s about balancing the interests of national security with environmental concerns. That makes it one of those complex issues about which reasonable people might reasonably disagree.
Now it had to happen eventually, and frankly, I’m as surprised as you are. But Jennifer is, in those last two sentences, well, wrong.
Diesel-electric submarines are indeed quiet — when they operate on electric power only. But submarines are heavy, and water dense, and moving the sub through the water takes a lot of power, and batteries don’t store all that much, and batteries are heavy too, so adding more of them reaches a point of diminishing returns. Thus the range of a diesel-electric sub under electric power only is rather limited. Eventually, the crew has to start up the diesel engines to recharge the batteries. Diesel engines are noisy, and thus detectable by passive sonar, a fancy phrase the Navy uses to describe the act of just listening for ships. And despite the rise in ocean noise over the last decades, the Navy does that just fine. In February 1997 Rear Admiral Edmund Giambasriani, the US Navy’s Director of Submarine Warfare, told Jane’s Defense Weekly,
Our view is that because of significant capabilities in processing, sensor apertures and the ability to net sensors together, passive [sonar] is not dead ... We feel there is [sic] still a lot of dB out there that we can mine.
“Capabilities in processing” have only increased since then. When Giambasriani said the above, the Cray T90 was the mythical supercomputer of record. They weighed fourteen tons and the US Government owned maybe three of them. I have a somewhat more powerful computer sitting next to me here playing Sam Cooke as it works. Sorting out diesel-electric sub noise from tanker and outboard noise becomes a routine task for Navy software engineers.
What’s more, diesel engines rely on burning their diesel fuel, which requires oxygen, which is in limited supply in a submerged hull and necessary to keep the crew alive besides. So in order to run the diesel engines, the crew has to surface. This exposes the sub not only to detection by way of passive sonar, but also by means of sophisticated sensing technologies such as these.
What this all means is that those 40 nations that deploy diesel-electric submarines in their naval fleets use them in littoral settings, close to the coast. This further means the subs are used in defensive settings. There they are effective: they can keep their batteries charged until someone invades and then hide, waiting for the right moment to sink the aggressor’s boats.
Were the US faced with the prospect of defending its shores, in fact, diesel-electric submarines would be far more useful than fancy whale-killing sonar. But the fact is, there are no diesel-electric submarines in the US Navy’s fleet. If they’re a new and terrifyingly effective way of defending coasts, why does the US Navy own none of them?
Because defending the US is not at issue here, that’s why.
With occasional odd exceptions, and unless US-Canadian relations continue to degrade, the US Navy will only encounter hostile diesel-electric submarines in the course of invading other countries. That is the only field of battle in which active sonar of any kind becomes necessary.
The active sonar issue is not, and never has been, a matter of balancing environmental protection and national defense. It’s a matter of defending the natural world, again, against the depredations of a US policy that is at best interventionist, at worst imperialist. We should be working to stop active sonar tests even if no marine life is harmed by them.
