||R/V Cory Chouest, the first US ship to deploy the SURTASS/LFA system
(Photo courtesy US Navy)
Sonars and Sonic Research in the Seas
NOTE: All of AEI's current coverage of active sonars has moved to our comprehensive AEI Special Report, which is continually updated:
[See AEI Special Report: Active Sonars]
Over the past several years, the Navy has been developing a new surveillance technology which promises to shine a sonic spotlight through the oceans, revealing the presence of enemy submarines, including modern "silent" subs. To accomplish this Herculean task, powerful sound waves will be created. . . .
The world's navies deploy several other sonars, including a mid-frequency active sonar that has been implicated in several beaked whale stranding events. In addition, researchers use side-scan sonars and sub-bottom profilers (also operating in mid-frequency ranges) as mapping tools, and fishermen and other boats routinely use high-frequency sonars to watch for fish and avoid rocks and other navigation hazards.
Much study has focused on the effects of the naval mid-frequency sonars since a series of strandings coincident with naval exercises. A 2005 overview of these events, and of the state of research into effects of sonar on cetaceans is available from ICES (International Council for the Exploration of the Seas). [DOWNLOAD REPORT(pdf)]
A good overview of the various sonar systems used in mapping is available from NOAA's Coastal Services Center. It includes web pages and pdfs explaining side-scan sonar, Single-beam bathymetry, Multi-beam bathymetry, Sub-bottom profiling, and ASCS (Acoustic Seafloor Classification Systems). [WEBSITE]
Sound-based Climate and Oceanography Research
Public concern about high-intensity ocean noise was first catalyzed in the mid and late 1990's as climate researchers installed transmitters and receivers designed to measure ocean temperatures using long-range sound waves. These programs are ongoing today, though it appears that there are fewer biological impacts than originally feared.
Acoustic Thermography of Ocean Currents (ATOC)
North Pacific Acoustic Laboratory (NPAL)
The ATOC climate study project began in 1995 amid concerns about its effects on ocean life. The scientific consensus is that the benefits (to us in understanding climate) outweigh possible costs (to ocean dwellers), and few long term effects have been noted on wildlife. ATOC involves a low pitched rumbling source, transmitted across stretches of ocean, with measurements made of the speed of travel, offering clues to the temperature of the sea. While most of the sonic effects remain in the deep oceans, there are marine mammals that dive to these depths. Studies have shown small but noticable changes in marine mammal activity during operation of the system. Despite efforts to minimize effects on marine mammals, the National Oceanographic and Atmospheric Administration has authorized the program to allow for some "incidental" deaths to occur in conjuction with the program.
In February 2002, the National Marine Fisheries Service gave its final go-ahead for the continuance of climate research under a new project name, the North Pacific Acoustic Laboratory NPAL). During the early phases of testing, the system employed two transmission sites: one on the Pioneer Seamount off San Francisco, and one near Kauaii, Hawaii. The Pioneer site is no longer authorized for transmissions, largely due to concerns over the biological productivity of marine resources in the area; it is now a passive receiving station only and is not a part of the NPAL system. The low power (260-watt) signals are sent for 20 minutes every four hours, typically for one day of every four (total operation time: 2%, with option for periods of up to 8%).
NPAL Record of Decision Source: Federal Register, USNavy 2/11/02 [WEB PAGE NO LONGER ACCESSIBLE]
NOAA Allowance of "incidental take" of marine mammals by NPAL. Source: Federal Register, 2/22/02 [WEB PAGE NO LONGER ACCESSIBLE]
UCSD ATOC Home page - [WEBSITE]
Information from UCSD in-house Marine Mammal Research project - [WEBSITE]
The NRDC report on undersea noise - contains a section on the ATOC program. Here's the chapter that includes this section. [SEE CHAPTER]
Indian Ocean Acoustic Climate Initiative (IOACI)
A similar program under development in the Indian Ocean. Reseachers here claim to have gone to great lengths to be sure their work will not impact local marine life (mostly by replicating the approaches in ATOC: low freqency, low power, sonic signatures unlike any animal, deep ocean transmission). As of early 2002, preliminary research was still under way, and there was no target date for deployment of the system. Researchers stress the low power nature of the sounds, which will be largely "below the ambient noise level of the ocean", detectable by scientists only thanks to sophisticated signal processing. Source: Sea Technology Magazine, February 2002 [PRESS RELEASE]