NPAL FAQ

What is NPAL?
NPAL stands for the North Pacific Acoustic Laboratory. NPAL is a continuation of the research that was conducted by the Acoustic Thermometry of Ocean Climate (ATOC) project. It is funded by the Office of Naval Research (ONR) and is being conducted by Scripps Institution of Oceanography, University of California San Diego, in conjunction with the Applied Physics Laboratory of the University of Washington.

The NPAL scientists have retained the seabed power cable and sound source installed by the ATOC project in their present locations, and are continuing transmissions with approximately the same signal parameters and transmission schedule used in the ATOC project. This consists of six 20-minute transmissions (one every four hours), every fourth day, with each transmission preceded by a 5-minute ramp-up period.

The purpose of the NPAL is to 1) perform the second phase of research on the feasibility and value of large-scale acoustic thermometry; 2) study the behavior of sound transmissions in the ocean over long distances; and 3) conduct studies on the possible long-term effects from the sound transmissions on marine life.

Why do you need to continue transmissions?
The results of the first phase of the ATOC Project demonstrated that acoustic travel times could be measured much more accurately than anticipated. These travel times can then be used to estimate ocean temperatures with a precision of about 0.006° C at ranges of 3,000 to 5,000 km. If we have a series of these measurements over a longer period of time, the NPAL scientists can use these measurements to study a variety of oceanographic phenomena, such as seasonal and interannual variability, El Niño, La Niña and the Pacific Decadal Oscillation (PDO). On a longer scale, the information can be used to test and refine ocean general circulation and climate models in order to gain a better understanding of the Earth's changing climate, including the link between global warming and sea level rise. The information obtained from the continuation of the ATOC sound source transmissions can also be used in combination with satellite altimeter data, subsurface drifter data, surface moorings and expendable thermograph (XBT) data to monitor the ocean and its variability.

A full understanding of long-range underwater sound transmission is important because all users of the ocean environment must rely on acoustic signals to sense their surroundings and to perform basic tasks, such as measuring ocean depth, locating underwater objects, navigation and communication. ONR is interested in studying ocean circulation and the way sound behaves over long distances in order to increase fundamental understanding of its operating environment.

Is NPAL the same as LFA?
No. NPAL uses the sound transmissions from the stationary ATOC source to do basic research on acoustic thermometry, long-range propagation characteristics of the ocean, and the potential effects of the sound transmission on marine life. The Surveillance Towed Array Sensor System (SURTASS) Low Frequency Active (LFA) Sonar system was proposed in support of the Navy's national defense mission. It uses an array of sound sources suspended from a ship to provide improved submarine detection capabilities.

Although NPAL and SURTASS LFA each employ low frequency sound, there are important differences:

a. The NPAL source level is significantly lower than that of LFA.

b. The NPAL signal will be generated from a stationary source at greater than 800 meters (over 2,500 feet) depth, considerably deeper than the SURTASS LFA signal. The NPAL signal intensity decreases considerably before the signal reaches the surface or even a few hundred meters of the surface, where marine mammals spend most of their time.

c. NPAL is secured in one place; SURTASS LFA is mobile.

Do the sound transmissions harm marine mammals and other marine life?
No. During the first phase of the study, the ATOC Marine Mammal Research Program (MMRP) used the source transmissions to look at how the sounds affected marine mammals and fish. In Hawaii, the MMRP mainly studied humpback whale behavior, since they were the species most likely to be able to hear the sounds. Visual and acoustic observations found no evidence that the transmissions affected the abundance or singing behavior of the whales in the vicinity of the sound source, i.e., they did not vacate the area or cease singing. The MMRP did find, however, after intensive statistical analysis, that the distance and time between successive surfacings increased slightly with increasing sound levels. In other words, the humpbacks showed no strong responses to the sounds. The MMRP marine biologists and the National Marine Fisheries Service (NMFS) have concluded that the effects that they did find are not believed to adversely impact the survival of an individual whale or the status of the North Pacific humpback whale population.

Additional laboratory studies conducted on whales, dolphins and fish demonstrated that animals must be located in extremely close proximity to the sound source to be able to detect the sound, and even then, no significant effects were observed. Since the source is located on the seafloor at a depth of 2648 feet (807 meters), it is unlikely that many species would dive that deep.

What about the strandings that have been supposedly linked to military sonar?
A review of the California stranding data while the Pioneer Seamount ATOC source was operational shows no significant changes in the number, frequency, or species composition during that time period.

The referenced military sonars have signal and operational characteristic very different from those of the Kauai source. According to NMFS, "Marine mammal stranding events elsewhere in the world that may be linked to acoustic noise, to date, have not been noted to be associated with low frequency sounds in the range of 60-90 Hz, but instead are more likely related to high intensity mid-frequency sounds." (NMFS Notice of proposed rulemaking, Federal Register, Vol. 65, No. 247, December 22, 2000, pg. 80820)

Although NMFS does recognize that loud, intense sound sources can cause injuries to marine mammals, "due to the water depth of the NPAL source and the fact that it is not of sufficient intensity to result in hearing damage, NMFS has no scientific reason to suspect that the NPAL source could result in injury or death to marine mammals through either hearing or other body function impairments." (NMFS Final Rule, Federal Register, Vol. 66, No. 160, August 17, 2001, pg. 43452)

Kauai Source Permitting

NPAL Frequently Asked Questions (FAQ)