NMFS Final Rule on LFA Sonar (fwd)

From: Pita Admininstrator (pita@whale.wheelock.edu)
Date: Tue Jul 16 2002 - 17:09:57 EDT

Subject: NMFS Final Rule on LFA Sonar

The US National Marine Fisheries Service released the Final Rule regarding
LFA sonar yesterday. A partial copy of the Federal Register notice
follows. Information on this can be found on the NOAA website at:


[Federal Register: July 16, 2002 (Volume 67, Number 136)]
[Page 46711-46789]
>From the Federal Register Online via GPO Access [wais.access.gpo.gov]

Part II

Taking and Importing Marine Mammals; Taking Marine Mammals Incidental to
Navy Operations of Surveillance Towed Array Sensor System Low Frequency
Active Sonar; Final Rule

National Oceanic and Atmospheric Administration

Taking and Importing Marine Mammals; Taking Marine Mammals Incidental to
Navy Operations of Surveillance Towed Array Sensor System Low Frequency
Active Sonar

AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and
Atmospheric Administration (NOAA), Commerce.

ACTION: Final rule.


SUMMARY: NMFS, upon application from the U.S. Navy, is issuing regulations
to govern the unintentional takings of small numbers of marine mammals
incidental to Navy operation of the Surveillance Towed Array Sensor System
(SURTASS) Low Frequency Active (LFA) Sonar. Issuance of regulations, and
Letters of Authorization under these regulations, governing unintentional
incidental takes of marine mammals in connection with particular
activities is required by the Marine Mammal Protection Act (MMPA) when the
Secretary of Commerce (Secretary), after notice and opportunity for
comment, finds, as here, that such takes will have a negligible impact on
the species and stocks of marine mammals and will not have an unmitigable
adverse impact on the availability of them for subsistence uses. These
regulations do not authorize the Navy's operation of SURTASS LFA sonar as
such authorization is not within the jurisdiction of the Secretary.
Rather, these regulations authorize the unintentional incidental take of
marine mammals in connection with this activity and prescribe methods of
taking and other means of effecting the least practicable adverse impact
on marine mammal species and their habitat, and on the availability of the
species for subsistence uses.

DATES: Effective from August 15, 2002 through August 15, 2007.

ADDRESSES: A copy of the Navy application and a list of references used in
this document may be obtained by writing to Donna Wieting, Chief, Marine
Mammal Conservation Division, Office of Protected Resources, National
Marine Fisheries Service, 1315 East-West Highway, Silver Spring, MD
20910-3226 or by telephoning the contact listed here (see FOR FURTHER
INFORMATION CONTACT). The NMFS' Administrative Record for this action is
available for viewing, by appointment during regular business hours, at
the above address. Copies of letters, documents and the public hearing
record are available, at copy cost, from this

Comments regarding the burden-hour estimate or any other aspect of the
collection of information requirement contained in this final rule should
be sent to the Chief, and to the Office of Information and Regulatory
Affairs, Office of Management and Budget (OMB), Attention: NOAA Desk
Officer, Washington, DC 20503.

FOR FURTHER INFORMATION CONTACT: Kenneth R. Hollingshead (301) 713-2322,
ext. 128.



Section 101(a)(5)(A) of the Marine Mammal Protection Act (MMPA) (16 U.S.C.
1361 et seq.) directs the Secretary of Commerce (Secretary) to allow, upon
request, the incidental, but not intentional taking of small numbers of
marine mammals by U.S. citizens who engage in a specified activity (other
than commercial fishing) within a specified geographical region if certain
findings are made and regulations are issued.

Permission may be granted for periods of 5 years or less if the Secretary
finds that the taking will be small, have a negligible impact on the
species or stock(s) of affected marine mammals, and will not have an
unmitigable adverse impact on the availability of the species or stock(s)
for subsistence uses, and if regulations are prescribed setting forth the
permissible methods of taking and the requirements pertaining to the
monitoring and reporting of such taking.

Summary of Request

On August 12, 1999, NMFS received an application from the U.S. Navy
requesting a small take exemption under section 101(a)(5)(A) of the MMPA
for the taking of marine mammals incidental to deploying the SURTASS LFA
sonar system for training, testing and routine military operations
anywhere within the world's oceans (except for Arctic and Antarctic
waters) for a period of time not to exceed 5 years. According to the
original Navy application, SURTASS LFA sonar would operate a maximum of 4
ship systems in the 10 geographic operating regions in which SURTASS LFA
sonar could potentially operate. There would be a maximum of four SURTASS
LFA sonar systems with an expected maximum of two systems at sea at any
one time.

The purpose of SURTASS LFA sonar is to provide the Navy with a reliable
and dependable system for long-range detection of quieter, harder-to-find
submarines. Low-frequency (LF) sound travels in seawater more effectively
and for greater distances than higher frequency sound used by most other
active sonars. According to the Navy, the SURTASS LFA sonar system would
meet the Navy's need for improved detection and tracking of new-generation
submarines at a longer range. This would maximize the opportunity for U.S.
armed forces to safely react to, and defend against, potential submarine
threats while remaining a safe distance beyond a submarine's effective
weapons range.

Description of the Activity

The SURTASS LFA sonar system is a long-range, LF sonar (between 100 and
500 Hertz) that has both active and passive components. It does not rely
on detection of noise generated by the target. The active component of the
system is a set of up to 18 LF acoustic transmitting source elements
(called projectors) suspended from a cable from underneath a ship. The
projectors are devices that transform electrical energy to mechanical
energy by setting up vibrations, or pressure disturbances with the water
to produce the pulse or ping. The SURTASS LFA sonar acoustic transmission
is an omnidirectional (full 360 degrees) beam in the horizontal. The
expected water depth of the center of the array is 400 ft (122 m), with a
narrow vertical beamwidth that can be steered above or below the
horizontal. The source level (SL) of an individual projector in the
SURTASS LFA sonar array is approximately 215 dB, and because of the
physics involved in beam forming and transmission loss processes, the
array can never have a sound pressure level (SPL) higher than the SPL of
an individual projector. The expected minimum water depth at which the
SURTASS LFA vessel will operate is 200 m (656.2 ft). Normally, the
shallowest depth that it can operate is 100 m (328.1 ft).

The typical SURTASS LFA sonar signal is not a constant tone, but rather a
transmission of various signal types that vary in frequency and duration
(including continuous wave (CW) and frequency-modulated (FM) signals). A
complete sequence of sound transmissions is referred to by the Navy as a
``ping'' and can last as short as 6 seconds (sec) to as long as 100 sec,
normally with no more than 10 seconds at any single frequency. The time
between pings is typically from 6 to 15 minutes. Average duty cycle (ratio
of sound ``on'' time to total time) can be controlled but cannot be
greater than 20 percent; typical duty cycle is between 10 and 15 percent.

The passive or listening component of the system is SURTASS, which detects
returning echoes from submerged objects, such as submarines, through the
use of hydrophones. The hydrophones are mounted on a horizontal array that
is towed behind the ship. The SURTASS LFA sonar ship maintains a minimum
speed of 3.0 knots (5.6 km/hr; 3.4 mi/hr) in order to keep the array

The Navy anticipates that a normal SURTASS LFA sonar deployment schedule
for a single vessel would involve about 270 days/year at sea (underway). A
normal at-sea mission would occur over a 30-day period, made up of two
9-day exercise segments. The remaining 12 days of the at-sea mission would
be spent in transit or repositioning the vessel. In an average year there
could be a maximum of 9 missions, six of which would involve the
employment of SURTASS LFA sonar in the active mode and three of which
would employ the SURTASS LFA sonar in the passive mode only. Active sonar
operations could be conducted up to 20 hrs during an exercise day,
although the system would actually be transmitting for only a maximum of 4
hrs/day (resulting in 432 hrs of active transmission time per year for
each SURTASS LFA sonar system in operation based on a maximum duty cycle
of 20 percent). Between missions, an estimated 95 days would be spent in
port for upkeep and repair.

At present, only one SURTASS LFA sonar system is available for deployment.
A second SURTASS LFA sonar system is expected to be available shortly.
Delivery of the third and fourth systems have been postponed until after
FY 2007. As a result, under the 5-year window of these regulations, NMFS
is authorizing marine mammal harassment takings for only 2 SURTASS LFA
sonar systems, on average with one vessel operating in the Pacific-Indian
Ocean area and one vessel in the Atlantic Ocean-Mediterranean Sea area.
With two vessels, there would normally be 6 SURTASS LFA sonar missions in
each of these oceanic basins (or equivalent shorter missions totaling no
more than 432 hours of transmission/vessel/ year), or a total of 12 active
sonar missions per year over the 5-year period of the regulations.

Description of Acoustic Propagation

The following is a very basic and generic description of the propagation
of LFA sonar signals in the ocean and is provided to facilitate
understanding of this action. However, because the actual physics
governing the propagation of SURTASS LFA sound signals is extremely
complex and dependent on numerous in-situ environmental factors, the
following is for illustrative purposes only.

In actual SURTASS LFA sonar operations, the crew of the SURTASS LFA sonar
platform will measure oceanic conditions (such as sea water temperature
and salinity versus depth) prior to and during transmissions and at least
every 12 hours, but more frequently when meteorological or oceanographic
conditions change. These technicians will then use U.S. Navy sonar
propagation models to predict and/or update sound propagation
characteristics. According to the Navy, these extremely sophisticated
computer simulations are among the most accurate in the world. The short
time periods between actual environmental observations and the subsequent
model runs further enhance the accuracy of these predictions.
Fundamentally these models are used to determine what path the LF signal
will take as it travels through the ocean and how strong the sound signal
will be at given range along a particular transmission path.

Accurately determining the speed at which sound travels through the water
is critical to predicting the path that sound will take. The speed of
sound in seawater varies directly with depth, temperature, and salinity.
Thus, an increase in depth or temperature or, to a lesser degree, salinity
will increase the speed of sound in seawater. However, the oceans are not
homogeneous and the contribution of each of these individual factors is
extremely complex and interrelated. The physical characteristics which
determine the sound speed change with depth (in the case of temperature
and salinity), season, geographic location, and locally, with time of day.
After accurately measuring these factors, mathematical formulas or models
can be used to generate a plot of sound speed versus water depth. This
type of plot is generally referred to as a sound speed profile (SSP). Near
the surface, ocean water mixing results in a fairly constant temperature
and salinity. In this mixed layer, depth (pressure) dominates the SSP and
sound speed increases with depth. Below the mixed layer, sea temperature
drops rapidly in an area referred to as the thermocline. In this region,
temperature dominates the SSP and speed decreases with depth. Finally,
beneath the thermocline, the temperature becomes fairly uniform and
increasing pressure causes the SSP to increase with depth.

One way to envision sound traveling though the sea is to think of the
sound as ``rays.'' As these rays travel though the sea, their direction of
travel changes as a result of speed changes, bending or refracting toward
areas of lower speed and away from areas of higher speed. Depending on
environmental conditions, refraction can either be toward or away from the
surface. Additionally, the rays can be reflected or absorbed when they
encounter the surface or the bottom. Under the correct environmental
conditions, sound rays can repeatedly be refracted upward and downward and
thus become trapped in a duct or ``sound channel.'' Similarly, reflections
from the surface or the bottom can combine with refraction to create a
duct. In the right circumstances, repeated refraction can result in
long-range focusing and defocusing of the sound. Because of the
possibility of multiple transmission paths, all of which are dependent on
environmental conditions, accurate predictions of how sound travels in
water is an extremely complex process.

Some of the more prevalent acoustic propagation paths in the ocean
include: acoustic ducting; convergence zone (CZ); bottom interaction; and
shallow-water propagation.

Acoustic Ducting

There are two types of acoustic ducting: surface ducts and sound channels.

Surface Ducts

As previously discussed, the top layer of the ocean is normally well mixed
and has relatively constant temperature and salinity. Because of the
effect of depth (pressure), surface layers exhibit a slightly positive
sound speed gradient (that is, sound speed increases with depth). Thus,
sound transmitted within this layer is refracted upward toward the
surface. If sufficient energy is subsequently reflected downward from the
surface, the sound can become ``trapped'' by a series of repeated upward
refractions and downward reflections. Under these conditions, a surface
duct, or surface channel is said to exist. Sound trapped in a surface duct
can travel for relatively long distances with its maximum range of
propagation dependent on the specifics of the SSP, the frequency of the
sound, and the reflective characteristics of the surface. As a general
rule, surface duct propagation will improve as the temperature uniformity
and depth of the layer increase. For example, transmission is improved
when cloudy, windy conditions create a well-mixed surface layer or in
high-latitude midwinter conditions where the mixed layer extends to
several hundred feet deep.

Sound Channels

Variation of sound speed, or velocity, with depth causes sound to travel
in curved paths. A sound channel is a region in the water column where
sound speed first decreases with depth to a minimum value, and then
increases. Above the depth of minimum value, sound is refracted (bent)
downward; below the depth of minimum value, sound is refracted upward.
Thus, much of the sound starting in the channel is trapped, and any sound
entering the channel from outside its boundaries is also trapped. This
mode of propagation is called sound channel propagation. This propagation
mode experiences the least transmission loss along the path, thus
resulting in long-range transmission.

At low and middle latitudes, the deep sound channel axis varies from 1,970
to 3,940 ft (600 to 1,200 m) below the surface. It is deepest in the
subtropics and comes to the surface in the high latitudes, where sound
propagates in the surface layer. Because propagating sound waves do not
interact with either the sea surface or seafloor, sound propagation in
sound channels do not attenuate as rapidly as bottom- or
surface-interacting paths. The most common sound channels used by SURTASS
LFA sonar are convergence zones (CZs).

Convergence Zones

CZs are special cases of the sound-channel effect. When the surface layer
is narrow or when sound rays are refracted downward, regions are created
at or near the ocean surface where sound rays are focused, resulting in
concentrated levels of high sounds. The existence of CZs depends on the
SSP and the depth of the water. Due to downward refraction at shorter
ranges, sound rays leaving the near-surface region are refracted back to
the surface because of the positive sound speed gradient produced by the
greater pressure at deep ocean depths. These deep-refracted rays often
become concentrated at or near the surface at some distance from the sound
source through the combined effects of downward and upward refraction,
thus causing a CZ. CZs may exist whenever the sound speed at the ocean
bottom, or at a specific depth, exceeds the sound speed at the source
depth. Depth excess, also called sound speed excess, is the difference
between the bottom depth and the limiting, or critical depth.

CZs vary in range from approximately 18 to 36 nm (33 to 67 km), depending
upon the SSP. The width of the CZ is a result of complex
interrelationships and cannot be correlated with any specific factor. In
practice, however, the width of the CZ is usually on the order of 5 to 10
percent of the range (see Figure 1). For optimum tactical performance, CZ
propagation of SURTASS LFA signals is desired and expected in open ocean

Bottom Interaction

Reflections from the ocean bottom and refraction within the bottom can
extend propagation ranges. For mid- to high-level frequency sonars
(greater than 1,000 Hz), only minimal energy enters into the bottom; thus
reflection is the predominant mechanism for energy return. However, at low
frequencies, such as those used by the SURTASS LFA sonar source, the sound
penetrates the ocean floor, and refraction within the seafloor, not
reflection, dominates the energy return. Regardless of the actual
transmission mode (reflection from the bottom or refraction within the
bottom), this interaction is generally referred to as ``bottom-bounce''

Major factors affecting bottom-bounce transmission include the sound
frequency, water depth, angle of incidence, bottom composition, and bottom
roughness. A flat ocean bottom produces the greatest accuracy in
estimating range and bearing in the bottom-bounce mode.

For SURTASS LFA sonar transmissions between 100 and 330 Hz, bottom
interaction would generally occur in areas of the ocean where depths are
between approximately 200 m (average minimum water depth for SURTASS LFA
sonar deployment) and 2,000 m (660 and 6,600 ft).

Shallow Water Propagation

In shallow water, propagation is usually characterized by multiple
reflection paths off the sea floor and sea surface. Thus, most of the
water column tends to become ensonified by these overlapping reflection
paths. As LFA signals approach the shoreline, they will be affected by
shoaling, experiencing high transmission losses through bottom and surface
interactions. Therefore, LFA sonar will not be effective in shallow,
coastal waters.

In summary, for the SURTASS LFA sonar signal in low- and mid-latitudes,
the dominant propagation paths for LFA signals are CZ and bottom
interaction (2000 m (6,600 ft) depth). In high-latitudes, surface ducting
provides the best propagation. In most open ocean water, CZ propagation
will be most prominent. An example of this propagation path is shown in
Figure 1. The SURTASS LFA sonar signals will interact with the bottom, but
due to high bottom and surface losses, SURTASS LFA sonar signals will not
penetrate coastal waters with appreciable signal strengths.

Comments and Responses

On October 22, 1999 (64 FR 57026), NMFS published an Advance Notice of
Proposed Rulemaking (ANPR) on the U.S. Navy application and invited
interested persons to submit comments, information, and suggestions
concerning the application and the structure and content of regulations,
if the application was accepted. During the 30-day comment period of that
notification, significant comments were received from several
organizations and individuals. On March 19, 2001 (66 FR 15375), NMFS
published a proposed rule to authorize the U.S. Navy to take small numbers
of marine mammals incidental to operation of SURTASS LFA sonar and
requested comments, information, and suggestions concerning the request
and the regulations proposed to govern the take. The comments provided to
NMFS during the ANPR's comment period were addressed in the notice of
proposed rulemaking. A copy of the proposed rulemaking document is
available at:

While the comment period on the proposed rule was for a period of 45 days,
the comment period was extended until May 31, 2001, a period of 73 days
(66 FR 26828, May 15, 2001). During that time period, NMFS received
several thousand comments from organizations and interested citizens. Most
of the comments received were petitions, postcards and form letters,
either mailed or faxed to NMFS. Approximately 87 letters contained
comments, information, and questions that NMFS determined warranted
response in this document. Moreover, these letters reflected the same
comments that were contained in the other letters and postcards, but in
greater detail. They are available for viewing at the following location:
http://fish.nmfs.noaa.gov/ibrm/OPRComments.lhtml?rulein=2. For those
without access to the Internet, copies of these letters and all comments
received by NMFS are available from NMFS at copy cost (see ADDRESSES).

In addition to written comments, NMFS held three public hearings to obtain
oral and written information from the public on NMFS' proposed rule (66 FR
19414, April 16, 2001). These public hearings were held in Los Angeles, CA
on April 26, 2001, Honolulu, HI on April 28, 2001, and Silver Spring, MD
on May 3, 2001. A copy of any or all of the hearing records is also
available from NMFS at copy cost (see ADDRESSES).

In this document, NMFS has (1) provided response to comments (RTCs) on
both its proposed rule and the Navy's Final EIS; (2) provided
cross-references to the appropriate response in the Navy's Final Overseas
Environmental Impact Statement and Environmental Impact Statement for
SURTASS LFA Sonar (Final EIS) for comments that were addressed in the
Navy's Final EIS; (3) edited some comments for clarity and brevity; and
(4) grouped similar comments or chosen one or two comments to represent
several similar comments. Some comments may not have been addressed
because their meaning or relevance was not clear.

In the following sections, NMFS is responding to comments on the Navy
activity whether or not the comment was relevant to the Navy's application
or the effect of SURTASS LFA sonar on marine mammals and thereby under the
purview of NMFS. This was done to further facilitate understanding of the
Navy's proposed action, the alternatives identified by the public to
SURTASS LFA sonar, and the potential impact of SURTASS LFA sonar on marine


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