The scientific study of sound, especially of its generation,
transmission, and reception.
Ambient noise: The typical or persistent environmental
background noise present in the ocean.
Anthropogenic noise: Noise related to or produced
by human activities.
Antisubmarine warfare (ASW): Naval operations conducted
against submarines, their supporting forces and operating
Baleen: The filtering plates that hang from the upper
jaw of baleen whales.
Baleen whales: The filter-feeding whales, also known
Biologically important activities/behaviors: Those
activities or behaviors essential to the continued existence
of a species, such as migration, breeding/calving, or feeding.
Biologically important areas (offshore): Offshore biologically
important areas are defined as those areas of the world’s
oceans outside of 22 km (12 nm) of a coastline where marine
animals of concern (those animals listed under the Endangered
Species Act and/or marine mammals) congregate in high densities
to carry out biologically important activities. Biologically
important areas include:
and calving grounds; and
Of or belonging to the order Cetacea, which includes aquatic
mammals with anterior flippers, no posterior limbs, and
a dorsal fin; such as whales, dolphins and porpoise.
Convergence zone (CZ): The region in the deep ocean
where sound rays, refracted from the depths, arrive at the
surface in successive intervals of 55 to 64 kilometers (30
to 35 nautical miles). The repeated occurrence of these
zones to several hundred miles from the sound source depends
on the refraction of sound at depth and the reflection of
these rays at the surface.
habitat: The area where the species of concern resides
that contains physical or biological characteristics essential
to the survival of the species, or the area surrounding such
habitats, which are essential to the survival of the species.
However, it does not include all habitats that could be used
by the species.
Decibel (dB): A unit used to express the relative difference
in power, usually between acoustic or electrical signals,
equal to ten times the common logarithm of the ratio of the
Duct: A layer in the ocean where refraction and probably
reflection result in the trapping of sound waves.
Duty cycle: The ratio of the time the sound is being
transmitted over the total time period, measured in percent.
Endangered species: Defined in 16 U.S.C. 1532 as any
species that is in danger of extinction throughout all or
a significant portion of its range (other than a species of
Class Insecta designated as a pest). Federally endangered
species are listed in 50 CFR 17.11 and 17.12.
Frequency: Description of the rate of disturbance,
or vibration, measured in cycles per second. Cycles per second
are usually referred to as the unit of measure of Hertz (Hz).
In acoustics, frequency is characterized in general terms
as low, mid, or high. The U.S. Navy categorizes these as follows:
- Low frequency
(LF) sound is below 1,000 Hz;
- Mid frequency
(MF) sound is between 1 and 10 kHz; and
frequency (HF) sound is above 10 kHz.
Place where an animal or plant normally lives, often characterized
by a dominant plant form or physical characteristic.
Harassment: Under the Marine Mammal Protection Act,
any act of pursuit, torment, or annoyance that has the potential
- Injure a
marine mammal or marine mammal stock in the wild; or
a marine mammal or marine mammal stock in the wild by
causing disruption of behavioral patterns, including,
but not limited to, migration, breathing, nursing, breeding,
feeding, or sheltering.
(Hz): The unit of measure of frequency in cycles per second.
1,000 Hz is usually referred to as 1 kiloHertz (kHz).
Impedance (acoustic): The product of density and sound
LFA mitigation zone: The LFA mitigation zone covers
a volume insonified to a level > 180 dB by the SURTASS LFA
sonar transmit array. Under normal operating conditions, this
zone will vary between the nominal ranges of 0.75 to 1.0 km
(0.40 to 0.54 nm) from the source array over a depth of approximately
87 to 157 m (285 to 515 ft).
Masking: The obscuring of sounds of interest by interfering
sounds, generally at similar frequencies.
Mysticete: Any of several whales having symmetrical
skulls, paired blow holes, and plates of whale bone (baleen
plates) instead of teeth of the suborder Mysticeti. Filter-feeding
whales, also referred to as baleen whales.
Odontocete: Any of the toothed whales (without baleen
plates) having a single blow hole and asymmetric skull of
the suborder Odontoceti, such as orcas, dolphins, and porpoises.
Otariid: One of three families of Pinnipedia having
small but well formed ears (known as "eared" seals) including
eared seals, sea lions, and fur seals.
Pelagic: Living in the water column. Plants and animals
that are free-floating and drift passively, or animals that
are strong swimmers.
Period: The time required for a wave crest to traverse
a distance equal to one wavelength.
Permanent threshold shift (PTS): The deterioration
of hearing due to prolonged or repeated exposure sounds which
accelerate the normal process of gradual hearing loss, and
the permanent hearing damage due to brief exposure to extremely
high sound levels.
Of or belonging to the Pinnipedia, an order of aquatic mammals
that include seals, sea lions, walruses and similar animals
having fin-like flippers for locomotion. They are carnivorous
and "haul out" on shore to have their pups.
Received level (RL): The level of sound that arrives
at the receiver, or listening device (hydrophone). It is measured
in decibels referenced to 1 microPascal root-mean-squared
(rms). Put simply, the received level is the source level
minus the transmission losses from the sound traveling through
Record of Decision (ROD): In regard to an Environmental
Impact Statement (EIS), the notice published in the Federal
Register that contains the lead agency's decision, and identifies
both the alternatives and the mitigation measures to be used.
Reflection: Process by which a traveling wave is deflected
by a boundary between two media. Angle of reflection equals
angle of incidence.
Refraction: Bending of a sound wave passing through
a boundary between two media; may also occur when physical
properties of a single medium change along the propagation
Root mean squared: The square root of the arithmetic
mean of the squares of a set of numbers.
Salinity: A measure of the quantity of dissolved salts
in seawater. It is formally defined as the total amount of
dissolved solids in seawater in parts per thousand (‰) by
weight when all the carbonate has been converted to oxide,
the bromide and iodide to chloride, and all organic matter
is completely oxidized.
Scoping: Early consultation with federal and state
agencies, and interested public to identify possible alternatives
and the significant issues to be addressed in the EIS.
Ping Equivalent (SPE): The single ping equivalent (SPE)
is the methodology used during the acoustic modeling of potential
impacts to marine animals from exposure to low frequency sound.
This method estimates the total exposure of each individually
modeled animal, which was exposed to multiple pings over an
extended period of time. This was accomplished by the summation
of the intensities for all received pings into an equivalent
exposure from one ping, which is always at a higher level
than the highest individual ping received.
Sirenian: A herbivorous aquatic mammal of the order
Sirenia, which include the manatee and dugong.
SONAR: An acronym for SOund NAvigation and Ranging.
It includes any system that uses underwater sound, or acoustics,
for observations and communications. There are two broad types
sonar detects the sound created by an object (source)
in the water. This is a one-way transmission of sound
waves traveling through the water from the source to
the receiver; and
sonar detects objects by creating a sound pulse,
or ping, that transmits through the water and reflects
off the target, returning in the form of an echo. This
is a two-way transmission (source to reflector to receiver)
and is a form of echolocation.
axis: The depth at which minimum sound velocity occurs
in the ocean.
Sound pressure level (SPL): Twenty times the logarithm
to the base 10 of the ratio of the pressure to the reference
pressure, in decibels at a specific point. The reference
pressure shall be explicitly stated. SPL is usually measured
in decibels referenced to 1 microPascal (rms).
Sound speed: Sound speed is the velocity that sound
waves travel through a medium. Sound speed through seawater
is approximately 1,500 meters per second (4,920 feet per
second). It varies with water temperature, salinity, and
depth (pressure). Sound speed increases with increases in
temperature and pressure (depth), and to a lesser extent
with increase in salinity. This change in speed as sound
travels through water causes the travel path to bend in
the direction of lower velocity.
speed profile (SSP): The sound speed profile (SSP) is
a graphic representation of the sound speed versus depth of
the ocean. These profiles vary with latitude, season, and
time of day.
Source Level (SL): The sound transmitted into the water
by a sound source, such as an active sonar ping. SL is usually
measured in decibels referenced to 1 microPascal at 1 m (3.28
SURTASS LFA sonar: Long-range, low frequency (between
100 and 500 Hz) sonar system composed of both active and passive
components. SURTASS (Surveillance Towed Array Sensor System)
is the passive component. LFA (Low Frequency Active) is the
Take: To harass, harm, pursue, hunt, shoot, wound,
kill, trap, capture, or collect, or to attempt any of these
Temporary threshold shift (TTS): Temporary increases
in threshold occurring after exposure to high noise levels,
which can last from minutes to hours.
Transmission loss (TL): Energy losses as the pressure
wave, or sound, travels through the water, the associated
wavefront diminishes due to the spreading of the sound over
an increasingly larger volume and the absorption of some of
the energy by seawater.
Threatened species: Any species that is likely to become
an endangered species within the foreseeable future throughout
all or a significant portion of its range. Threatened species
are listed in 50 CFR 17.12.
Vertebrate: A member of the subphylum Vertebrata, a
primary division of the phylum Chordata that includes fishes,
amphibians, reptile, birds, and mammals, all which are characterized
by a segmented bony or cartilaginous spinal column (i.e. backbone).
Wavelength: The distance between corresponding points
of two successive waves.