Glossary - H
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to become accustomed to something through repeated or prolonged exposure
Melanogrammus aeglefinus
hair cells
mechano-transducers that detect energy or pressure changes. They are complex structures that include a cell body on the surface of a membrane. At the base of the hair cell are one or more neural synapses. On the upper surface of the hair cell are hair-like projections called stereocilia, commonly in bundles. These stereocila bend in response to a range of stimuli based on the species, some from fluid motion, some in association with crystals or otoliths, some because of being embedded in a second membrane. When these stereocila bend, they trigger a release of chemicals that initiates the electrical signal (neural impulse) that is carried to and processed by the brain.
harbor porpoise
Phocoena phocoena
harbor seal
Phoca vitulina
harmonic distortion
distortion of a pure tone associated with the presence of undesired harmonics at frequencies that are a multiple of the fundamental frequency of the signal.
harmonic frequency
the part of a signal whose frequency is an integer multiple of the fundamental frequency. Harmonic frequencies are related to each other by simple whole number ratios, for example if the fundamental frequency is f, the harmonics have frequencies of 2f, 3f, 4f, etc.
hawaiian monk seal
Monachus schauinslandi
Heard Island Feasibility Test (HIFT)
an expedition to Heard Island in the southern Indian Ocean during which acoustic sources suspended below a ship transmitted acoustic signals to receivers around the globe. Heard Island was selected because signals transmitted from that location can reach both coasts of North America. HIFT showed that underwater acoustic signals could be received worldwide and serve as a method for measuring global ocean warming.
hearing generalist
a fish species in which the swim bladder aids very little or not at all in hearing sensitivity
hearing groups
groups of marine mammals defined by the generalized range of frequencies that species in the group can hear.
hearing range
the range of frequencies the ear of an animal can detect.
hearing specialist
a fish species in which the swim bladder is directly connected to the inner ear and provides increased hearing sensitivity
flow of blood from a ruptured blood vessels; excessive bleeding
an animal or plant having both male and female reproductive organs
the unit of frequency; the number of cycles, or wavelengths, in a second (cycles/second)
a system or organization in which people, animals, or groups are ranked one above the other according to status or authority.
a representation of a distribution by means of rectangles whose widths represent class intervals and whose areas are proportional to the corresponding frequencies of occurrence.
similar in position, structure, and evolutionary origin but not necessarily in function.
humpback whale
Megaptera novaeangliae
hydraulic hammer
a large, industrial hammer that is operated by a fluid that is under pressure (hydraulics). A hydraulic hammer is a modern type of piling hammer used in place of diesel and air hammers for driving steel pipe, precast concrete, and timber piles.
acoustics in water
of, relating to, or operated by the force of liquid in motion
a vessel that is lifted partially above the water by wing-like structures mounted on struts below the hull of a boat.
an underwater microphone that will listen to, or pick up, acoustic signals. A hydrophone converts acoustic energy into electrical energy and is used in passive underwater systems to listen only.
hydrophone array
several hydrophones attached to each other at known fixed distances so the location of sound sources can be calculated
hydrostatic pressure
The pressure at a point in a fluid at rest due to the weight of the fluid above it.
relating to hot water circulation in the ocean crust.
hydrothermal vent
a hot spring on the seafloor
a condition where the body produces or absorbs more heat than it can dissipate, causing one's body temperature to become elevated to a potentially dangerous level.
A tentative explanation proposed by a scientist for observations that cannot be explained by existing scientific theories. A careful statement of a tentative or provisional conclusion to be tested.