Outdoor Glossary: I
igneous rock Rocks formed when high temperature, molten mineral
matter cooled and solidified.
impermeable groin A groins through which sand can not pass.
incident wave Wave moving landward.
incident wave Wave moving landward.
incremental shaft encoder A component of a tide gauge for
converting length to a shaft angle on a rotating disk. The position of the
rotating disk is determined by single or dual optical or magnetic sensors to
provide an electrical output. No electro-mechanical components or gears are
used, so extremely low torque is required to move the float wheel, wire, and
float mechanism.
incremental shaft encoder A component of a tide gauge for
converting length to a shaft angle on a rotating disk. The position of the
rotating disk is determined by single or dual optical or magnetic sensors to
provide an electrical output. No electro-mechanical components or gears are
used, so extremely low torque is required to move the float wheel, wire, and
float mechanism.
Indian spring low water A datum originated by Professor G. H.
Darwin when investigating the tides of India. It is an elevation depressed below
mean sea level by an amount equal to the sum of the amplitudes of he harmonic
constituents M2, S2, K1, and O1. Indian tide plane: Same as Indian spring low
water.
Indian spring low water A datum originated by Professor G. H.
Darwin when investigating the tides of India. It is an elevation depressed below
mean sea level by an amount equal to the sum of the amplitudes of he harmonic
constituents M2, S2, K1, and O1. Indian tide plane: Same as Indian spring low
water.
Indian tide plane Same as Indian spring low water.
Indian tide plane Same as Indian spring low water.
indicator species A plant or animal species related to a particular
kind of environment. Its presence indicates that specific habitat conditions are
also present.
indigenous (species) Any species of wildlife native to a given land
or water area by natural occurrence.
individual tree selection The removal of individual trees from
certain size and age classes over an entire stand area. Regeneration is mainly
natural, and an uneven aged stand is maintained.
inequality A systematic departure from the mean value of a tidal
quantity. See diurnal inequality, parallax inequality, and phase inequality.
inequality A systematic departure from the mean value of a tidal
quantity. See diurnal inequality, parallax inequality, and phase inequality.
inertial flow A solution of the relative hydrodynamic equations of
motion in which only the horizontal component of the Coriolis and centrifugal
forces are balanced. This anticyclonic flow results from a sudden application
and release of a driving force which then allows the system to continue on under
its own momentum without further interference.
inertial flow A solution of the relative hydrodynamic equations of
motion in which only the horizontal component of the Coriolis and centrifugal
forces are balanced. This anticyclonic flow results from a sudden application
and release of a driving force which then allows the system to continue on under
its own momentum without further interference.
infragravity waves Waves with periods above about 30 seconds
generated by wave groups breaking in the surf zone. See LONG WAVES.
inlet (1) A narrow strip of water running into the land or between
islands. (2) An arm of the sea (or other body of water) that is long compared to
its width, and that may extend a considerable distance inland.
inlet gorge Generally, the deepest region of an inlet.
inner primaries Group of primaries closest to the body.
inner secondaries Group of secondaries closest to the body.
inner wing Shoulder, secondaries and secondary coverts.
inshore (1) The region where waves are transformed by interaction
with the sea bed. (2) In beach terminology, the zone of variable width extending
from the LOW WATER LINE through the BREAKER ZONE.
inshore current Any current inside the surf zone.
instream flow The quantity of water necessary to meet seasonal
stream flow requirements to accomplish the purposes of the National Forests,
including, but not limited to fisheries, visual quality, and recreational
opportunities.
integrated pest management an ecologically based pest-control
strategy that relies on natural mortality factors such as natural enemies,
weather, and crop management, and seeks to disturb these factors as little as
possible. IPM evaluates alternatives for managing forest pest populations, based
on consideration of pest-host relationships.
interdisciplinary team A team of individuals with skills from
different disciplines that focuses on the same task or project.
intermediate cut The removal of trees from a stand sometime between
the beginning or formation of the stand and the regeneration cut. Types of
intermediate cuts include thinning, release, and improvement cuttings.
intermittent stream A stream that flows only at certain times of
the year when it receives water from streams or from some surface source, such
as melting snow.
intermountain region The portion of the USDA Forest Service, also
referred to as Region Four, that includes National Forests in Utah, Nevada,
southern Idaho, and southwestern Wyoming.
internal tide A tidal wave propagating along a sharp density
discontinuity, such as a thermocline, or in an area of gradually changing
(vertically) density.
International Great Lakes Datum (1955) [IGLD (1955)] Mean water
level at Pointe-au-Pere, Quebec, on the Gulf of St. Lawrence over the period
1941 through 1956, from which geopotential elevations (geopotential differences)
throughout the Great Lakes region are measured. The term is often used to mean
the entire system of geopotential elevations rather than just the referenced
water level. See low water datum (1).
International Hydrographic Organization (formerly Bureau) An
institution consisting of representatives of a number of nations organized for
the purpose of coordinating the hydrographic work of the participating
governments. It had its origin in the International Hydrographic Conference in
London in 1919. It has permanent headquarters in the Principality of Monaco and
is supported by funds provided by the member nations. Its principal publications
include the Hydrographic Review and special publications on technical
subjects.
international low water A hydrographic datum originally suggested
for international use at the International Hydrographic Conference in London in
1919, and later discussed at the Monaco Conference in 1926. The proposed datum,
which has not yet been generally adopted, was to be "a plane so low that the
tide will but seldom fall below it." This datum was the subject of the
International Hydrographic Bureau's Special Publication No. 5 (March 1925) and
No. 10 (January 1926), reproduced in the Hydrographic Review for May 1925 and
July 1926.
intertidal The zone between the high and low water marks.
intertidal zone (technical definition) The zone between the mean
higher high water and mean lower low water lines
interval See lunitidal interval and lunicurrent interval.
intrinsic rate of increase (rm) the maximum rate at which a
population will grow if resources are unlimited.
inverse barometer effect The inverse response of sea level to
changes in atmospheric pressure. A static reduction of 1.005 mb in atmospheric
pressure will cause a stationary rise of 1 cm in sea level.
iris Colored part of eye.
iris Thin, contractile disc with a central opening (the pupil) in
front of the lens in vertebrate eyes
irminger Current A North Atlantic Ocean current setting westward
off the south-west coast of Iceland.
irregular waves Waves with random wave periods (and in practice,
also heights), which are typical for natural wind-induced waves.
irretrievable One of the categories of impacts mentioned in the
National Environmental Policy Act to be included in statements of environmental
impacts. An irretrievable effect applies to losses of production or commitment
of renewable natural resources. For example, while an area is used as a ski
area, some or all of the timber production there is irretrievably lost. If the
ski area closes, timber production could resume; the loss of timber production
during the time that the area was devoted to winter sports is irretrievable.
However, the loss of timber production during that time is not irreversible,
because it is possible for timber production to resume if the area is no longer
used as a ski area.
irreversible A category of impacts mentioned in statements of
environmental impacts that applies to non-renewable resources, such as minerals
and archaeological sites. Irreversible effects can also refer to effects of
actions that can be renewed only after a very long period of time, such as the
loss of soil productivity.
isanostere An isopleth of either specific volume anomaly or
thermosteric anomaly.
isobar An isopleth of pressure.
isobaric surface A surface of constant or uniform pressure.
isobath Line connecting points of equal water debth on a chart; a
seabed contour.
isohaline An isopleth of salinity. Constant or uniform in salinity.
isopleth A line of constant or uniform value of a given quantity.
See isanostere, isobar, isohaline, isopycnic, and isotherm.
isopycnic An isopleth of density. Constant or uniform in density.
isostasy The tendency of the Earths crust to maintain a state of
near equilibrium, i.e., if anything occurs to modify the existing state, a
compensation change will occur to maintain a balance. Isotope: An atom with a
specified number of protons and a specified number of neutrons.
isotherm An isopleth of temperature.
|