A math model representing the size and shape of the
earth (or a portion of it).
GEOGRAPHIC INFORMATION SYSTEM (GIS)
A computer system
or software capable of assembling, storing, manipulating and
displaying geographically referenced information (i.e., data
identified according to their location). In practical use, GIS
often refers to the computer system, software and the data
collection equipment, personnel, and actual data.
A specific orbit
around where a satellite rotates around the earth at the same
rotational speed as the earth. A satellite rotating in
geosynchronous orbit appears to remain stationary when viewed from
a point on or near the equator. It is also referred to as a
GLOBAL POSITIONING SYSTEM
A global navigation
system based on 24 or more satellites orbiting the earth at an
altitude of 12,000 statue miles and providing very precise,
worldwide positioning and navigation information 24 hours a day,
in any weather. Also called the NAVSTAR system.
The Russian Global
A route consisting
of one leg with your present position being the start of the route
and a single defined waypoint as the destination.
GREENWICH MEAN TIME
The mean solar time
for the meridian at Greenwich, England, used as a basis for
calculating time throughout most of the world. Also called
coordinated universal time.
A pattern of
regularly spaced horizontal and vertical lines forming square
zones on a map used as a reference for establishing points. Grid
examples are UTM, MGRS, and Maidenhead.
The direction in
which a vehicle is moving. For air and sea operations, this may
differ from actual COG due to winds, currents, etc.
A term used when an
orbiting GPS satellite is suitable for use.
transfer of GPS information with another device, such as a nav
plotter, autopilot, or another GPS unit.
The first time a
GPS receiver orients itself to its current location and collects
almanac data. After initialization has occurred, the receiver
remembers its location and acquires a position more quickly
because it knows which satellites to look for.
A region of the
earth's atmosphere where ionization caused by incoming solar
radiation affects the transmission of GPS radio waves. It extends
from a height of 50 kilometers (30 miles) to 400 kilometers (250
miles) above the surface.
To display and
navigate a route from end to beginning for purposes of returning
to the route's starting point.
One of the two radio frequencies transmitted by the GPS
satellites. This frequency carries the Coarse Acquisition Code
(C/A code), P-Code, and the nav message and is transmitted on a
frequency of 1575.42 MHz.
One of the two radio frequencies transmitted by the GPS
satellites. This frequency carries only the P-Code, and is
transmitted on a frequency of 1227.6 MHz.
frequencies that extend from 390 MHz to 1550 MHz. The GPS carrier
frequencies are in the L band (1227.6 MHz and 1575.42
distance north or south of the equator measured by degrees from
zero to 90. One minute of latitude equals one nautical
A portion of a
route consisting of a starting (from) waypoint and a destination
(to) waypoint. A route that is comprised of waypoints A, B, C, and
D would contain three legs. The route legs would be from A to B,
from B to C, and from C to D.
A soft, silvery,
highly reactive metallic element that is used in batteries where
weight and cold weather conditions are concerns.
LINE OF SIGHT PROPAGATION
electromagnetic wave, propagation in which the direct transmission
path from the transmitter to the receiver is unobstructed. The
need for LOS propagation is most critical at GPS
LIQUID CRYSTAL DISPLAY (LCD)
A display circuit
characterized by a liquid crystal element sandwiched between two
glass panels. Characters are produced by applying an electric
field to liquid crystal molecules and arranging them to act as
LOCAL AREA AUGMENTATION SYSTEM (LAAS)
of ground-based DGPS to support aircraft landings in a local area
(20 mile range).
The distance east
or west of the prime meridian (measured in degrees), which runs
from the north to south pole through Greenwich, England.
Loran, which stands
for LOng RAnge Navigation, is a grid of radio waves in many areas
of the globe that allows accurate position plotting. Loran
transmitting stationsaround the globe continually transmit 100
kilohertz radio signals. Special shipboard Loran receivers
interpret these signals and provide readings that correspond to a
grid overprinted on nautical charts. By comparing signals from two
different stations, the mariner uses the grid to determine the
position of the vessel.
direction of the north magnetic pole from the observer's position.
The direction a compass points.
In navigation, at
a given place and time, the horizontal angle (or difference)
between true north and magnetic north. Magnetic variation is
measured east or west of true north.
A graphic representation of a geographic
area and the features in it.
MEAN SEA LEVEL
The average level
of the ocean's surface, as measured by the level halfway between
mean high and low tide. Used as a standard in determining land
elevation or sea depths.
An error caused
when a satellite signal reaches the GPS receiver antenna by more
than one path. Usually caused by one or more paths being bounced
or reflected. The TV equivalent of multipath is
A GPS receiver that
switches at a very rapid rate between satellites being tracked.
Typically, multiplexing receivers require more time for satellite
acquisition, and are not as accurate as parallel channel
receivers. Multiplexing receivers are also more prone to lose a
satellite fix in dense woods than parallel channel GPS receivers.