E


ECEF coordinates

Earth Centered Earth Fixed rectangular coordinate system (Cartesian coordinates), where the positive X axis lies on the
equatorial plane passing through the prime meridian (Greenwich), the positive Y axis lies on the equatorial plane at 90 east, and positive Z passes north through the mean rotational axis of the earth

Electromagnetic Spectrum

The continuous distribution of energy in the form of electromagnetic waves, which are arranged in order of their frequencies or
wavelengths

Elevation

The vertical distance of a point above or below a reference surface, such as sea level

Ellipsoid

Spheroid. The mathematical function used to describe the shape of the earth for geodetic computations



Ellipsoid height

The distance from a point to the reference ellipsoid along a line normal to the ellipsoid

En Route

Navigation between the point of departure and point of arrival

EPE

Estimated Position Error. How much the unit thinks it is off target

Ephemeris

A description of the path of a celestial body indexed by time. The navigation message from each GPS satellite includes a
predicted ephemeris for the orbit of that satellite valid for the current hour. The ephemeris is repeated every 30 seconds

Ephemeris Errors

Errors which originate in the ephemeris data transmitted by a GPS satellite. Ephemeris errors are removed by differential
correction

Epoch

A specific instant in time. GPS carrier phase measurements are made at a given frequency (e.g. every 30 seconds) or epoch rate

Equator

Zero degrees Latitude. A line around the center of earth 24,901.55 miles (40,075.16 kilometers) long.

Error Budget

A set of individual error sources with statements of the percentage of the total system error contributed by each source

Error ellipse

A statistical measure of the positional error at a given point computed from the propagation of all errors contributing to the
position

Estimated Time Enroute (ETE)

The time left to your destination at your present speed

Estimated Time of Arrival (ETA)

The time of day of your arrival at your destination

ETA

Estimated Time of Arrival. The time of day of your arrival at your destination

ETE

Estimated Time Enroute. The time left to your destination at your present speed

F


Fast switching channel

A single channel which rapidly samples a number of satellite ranges. Switching time is sufficiently fast (2 to 5 milliseconds) to
recover the data message

FGDC

The Federal Geographic Data Committee (FGDC) is an interagency committee, organized in 1990 under OMB Circular A16 that promotes
the coordinated use, sharing, and dissemination of geospatial data on a national basis

Fix

A position that is determined by the navigation unit (consisting of latitude, longitude (or grid position), altitude, time, and
date)

FM

Frequency Modulation. A method of encoding information about a carrier signal by altering the frequency while amplitude remains
constant

Frequency

The number of waves passing a specific point within a unit period of time, expressed in Hertz (cycles per second)

Frequency band

A particular range of frequencies

Frequency Modulation (FM)

A method of encoding information about a carrier signal by altering the frequency while amplitude remains constant

Frequency spectrum

The distribution of signal amplitudes as a function of frequency
