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188 | Appendix E - Glossary

ELEVATION ANGLE

The angle made by the line-of-sight range to the satellite and the horizontal plane

of the navigator antenna. Thus, the elevation angle is 90 degrees when the

satellite is overhead and 0 degrees when it first appears on the horizon. Satellites

whose maximum elevation angle is less than 5 degrees are not good candidates

for provid ing an accurate position (latitude and longitude) update.

ELIPSOID

A spheroid whose north-south axis is shorter than the east-west axis (oblate

spheroid).

ENTER

To store data in the memory of the navigator.

EPHEMERIDES (Singular: EPHEMERIS)

Tabulations of accurate data describing celestial position and health of the

satellites over a 24-hour period. The data is uploaded to the satellites every 12

hours.

ETA

Estimated Time of Arrival. Calculated on basis of the distance to the destination

and the current (or estimated) speed.

FATDMA

Fixed Access Time Division Multiple Access – Data link access protocol used by

base station transponders to allocate transmission slots on the data link. These

slots are fixed and will thus not change until the base station transponder is re-

configured.

FILTER TIME

If the GPS signals are distorted by Selective Availability (S/A) the COG and SOG

readings will be unstable, especially at low speeds. In order to smooth out the

readings you can adjust the COG/SOG filter time (CFG 1, COG SOG)

FLUX GATE COMPASS

A magnetic compass sensor without needle or card, whose two- or three-phase

sinusoidal output is a heading reference. Interfaced to the navigator via the NMEA

interface.

Frequency Modulation – The method by which a signal offsets the

frequency in order to modulate it on a data link.

FORCE HEALTHY

A feature of the navigator that permits the user to override the data flag in the

almanac that tells the navigator that the quality of the data from a satellite is

inadequate for navigation. This feature should be used only with the greatest

care.

FORCE UNHEALTHY

A feature of the navigator that permits the operator to inhibit a satellite position

update even though the quality of the data from that satellite apparently is

acceptable.

FUNCTION

A specific operational capability of the navigator.

FUNCTION KEY

A key on the front panel of the navigator that selects a specific function.

GEODETIC

Associated with the science of Geodesy, which includes the means of determining

absolute position with uni form accuracy at all points on the Earth’s surface.

GEOGRAPHIC COORDINATES

Angular displacements along parallels of latitude and meridians of longitude on an

ellipsoidal surface. Ellipsoi dal coordinates.

1 2 ... 185 186 187 188 189 190 191 192 193 194 195 ... 199 200

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