altimeter

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altimeter

(ăltĭm`ĭtər, ăl`tĭmē'tər), device for measuring altitude. The most common type is an aneroid barometerbarometer
, instrument for measuring atmospheric pressure. It was invented in 1643 by the Italian scientist Evangelista Torricelli, who used a column of water in a tube 34 ft (10.4 m) long.
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 calibrated to show the drop in atmospheric pressure in terms of linear elevation as an airplane, balloon, or mountain climber rises. It shows height above sea level, but not above such land features as hills, mountains, and valleys. The radio altimeter, or terrain-clearance indicator, is an absolute altimeter; it indicates the actual altitude over water or over terrain, however uneven. It operates by first sending either continuous or pulse radio signals from a transmitter in an aircraft to the earth's surface. A receiver in the aircraft then picks up the reflection of the signals from the surface. The time it takes for the signals to travel to the earth and back is converted automatically into absolute altitude that can then be read from a calibrated indicator. The radio altimeter is used in the automatic landing systems of aerospace vehicles; systems developed from radio altimeters can automatically control military aircraft flying at high speeds and low altitudes.

altimeter

[al′tim·əd·ər]
(engineering)
An instrument which determines the altitude of an object with respect to a fixed level, such as sea level; there are two common types: the aneroid altimeter and the radio altimeter.

altimeter

altimeter
Altimeter indicator dial.
altimeter
Construction of a simple altimeter.
An instrument to indicate the height of an aircraft above a predetermined datum, normally sea level. Specifically, an instrument similar to an aneroid barometer that utilizes the change of atmospheric pressure with altitude to indicate the approximate elevation above a given point or plane used as a reference. A simple pressure altimeter is an airtight metal case, the interior of which is kept at atmospheric pressure by a tube connecting it to the static tube of the ASI (airspeed indicator). Inside the instrument case, a partially evacuated aneroid capsule is secured at the center of one of its faces to a base rigidly fixed to the casing. A leaf spring prevents the collapse of the capsule. The capsule expands as aircraft gains height. The expansion of the capsule is converted into height through a system of gears. A pressure altimeter suffers from barometric, temperature, instrument, and lag errors. Radio or radar altimeters indicate heights above ground level.

altimeter

an instrument that indicates height above sea level, esp one based on an aneroid barometer and fitted to an aircraft
References in periodicals archive ?
For all other test points and in all sessions considered the value of the altimetric precision is better than 0.
At values of the FM period equal or less than the critical value, the comparator switches on the GW mode, In the CW mode, the comparator compares the current value of the altimetric beat frequency [f.
They found that the wave drag dissipated a substantial fraction of the wind energy input, significantly reduced both kinetic energy and stratification near the bottom, and reduced the model sea surface height variance and geostrophic surface kinetic energy by measurable amounts of ~20%, while the performance of the model relative to in situ and altimetric measurements of eddy kinetic energy was not negatively impacted.
and can be obtained by the time and location information in the altimetric data (Hwang& Parsons, 1995; Sandwell & Smith, 1997).
Intensive activity of the space geodesy community in developing global models of ocean tides started in the 1990s in connection with new altimetric missions, especially with TOPEX/Poseidon.
Thanks to altimetric data from the Lunar Reconnaissance Orbiter (LRO), it's now possible to measure these slopes much more accurately.
An assessment of the altimetric information derived from spaceborne SAR (RADARSAT-1, SRTM3) and optical (ASTER) data for cartographic application in the Amazon region.
Best use of different altimetric determination techniques, in The importance of Heights PROCEEDINGS Geodesy and Surveying in the future, March 15-17, 1999.
Specially designed tide gauges are necessary to improve the quality of altimetric data, preferably near the satellite track.
The recent launching of civil radar systems such as ERS and RADARSAT has led to the rapid development of techniques for extracting altimetric data on the basis of data from synthetic aperture radar.