Altimeter

altimetrybarometric altimeterpressure altimeterbarometric sensoraltimeter pressuresaltimeter settingaltimetricAltitude driftaltitude sensorsBarometric altimeters
An altimeter or an altitude meter is an instrument used to measure the altitude of an object above a fixed level.wikipedia
303 Related Articles

Altitude

high altitudealtitudeshigh-altitude
An altimeter or an altitude meter is an instrument used to measure the altitude of an object above a fixed level.
On the flight deck, the definitive instrument for measuring altitude is the pressure altimeter, which is an aneroid barometer with a front face indicating distance (feet or metres) instead of atmospheric pressure.

Barometer

barometricaneroid barometerbarometers
When a barometer is supplied with a nonlinear calibration so as to indicate altitude, the instrument is called a pressure altimeter or barometric altimeter.
Barometers and pressure altimeters (the most basic and common type of altimeter) are essentially the same instrument, but used for different purposes.

Reference atmospheric model

atmospheric modelsstatic atmospheric modelglobal atmospheric models
The aneroid altimeter is calibrated to show the pressure directly as an altitude above mean sea level, in accordance with a mathematical model atmosphere defined by the International Standard Atmosphere (ISA).
Typical usages are as a basis for pressure altimeter calibrations, aircraft performance calculations, aircraft and rocket design, ballistic tables, and meteorological diagrams."

Inch of mercury

inHginches of mercuryinches
Air pressure decreases with an increase of altitude—approximately 100 hectopascals per 800 meters or one inch of mercury per 1000 feet near sea level. The reference pressure, in inches of mercury in Canada and the United States, and hectopascals (previously millibars) elsewhere, is displayed in the small Kollsman window, on the face of the aircraft altimeter.
Aircraft altimeters measure the relative pressure difference between the lower ambient pressure at altitude and a calibrated reading on the ground.

Altimeter setting

altimeter is set
In aviation terminology, the regional or local air pressure at mean sea level (MSL) is called the QNH or "altimeter setting", and the pressure that will calibrate the altimeter to show the height above ground at a given airfield is called the QFE of the field.
Altimeter setting is the value of the atmospheric pressure used to adjust the sub-scale of a pressure altimeter so that it indicates the height of an aircraft above a known reference surface.

Radar altimeter

radio altimeterradar altimetryelectronic altimeter
A radar altimeter measures altitude more directly, using the time taken for a radio signal to reflect from the surface back to the aircraft.
This type of altimeter provides the distance between the antenna and the ground directly below it, in contrast to a barometric altimeter which provides the distance above a defined datum, usually mean sea level.

Flight level

FLtransition altitudetransition level
This module measures altitude, speed of flight and outside temperature to provide more precise output data allowing automatic flight control and flight level division.
Historically, altitude has been measured using a pressure altimeter, which is essentially a calibrated barometer.

Fixed-wing aircraft

fixed-wingaircraftfixed wing
Audible altimeters (also known as "dytters", a genericised trademark of the first such product on the market). These are inserted into one's helmet, and emit a warning tone at a predefined altitude. Contemporary audibles have evolved significantly from their crude beginnings, and sport a vast array of functions, such as multiple tones at different altitudes, multiple saved profiles that can be switched quickly, electronic logbook with data transfer to a PC for later analysis, distinct free fall and canopy modes with different warning altitudes, swoop approach guiding tones, etc. Audibles are strictly auxiliary devices, and do not replace, but complement a visual altimeter which remains the primary tool for maintaining altitude awareness. The advent of modern skydiving disciplines such as freeflying, in which the ground might not be in one's field of view for long periods of time, has made the use of audibles nearly universal, and virtually all skydiving helmets come with one or more built-in ports in which an audible might be placed. Audibles are not recommended and often banned from use by student skydivers, who need to build up a proper altitude awareness regime for themselves.
3) The altimeter indicates the altitude or height of the plane above mean sea level (AMSL).

Sea level

mean sea levelMSLAMSL
The aneroid altimeter is calibrated to show the pressure directly as an altitude above mean sea level, in accordance with a mathematical model atmosphere defined by the International Standard Atmosphere (ISA). Air pressure decreases with an increase of altitude—approximately 100 hectopascals per 800 meters or one inch of mercury per 1000 feet near sea level.
Pilots can estimate height above sea level with an altimeter set to a defined barometric pressure.

Acronyms and abbreviations in avionics

Acronyms and abbreviations in avionics
ALT: Either; altimeter or altitude

Ocean Surface Topography Mission

Jason-2JasonJason-2 (Ocean Surface Topography Mission)
Jason-1 and Ocean Surface Topography Mission (Jason-2) are satellite missions that use altimeters to measure sea surface height
Like its two predecessors, OSTM/Jason-2 uses high-precision ocean altimetry to measure the distance between the satellite and the ocean surface to within a few centimeters.

Paul Kollsman

Kollsman
The reference pressure, in inches of mercury in Canada and the United States, and hectopascals (previously millibars) elsewhere, is displayed in the small Kollsman window, on the face of the aircraft altimeter.
The altimeter setting window of the sensitive aircraft altimeter is named the "Kollsman window" after him.

Jason-1

Jason-1 mission
Jason-1 and Ocean Surface Topography Mission (Jason-2) are satellite missions that use altimeters to measure sea surface height
As did TOPEX/Poseidon, Jason-1 uses an altimeter to measure the hills and valleys of the ocean's surface.

Ground-effect vehicle

ekranoplanground effect vehicleground effect
After extensive research and experimentation, it has been shown that "phase radio-altimeters" are most suitable for ground effect vehicles, as compared to laser, isotropic or ultrasonic altimeters.
After extensive research and experimentation, it has been shown that "phase radio altimeters" are most suitable for such applications as compared to laser altimeter, isotropic or ultrasonic altimeters.

United Airlines Flight 389

Flight 389389
United Airlines Flight 389, an accident attributed to misreading of an altimeter
However, it was believed that the crash was most likely the result of the pilots misreading their three-pointer (3p) altimeters by 10,000 feet.

Satellite geodesy

satellite altimetrygeodeticAltimetry
Satellite geodesy
It is the most accurate technique currently available to determine the geocentric position of an Earth satellite, allowing for the precise calibration of radar altimeters and separation of long-term instrumentation drift from secular changes in ocean surface topography.

Primary flight display

PFDprimary flightprimary flight display (PFD)
Primary flight display
As in the PFD's attitude indicator, these systems are merely displayed data from the underlying mechanical systems, and do not contain any mechanical parts (unlike an aircraft's airspeed indicator and altimeter).

Flight instruments

flight instrumentinstrumentinstruments
Flight instruments
altimeter (feet)

Pressure sensor

pressure transducerpressure sensorspressure
Pressure sensor
This equation is calibrated for an altimeter, up to 36,090 feet (11,000 m). Outside that range, an error will be introduced which can be calculated differently for each different pressure sensor.

Bathymetry

bathymetricisobathbathymetric survey
The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth under water.

Atmospheric pressure

barometric pressureair pressurepressure
In aviation terminology, the regional or local air pressure at mean sea level (MSL) is called the QNH or "altimeter setting", and the pressure that will calibrate the altimeter to show the height above ground at a given airfield is called the QFE of the field. Altitude can be determined based on the measurement of atmospheric pressure.

Aircraft

heavier-than-airflying machineheavier-than-air flight
A pressure altimeter is the altimeter found in most aircraft, and skydivers use wrist-mounted versions for similar purposes.

Formation skydiving

400-way400-Way World Skydiving Record51 person formation
Main goal of this type of altimeter is strong security feature for experienced skydivers, so they always know own current position that very useful for FS load organizers or AFF instructors as well.

Accelerated freefall

AFFAccelerated freefall (AFF)tandem freefall
Main goal of this type of altimeter is strong security feature for experienced skydivers, so they always know own current position that very useful for FS load organizers or AFF instructors as well.

Freeflying

freeflyvertical freefly
Audible altimeters (also known as "dytters", a genericised trademark of the first such product on the market). These are inserted into one's helmet, and emit a warning tone at a predefined altitude. Contemporary audibles have evolved significantly from their crude beginnings, and sport a vast array of functions, such as multiple tones at different altitudes, multiple saved profiles that can be switched quickly, electronic logbook with data transfer to a PC for later analysis, distinct free fall and canopy modes with different warning altitudes, swoop approach guiding tones, etc. Audibles are strictly auxiliary devices, and do not replace, but complement a visual altimeter which remains the primary tool for maintaining altitude awareness. The advent of modern skydiving disciplines such as freeflying, in which the ground might not be in one's field of view for long periods of time, has made the use of audibles nearly universal, and virtually all skydiving helmets come with one or more built-in ports in which an audible might be placed. Audibles are not recommended and often banned from use by student skydivers, who need to build up a proper altitude awareness regime for themselves.