altimetr

Altimetr, typically referred to in English as an altimeter, is an instrument that measures altitude, or height above a reference level. It is used in aviation, mountaineering, and various consumer devices to determine vertical position.

There are several types of altimeters. Barometric or pressure-based altimeters estimate altitude from ambient air pressure, converting pressure readings into height using a standard atmosphere model. Mechanical aneroid versions use sealed, flexible diaphragms that compress with changing pressure, while electronic models rely on sensors and a microprocessor. Radio or radar altimeters determine altitude by measuring the time delay or reflected signals from a ground surface, and laser or lidar altimeters use light pulses for precise elevation measurements, often employed in surveying, spacecraft, and some drones. Global positioning system (GPS) receivers can provide altitude data by trilateration, though GPS altitude can be less precise than horizontal positioning in some conditions.

Operation of a barometric altimeter requires calibration to a reference pressure, commonly called QNH (sea level pressure adjusted to local conditions) or QFE (pressure at the reference airfield). Temperature and weather changes affect the accuracy, so pilots routinely set and cross-check readings with other instruments. Indicated altitude refers to the device’s height above the reference level, while true altitude accounts for atmospheric conditions and terrain.

Applications include flight navigation, pressure-altitude measurements for airspace rules, aviation safety, and terrain mapping. In consumer electronics, altimetry supports fitness tracking, adventure sports, and autonomous navigation. Potential limitations involve pressure changes, sensor lag, calibration drift, and line-of-sight or atmospheric constraints for non-barometric methods. See also barometer, GPS altitude, and radar altimeter.