altitudesensing

Altitudesensing is the measurement of an object's height relative to a reference surface, typically mean sea level or the terrain beneath. It is used in aviation, unmanned systems, surveying, and robotics to determine vertical position and support navigation, flight control, and terrain awareness.

The main sensing modalities are barometric pressure sensing, GNSS-based altitude, radar or radio altimetry, and laser altimetry (LIDAR). In some contexts, underwater altitude is measured with acoustic depth sensors, but this article focuses on terrestrial and aerial applications.

Barometric altitude derives from ambient pressure measured by a barometer. Using a standard atmosphere model, pressure is converted to altitude, and calibration to local surface pressure (and sometimes temperature) is required. Barometric sensors are compact and inexpensive but drift with weather changes and sensor aging.

GNSS altitude estimates height relative to a reference ellipsoid. Vertical accuracy is affected by atmospheric delays, satellite geometry, multi-path, and obstructions. Consumer devices often report AMSL heights with vertical errors of several meters; accuracy improves with augmentation and processing.

Radar altimeters measure height above terrain by emitting signals and measuring round-trip travel time; they provide direct height during low-altitude flight and for obstacle detection. Laser altimeters offer higher resolution distance measurements and are common in drones and mapping, though they require clear line-of-sight and can be affected by surface reflectivity.

Data fusion integrates multiple sensors to improve robustness. Common references include AMSL and AGL. Filtering approaches such as Kalman filters reduce noise and compensate drift.

Applications include aviation, robotics, surveying, and meteorology. Limitations vary by method: weather and temperature effects for barometers, line-of-sight and reflectivity for LIDAR, GNSS vulnerability to obstructions and atmospheric delays, and calibration needs for all systems.