Height above average terrain (HAAT), or (less popularly) effective height above average terrain (EHAAT), is the vertical position of an antenna site is above the surrounding landscape.
In the aerospace context, HAAT stands for "Height Above Average Terrain", it is a measure of the height of a radio antenna above the surrounding terrain. It is used to determine the coverage area and signal strength of a radio transmitter, such as those used in television and radio broadcasting, as well as in mobile communications.
The HAAT is calculated by determining the average elevation of the terrain within a specified radius around the antenna, and subtracting that value from the height of the antenna above ground level. The higher the HAAT, the greater the coverage area of the signal, and the stronger the signal will be at a given distance from the antenna.
Examples of how HAAT is used in the aerospace context:
- In television and radio broadcasting, HAAT is used to determine the coverage area of a transmitter and to ensure that the signal can be received over a wide area.
- In mobile communications, HAAT is used to determine the coverage area of a cellular tower, and to ensure that the signal can be received by mobile devices over a wide area.
- In air navigation, HAAT is used to determine the coverage area of an air navigation aid and to ensure that the signal can be received by aircraft over a wide area.
- In satellite communications, HAAT is used to determine the coverage area of a satellite and to ensure that the signal can be received by ground stations over a wide area.
HAAT is an important factor to consider when designing and operating radio communications systems, as it can affect the signal strength, coverage area, and overall effectiveness of the system.