Height Above Average Terrain


Height Above Average Terrain (HAAT) is a measure used in the broadcasting industry, specifically for radio and television antennas. It indicates the elevation of an antenna in relation to the surrounding terrain’s average height. By taking into account the Earth’s curvature and obstacles, HAAT helps in estimating the coverage area and signal strength of a transmitter.


The phonetic pronunciation of the keyword “Height Above Average Terrain” is:-Height: Hayt-Above: ə-BUHV-Average: AV-rij-Terrain: tə-RAYN

Key Takeaways

  1. Height Above Average Terrain (HAAT) is a measurement used by the Federal Communications Commission (FCC) to determine the optimal height for radio and television antennas to provide maximum signal coverage, based on the average height of the surrounding terrain.
  2. HAAT is calculated by subtracting the reference height of the location (usually mean sea level) from the antenna height, taking into account the elevation profile of the terrain within a specified radius around the antenna site.
  3. A higher HAAT value is desirable for broadcasters, as it can result in increased signal coverage and improved reception for viewers and listeners. However, there may be limitations on the maximum allowable HAAT to avoid interference with nearby stations or to comply with regulatory constraints.


The technology term Height Above Average Terrain (HAAT) is important because it plays a crucial role in determining the signal strength and coverage area of a broadcast station, such as a radio or television tower.

HAAT refers to the average height of the transmitting antenna above the surrounding terrain, which influences the signal’s reach and prevents potential disruptions caused by natural obstructions like mountains or tall buildings.

By optimizing the HAAT value, broadcasters can maximize their signal coverage while minimizing interference, allowing efficient and reliable communication to reach the intended audience.

Consequently, understanding and considering HAAT in setting up broadcast stations is essential for providing quality broadcasting services to a broader population.


Height Above Average Terrain (HAAT) serves an essential purpose in broadcasting and telecommunication industries, specifically pertaining to radio and television signal transmissions. In relation to these industries, HAAT represents the height of a transmitting antenna installed above the average terrain surrounding its location.

Accurate HAAT measurements are of paramount importance for ensuring the quality and coverage of signal transmissions. To calculate HAAT, the terrain elevation over a certain distance—usually a radius of 3 to 16 kilometers (1.9 to 10 miles) surrounding the antenna location—is averaged, and the antenna height is then determined relative to this average elevation.

The utilization of HAAT measurements aids engineers and operators in the proper design and installation of antennas and broadcasting systems. More specifically, HAAT measurements help establish optimal antenna height to reduce signal losses and improve coverage.

Furthermore, these measurements are required by regulatory bodies such as the Federal Communications Commission (FCC) in the United States to allocate frequency bands and ensure non-interference between different communication systems within that region. With an accurate HAAT measurement, broadcasters can comply with regulations and deliver high-quality signal reception to target audiences while avoiding interference with nearby communication systems.

Examples of Height Above Average Terrain

Height Above Average Terrain (HAAT) is a crucial parameter for engineers, particularly in the fields of broadcast engineering, radio planning, and aviation. Here are three real-world examples of how HAAT is used:

Radio and Television Broadcasting: In the context of broadcast engineering, HAAT is used to determine the operating range of radio and television broadcast stations. It helps the Federal Communications Commission (FCC) in the United States and other regulatory organizations worldwide to calculate the coverage area and transmission power for these stations. Higher HAAT values indicate that the transmitter is located at a higher elevation than the surrounding terrain, resulting in better coverage and signal strength for people living within the coverage area.

Wireless Communication Networks: Mobile phone carriers often utilize HAAT values to optimize their network coverage and capacity. By properly selecting the height above average terrain for a cell tower, service providers can ensure a reliable signal and maximize the efficiency of their network. This might include strategically placing the antennas at higher elevations relative to the surrounding area to avoid signal degradation due to terrain-induced interference, such as hills or forests.

Aviation and Air Navigation: In aviation, HAAT is used to calculate obstacle clearance altitude and routing for aircraft. Accurate assessment of HAAT is critical in ensuring the safe and efficient navigation of airspace around high terrain features, particularly near airports and in mountainous regions. In this context, the height above average terrain is factored into calculations for minimum descent altitude (MDA), instrument flight rules (IFR), and other navigational parameters to ensure the safety of aircraft while flying through complex and potentially hazardous landscapes.

Height Above Average Terrain FAQs

1. What is Height Above Average Terrain (HAAT)?

The Height Above Average Terrain (HAAT) is a measure that represents the elevation of a specific point, such as an antenna or a radio transmitter tower, in comparison to the average elevation of the surrounding terrain.

2. Why is HAAT important in broadcasting and telecommunications?

HAAT is a crucial factor in determining the coverage area of radio, television, and other transmission signals. A higher HAAT value often leads to a better signal coverage and reduced interference, ensuring a wider reach and improved reception quality for the audience.

3. How is HAAT calculated?

HAAT is calculated by taking the antenna height above the ground, subtracting the average terrain height in the vicinity of the antenna, and adding the Earth’s effective radius curve correction.

4. What factors can affect HAAT values?

Factors that affect HAAT values include the height of the antenna, distance to the horizon, transmitter power, and terrain features, such as hills, valleys, and buildings. These can either increase or decrease the HAAT values, having a direct impact on signal coverage and reception quality.

5. Can HAAT be negative?

Yes, HAAT can be negative in cases where the terrain surrounding the transmitting antenna is higher than the antenna itself. In such instances, the antenna is located below the average terrain height, resulting in a negative value for HAAT. Negative HAAT values can lead to poor signal coverage and potential interference issues.

Related Technology Terms

  • Elevation
  • Topographic Map
  • Radio Frequency Propagation
  • Line of Sight
  • Antenna Height

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