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HAAT is used extensively in radio, as it is actually much more important than power. For international coordination, it is officially measured in meters, even by the FCC in the USA. Stations that want to increase above a certain HAAT must reduce their power accordingly, based on the maximum distance their station class is allowed to cover.
Before metrification at the FCC, the procedure to figure HAAT was relatively simple: from the proposed or actual antenna site, either 12 or 16 radials were drawn, and points at 2, 4, 6, 8, and 10 miles radius along each radial were used. The entire radial graph could be rotated to achieve the best effect for the station. The average altitude of all the specified points, minus the altitude of the antenna site, was the HAAT.
Contour data with 120 radials spaced 3 degrees apart can be downloaded from the FCC Mass Media Contour webpage (http://ftp.fcc.gov/oet/info/maps/mmb/).
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