Height above ground level
In aviation, atmospheric sciences and broadcasting, a height above ground level (AGL or HAGL) is a height measured with respect to the underlying ground surface. This is as opposed to height above mean sea level (AMSL or HAMSL), height above ellipsoid (HAE, as reported by a GPS receiver), or height above average terrain (AAT or HAAT, in broadcast engineering). In other words, these expressions (AGL, AMSL, HAE, AAT) indicate where the "zero level" or "reference altitude" – the vertical datum – is located.
| Abbreviation | Stands for | Main usage | Zero level | Measuring devices |
|---|---|---|---|---|
| AGL, HAGL | height above ground level | aviation, atmospheric science, broadcasting | ground surface | radar altimeter |
| AMSL, HAMSL | height above mean sea level | nautic, technics, geography | sea level average | barometric altimeter |
| HAE | height above ellipsoid | navigation, science | math surface model WGS84 | GPS receiver |
| AAT, HAAT | height above average terrain | broadcasting, cellular networks | average surrounding surface |
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