Above ground level

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In aviation, Above Ground Level (AGL) denotes that a given altitude is measured above the ground, rather than above sea level (ASL). It is important for aviators to differentiate between AGL and an altitude given ASL as the two could be very different in mountainous terrain. Over the ocean, altitude AGL and ASL will be identical.

This acronym is also used in Radio and Telecommunications to indicate antenna height above ground level.