How is Absolute Altitude defined?

Absolute altitude is defined as the height of an object, such as an aircraft, above the terrain directly below it. This measurement is often referred to as the height above ground level (AGL). It is an important concept in aviation and drone operations because it provides information about how high above the ground the aircraft is flying. For example, if a drone is navigating over varying terrain, its absolute altitude will change depending on the elevation of the ground beneath it.

The other options do not accurately define absolute altitude. Height above mean sea level refers to altitudinal measurements relative to sea level rather than the ground directly below, while the altitude at which an aircraft is detected by radar relates to its position in the atmosphere without a direct context to ground level. Similarly, the cruising altitude of an aircraft does not provide a specific measure of how high the aircraft is from the ground, as it can vary widely based on the aircraft's flight path and surrounding topography.