The line of sight distance between two points not at the same elevation (normally a determined range from a radar set and the aircraft detection range). The line-of-sight distance between two points in space.
The distance from an explosion to an observer is called the slant range. For a burst height, h, and a distance, d, from ground zero to a given point, the slant range, D, is from the Pythagorean theorem.
In telecommunication, slant range is the line-of-sight distance between two points, not at the same level relative to a specific datum. An example of slant range is the distance to an airborne radar target, e.g., an aircraft flying at high altitude with respect to that of the radar antenna. The slant range is the hypotenuse of the triangle represented by the altitude of the aircraft and the distance between the radar antenna and the aircraft's ground track (the point on the Earth at which it is directly overhead).