groundrange

Groundrange, often written as ground range or groundrange, is a distance concept defined as the distance along the Earth’s surface between a reference point (such as a launch site, radar, or observation location) and a target or point of interest. It contrasts with slant range, which is the straight-line distance through space or air to the target. The exact interpretation of groundrange can vary by field, but it typically refers to a surface distance rather than a line-of-sight distance.

In ballistics, groundrange denotes the horizontal distance traveled on the ground from the firing point to the point of impact. In simple, flat-earth models, the horizontal range of a projectile with initial speed v and launch angle θ is given by R = v^2 sin(2θ)/g, neglecting air resistance and curvature. More accurate calculations incorporate air drag and Earth’s curvature, but the general idea remains: groundrange is the projection of the trajectory onto the ground plane.

In geodesy and navigation, groundrange is the length of the surface arc between two geographic coordinates, representing the distance one would measure along the Earth’s surface. It is commonly computed as a great-circle distance on a sphere or an ellipsoidal model of the Earth, using methods such as the haversine formula or Vincenty’s formulas.

In radar and remote sensing, groundrange refers to the distance on the ground from the radar to the illuminated area, as opposed to slant range (the distance along the radar’s line of sight). Groundrange can be derived from slant range using geometry that accounts for the radar’s look angle and terrain.

Variations in terminology exist across disciplines, with some sources using groundrange as a single word and others as two words.