Ground Range is the perpendicular distance from the ground track to a given object on the Earth'"s surface. Also defined as the range direction of a side-looking radar image as projected onto the nominally horizontal reference plane, similar to the spatial display of conventional maps. Ground range projection requires a geometric transformation from slant range to ground range; for spacecraft data, a geoid model of the Earth is used, whereas for airborne radar data, a planar approximation is sufficient. This can lead to relief or elevation displacement, foreshortening, and layover on radar images. However, if terrain elevation information is used, the effect on viewing geometry can be minimised.

https://earth.esa.int/handbooks/asar/CNTR5-5.html#eph.asar.gloss.geo:geometry