> Ground-based surface radars can work (somehow) with just no Doppler info > you can also somehow build a 3D map or at least map surface features/masks The pro

> Ground-based surface radars can work (somehow) with just no Doppler info > you can also somehow build a 3D map or at least map surface features/masks The problem is this case was that there was nothing to reflect off of, except for a planar field of sand. You can't know how fast you're moving over a bare plane, without a feature being on that plane, that you can observe.