Abstract: An airborne geophysical measurement and recording system and apparatus in which radar signals are focused onto terrain below an aircraft flying in a straight line between microwave tower sites. The echo signals are detected and signals produced and recorded on a strip chart recorder indicating path profile and terrain reflectivity. In addition, atmospheric pressure, temperature and humidity data are recorded as functions of aircraft altitude, so that atmospheric refractivity gradients can be calculated, either by an on-board computer or later, and this factor taken into account during path design or performance simulation.