Patent US 4,100,481

In the exploration for hydrocarbon gas, microwave energy is radiated from an antenna transported along a traverse above the surface of the earth. Microwave energy re-radiated from gas seeps is detected. Microwave energy reflected from hard targets along the traverse is also detected. Video monitors simultaneously display the detected re-radiated and reflected microwave energy. In this way, hydrocarbon gas seeps are displayed in relation to topographical features along the traverse.