Holy cow, what detail --even down to rivulets coming off the highlands.
High pressured air is released from metal cylinders, producing sound waves that travel to the ocean floor and beneath it, through layers of sediment. (quote op. cit)
Interesting technique. I thought most geo-echo-exploration was done with conventional explosives. (I assume they let the air out suddenly to generate shock waves... or did they let it scream out of the containers and get echoes from that?)