Measuring the depths of the oceans.

synonym: plumbing.

Roget 208: depth; deepness etc. adj.; profundity, depression etc. (concavity) 252.    hollow, pit, shaft, well, crater; gulf etc. 198; bowels of the earth, botttomless pit^†, hell.    soundings, depth of water, water, draught, submersion; plummet, sound, probe; sounding rod, sounding line; lead.    bathymetry.    [instrument to measure depth] sonar, side-looking sonar; bathometer^†.    ... show more