Coba jelasin Rujukan dari Pemeruman gema dalam bahasa melayu dong

"How Echoes Tell Depth of Water Under Ship" Popular Mechanics Monthly, July 1930 - drawing of details of early depth finders using echoes

ELAC (1982) An Introduction to Echosounding. Honeywell-ELAC-Nautik GmbH, Kiel, 88 pp, (pdf 27.5 MB)