A new high-frequency (3.5-kHz) sub-bottom profiling system is capable of relatively deep penetration into sedimentary deposits, with good resolution of thin reflecting layers. This system has been operated at cruising speeds up to 11 knots and gives up to 0.15 seconds of penetration....
Moore, T. C., and L. D. Kulm. 1970. "A high-resolution sub-bottom profiling system for use in ocean basin." Journal of Marine Research 28, (2). https://elischolar.library.yale.edu/journal_of_marine_research/1187