Experiments to study continuous subbottom reflection profiling techniques were made in Long Island Sound. The data were taken with a ship-towed source and hydrophone. The electromagnetic source was tuned to 150 cps and had a Q of about 15. The 50-ft long hydrophone was towed behind the ship on a single cable. The hydrophone consists of 28 spaced barium titanate elements inside of an oil-filled hose. The elements are tied in parallel. The source transmits a plug or coded pings. The receiver includes a shift register time delay type of matched filter. Subbottom profiles were taken to compare coded pulse-matched filter data with the simple ping system. The seismic profiles in Long Island Sound indicated a “basement” reflection to about 800-ft depth in about 50-ft water depth. In addition to the “basement” reflection, subbottom “hills” were observed. The subbottom topography changes considerably in a profile that was a few miles long.(This work was supported by the Office of Naval Research.)