sentences:  During the 1960s, Spiess and his engineers at the Marine Physical Laboratory of Scripps developed the deep-tow instrument for mapping the deep sea floor from an altitude of tens of meters.The deep-tow instrument used a narrow-beam downward-looking echosounder, side-looking sonars, and subbottom profiling system to map features in unprecedented detail, e.g., geologic observations that approached that of outcrop mapping for land geologists.Evolution of the deep-tow to improve sea-floor mapping saw the addition of a magnetometer, cameras, video, water samplers, plankton nets, and other instruments as more varied seafloor environments were examined.