Using the same transducer, both high and low frequencies are gathered simultaneously providing more information on bottom type as well as depth.  The low frequency pulse can penetrate softer (mud/silt) material to show hard bottom, while the high frequency shows the top of the softer material. "TIC is the only firm on the East Coast using tunable transducers that can frequency-match any USACE District surveys." This is useful in the dredging and marine construction fields.