processing said echo signals to determine {HEAD ~ the distance} from {TAIL ~ said transducer} to said surface, 
from
processing said echo signals to determine { HEAD ~ the distance } from { TAIL ~ said transducer } to said surface ,
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH