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