receiving {HEAD ~ echo signals} arising from said pulses being reflected from {TAIL ~ said surface}; and 
receiving { HEAD ~ echo signals } arising from said pulses being reflected from { TAIL ~ said surface } ; and
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH