A modulated laser beam is scanned across the object to create {TAIL ~ a plurality} of spots which are viewed by {HEAD ~ a pair} of well matched receivers 
A modulated laser beam is scanned across the object to create { TAIL ~ a plurality } of spots which are viewed by { HEAD ~ a pair } of well matched receivers
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH