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