LASER FOR LONG DISTANCE ALIGNMENT

THE LASER HAS PROGRESSED FROM A LABORATORY INSTRUMENT TO A WORKING TOOL CAPABLE OF USE IN A HOSTILE ATMOSPHERIC ENVIRONMENT; CONSEQUENTLY, VARIOUS OPTICAL TECHNIQUES OF ALIGNMENT NOW BECOME POSSIBLE OVER RANGES MUCH LONGER THAN WAS FORMERLY THE CASE. HOWEVER, ACCURACY OF PERFORMANCE MUST BE INCREASINGLY INFLUENCED BY THE ATMOSPHERE AS THE RANGE INCREASES, AND THIS PAPER DESCRIBES WORK DIRECTED AT ESTABLISHING THE EXTENT TO WHICH THE UNDESIRABLE BUT INEVITABLE EFFECTS OF ATMOSPHERIC REFRACTION MAY BE COMPENSATED FOR IN PRECISION ALIGNMENT WORK OVER RANGES OF THE ORDER OF 1 KM. ALIGNMENT TECHNIQUES ARE CONSIDERED, BUT NONE USES THE LASER BEAM TO DEFINE A REFERENCE AXIS BOTH FOR POSITION AND DIRECTION. THE PREFERRED ARRANGEMENT IS ONE IN WHICH THE LASER IS USED IN ASSOCIATION WITH AN OPTICAL DEVICE PLACED SOME WAY DOWN THE RANGE TO DEFINE THE REQUIRED AXIS. CONSIDERABLE ATTENTION HAS BNEEN PAID TO THE MEASUREMENT OF TEMPERATURE LAPSE RATE, AND THE DERIVATION OF CORRECTIONS TO COMPENSATE FOR THE EFFECT OF THE REFRACTIVE INDEX GRADIENT THUS CAUSED. GENERAL RECOMMENDATIONS ARE MADE CONCERNING WEATHER CONDITIONS BEST SUITED TO THIS FORM OF MEASUREMENT. IT IS CONCLUDED THAT, IF THE PRECAUTIONS RECOMMENDED ARE ADHERED TO, AN ALIGNMENT ACCURACY IN THE VERTICAL DIRECTION OF PLUS OR MINUS 1 MM IS REALIZABLE ON A RANGE OF 1 KM AND AT A HEIGHT OF 2M, THERE BREING SOME DEGRADATION AT A HEIGHT OF 1.3M; IT IS A REASONABLE SUPPOSITION THAT EVEN BETTER ACCURACIES COULD BE ACHIEVED ON SMALLER RANGES WHEN THE CIRCUMSTANCES ARE BROADLY THE SAME AS THOSE PREVAILING AT THE TWO EXPERIMENTAL SITES. THE STATIC AND DYNAMIC DEFLEXION OF STRUCTURES, PARTICULARLY BRIDGES, MAY BE REGARDED AS A CHANGE IN ALIGNMENT TO WHICH THIS MEASURING TECHNIQUE MAY BE APPLIED. /TRRL/

Media Info

  • Features: Figures; Photos; References; Tables;
  • Pagination: p. 1-24
  • Serial:
    • Volume: 52 N

Subject/Index Terms

Filing Info

  • Accession Number: 00203062
  • Record Type: Publication
  • Files: TRIS
  • Created Date: May 15 1974 12:00AM