A Comparison of Precision Alignment Methods

Abstract

The following four methods of precision alignment surveys have been compared on a 816-m test line: 1) conventional optical alignment with a DKM-3 telescope and movable targets, 2) conventional traversing with forced centering using a closed (loop) traverse, fitted traverse and a narrow triangles method, 3) direct alignment with a collimated He-Ne laser and photoelectric targets, 4) diffraction method employing Fresnel zone gratings, He-Ne laser and photoelectric or visual centerings. Fourteen alignments of points B and C (Figure 1) on the line A-D were performed in different atmospheric conditions. Measurements of horizontal gradients of temperature indicated that discrepancies of up to 8 mm in the alignment could be expected because of the side refraction effects. Results of the alignments are listed in Tables 1 and 3. Laser alignments were performed with prototypes of instruments (Figures 5, 6, 8 and 10) that had been designed and constructed at the University of New Brunswick.