An Interferometric Goniometer for Sextant and Other Precision Applications

George G. Barton

Abstract:	A method for the application of a Ilichelson Interferometer and Laser illuminator to the precise measurement of angles. A secondary aspect of this technique is the direct measurment of sextant altitude angles in lieu of the reflective angle doubling effect as is commonly employed. To convert angular to linear displacement as required by the interferometer employs a drum (circular) and Invar tape (linear> drive. To determine the null position of the interferometer incorporates a white light source and two peripheral field photo-detectors. A He-Ne Laser illuminator produces a" accuracy of 0.2278’ of arc for a 1 cm. interferometer beam length change over a 120 deg. arc swing. Increasing the drum diameter to produce a movment of 2.278 cm.(0.897 inches) for the 120 degree arc i “creases the digital accuracy to 0.1' of arc. Incorporating additional analog techniques to determine the phase angle of the fringe can readily extend the accuracy to the sub-second range. Rearranging the sextant index and horizon mirrors along a horizontal axis instead of the vertical axis allows direct angle measurement instead of the half-angle measurment presently employed. With this horizontal configuration the field of view is not constricted at large elevation angles as is normally experienced.
Published in:	Proceedings of the 46th Annual Meeting of The Institute of Navigation (1990) June 26 - 28, 1990 Atlantic City, NJ
Pages:	99 - 103
Cite this article:	Barton, George G., "An Interferometric Goniometer for Sextant and Other Precision Applications," Proceedings of the 46th Annual Meeting of The Institute of Navigation (1990), Atlantic City, NJ, June 1990, pp. 99-103.
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