Bulletin géodésique

, Volume 89, Issue 1, pp 277–291

The use of atmospheric dispersion in optical distance measurement

  • J. C. Owens
Article

Abstract

The development of lasers, new electro-optic light modulation methods, and improved electronic techniques have made possible significant improvements in the range and accuracy of optical distance measurements, thus providing not only improved geodetic tools but also useful techniques for the study of other geophysical, meteorological, and astronomical problems. One of the main limitations, at present, to the accuracy of geodetic measurements is the uncertainty in the average propagation velocity of the radiation due to inhomogeneity of the atmosphere. Accuracies of a few parts in ten million or even better now appear feasible, however, through the use of the dispersion method, in which simultaneous measurements of optical path length at two widely separated wavelengths are used to determine the average refractive index over the path and hence the true geodetic distance. The design of a new instrument based on this method, which utilizes wavelengths of6328 Å and3681 Å and3 GHz polarization modulation of the light, is summarized. Preliminary measurements over a5.3 km path with this instrument have demonstrated a sensitivity of3×10−9 in detecting changes in optical path length for either wavelength using1-second averaging, and a standard deviation of3×10−7 in corrected length. The principal remaining sources of error are summarized, as is progress in other laboratories using the dispersion method or other approaches to the problem of refractivity correction.

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Copyright information

© Bureau Central de L’Association Internationale de Géodésie 1968

Authors and Affiliations

  • J. C. Owens
    • 1
  1. 1.Institutes for Environmental ResearchEnvironmental Science Services AdministrationBoulder

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