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  • Print publication year: 2012
  • Online publication date: December 2012

9 - The Earth's atmosphere: refraction, turbulence, delays, and limitations to astrometric precision

from Part III - Observing through the atmosphere



The Earth's atmosphere imposes several limitations on our ability to perform astrometric measurements from the ground in both the optical and radio regions of the spectrum. First, we are limited to wavelengths where the absorption is not too great, i.e. the broad optical region from the ultraviolet to the near-infrared, scattered regions in the infrared and broad regions at radio wavelengths. The fundamental limitations imposed by the atmosphere are different in the optical and radio and in this chapter we will deal with those important for the optical; the radio part is largely dealt with in Chapter 12 on radio interferometry, except for a summary given here on the precision limitations imposed by the atmosphere. The second problem created by observing through the atmosphere is refraction of the light waves as they pass through different levels of the atmosphere. If it were only refraction through a stable medium, the problem would be very simple; however, the atmosphere is a turbulent medium that causes variations in the amount of refraction both spatially and temporally and it therefore limits the precision and accuracy of our observations. In this chapter we will deal with both effects using the developments in Schroeder (1987, 2000) as the basic reference.

Refraction through a plane-parallel atmosphere

When we are dealing with relative positions in fields of view less than several degrees, it is sufficient to adopt a plane-parallel atmosphere for the model. In cases where we need to consider the total displacement, such as with meridian circles, it is necessary to adopt atmospheric models that are substantially more complicated, such as those developed by Garfinkel (1967) and Auer and Standish (2000). For the purposes of this chapter we can safely use the plane-parallel atmosphere.

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Astronomical Almanac for the year 1990, London: Her Majesty's Stationary Office, p. B62.
Auer, L. H. and Standish, E. M. (2000). Astronomical refraction: computational method for all zenith angles. AJ, 119, 2472.
Bessell, M. (1990). UBVRI passbands. PASP, 102, 1181.
Blandford, R. D. and Konigl, A. (1979). Relativistic jets as compact radio sources. ApJ, 232, 34.
Cameron, P. B., Britton, M. C., and Kulkarni, S. R. (2009). Precision astrometry with adaptive optics. AJ, 137, 83.
Charlot, P., Boboltz, D. A., Fey, A. L., et al. (2010). The Celestial Reference Frame at 24 and 43 GHz. II. Imaging. AJ, 139, 1713.
Cornwell, T. and Fomalont, E. (1999). Self-calibration. ASP Conf. Proc., 180, 187.
Fey, L., Gordon, D., and Jacobs, C. S., eds. (2010). The Second Realization of the International Celestial Reference Frame by Very Long Baseline Interferometry. IERS Technical Note No. 35. See:
Fomalont, E. B. and Kopeikin, S. M. (2005). The measurement of the light deflections from Jupiter: experimental results. ApJ, 598, 704.
Fomalont, E. B., Johnston, K. J., Fey, A., Boboltz, D., Oyama, T., and Honma, M. (2010). The position/structure stability of four ICRF2 sources. AJ, 141, 91.
Fritz, T., Gillessen, S., Trippe, S., et al. (2010). What is limiting near-infrared astrometry in the Galactic Center. MNRAS, 401, 1177.
Garfinkel, B. (1967). Astronomical refraction in a polytropic atmosphere. AJ, 72, 235.
Han, I. (1989). The accuracy of differential astrometry limited by the atmospheric turbulence. AJ, 97, 607.
Helminiak, K. G., Konacki, M., Kulkarni, S. R., and Eisner, J. (2009). Precision astrometry of a sample of speckle binaries and multiples with the adaptive optics facilities at the Hale and Keck II telescopes. MNRAS, 400, 406.
Hirabayashi, H., Fomalont, E. B., Horiuchi, S., et al. (2000). The VSOP 5 GHz AGN Survey I. Compilation and observations. PASJ, 52, 997.
Hoeg, E. (1968). The mean power spectrumof star image motion. Zeitschrift für Astrophysik, 69, 313.
Horch, E. P., Gomez, S. C., Sherry, W. H., et al. (2011). Observations of binary stars with the differential speckle survey instrument. II. Hipparcos stars observed in January and June 2010. AJ, 141, 45.
Jacobs, C. S., Keihm, S. J., Lanyi, G. E., et al. (2006). Improving astrometric VLBI by using water vapor radiometer calibrations. IVS 2006 General Meeting Proceedings, Concepcion, Chile, January 9–11. See
Konig, A. (1962). Astrometry with astrographs. In Astronomical Techniques, ed. W. A., Hiltner. Chicago, IL: University of Chicago Press, ch. 20.
Lindegren, L. (1978). Photoelectric astrometry – a comparison of methods for precise image location. In Modern Astrometry; Proceedings of the Colloquium. Vienna: Universitaets-Sternwarte Wien, p. 197.
Lindegren, L. (1980). Atmospheric limitations of narrow-field optical astrometry. A&A, 89, 41.
Lindegren, L. (2010). High-accuracy positioning: astrometry. ISSI Sci. Rep. Ser., 9, ch. 16.
Ma, C., Arias, E. F., Eubanks, T. M., et al. (1998). The International Celestial Reference Frame as realized by very long baseline interferometry. ApJ, 116, 516.
Moffatt, A. F. J. (1969). A theoretical investigation of focal stellar images in the photographic emulsion and application to photographic photometry. A&A, 3, 455.
Monet, D. G., Dahn, C. C., Vrba, F. J., et al. (1992). U.S. Naval Observatory CCD parallaxes of faint stars. I – Program description and first results. AJ, 103, 638.
Nikolic, B., Hills, R. E., and Richer, J. S. (2007). Limits on phase correction performance due to differences between astronomical and water-vapour radiometer beams. ALMA Memo Ser., 573.
Pickles, A. J. (1998). A stellar spectral flux library: 1150–25 000 A°. PASP, 110, 863.
Platais, I., Kozhurina-Platais, V., Girard, T. M., et al. (2002). WIYN open cluster study. VIII. The geometry and stability of the NOAO CCD mosaic imager. AJ, 124, 601.
Pravdo, S. H. and Shaklan, S. B. (1996). Astrometric detection of extrasolar planets: results of a feasibility study with the Palomar 5 meter telescope. ApJ, 465, 264.
Reid, M. J., Menten, K. M., Zheng, X.W., Brunthaler, A., and Xu, Y. (2009). A trigonometric parallax of SGR B2. ApJ, 705, 1548.
Roddier, F. (1981). The effects of atmospheric turbulence in optical astronomy. Progr. Opt., 19, ch. 5.
Rogers, A. E. E. (1970). Very long baseline interferometry with large effective bandwidth for phase-delay measurements. Radio Science, 5, 1289.
Schroeder, D. (1987). Astronomical Optics. San Diego, CA: Academic Press.
Schroeder, D. (2000). Astronomical Optics, 2nd edn. San Diego, CA: Academic Press.
Sovers, O. J., Fanslow, J. L., and Jacobs, C. S. (1998). Astrometry and geodesy with radio interferometry: experiments, models, results. Rev. Mod. Phys., 70, 1393.
Sovers, O. J., Jacobs, C. S., and Lanyi, G. E. (2004). MODEST: a tool for geodesy and astrometry. IVS 2004 General Meeting Proceedings, Ottawa, Canada, February 9–11. See:
Stone, R. C. (1996). An accurate method for computing atmospheric refraction. PASP, 108, 1051.
Tatarski, V. I. (1971). The Effects of the Turbulent Atmosphere on Wave Propagation. Jerusalem: Israel Program for Scientific Translations.
Tokovinin, A., Mason, B. D., and Hartkopf, W. I. (2010). Speckle interferometry at the Blanco and SOAR telescopes in 2008 and 2009. AJ, 139, 743.
Unwin, S. C., Shao, M., Tanner, A. M., et al. (2008). Taking the measure of the Universe: precision astrometry with SIM PlanetQuest. PASP, 120, 38.
van Altena, W. F. (1971). Trigonometric parallaxes determined with the Yerkes Observatory 40-inch refractor. I. Methods of observation, measurement reduction, and first results. AJ, 76, 932.
Vieira, K., van Altena, W. F., and Girard, T. M. (2005). Astrometry with OPTIC at WIYN. ASP Conf. Series, 338, 130.
Vieira, K., Girard, T., van Altena, W., et al. (2010). Proper motion study of the Magellanic Clouds using SPM data. AJ, 140, 1934.
Zacharias, N. (1996). Measuring the atmospheric influence on differential astrometry: a simple method applied to wide-field CCD frames. PASP, 108, 1135.
Zacharias, N. (1997). Astrometric quality of the USNO CCD astrograph (UCA). AJ, 113, 1925.
Zacharias, N., Urban, S. E., Zacharias, M. I., et al. (2004). The Second US Naval Observatory CCD Astrograph Catalog (UCAC2). AJ, 127, 3043.