Comparison of Measurements of Atmospheric Wet Delay by Radiosonde, Water Vapor Radiometer, GPS, and VLBI

A. E. Niell MIT Haystack Observatory, Westford, Massachusetts

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A. J. Coster MIT Lincoln Laboratory, Millstone Radar, Lexington, Massachusetts

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F. S. Solheim Radiometrics Corporation, Boulder, Colorado

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V. B. Mendes Geodetic Research Laboratory, University of New Brunswick, Fredericton, New Brunswick, Canada

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P. C. Toor Geodetic Research Laboratory, University of New Brunswick, Fredericton, New Brunswick, Canada

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R. B. Langley Geodetic Research Laboratory, University of New Brunswick, Fredericton, New Brunswick, Canada

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C. A. Upham MIT Lincoln Laboratory, Millstone Radar, Lexington, Massachusetts

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Abstract

The accuracy of the Global Positioning System (GPS) as an instrument for measuring the integrated water vapor content of the atmosphere has been evaluated by comparison with concurrent observations made over a 14-day period by radiosonde, microwave water vapor radiometer (WVR), and Very Long Baseline Interferometry (VLBI). The Vaisala RS-80 A-HUMICAP radiosondes required a correction to the relative humidity readings (provided by Vaisala) to account for packaging contamination; the WVR data required a correction in order to be consistent with the wet refractivity formulation of the VLBI, GPS, and radiosondes. The best agreement of zenith wet delay (ZWD) among the collocated WVR, radiosondes, VLBI, and GPS was for minimum elevations of the GPS measurements below 10°. After corrections were applied to the WVR and radiosonde measurements, WVR, GPS, and VLBI (with 5° minimum elevation angle cutoff) agreed within ∼6 mm of ZWD [1 mm of precipitable water vapor (PWV)] when the differences were averaged, while the radiosondes averaged ∼6 mm of ZWD lower than the WVR. After the removal of biases between the techniques, the VLBI and GPS scales differ by less than 3%, while the WVR scale was ∼5% higher and the radiosonde scale was ∼5% lower. Estimates of zenith wet delay by GPS receivers equipped with Dorne–Margolin choke ring antennas were found to have a strong dependence on the minimum elevation angle of the data. Elevation angle dependent phase errors for the GPS antenna/mount combination can produce ZWD errors of greater than 30 mm over a few hour interval for typical GPS satellite coverage. The VLBI measurements of ZWD are independent of minimum elevation angle and, based on known error sources, appear to be the most accurate of the four techniques.

Corresponding author address: Dr. Arthur E. Niell, MIT Haystack Observatory, Westford, MA 01886.Email: aniell@haystack.mit.edu

Abstract

The accuracy of the Global Positioning System (GPS) as an instrument for measuring the integrated water vapor content of the atmosphere has been evaluated by comparison with concurrent observations made over a 14-day period by radiosonde, microwave water vapor radiometer (WVR), and Very Long Baseline Interferometry (VLBI). The Vaisala RS-80 A-HUMICAP radiosondes required a correction to the relative humidity readings (provided by Vaisala) to account for packaging contamination; the WVR data required a correction in order to be consistent with the wet refractivity formulation of the VLBI, GPS, and radiosondes. The best agreement of zenith wet delay (ZWD) among the collocated WVR, radiosondes, VLBI, and GPS was for minimum elevations of the GPS measurements below 10°. After corrections were applied to the WVR and radiosonde measurements, WVR, GPS, and VLBI (with 5° minimum elevation angle cutoff) agreed within ∼6 mm of ZWD [1 mm of precipitable water vapor (PWV)] when the differences were averaged, while the radiosondes averaged ∼6 mm of ZWD lower than the WVR. After the removal of biases between the techniques, the VLBI and GPS scales differ by less than 3%, while the WVR scale was ∼5% higher and the radiosonde scale was ∼5% lower. Estimates of zenith wet delay by GPS receivers equipped with Dorne–Margolin choke ring antennas were found to have a strong dependence on the minimum elevation angle of the data. Elevation angle dependent phase errors for the GPS antenna/mount combination can produce ZWD errors of greater than 30 mm over a few hour interval for typical GPS satellite coverage. The VLBI measurements of ZWD are independent of minimum elevation angle and, based on known error sources, appear to be the most accurate of the four techniques.

Corresponding author address: Dr. Arthur E. Niell, MIT Haystack Observatory, Westford, MA 01886.Email: aniell@haystack.mit.edu

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  • Alber, C., Ware R. , Rocken C. , and Solheim F. , 1997: GPS surveying with 1 mm precision using corrections for atmospheric slant path delay. Geophys. Res. Lett., 24 , 18591862.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Bar-Sever, Y. E., Kroger P. M. , and Borjesson J. A. , 1998: Estimating horizontal gradients of tropospheric path delay with a single GPS receiver. J. Geophys. Res., 103 , (B3),. 50195035.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Bevis, M., Businger S. , Herring T. A. , Rocken C. , Anthes R. A. , and Ware R. H. , 1992: GPS meteorology: Remote sensing of atmospheric water vapor using the Global Positioning System. J. Geophys. Res., 97 , 15 78715 801.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • ——, ——, Chiswell, S., Herring T. A. , Anthes R. A. , Rocken C. , and Ware R. H. , 1994: GPS meteorology: Mapping zenith wet delays onto precipitable water vapor. J. Appl. Meteor., 33 , 379386.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Businger, S., and and Coauthors, 1996: The promise of GPS in atmospheric monitoring. Bull. Amer. Meteor. Soc., 77 , 518.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Carter, W. E., Rogers A. E. E. , Counselmann III C. C. , and Shapiro I. I. , 1980: Comparison of geodetic and radio interferometric measurements of the Haystack-Westford base line vector. J. Geophys. Res., 85 , (B5),. 26852687.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Chen, G., and Herring T. A. , 1997: Effects of atmospheric azimuthal asymmetry on the analysis of space geodetic data. J. Geophys. Res., 102 , (B9),. 20 48920 502.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Clark, T. A., and and Coauthors, 1998: Earth rotation measurement yields valuable information about the dynamics of the earth system. EOS, Trans. Amer. Geophys. Union, 79 , 205209.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Collins, J. P., and Langley R. B. , 1999: Possible weighting schemes for GPS carrier phase observations in the presence of multipath. U.S. Army Corps of Engineers Topographic Engineering Center Contract Rep. DAAH04-96-C-0086/TCN 98151, 33 pp.

    • Search Google Scholar
    • Export Citation
  • Cruz Pol, S. L., Ruf C. S. , and Keihm S. J. , 1998: Improved 20- to 32-GHz atmospheric absorption model. Radio Sci., 33 , 13191333.

  • Davis, J. L., Herring T. A. , Shapiro I. I. , Rogers A. E. E. , and Elgered G. , 1985: Geodesy by radio interferometry: Effects of atmospheric modeling errors on estimates of baseline length. Radio Sci., 20 , 15931607.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Elgered, G., 1993: Tropospheric radio-path delay from ground-based microwave radiometry. Atmospheric Remote Sensing by Microwave Radiometry, Michael A. Janssen, Ed., John Wiley and Sons, 215–258.

    • Search Google Scholar
    • Export Citation
  • ——, Davis, J. L., Herring T. A. , and Shapiro I. I. , 1991: Geodesy by radio interferometry: Water vapor radiometry for estimation of the wet delay. J. Geophys. Res., 96 , 65416555.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Elósegui, P., Davis J. L. , Jaldehag R. T. K. , Johansson J. M. , Niell A. E. , and Shapiro I. I. , 1995: Geodesy using the global positioning system: The effects of signal scattering on estimates of site position. J. Geophys. Res., 100 , 99219934.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Emardson, T. R., Johansson J. M. , and Elgered G. , 2000: The systematic behavior of water vapor estimates using four years of GPS observations. IEEE Trans. Geosci. Remote Sens.,. 38 , 324329.

    • Search Google Scholar
    • Export Citation
  • England, M. N., Schmidlin F. J. , and Johansson J. M. , 1993: Atmospheric moisture measurements: A microwave radiometer–radiosonde comparison. IEEE Trans. Geosci. Remote Sens., 31 , 389398.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Guo, Y-R., Kuo Y-H. , Dudhia J. , and Parsons D. , 1999: Four-dimensional variational data assimilation of heterogeneous mesoscale observations for a strong convective case. Mon. Wea. Rev., 128 , 619643.

    • Search Google Scholar
    • Export Citation
  • Hauser, J. P., 1989: Effects of deviations from hydrostatic equilibrium on atmospheric corrections to satellite and lunar laser range measurements. J. Geophys. Res., 94 , 10 18210 186.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Herring, T. A., 1992: Submillimeter horizontal position determination using very long baseline interferometry. J. Geophys. Res., 97 , 19811990.

  • ——, Davis, J. L., and Shapiro I. I. , 1990: Geodesy by radio interferometry: The application of Kalman filtering to the analysis of very long baseline interferometry data. J. Geophys. Res., 95 , 12 56112 581.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Jaldehag, R. T. K., Johansson J. M. , Davis J. L. , and Elósegui P. , 1996a: Geodesy using the Swedish permanent GPS network: Effects of snow accumulation on estimates of site position. Geophys. Res. Lett., 23 , 16011604.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • ——, ——, Elósegui, P., Davis J. L. , Niell A. E. , Rönnang B. O. , and Shapiro I. I. , 1996b: Geodesy using the Swedish permanent GPS network: Effects of signal scattering on estimates of relative site positions. J. Geophys. Res., 101 , 17 81417 860.

    • Search Google Scholar
    • Export Citation
  • Kuo, Y-H., Guo Y-R. , and Westwater E. R. , 1993: Assimilation of precipitable water measurements into mesoscale numerical models. Mon. Wea. Rev., 121 , 12151238.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lanyi, G., 1984: Tropospheric delay effects in radio interferometry. TDA Progress Rep. 42-78, April–June 1984, Jet Propulsion Laboratory, Pasadena, CA, 37 pp. (The sign of Fbend4 was misprinted in this paper.).

    • Search Google Scholar
    • Export Citation
  • Liljegren, J., Lesht B. , VanHove T. , and Rocken C. , cited 1999: A comparison of integrated water vapor from microwave radiometer, balloon-borne sounding system and Global Positioning System. Proc. Ninth Atmospheric Radiation Measurement Program Science Team Meeting, San Antonio, TX, ARM Program, 8 pp. [Available online at www.arm.gov/docs/documents/technical/conf_9903/liljegren(3)-99.pdf.].

    • Search Google Scholar
    • Export Citation
  • MacMillan, D. S., 1995: Atmospheric gradients from very long baseline interferometry observations. Geophys. Res. Lett., 22 , (9),. 10411044.

  • ——, and Ma, C., 1994: Evaluation of very long baseline interferometry atmospheric modeling improvements. J. Geophys. Res., 99 , 637651.

  • Mendes, V. B., 1999: Modeling the neutral-atmosphere propagation delay in radiometric space techniques,. Ph.D. dissertation, Department of Geodesy and Geomatics, Engineering Tech. Rep. 199, University of New Brunswick, Fredericton, New Brunswick, Canada, 353 pp.

    • Search Google Scholar
    • Export Citation
  • Nash, J., and Schmidlin F. J. , 1987: WMO international radiosonde intercomparison (U.K., 1984; U.S.A., 1985) final report. World Meteorological Organization, Instruments and Observing Methods Rep. 30, WMO/TD-No. 195.

    • Search Google Scholar
    • Export Citation
  • Niell, A. E., 1996: Global mapping functions for the atmosphere delay at radio wavelengths. J. Geophys. Res., 101 , 32273246.

  • ——,. 2000: Improved atmospheric mapping functions for VLBI and GPS. Earth, Planets, Space, 52 , 699702.

  • ——, King, R. W., McClusky S. C. , and Herring T. A. , 1996: Radome effects on GPS height measurements with choke-ring antennas. EOS, Trans. Amer. Geophys. Union, May, p. S70.

    • Search Google Scholar
    • Export Citation
  • Rocken, C., and and Coauthors, 1995a: UNAVCO Academic Research Infrastructure (ARI) Receiver and Antenna Test Rep.,. 134 pp.

  • ——, Van Hove, T., Johnson J. , Solheim F. , and Ware R. , 1995b: GPS/STORM–GPS sensing of atmospheric water vapor for meteorology. J. Atmos. Oceanic Technol., 12 , 468478.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Saastamoinen, J., 1972: Atmospheric correction for the troposphere and stratosphere in radio ranging of satellites. The Use of Artificial Satellites for Geodesy, Geophys. Monogr., Vol. 15, Amer. Geophys. Union, 247–251.

    • Search Google Scholar
    • Export Citation
  • Schroeder, J. A., and Westwater E. R. , 1991: Users' guide to WPL microwave radiative transfer software. NOAA Tech. Memo. ERL WPL-213, NOAA Wave Propagation Laboratory, Boulder, CO, 84 pp.

    • Search Google Scholar
    • Export Citation
  • Schupler, B. R., Clark T. A. , and Allshouse R. L. , 1994: Signal characteristics of GPS user antennas. Navigation, 41 , (3),. 277295.

  • Solheim, F. S., 1993: Use of pointed water vapor radiometer observations to improve vertical GPS surveying accuracy. Ph.D. dissertation, Department of Physics, University of Colorado, 128 pp.

    • Search Google Scholar
    • Export Citation
  • ——, Godwin, J., Westwater E. , Han Y. , Keihm S. , Marsh K. , and Ware R. , 1998: Radiometric profiling of temperature, water vapor, and cloud liquid water with various inversion methods. Radio Sci., 33 , 393404.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Staelin, D. H., 1966: Measurement and interpretation of the microwave spectrum of the terrestrial atmosphere near 1-centimeter wavelength. J. Geophys. Res., 71 , 28752881.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Treuhaft, R. N., and Lanyi G. E. , 1987: The effect of the dynamic wet troposphere on radio interferometric measurements. Radio Sci., 22 , 251265.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wade, C. G., 1994: An evaluation of problems affecting the measurement of low relative humidity on the United States radiosonde. J. Atmos. Oceanic Technol., 11 , 687700.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • ——, and Schwartz, B., 1993: Radiosonde humidity observations near saturation. Preprints, Eighth Symp. on Meteorological Observations and Instrumentation, Anaheim, CA, Amer. Meteor. Soc., 44–49.

    • Search Google Scholar
    • Export Citation
  • Wallace, J. M., and Hobbs P. V. , 1977: Atmospheric Science: An Introductory Survey. Academic Press, 350 pp.

  • Webb, F. H., and Zumberge J. F. , 1995: An introduction to GIPSY/OASIS-II. Tech. Rep. JPL-D-11088, California Institute of Technology, Pasadena, CA.

    • Search Google Scholar
    • Export Citation
  • Wessel, P., and Smith W. H. F. , 1995: New version of the Generic Mapping Tools released. EOS, Trans. Amer. Geophys. Union, 76 , 329. [Available online at http://www.agu.org/eos_elec.].

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Westwater, E. R., 1997: Remote sensing of tropospheric temperature and water vapor by integrated observing systems. Bull. Amer. Meteor. Soc., 78 , 19912006.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • ——, Falls, M. J., and Popa Fatinga I. A. , 1989: Ground-based microwave radiometric observations of precipitable water vapor: A comparison with ground truth from two radiosonde observing systems. J. Atmos. Oceanic Technol., 6 , 724730.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • ——, and Coauthors, 1999: Ground-based remote sensor observations during PROBE in the tropical western Pacific. Bull. Amer. Meteor. Soc., 80 , 257270.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Zumberge, J. F., Heflin M. B. , Jefferson D. C. , Watkins M. M. , and Webb F. H. , 1997: Point positioning for the efficient and robust analysis of GPS data from large networks. J. Geophys. Res., 102 , 50055017.

    • Crossref
    • Search Google Scholar
    • Export Citation
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