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Earth Rotation from the IRIS Project

Published online by Cambridge University Press:  03 August 2017

D. S. Robertson ,
W. E. Carter  and
F. W. Fallon
D. S. Robertson
Affiliation:
National Geodetic Survey, Charting and Geodetic Services, National Ocean Service, NOAA, Rockville, Maryland 20852
W. E. Carter
Affiliation:
National Geodetic Survey, Charting and Geodetic Services, National Ocean Service, NOAA, Rockville, Maryland 20852
F. W. Fallon
Affiliation:
National Geodetic Survey, Charting and Geodetic Services, National Ocean Service, NOAA, Rockville, Maryland 20852

Abstract

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Project IRIS (International Radio Interferometric Surveying) was set up under the IAG and COSPAR to provide an operational system that would employ Very-Long-Baseline Interferometry (VLBI) techniques to monitor variations in the rotation of the Earth. Currently the IRIS-A network, with stations at Westford, MA, Ft. Davis, TX, Richmond, FL, and Wettzell, FRG, conducts 24-hour observing sessions every five days to produce determinations of pole position, UT1, and nutation in addition to other parameters of geophysical and astrometric interest. The resulting Earth orientation parameters (EOP) have been shown to have an accuracy of 1 to 2 milliseconds of arc in pole position, and 0.05 to 0.1 milliseconds of time in UT1. In order to observe the relatively large higher frequency variations in UT1, daily 45-minute observing sessions are conducted using the single baseline between Westford and Wettzell. Intercomparison of the UT1 values from the daily and the 5-day series indicates that the accuracy of the daily values is better than 0.1 millisecond of time.

The longer term objectives of the IRIS project include improving the monitoring of Earth orientation by increasing the sampling rate and accuracy of the observations. In April, 1987, the IRIS-P network, with stations in Kashima, Japan, Fairbanks, AK, Ft, Davis, TX, and Richmond, FL began monthly 24-hour observing sessions, and a second series of daily UT1 observing sessions was begun using the stations in Richmond and Bologna, Italy. The additional networks will provide redundancy that will improve the reliability of the system and allow the accuracy of the EOP values to be estimated.

The IRIS UT1 time series provides, for the first time, sufficient accuracy and temporal resolution to look for the few percent increase in k/C caused by the anelastic response of the mantle. Initial results presented here suggest that improved methods of accounting for the dynamics of the oceans and atmosphere may be required before the intertwined variations in UT1 can be fully separated.

Type
Geophysics
Information
Symposium - International Astronomical Union , Volume 129: The Impact of VLBI on Astrophysics and Geophysics , 1988 , pp. 391 - 400
Copyright
Copyright © Reidel 1988 

References

Bossler, J.D., Federal Implementation Plan for the Application of Space Technology to Crustal Dynamics and Earthquake Research, prepared by the Interagency Coordinating Committee for Geodynamics, 113 pp., 1982.Google Scholar
Carter, W.E., Modern Methods for the Determination of Polar Motion and UT1, Proceedings of Tenth Annual Precise Time and Time Interval Applications and Planning Meeting, NASA Memorandum #80250, 1978.Google Scholar
Carter, W.E. and Strange, W.E., The National Geodetic Survey Project “POLARIS,” Tectonophysics, 52, 39–46, 1979.CrossRefGoogle Scholar
Carter, W.E. and Robertson, D.S., IRIS Earth Rotation and Polar Motion Results, in Proc. International Symposium on Space Techniques for Geodynamics, Sopron, Hungary, 1984.Google Scholar
Gwinn, C.R., Herring, T.A. and Shapiro, I.I., Geodesy by Radio Interferometry: Studies of the Forced Nutations of the Earth, Part II: Interpretation, J. Gepphys. Res., 91, 4755–4765, 1986.Google Scholar
Herring, T.A., Gwinn, C.R., and Shapiro, I.I., Geodesy by Radio Interferometry: Studies of the Forced Nutations of the Earth, Part I: Data Analysis, J. Geophys. Res., 91, 4745–4754, 1986.Google Scholar
Herring, T.A., VLBI Studies of the Nutations of the Earth, this volume, 1987.Google Scholar
Robertson, D.S., Carter, W.E., Tapley, B.D., Schutz, B.E., Eanes, R.J., Polar Motion Measurements: Sub-Decimeter Accuracy Verified by Intercomparison, Science, 229, 1259–1261, 1985a.Google Scholar
Robertson, D.S., Carter, W.E., Campbell, J.A., and Schuh, H., Daily UT1 Determinations from IRIS Very Long Baseline Interferometry, Nature, 316, 424–427, 1985b.Google Scholar
Rosen, R. D., and Salstein, D. A., Variations in Atmospheric Angular Momentum on Global and Regional Scales and the Length of Day, J. Geophys. Res., 88., 5451–5470, 1983.Google Scholar
Schwiderski, E.W., On Charting the Global Tides, Rev. Geophys. and Sp. Phys., 18, 243–268, 1980.Google Scholar
Wahr, J.M., The Forced Nutations of an Elliptical, Rotating, Elastic and Oceanless Earth, Geophys. J. R. Astron. Soc., 64, 705–728, 1981.Google Scholar
Wahr, J.M., Earth Orientation and Nutation, this volume, 1987.Google Scholar
Wahr, J.M., and Bergen, Z., The Effects of Mantle Anelasticity on Nutations, Earth Tides, and Tidal Variations in the Rotation Rate, Geophys. J. R. Astron. Soc., 87, 633–668, 1986.CrossRefGoogle Scholar
Wilkins, G.A., (ed.), Project MERIT: A Review of the Techniques to be Used During Project MERIT to Monitor the Rotation of the Earth, Royal Greenwich Observatory, Herstmonceux, 77 pp., 1980.Google Scholar
Yoder, C.F., Williams, J.G., and Parke, M.E., Tidal Variations of Earth Rotation, J. Geophys. Res., 86, 881–891, 1981.Google Scholar