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  • GEOPHYSICS  (2)
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  • 1990-1994  (2)
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  • 1991  (2)
  • 1
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    Geodesy by radio interferometry - Water vapor radiometry for estimation of the wet delay (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: An important source of error in VLBI estimates of baseline length is unmodeled variations of the refractivity of the neutral atmosphere along the propagation path of the radio signals. This paper presents and discusses the method of using data from a water vapor radiomete (WVR) to correct for the propagation delay caused by atmospheric water vapor, the major cause of these variations. Data from different WVRs are compared with estimated propagation delays obtained by Kalman filtering of the VLBI data themselves. The consequences of using either WVR data or Kalman filtering to correct for atmospheric propagation delay at the Onsala VLBI site are investigated by studying the repeatability of estimated baseline lengths from Onsala to several other sites. The repeatability obtained for baseline length estimates shows that the methods of water vapor radiometry and Kalman filtering offer comparable accuracies when applied to VLBI observations obtained in the climate of the Swedish west coast. For the most frequently measured baseline in this study, the use of WVR data yielded a 13 percent smaller weighted-root-mean-square (WRMS) scatter of the baseline length estimates compared to the use of a Kalman filter. It is also clear that the 'best' minimum elevationi angle for VLBI observations depends on the accuracy of the determinations of the total propagation delay to be used, since the error in this delay increases with increasing air mass.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 6541-655
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Effects of atmospheric modeling errors on determinations of baseline vectors from very long baseline interferometry (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: An investigation is conducted in order to expose errors in the formula for the elevation angle dependence of the hydrostatic atmospheric propagation delay, called the mapping function. A series of special VLBI experiments that involve a large fraction of group delay data from very low elevation angles are performed. Twenty-two experiments, each 26 hours in duration, were performed using VLBI antennas at Goldstone, California and at Westford, Massachusetts. Elevation angle cutoff tests were used to examine the contribution of these errors to the estimates of the vertical coordinate of site position. This contribution is determined to be about 19 mm. It is also found that, for the spacing of 1-2 months between experiments, the mapping function errors do not exhibit a coherent annual signature, but appear to be random in the long term.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 643-650
    Format: text
    Location Call Number Expected Availability
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    NASA TECHNICAL REPORTS
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