Citation
Abstract
Mobile VLBI and GPS geodetic measurements have many error sources in common. Calibration of the effects of water vapor on signal transmission through the atmosphere, however, remains the primary limitation to the accuracy of vertical crustal motion measurements made by either technique. The two primary methods of water vapor calibration currently in use for mobile VLBI baseline measurements have been evaluated: radiometric measurements of the sky brightness near the 22 GHz emission line of free water molecules and surface meteorological measurements used as input to an atmospheric model. Based upon a limited set of 9 baselines, it is shown that calibrating VLBI data with water vapor radiometer measurements provides a significantly better fit to the theoretical delay model than calibrating the same data with surface meteorological measurements. The effect of estimating a systematic error in the surface meteorological calibration is shown to improve the consistency of the vertical baseline components obtained by the two calibration methods. A detailed error model for the vertical baseline component indicates current mobile VLBI technology should allow accuracies of order 5 cm with WVR calibration and 10 cm when surface meteorological calibration is used. A statistical analysis of the results of repeated measurements of the 336-km baseline from Big Pine, CA, to Pasadena, CA, shows the scatter in the vertical baseline component to be consistent with this model. A similar model for a hypothetical GPS baseline measurement is presented. A covariance analysis based upon this model shows current GPS technology to be capable of accuracies in the vertical baseline component comparable to present mobile VLBI measurements. Expected improvements in system components for both technologies should allow reduction of the uncertainty in the vertical component to less than 3.cm by 1989.
Details
- Volume
- 42-82
- Published
- August 15, 1985
- Pages
- 185–198
- File Size
- 744.7 KB