Research in Geodesy Based Upon Radio Interferometric Observations of Extragalactic Radio Sources.
Abstract
Very-long-baseline interferometric (VLBI) observations obtained from a network of radio telescopes distributed in North America and Europe have been analyzed to estimate the relative positions of the radio telescopes and the nutations of the Earth's rotation axis. In addition to the estimation of these geodetic parameters we have also used some of these data to study the Mark III instrumental performance, and the calibration of the atmospheric delay. Analysis of the Mark III instrumentation allowed us to isolate the probable cause of S-band group delay closure errors. These closure errors appear to be due to the effects of 'leakage' of left-circularly polarized radiation into the output of feed horns which are designed to receive only right-circularly polarized radiation. This instrumental error appears to have affected the ionospheric-calibrated group delays at the 1 cm level. Investigations of the effects of the atmospheric delay calibration on estimates of geodetic parameters have disclosed that the elevation angle dependence of the dry atmospheric delay model (Marini model) may be biased. We suspect that this delay model may be biased by about 10 cm at 10 deg elevation angle. A bias of this magnitude is not unlikely because two models of the elevation angle dependence of the atmospheric delay differ by about 6 cm at 10 deg elevation angle.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1984
- Accession Number
- ADA147581
Entities
People
- I. I. Shapiro
- J. L. Davis
- T. A. Herring
Organizations
- Harvard College Observatory