Measuring deflection of the vertical via local reference point surveying
and pointing calibration of VLBI telescope: a case study at Urumqi
station
Abstract
Deflection of the Vertical (DOV) is vital to astro-geodetic and
geophysics research and application. In the Urumqi station, two new
non-optical methods including small network coordinate transformation
(SNCT) and azimuth-axis inclination inversion (AAII),are proposed to
determine the DOV of the VLBI telescope. The generalized expression of
the pointing calibration (PC) model regarding of axis-related errors is
also presented. Therefore, the PC model and indirect model (IM) used for
reference point determination (RPD) are unified by redefining their
coordinate system, angle direction, axis related errors. The DOV result
of the SNCT method has good agreement with those DOVs solved by the real
surveying and other different models, e.g., early Global Navigation
Satellite System (GNSS) and leveling measurements (EGL), mass
integration model(MIM), etc. Due to the possible asymmetric coverage of
calibrating sources in the north-south direction in PC, the north-south
DOV component of AAII varies in its value with the surveyed value.
However, the west-east DOV component fits well in both direction and
magnitude. The proposed methods enable the VLBI telescope to sense the
direction of the local plumb line via introducing local leveling. We
also establish the connections among VLBI delay observing, RPD, and
telescope PC, which has a benefit to muti-tech systematic error
identification, monitoring, and correction. The research indicates that,
similar to local surveying and VLBI observing, the telescope point
calibration can be also taken as a regular technique to monitoring
systematic error.