As high-resolution global coverage cannot easily be achieved by direct bathymetry, the use of gravity data is an alternative method to predict seafloor topography. Currently, the commonly used algorithms for predicting seafloor topography are mainly based on the approximate linear relationship between topography and gravity anomaly. In actual application, it is also necessary to process the corresponding data according to some empirical methods, which can cause uncertainty in predicting topography. In this paper, we established analytical observation equations between the gravity anomaly and topography, and obtained the corresponding iterative solving method based on the least square method after linearizing the equations. Furthermore, the regularization method and piecewise bilinear interpolation function are introduced into the observation equations to effectively suppress the high-frequency effect of the boundary sea region and the low-frequency effect of the far sea region. Finally, the seafloor topography beneath a sea region (117.25°-118.25° E, 13.85°-14.85° N) in the South China Sea is predicted as an actual application, where gravity anomaly data of the study area with a resolution of 1′×1′ is from the DTU17 model. Comparing the prediction results with the data of ship soundings from the National Geophysical Data Center (NGDC), the root-mean-square (RMS) error and relative error can be up to 127.4 m and approximately 3.4%, respectively.

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.