Okyanus Gelgit Yüklemesi Konum Değişimlerinin VLBI Ölçülerinden Kestirimi ve Global Okyanus Gelgit Modelleri ile Doğrulanması

Abstract

As a result of the analysis of the measurements of space/satellite geodetic techniques, the defined coordinates of the terrestrial reference frame (TRF) of the earth fixed geodetic control points are estimated. Since the measurement model used for the estimation of the coordinates from the measurement of space/satellite geodesic techniques is not linear, correction estimation is performed to the approximate value of each parameter by linearizing the measurement model before applying the least-squares estimation method. Since the convergence diameter of the least-squares is small, the approximate values should be chosen as close to the exact values as possible. In the Kalman filter, unknown parameters in the first epoch are started with a prediction. The filter moves forward over time until the last epoch is processed. Parameters that are constantly modeled over time are improved in every epoch, and the estimates in the last epoch are the final estimates of these parameters.

The approximate values of the station coordinates are obtained as a result of linear velocity correction for each measurement epoch and bringing together some geodynamic position corrections, and the station coordinates a priori values are calculated. According to the magnitude of these geodynamic corrections, respectively; displacements of solid Earth tides, ocean tidal and non-tidal loading, hydrology loading, polar tides, atmospheric tidal and non-tidal loading.

The position errors due to the inadequacies of these ocean tide corrections, which are calculated from the ocean tide models for each measurement epoch and brought to each measure, are reflected not only on the station coordinates but also on other parameters with parameter estimation. It is only possible to prevent this situation by developing better ocean tide models. Within the scope of this thesis, International VLBI Service for Geodesy & Astrometry (IVS) daily sessions of VLBI co-located sites (22 stations) homogeneously distributed around the world were analyzed and the position time series of VLBI stations were produced and compared with the values calculated from the ocean tide models for the same epochs. Thus, model inadequacies were revealed for each tidal period. To be compatible with the global ocean models (e.g. FES2014b, GOT4.10c, TPXO9-Atlas), the positive direction in the displacements estimated from VLBI measurements is taken as radial, west and south. Local topocentric coordinates (radial, west, south) time series with 2-hour intervals for each station are taken as a measure again and ocean tide loading semi-diurnal (M2, S2, N2, K2) and diurnal (K1, O1, P1, Q1) tides of amplitudes and Greenwich phase delay components are estimated with using least-squares and Kalman filter. The agreement between the time series of ocean tide displacements from VLBI measurements and global models was examined by statistical methods for each tidal period, and global ocean models and inadequacies due to VLBI measurements were revealed.