Wyniki wyszukiwania - BazTech

1

Piecewise acceleration orbital modeling: a GOCE satellite case study

Bobojć Andrzej, Cellmer Sławomir

Acta Geophysica

|

2022

|

Vol. 70, no 1

399--413

EN

In this work, the Precise Science Orbit (PSO) of the Gravity Field and Steady-State Ocean Circulation Explorer Mission (GOCE) satellite, acquired via the European Space Agency, served as the reference orbit for the testing various variants of the GOCE satellite orbit modeling. The GOCE satellite positions along the reduced-dynamic PSO orbit were treated as pseudo-observations in the satellite orbit improvement process in the least squares sense. This process was realized using dedicated extended Toruń Orbit Processor software which enabled determining corrections to the orbital initial conditions and the set of parameters, necessary to determine additional empirical accelerations of the satellite in the radial-track, along track and cross-track directions. These piecewise accelerations were determined in successive equal intervals (pieces) into which the processed orbital arcs were divided. For modeling the accelerations, polynomials of different degrees were used. The obtained RMS differences between the improved orbits and the reference PSO orbit were determined for various orbital arc lengths up to 1-day. The best RMS of the fts for the 1-day arcs was in the range from 2.0 to 3.2 mm with significantly worst results for along-track direction. Based on the set of solutions determined, the number of orbital parameters for adopted accuracy thresholds and the upper limit of their number, that can be estimated depending on the length of the orbital arc, under given numerical conditions were obtained. The optimal form of the polynomial modeling of the estimated accelerations also depends partly on the length of the processed orbital arc. For shorter arcs (45 min and less), the second- third- and fourth-order polynomial gives the best results, while for longer arcs (90, 180, 360, 720 and 1440 min), zero- and first-degree polynomials are the most effective. A very promising solution with the RMS of the ft of 0.1 mm for a 1-min arc using the fourth-order polynomial was obtained in a perspective of the future use of the short arc approach to the ft of 1-day arcs. Additionally, solution variants with non-equal numbers of orbital pieces for the radial-along-and cross-track directions were obtained. In the case of the solution for an arc length of 1-day, the distribution of residuals and their statistics in the aforementioned radial-, along-and cross-track directions are presented.

2

Optimization Method Based on Minimization M-Order Central Moments Used In Surveying Engineering Problems

Cellmer Sławomir, Bobojć Andrzej

Technical Sciences / University of Warmia and Mazury in Olsztyn

|

2021

|

nr 24(1)

39--49

EN

A new optimization method presented in this work – the Least m-Order Central Moments method, is a generalization of the Least Squares method. It allows fitting a geometric object into a set of points in such a way that the maximum shift between the object and the points after fitting is smaller than in the Least Squares method. This property can be very useful in some engineering tasks, e.g. in the realignment of a railway track or gantry rails. The theoretical properties of the proposed optimization method are analyzed. The computational problems are discussed. The appropriate computational techniques are proposed to overcome these problems. The detailed computational algorithm and formulas of iterative processes have been derived. The numerical tests are presented, in order to illustrate the operation of proposed techniques. The results have been analyzed, and the conclusions were then formulated.

3

Assessment of chosen GRACE related gravity models based on the GOCE satellite precise science orbit

Bobojć Andrzej

Acta Geophysica

|

2019

|

Vol. 67, no. 4

1265--1275

EN

Eight selected geopotential models obtained through the International Center for Global Earth Models were used in the dynamic orbit determination process of the satellite of the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) mission. For the estimation of various GOCE orbital arc variants, the following gravity models were taken into account: HUST-GRACE2016S, ITU_GRACE16, ITSG-GRACE2014S, ITSG-GRACE2014K, TONGJI-GRACE01, EIGEN-51C, EIGEN5S, EGM2008. The ofcial kinematic and reduced-dynamic precise science orbit (PSO) of the GOCE satellite received via the European Space Agency was adopted as the reference orbit. Cartesian coordinates of the GOCE satellite in this orbit were treated as pseudo-observations in the estimation process using the classical least-squares method. The estimated orbital arcs were ftted to the corresponding arcs of the reference orbit. This allowed the values of 3D root-mean-square (RMS) of the distance between the estimated and reference arcs to be computed. The averages for these 3D RMS values, computed for ten and ffty orbital arcs, made it possible to compare the orbital performance of selected gravity models. Additionally, the ft to both types of the GOCE PSO, i.e., the kinematic orbit and the reduced-dynamic orbit made it possible to compare their quality. Investigation of the gravity model performance was also the opportunity to describe the efectiveness of dynamic orbit determination solutions, depending on the estimated arc lengths, type of reference orbit and the use (or not) of the background models.