Abstract
A global geodetic reference system (GGRS) is realized by physical points on the Earth’s surface and is referred to as a global geodetic reference frame (GGRF). The GGRF is derived by combining several space geodetic techniques, and the reference points of these techniques are the physical points of such a realization. Due to the weak physical connection between the space geodetic techniques, so-called local ties are introduced to the combination procedure. A local tie is the spatial vector defined between the reference points of two space geodetic techniques. It is derivable by local measurements at multitechnique stations, which operate more than one space geodetic technique. Local ties are a crucial component within the intertechnique combination; therefore, erroneous or outdated vectors affect the global results. In order to reach the ambitious accuracy goal of 1 mm for a global position, the global geodetic observing system (GGOS) aims for strategies to improve local ties, and, thus, the reference point determination procedures. In this contribution, close range photogrammetry is applied for the first time to determine the reference point of a laser telescope used for satellite laser ranging (SLR) at Geodetic Observatory Wettzell (GOW). A measurement campaign using various configurations was performed at the Satellite Observing System Wettzell (SOS-W) to evaluate the achievable accuracy and the measurement effort. The bias of the estimates were studied using an unscented transformation. Biases occur if nonlinear functions are replaced and are solved by linear substitute problems. Moreover, the influence of the chosen stochastic model onto the estimates is studied by means of various dispersion matrices of the observations. It is shown that the resulting standard deviations are two to three times overestimated if stochastic dependencies are neglected.
Highlights
To get a better understanding of the dynamic processes on Earth, the global geodetic observing system aims for a global geodetic reference frame, which yields an accuracy of 1 mm for positions and a temporal stability of 0.1 mm yr−1 [1]
A global geodetic reference frame (GGRF) is derived by combining several space geodetic techniques such as very long baseline interferometry (VLBI), satellite laser ranging, Doppler orbitography and radiopositioning integrated by satellite (DORIS), and the global navigation satellite system (GNSS) [4]
Since most of the functional relations of the analysis process are nonlinear, we address the bias of the estimates, which arises if the nonlinear function is replaced and is solved by its linear substitute problem
Summary
To get a better understanding of the dynamic processes on Earth, the global geodetic observing system aims for a global geodetic reference frame, which yields an accuracy of 1 mm for positions and a temporal stability of 0.1 mm yr−1 [1]. Due to the weak physical connection between the space geodetic techniques, further information that ties these techniques is necessary to derive a reliable frame In this respect, so-called local ties are introduced to the combination procedure [6]. The common procedure of local tie determination consists of three analysis steps: The determination of the reference points of the space geodetic techniques in a local reference frame, preparing the local ties and the related dispersion matrices, and the mandatory transformation of the local ties into the GGRF using, for instance, homologous points. Laser Ranging Service (ILRS), which contributes to the origin and the scale of the GGRF This investigation focuses on the analysis procedure of the ILRS reference point determination in a local frame.
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