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Global Geodetic Observing System 2015–2018

Sośnica Krzysztof, Bosy Jarosław

Geodesy and Cartography

2019

Vol. 68, no. 1

121--144

Global Geodetic Observing System (GGOS) was established in 2003 by the International Association of Geodesy (IAG) with the main goal to deepen understanding of the dynamic Earth system by quantifying human-induced Earth’s changes in space and time. GGOS allows not only for advancing Earth Science, including solid Earth, oceans, ice, atmosphere, but also for better understanding processes between different constituents forming the system Earth, and most importantly, for helping authorities to make intelligent societal decisions. GGOS comprises different components to provide the geodetic infrastructure necessary for monitoring the Earth system and global changes. The infrastructure spreads from the global scale, through regional, to national scales. This contribution describes the GGOS structure, components, and goals with the main focus on GGOS activities in Poland, including both the development of the geodetic observing infrastructure as well as advances in processing geodetic observations supporting GGOS goals and providing high-accuracy global geodetic parameters.

The combined geodetic network adjusted on the reference ellipsoid – a comparison of three functional models for GNSS observations

Kadaj R.

Geodesy and Cartography

2016

Vol. 65, no. 2

229--257

The adjustment problem of the so-called combined (hybrid, integrated) network created with GNSS vectors and terrestrial observations has been the subject of many theoretical and applied works. The network adjustment in various mathematical spaces was considered: in the Cartesian geocentric system on a reference ellipsoid and on a mapping plane. For practical reasons, it often takes a geodetic coordinate system associated with the reference ellipsoid. In this case, the Cartesian GNSS vectors are converted, for example, into geodesic parameters (azimuth and length) on the ellipsoid, but the simple form of converted pseudo-observations are the direct differences of the geodetic coordinates. Unfortunately, such an approach may be essentially distorted by a systematic error resulting from the position error of the GNSS vector, before its projection on the ellipsoid surface. In this paper, an analysis of the impact of this error on the determined measures of geometric ellipsoid elements, including the differences of geodetic coordinates or geodesic parameters is presented. Assuming that the adjustment of a combined network on the ellipsoid shows that the optimal functional approach in relation to the satellite observation, is to create the observational equations directly for the original GNSS Cartesian vector components, writing them directly as a function of the geodetic coordinates (in numerical applications, we use the linearized forms of observational equations with explicitly specified coefficients). While retaining the original character of the Cartesian vector, one avoids any systematic errors that may occur in the conversion of the original GNSS vectors to ellipsoid elements, for example the vector of the geodesic parameters. The problem is theoretically developed and numerically tested. An example of the adjustment of a subnet loaded from the database of reference stations of the ASG-EUPOS system was considered for the preferred functional model of the GNSS observations.