Jorma Jokela

The upgraded PTB 600 m baseline: a high-accuracy reference for the calibration and the development of long distance measurement devices

The calibration and verification of high-precision electronic distance meters (EDMs) requires well-characterized and calibrated geodetic baselines. As the length measurements are performed typically over several hundred metres in air, a thorough understanding of the environmental conditions is necessary. In the course of a major refurbishment, the 600 m baseline of the Physikalisch-Technische Bundesanstalt at Braunschweig, Germany, was equipped with a dense environmental sensor network. This paper presents the characterization of this novel reference baseline, including the calibration of the inter-pillar distances, and identifies the major sources of uncertainty for such a length standard. A preliminary expanded standard uncertainty (k = 2) of is deduced for single-slope distance comparisons on the baseline. In the course of a full calibration, the additive constant cEDM of an EDM can currently be determined with an expanded uncertainty of U(cEDM)k = 2 = 6.1 × 10−5 m, and its scale correction sEDM with an expanded uncertainty of U(sEDM)k = 2 = 8.2 × 10−7. As an example, a femtosecond laser-based distance measurement over 600 m on this baseline is presented.

Scale variation of GPS time series

We give an overview of time series analyses of permanent GPS stations using solutions of the IGS and FinnRef® networks. Lomb periodograms show in most cases a statistically significant annual period both in station coordinates and inter-station distances. In regional networks the scale of the whole network changes periodically, and in some cases there is also a secular trend. There are several possible causes of scale variations, which may not be separable in the data. These include computational artefacts, periodic systematic errors in satellite orbits, signal path delay variations, and geophysical causes like loading and postglacial rebound. We discuss possible reasons, their significance, and their consequences on high-precision GPS observations. Additional constraints, e.g. time series from the superconducting gravimeter, are also discussed.

GPS Metrology: Bringing Traceable Scale to a Local Crustal Deformation GPS Network

A constant scale difference between GPS solutions and traceable electronic distance measurement (EDM) results was found during semi-annually repeated campaigns performed in Olkiluoto, Finland. Since EDM results are very accurate and uncertainties are well-defined, this leads to an assumption that the GPS solution is biased.

Improving Length and Scale Traceability in Local Geodynamical Measurements

Traceability is a feature that is required more frequently in local geodetic high-precision measurements. This basic term of metrology, a measurement science, describes the property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty (BIPM International vocabulary of metrology – basic and general concepts and associated terms (VIM). JCGM 200:2008. Joint Committee for Guides in Metrology, 2008b).

Control Measurements Between the Geodetic Observation Sites at Metsähovi

The Metsahovi research station of the Finnish Geodetic Institute hosts instruments of all basic space geodetic techniques, including geodetic VLBI, SLR, GNSS and DORIS. The local control network is an essential part of the station. Tie measurements between the network benchmark bolts and pillars and instrument reference points are needed to control the stability of the installations, and to tie them with each others and to the global reference frame.

Vectors Connecting the Geodetic Points at Metsähovi and Sjökulla

The Finnish Geodetic Institute has carried out geodetic operations at the Metsahovi research station since the 1970s. During the last ten years a number of new observation sites have been founded for GPS, SLR, VLBI etc. Some of these are located at Sjokulla, 3 km NNW from the original Metsahovi. Questions concerning the positions of the points relative to each other are frequently asked. Both terrestrial and GPS measurements have been used to determine the centering elements and connecting vectors, and measurements have been repeated to detect possible movements of the benchmarks. A brief summary of the observation sites and the local measurements carried out between them is now given.