GeoMetre at JISDM 2022 - save the date!

We are honoured that we will get the opportunity to present our results at the 5th Joint International Symposium on Deformation Monitoring at Valencia, Spain, April 6-8, 2022 (JISDM 2022). We are looking forward to your feedback and exciting discussions with the community!

Mechanical uncertainty contributions of the multilateration system components assessed

We develop a multilateration system with a range of several ten to two hundred meters. Its core is the telemetric unit (ADM) which performs the absolute distance measurement using radio frequency modulation. Its signal is distributed by optical fibres to four measurement heads and a rotating, 'smart' reflector as target. In a combined experimental and theoretical study, we demonstrate the mechanical uncertainty contributions of the measurement heads to remain below 2 µm and of the target not to exceed 9 µm. The study is described in detail in reference [1].

[1] J. Guillory, D. Truong and J.-P. Wallerand, “Assessment of the mechanical errors of a prototype of an optical multilateration system”, Review of Scientific Instruments 91, 025004 (2020) (DOI:10.1063/1.5132933)

Multilateration system on a laboratory table. (Fig. unaltered from [1] under CC BY 4.0 license. Click to enlarge.)

Enhanced environment sensor data interpolation for refractive index compensation

Often, the effective refractive index along a beam is derived from point measurements of an extended sensor networks along the beam. For this standard approach, we developed an improved interpolation scheme that reduces the uncertainty of the derived effective mean value considerably. Details can be found in references [1, 2].

[1] P. Neyezhmakov, V. Kupko, T. Panasenko, A. Prokopov, V. Skliarov, and A. Shloma, “Analysis of accuracy requirements to the meteorological sensors used to compensate for the influence of the Earth’s atmosphere in high precision length measurement,” in Proceedings of SMSI Sensor and Measurement Science International, 2020 (DOI:10.5162/SMSI2020/D3.3)

[2] P. Neyezhmakov, T. Panasenko, A. Prokopov, V. Skliarov, A. Shloma, I. Trevoho, “Comparative analysis of quadrature formulas for the mean integral refractive index of air in high-precision ranging”, Modern achievements of geodesic science and industry 39, pp. 69-73, 2020 (DOI:10.33841/1819-1339-1-39-13)

Antenna calibration error assessment

We present a novel method to assess the performance of GNSS absolute antenna calibrations with a combination of inter-antenna differentials and laser tracker measurements. The approach can also be used to determine the phase centers of as-installed individual receiver antennas at system critical sites to the same level without compromising the permanent installations. Details can be found in [1].

[1] S. Bergstrand, P. Jarlemark, M. Herbertsson, "Quantifying errors in GNSS antenna calibrations", J Geod 94, 105 (2020). (DOI:10.1007/s00190-020-01433-0)

Substantial correction for standard group refractive index formula

In our work on intrinsic refractive index compensation, we discovered a fatal sign error in the published algorithm for the group refractive index by Ciddor and Hill in 1999 [1]. The derivative of the major dispersive term was taken incorrectly. Unfortunately, if applied as published, the original algorithm delivers a value which deviates up to several parts-per-million from the real group index. This magnitude is critical for state-of-the-art ranging applications. More details and the corrected term are published in [2], a python code example can be downloaded from [3].

[1] P. E. Ciddor and R. J. Hill, “Refractive index of air. 2. Group index,” Appl. Opt. 38, 1663–1667 (1999)  (DOI:10.1364/AO.38.001663

[2] F. Pollinger, “Refractive index of air. 2. Group index: comment,” Appl. Opt. 59, 9771-9772, (2020) (DOI:10.1364/AO.400796)

[3]F. Pollinger, CiddorPy: python functions for phase and group refractive index in air, figshare (2020) (DOI:10.6084/m9.figshare.12515320)

Modified Algorithm for Dynamic Telescope Reference Monitoring

The GeoMetre project partners Frankfurt University of Applied Science and Bundesamt für Kartographie und Geodäsie (BKG) have developed a new algorithm for dynamic reference point determination of VLBI and SLR telescopes which considerably eases the synchronization requirements for telescope and measurement system. The new approach allows for an in-process metrological determination of the reference point. It has been successfully implemented and validated at the Geodetic Observatory at Wettzell. The movie shows an mobile laser tracker measuring positions of targets mounted on the moving SLR telescope in the measurement process. The target positions for each telescope orientation are then used to determine the location of the telescope’s reference point. Knowledge of the exact location is critical for the correct spatial referencing of the telescope’s observation data.

Scientific publication:

M. Lösler, C. Eschelbach, S. Riepl, T. Schüler (2019) A Modified Approach for Process-Integrated Reference Point Determination. Proceedings of the 24th European VLBI Group for Geodesy and Astrometry Working Meeting, 17-19 March 2019, Las Palmas de Gran Canaria, Spain, Eds. R. Haas, S. Garcia-Espada, and J. A. López Fernández, :172-176 DOI: 10.7419/162.08.2019