2nd Geomagnetic Information Renewal Cycle in the Republic of Croatia – First Results

Abstract

The 2nd Geomagnetic Information Renewal Cycle started in 2017, pursuant to a request from the State Geodetic Administration and Ministry of Defence to ensure actual declination and its annual variation across the territory of Republic of Croatia. A test survey was performed at POKUpsko as part of the project in 2017. The PRM1 Primary Repeat Station had been destroyed, and the survey performed at a secondary location established in 2011, which subsequently became the primary location, known as PRM2. In this paper, the results of 2017 measurements reductions are presented, along with reductions in PRM1 and PRM2 measurements in 2011, and differences between the PRM1 and PRM2 locations, which are necessary to maintain the continuity of measurements at Pokupsko.

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“…The declared maximum declination uncertainty of GI2015v1.2 was £ 7' at BGNRC locations. This was checked at the POKUpsko repeat station during a two-day survey in 2017, the first year of the 2nd Geomagnetic Information Renewal Cycle (Brkić et al, 2018). The reliability of the model was also confirmed at the LON geomagnetic observatory (Lonjsko polje) during instrument comparison before and after the 2017 campaign, see section 2.…”

“…In the GI2015v1.2 model, the declinations at BGNRC and surrounding stations refer to epoch 2015.0 (Brkić et al, 2018). These declinations originated from the 2008, 2009 and 2010 surveys in southern, western, and northern Croatia, reduced to 2008Croatia, reduced to .5, 2009.5 and 2010.5 epochs respectively, and then to the common epoch solution of 2009.5.…”

“…The partial solutions of 2008.5, 2009.5 and 2010.5 had a maximum declination scatter of 0.8', 0.7', and 0.9' respectively, while the common solution maximum scatter was 2.1' for 98 BGNRC locations (Brkić et al, 2013). In addition, the common or 'start' solution was reduced to 2015.0 by using IGRF-12, assuming the IGRF-12model declination variation and variation observed at BGNRC stations between two epochs were equal (Brkić et al, 2018). The 2015.0 epoch was chosen since it was the starting epoch of the actual generation of the International Reference Geomagnetic Field IGRF-12 model, and its annual variation across territory of Croatia was implemented in the GI2015v1.0 model (Brkić et al, 2017).…”

“…Finally, the selected GI2017 model was the one obtained with PA1 normal AVD for 2016-2017. The model GI2017 ('PA1 variant') was then tested on the LON OBS and POKU RS 2017 absolute observations (Brkić et al, 2018). Comparison of GI2015v1.2 and GI2017(PA1) to POKU gave max.…”

“…However, the series of GI models that comprise the Earth's internal magnetic field, excluding prominent local anomalies and time-varying fields, whether man-made or natural, was prepared each year to provide actual GI. The last such model was GI2015v1.2 (Brkić et al, 2018). It relied of necessity on IGRF-12 to accomplish reductions of D to epoch 2015.0, and on D predictions in the period 2015.0-2020.0.…”