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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Different space-borne geodetic observation methods combined with in-situ measurements enable resolving the single-point vertical land motion (VLM) and/or the VLM of an area. Continuous Global Navigation Satellite System (GNSS) measurements can solely provide very precise VLM trends at specific sites. VLM area monitoring can be performed by Interferometric Synthetic Aperture Radar (InSAR) technology in combination with the GNSS in-situ data. In coastal zones, an effective VLM estimation at tide gauge sites can additionally be derived by comparing the relative sea-level trends computed from tide gauge measurements that are related to the land to which the tide gauges are attached, and absolute trends derived from the radar satellite altimeter data that are independent of the VLM. This study presents the conjoint analysis of VLM of the Dubrovnik area (Croatia) derived from the European Space Agency’s Sentinel-1 InSAR data available from 2014 onwards, continuous GNSS observations at Dubrovnik site obtained from 2000, and differences of the sea-level change obtained from all available satellite altimeter missions for the Dubrovnik area and tide gauge measurements in Dubrovnik from 1992 onwards. The computed VLM estimates for the overlapping period of three observation methods, i.e., from GNSS observations, sea-level differences, and Sentinel-1 InSAR data, are −1.93±0.38 mm/yr, −2.04±0.22 mm/yr, and −2.24±0.46 mm/yr, respectively.

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