Abstract
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.
Highlights
Displacements of the Earth’s surface are generally caused by spatio-temporal varying geophysical processes
This study presents the conjoint analysis of vertical land motion (VLM) of the Dubrovnik area (Croatia) derived from the European Space Agency’s Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) data available from 2014 onwards, continuous Global Navigation Satellite System (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 1990s have brought the first studies on the VLM calculations based on the comparison of the relative sea-level change rates derived from tide gauges, which are related to the adjacent land so they integrate both sea-level and VLM change, and absolute sea-level rates computed from satellite altimetry, which are referred to in the global geodetic reference frame and are not influenced by the VLM (e.g., [13,14])
Summary
Displacements of the Earth’s surface are generally caused by spatio-temporal varying geophysical processes. The 1990s have brought the first studies on the VLM calculations based on the comparison of the relative sea-level change rates derived from tide gauges, which are related to the adjacent land so they integrate both sea-level and VLM change, and absolute sea-level rates computed from satellite altimetry, which are referred to in the global geodetic reference frame and are not influenced by the VLM (e.g., [13,14]). The VLMs derived from InSAR in this study were evaluated and compared against VLMs derived from (1) GNSS, and (2) differences of the sea-level change rates derived from tide gauge measurements and satellite altimetry. The VLMs were computed for the periods for which the data existed, i.e., from 1992 for computations from sea-level differences, from 2000 for the GNSS estimates and from 2014 for computations using InSAR technologies. Different trends were afterwards compared and analyzed for the observation overlapping period from 2014 to 2020
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