Developments in sensor technology called Synthetic Antenna Radar (SAR) and associated data processing software have helped satellite radar interferometry (InSAR), a method that uses multiple SAR images of the same area collected from satellites, to become a widely used method for estimating soil deformation as well as other geophysical processes, because it provides millimeter precision with great spatial coverage. The paper deals with 24 Sentinel-1A images for the area of western Herzegovina, taken during 2020, and determined the average speeds of vertical displacements using the SNAP program (Sentinel Application Platform). Vertical displacements of ± 10 millimeters were recorded, while the mean annual displacement velocities were 8 millimeters in the vertical direction, without taking into account the correction for the influence of horizontal displacements. The first results in the study area indicate a trend of ground movement, but due to several types of atmospheric corrections, geomorphological characteristics of the study area and lack of in-situ measurements for comparison, external evaluation of the reliability of deformations will have to be assessed in future studies.

Bathymetry underpins all marine and ocean research. It is common knowledge that there is a global deficit of high-resolution bathymetry based on modern acoustic techniques. Satellite altimetry enabled modeling of the global seafloor topography and revealed new morphological features in the unmapped areas of the oceans and seas. This chapter gives an overview of the physical problem and different approaches to estimating the bathymetry from satellite altimeter-derived gravity data. Characteristics of recent versions of frequently used global bathymetry models are presented. Moreover, this chapter demonstrates the possibility of regional bathymetry modeling by the gravity-geologic method in the Adriatic Sea.

The primary objective of the 1-cm geoid experiment in Colorado (USA) is to compare the numerous geoid computation methods used by different groups around the world. This is intended to lay the foundations for tuning computation methods to achieve the sought after 1-cm accuracy, and also evaluate how this accuracy may be robustly assessed. In this experiment, (quasi)geoid models were computed using the same input data provided by the US National Geodetic Survey (NGS), but using different methodologies. The rugged mountainous study area (730 km ×\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\times $$\end{document} 560 km) in Colorado was chosen so as to accentuate any differences between the methodologies, and to take advantage of newly collected GPS/leveling data of the Geoid Slope Validation Survey 2017 (GSVS17) which are now available to be used as an accurate and independent test dataset. Fourteen groups from fourteen countries submitted a gravimetric geoid and a quasigeoid model in a 1′×\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\times $$\end{document}1′ grid for the study area, as well as geoid heights, height anomalies, and geopotential values at the 223 GSVS17 marks. This paper concentrates on the quasigeoid model comparison and evaluation, while the geopotential value investigations are presented as a separate paper (Sánchez et al. in J Geodesy 95(3):1. https://doi.org/10.1007/s00190-021-01481-0, 2021). Three comparisons are performed: the area comparison to show the model precision, the comparison with the GSVS17 data to estimate the relative accuracy of the models, and the differential quasigeoid (slope) comparison with GSVS17 to assess the relative accuracy of the height anomalies at different baseline lengths. The results show that the precision of the 1′ × 1′ models over the complete area is about 2 cm, while the accuracy estimates along the GSVS17 profile range from 1.2 cm to 3.4 cm. Considering that the GSVS17 does not pass the roughest terrain, we estimate that the quasigeoid can be computed with an accuracy of ~ 2 cm in Colorado. The slope comparisons show that RMS values of the differences vary from 2 to 8 cm in all baseline lengths. Although the 2-cm precision and 2-cm relative accuracy have been estimated in such a rugged region, the experiment has not reached the 1-cm accuracy goal. At this point, the different accuracy estimates are not a proof of the superiority of one methodology over another because the model precision and accuracy of the GSVS17-derived height anomalies are at a similar level. It appears that the differences are not primarily caused by differences in theory, but that they originate mostly from numerical computations and/or data processing techniques. Consequently, recommendations to improve the model precision toward the 1-cm accuracy are also given in this paper.

Drought causes great damage to the economy and agriculture in Croatia. Therefore, it is important to gain a better insight into the spatial distribution of water balance components (precipitation (P), potential evapotranspiration (PET), actual evapotranspiration (ET), soil moisture content (S), runoff (RO), recharge (R), and soil moisture loss (L)) and their long-term changes in Croatia. Since measurements of the mentioned components in Croatia are very rare, the Palmer model has been applied to estimate them. The meteorological data from 82 stations have been used in the period 1981–2010. To determine the climate variations long-term trends in water balance components have been analyzed in the period 1901–2017. The PET and ET linear trends in the last decades show a faster growth than in the long-term trends, and the increase in PET (50–80 mm/decade) is significant in most of Croatia, except in the eastern part (27 mm/decade). The results of the mean annual PET and ET spatial distribution revealed that the maximum PET is estimated in the mid-Adriatic area of about 1500 mm, but the lack of precipitation caused the ET (about 700 mm) to be insignificantly different from the values in other parts of Croatia. The analyzed meteorological data from the period 1981–2010 indicated a higher air temperature and lower precipitation amount than in the reference climatic period of 1961–1990. This reduces the ET in areas with insufficient precipitation, i.e., on the Adriatic coast and in the eastern part of Croatia, where an increasing soil moisture deficit during the vegetation period can have a potentially negative effect on agricultural production.

At the very end of the year 2020, at 29th of December, hazard earthquake of M=6.2 hit near Petrinja, at NW of Croatia. Earthquake have been felt in a circumstance of a 400 kilometers, leaving in an epicenter vicinity inconceivable damage, devastated towns and obstructed lives. In order to obtain the first emergency crisis numbers over the impact of the earthquake on a ground motion, we have analyzed open satellite radar images of Copernicus Sentinel-1 along with the seismic faults. Multiple spatio-temporal Copernicus Sentinel-1 C-SAR images were used and processed for the differentiating the before and after earthquake state of the art. This presentation shows the results of the SAR conducted analysis, with the results of ground displacement in vertical up-down and horizontal east-west direction. The results show the vertical ground displacement to extent of -12 cm at southern area to +22cm at north-west part of a wide area covered by the earthquake impact regarding the epicenter. The horizontal displacement is detected in range between 30 cm towards west and 40 cm towards east is detected around the epicenter area, and +/-5cm horizontal displacement over a wider affected area indicate a spatial extent and hazardous impact the mainshock event made. The SAR results were verified by including the analysis over one station from the national positioning reference frame CROPOS. Accordingly, we obtained matching results of 5 cm easting shift and -3 cm subsidence on Sisak GNSS CROPOS station which coressponds to our SAR findings. Furthermore, geological interepretation of new findings is given based on results detecting Pokupsko and Petrinja fault.

At the very end of the year 2020, on 29 December, a hazardous earthquake of Mw = 6.2 hit the area of Petrinja and its surroundings, in the NW of Croatia. The earthquake was felt across the area of 400 km, leaving an inconceivable damage in the vicinity of the epicenter, devastated towns and ruined lives. In order to map the spreading of earthquake waves and to determine the coseismic ground displacement after the mainshock, we have analyzed open satellite radar images of Sentinel-1 and the GNSS data from the nearest CORS station related to the epicenter, along with the seismic faults. In this paper, we addressed and mapped the displacement linear surface ruptures detected by the SAR interferometry. The results show the vertical ground displacement to the extent of −12 cm in the southern area and up to 22 cm in the north-western part of a wide area struck by the earthquake impact, related to the epicenter. Subsidence and uplift in a range of ±5 cm over a wider affected area indicate a spatial extent and hazardous impact made by the earthquake. The ground displacement of 30 cm to the West and 40 cm to the East has been identified considering the intersection of Pokupsko and Petrinja strike-slip fault system in the seismic zone of Pannonian basin. Accordingly, we obtained matching results of 5 cm south-easting shift and −3 cm subsidence on Sisak GNSS CROPOS station, addressing the tectonic blocks movement along the activated complex fault system. The results compared with the geology data confirm the existence of two main faults; the Pokupsko and the Petrinja strike-slip faults and interpret the occurrence of secondary post-seismic events over the observed area.

The precision of geodetic measurements is reliable as much as the reference on which the measurements relies on. From the aspect of todays' most used geodetic method, the GNSS measurements, its reference is defined through a national reference frame established with corresponding reference stations. Hazardous earthquake of M=6.2 occurred in NW Croatia at the very end of year 2020. Earthquake was one of the most hazardous natural phenomena in Croatia in the last century. Due to the tremendous damages left behind, in which also one of the national GNSS reference station temporarily out of the service, we analyzed how much earthquake had impacted the surrounding reference stations and overall the Croatian national reference frame CROPOS. The presentation shows the analysis of GNSS time series in order to determine the scale of displacement of the CROPOS CORS GNSS reference stations due to the earthquake. The results show the greatest shift of 5 cm east on Sisak reference station, with stations in circumstances of 100 km impacted by the earthquake and shifted between 1 and 2.5 cm positional and 2-4 cm in height. Identified displacement of national reference frame and the ground displacement over the affected area will have domino effect on the geodetic field measurements and cadastral survey on that area.

Bathymetric models representing the topography of the seafloor are an important parameter in almost all maritime related research. Traditional bathymetric shipborne or airborne surveys are cost and/or time consuming, and access to the measured data is mostly limited or expensive. Alternative bathymetric data sources for marine researchers are publicly available bathymetric models whose quality is often unknown and/or uneven. This research presents the study on the bathymetric prediction for the Adriatic Sea from altimetry-derived gravity anomalies and in-situ soundings using the gravity - geologic method (GGM). Bathymetric soundings used to determine the density contrast between seawater and bedrock were derived from nautical charts, EMODnet (European Marine Observation and Data Network) bathymetric grid, and GEBCO (General Bathymetric Chart of the Oceans) One Minute grid. More than 3000 chart soundings distributed across the Adriatic Sea were used to estimate the quality of the predicted bathymetric model as well as the quality of the latest versions of publicly available bathymetric models: DTU10Bat (Technical University of Denmark), GEBCO 2020, EMODnet 2018, ETOPO1, Smith and Sandwell v.19.1, and SRTM (Shuttle Radar Topography Mission) 15+ V.2.1. The results show that the computed model represents an update to bathymetric data in the Adriatic Sea, especially along its eastern coast.

This paper studies the contribution of airborne gravity data to improvement of gravimetric geoid modelling across the mountainous area in Colorado, USA. First, airborne gravity data was processed, filtered, and downward-continued. Then, three gravity anomaly grids were prepared; the first grid only from the terrestrial gravity data, the second grid only from the downward-continued airborne gravity data, and the third grid from combined downward-continued airborne and terrestrial gravity data. Gravimetric geoid models with the three gravity anomaly grids were determined using the least-squares modification of Stokes’ formula with additive corrections (LSMSA) method. The absolute and relative accuracy of the computed gravimetric geoid models was estimated on GNSS/levelling points. Results exhibit the accuracy improved by 1.1 cm or 20% in terms of standard deviation when airborne and terrestrial gravity data was used for geoid computation, compared to the geoid model computed only from terrestrial gravity data. Finally, the spectral analysis of surface gravity anomaly grids and geoid models was performed, which provided insights into specific wavelength bands in which airborne gravity data contributed and improved the power spectrum.

Radar satellite altimetry has revolutionized our understanding of the Earth’s sea-level shape and its change over time, monitoring of the natural and human-induced water cycle, marine gravity computations, seafloor relief (bathymetry) reconstruction, tectonics, water mass balance change monitoring, etc., thus providing significant impact in geodesy. Today satellite radar altimetry is critical for unifying the vertical height systems, regional and global geoid modeling, monitoring of the sea level rise impact, monitoring of the ice sheet melting, and others. This chapter gives an overview of the technology itself and the recent developments including the SAR (Synthetic Aperture Radar) altimetry, coastal altimetry retracking methods, and new satellite missions (e.g. Sentinel-6). Besides, the chapter presents recent applied studies utilizing the altimeter data for ice sheet monitoring, vertical land motion estimating, bathymetric computations, and marine geoid modeling.

Ice-sheet mass balance and ice behaviour have been effectively monitored remotely by space-borne laser ranging technology, i.e. satellite laser altimetry, and/or satellite gravimetry. ICESat mission launched in 2003 has pioneered laser altimetry providing a large amount of elevation data related to ice sheet change with high spatial and temporal resolution. ICESat-2, the successor to the ICESat mission, was launched in 2018, continuing the legacy of its predecessor. This paper presents an overview of the satellite laser altimetry and a review of Greenland ice sheet change estimated from ICESat data and compared against estimates derived from satellite gravimetry, i.e. changes of the Earth’s gravity field obtained from the GRACE data. In addition to that, it provides an insight into the characteristics and possibilities of ice sheet monitoring with renewed mission ICESat-2, which was compared against ICESat for the examination of ice height changes on the Jakobshavn glacier. ICESat comparison (2004–2008) shows that an average elevation change in different areas on Greenland varies up to ±0.60 m yr−1. Island’s coastal southern regions are most affected by ice loss, while inland areas record near-balance state. In the same period, gravity anomaly measurements showed negative annual mass balance trends in coastal regions ranging from a few cm up to -0.36 m yr-1 w.e. (water equivalent), while inland records show slightly positive trends. According to GRACE observations, in the following years (2009–2017), negative annual mass balance trends on the coast continued.

One of the main challenges in physical geodesy today is achieving the 1-centimetre gravimetric quasi-geoid model, since a model of such accuracy could be used in the definition and realisation of the height reference frame. One of the main obstacles in this challenge is the lack of terrestrial gravity data or its uneven distribution. Therefore, the main question arises: what density of gravity points is necessary in order to obtain a gravimetric quasi-geoid model with an accuracy of 1 centimetre or even better? In this simulated study, the results show a trend of decreasing RMS related to the sparser dataset used in computation, leading to the conclusion that the determination of thesub-centimetre quasi-geoid model is no longer a theory, but can be achieved with the exact density of terrestrial gravity data: gravity observation stations have to be distributed no farther than 500 m from one another. When dealing with a very rough topography, the distance should be even shorter.

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.

Popravak kompasa je kut koji u točki na karti definira projekcija magnetskog meridijana točke s ordinatom kartografskog projekcijskog sustava, a jednak je razlici magnetske deklinacije i konvergencije meridijana. U praksi topografsko-geodetske pripreme i osiguranja primjenjuje se tzv. radni popravak kompasa, u kojemu se deklinacija sastoji od dnevnog srednjaka i dnevne promjene deklinacije. Inicijalni model radnog popravka kompasa izrađen je radi promocije daljnje suradnje Geodetskog fakulteta Sveučilišta u Zagrebu i Ministarstva obrane Republike Hrvatske. Model radnog popravka kompasa dAzmr2020 oslanja se na aktualni model geomagnetske informacije GI2020v1, parametre službene kartografske projekcije Republike Hrvatske i empirijski model dnevne promjene deklinacije. Osim postupaka obnove geomagnetske informacije, računanja konvergencije meridijana i modeliranja dnevne promjene, zajedno s procjenama pouzdanosti, u ovom se radu pružaju informacije i o računalnom programu dAzmr2020 za računanje radnog popravka kompasa preko Hrvatske u 2020. godini.

High-resolution digital elevation models (DEMs) have become available in the last decade. They are used in geodesy and geophysics as the main data for modeling of topographic mass effects included in gravimetric and gradiometric measurements. In modeling process, gravimeric terrain correction is the central quantity which accounts for the variations of topographic masses around measured stations. This study deals with one segment of terrain correction computation: the impact of the resolution of digital elevation models. Computations are performed on study area of Republic of Croatia. Newly created DEM/DBM for the study area is created from global digital surface model ASTER for continental area, and digital bathymetric model GEBCO for the sea area. DEMs with lower resolution were created by resampling of the created ASTER/GEBCO DEM/DBM in 1″ resolution. Terrain correction map is computed and published for the first time for the Republic of Croatia. The differences between terrain correction solutions obtained by using lower resolution DEMs compared to the solution obtained by using DEM with 1″ are indicating average influence of DEM resolution on terrain correction from 0,5·10–5 to 3·10–5 ms–2, for DEMs with lower resolution than 5″. The results also reveal that rugged and mountainous areas are particularly problematic in such computations.

Tides have largest impact on gravity measurements compared to all other environmental effects. They are a direct result of the gravitational forces of the planetary bodies, mainly the Moon and the Sun. The magnitude of tidal effects depends on the relative position of planetary bodies around the Earth and can be computed from the astronomical ephemeris. In this paper, LTide software is presented, a lightweight application for computation of the tidal gravity acceleration effects according to Longman formulas. The software solves a problem of laborious calculations and simplifies the analysis of gravity data over any time period and any surveyed area worldwide. The code is open-sourced, platform independent, written in Matlab/Octave programming language. It has graphical user interface which offers several options for import, export and visualization of the results. The software is meant to be an easy-to-use tool for geoscientists and other users in processing relative gravity measurements and tempo-spatial analysis of tidal gravity effects.

Models of geomorphometric parameters and drainage networks are widely used in many scientific and civilian branches and activities. They are created using the Earth's land surface data, which are today mostly represented by digital elevation models (DEMs). The main objective of this study is to create models of slope, aspect, and drainage networks for the first time for the entire continental part of the Republic of Croatia, using the most detailed DEMs. In this paper, developed models are described, compared, and analysed, giving insights into morphological characteristics and structures of topographic surface. The quality of the derived models has been validated using existing independent data. Furthermore, because models were derived using various global DEMs, the differences between output models have been addressed and studied. Drainage network models were further analysed depending on several available computation algorithms (single and multiple flow direction) and threshold values. The analysis of the sensitivity and influence of input parameters and models on output models has been assessed in order to create reliable drainage network models for the future for other local or regional areas.