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.
Earthquakes in the Zagreb area on 22nd March 2020 were an occasion to estimate earthquake-related noise in minute magnetograms and its significance to the geomagnetic information renewal i.e., survey ...of geomagnetic networks, reduction, and modelling of the geomagnetic information (that is, declination and its annual variation). Firstly, the distinction of geomagneticaly quiet and disturbed days was vividly portrayed by comparison of Q1 (quiet) and D1* (disturbed) days of March 2020 in the geomagnetic observatory Lonjsko polje magnetograms. The day of 22nd March was rather quiet geomagnetic day, therefore the comparison of available magnetograms of the observatories Lonjsko polje and Nagycenk was performed. Identification of earthquakes on magnetograms was limited by the uncertainties of observatory and epicentre coordinates, magnitudes of the earthquake waves' velocities, times of their occurrence at observatories, rounding of earthquakes times to whole minutes, and filtering observatories' records into minute (and preliminary) magnetograms. Comparisons of observatories minute magnetograms during the observed day did not unequivocally indicate earthquakes; seemingly the earthquakes noise was less than the effects of the quiet days' geomagnetic disturbances. The differences of variations, obtained by removing the diurnal variation from centred magnetograms, in Lonjsko polje and Nagycenk, at the earthquakes' times were found negligible, less than 10" for the declination, 5" for the inclination, and 0.6 nT for the total intensity. Thus, the contribution of the noise of earthquakes of comparable features was estimated negligible in the context of the geomagnetic information renewal.
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.
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.
This paper presents empirical research on coordinate transformation models that enable coordinate transformations between the historical astro-geodetic datums and datums related to the European ...Terrestrial Reference System (ETRS), through a case study of the Republic of Croatia. Thirteen models were investigated for the transformation from the historical Croatian State Coordinate System (HDKS) to the Croatian Terrestrial Reference System (HTRS96): Molodensky 3 and 5 parameter (standard and abridged) conformal transformation models, 7 parameter transformation models (Bursa-Wolf and Molodensky-Badekas model), Affine transformation models (8, 9, 12 parameter), Multiple Regression Equation approach, and several transformation models that include extending of the aforementioned 7 parameter and 8, 9, 12 parameter Affine transformation models with distortion modelling. Most of the models were investigated for the first time over the Croatian territory. Analysis of transformation models performance was conducted using an independent data set of reliable geodetic points. The study provides mutual comparison of the models and their comparison with the official Croatian transformation model called T7D. Furthermore, the most appropriate transformation model(s) were defined regarding the required accuracy and the available resources for the coordinate transformation models implementation. In addition, the paper provides a brief theoretical background and equations of each transformation model and summarises the bibliography on the research topic.
Changes in the height of the ocean can be described through the relative and absolute sea level changes depending on the geodetic reference the sea level records are related to. Satellite altimetry ...provides absolute sea level (ASL) measurements related to the global geodetic reference, whereas tide gauges provide relative sea level (RSL) measurements related to the adjacent land. This study aims at computing the ASL surfaces for different time epochs from combined satellite altimeter and tide gauge records. A method of sea level data fusion is proposed to enable modeling of the impact of present and future sea level changes on the coast. Sea surface modeling was investigated for ten different gridding methods commonly used for the interpolation of altimeter data over the open ocean and extrapolation over the coastal zones. The performance of gridding methods was assessed based on the comparison of the gridded altimeter data and corrected tide gauge measurements. Finally, the sea level surfaces related to the GRS80 global reference ellipsoid were computed for the Mediterranean Sea over the altimeter period. In addition, the current sea level trends were estimated from both sea level measurements.
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.
Na zahtjev Državne geodetske uprave i Ministarstva obrane 2017. godine započeo je II. ciklus obnove geomagnetske informacije u cilju osiguranja aktualne deklinacije i njene godišnje promjene na prostoru RH. Prošlogodišnjim projektom provedena je test izmjera na lokaciji POKUpsko, primarna sekularna točka PRM1 je uništena, a izmjera je provedena na sekundarnoj lokaciji iz 2011. godine. Sada je ta lokacija primarna i nosi oznaku PRM2. U ovom su radu prikazani rezultati redukcija izmjere 2017. Dodatno je u ovom radu reducirana izmjera PRM1 i PRM2 iz 2011. te odrebena razlika lokacija PRM1 i PRM2 potrebna za ocuvanje kontinuiteta opažanja na Pokupskom.
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.
According to GRACE observations, in the following years (2009-2017), negative annual mass balance trends on the coast continued. (2019), glacial melt in Greenland has raised global sea level by 13.7 ...mm since the early 1970s, half of which has taken place between 2010 and 2018. Besides causing the sea level rise that endangers coastal zones, ice loss influences ocean currents (Joughin et al., 2012), threatens animal habitats (e.g. Amstrup et al., 2010), destroys historical data on the environmental conditions of the Earth captured inside ice (e.g. Bintanja et al., 2013), and likely provokes new outbreaks of diseases (Wu et al., 2016). ...ICESat data demonstrated interdisciplinary applications providing global measurements of cloud heights and the vertical structure of clouds and aerosols; precise measurements of land topography and vegetation canopy heights; measurements of sea ice roughness and thickness, ocean surface elevations, as well as surface reflectivity. ...various designs of spacecraft and different methods of collecting elevation data are reflected in error budgets.
Radarska satelitska altimetrija metoda je prikupljanja globalnih visokopreciznih podataka o razini mora u odnosu na odabrani geocentrični referentni okvir. Opažanja satelitskom altimetrijom omogućuju ...određivanje oblika i veličine Zemlje te računanje Zemljina polja ubrzanja sile teže što su i osnovne geodetske zadaće zadane definicijom geodezije. Mjerenja promjene srednje razine mora prikupljena satelitskom altimetrijom služe kao izravni pokazatelj djelovanja klimatskih promjena i drugih geofizičkih procesa na Zemlji, a primijenjena su i za definiranje visinskih sustava na kopnu i moru, izradu karata dubina, procjenu vertikalnih gibanja obalnih područja i sl. U ovom radu detaljno je prikazan osnovni koncept tehnologije uz primijenjene principe obrade radarskih opažanja. Poseban je naglasak na prikazu i analizi korekcija altimetrijskih opažanja potrebnih zbog propagacije signala kroz atmosferu te utjecaja geofizičkih fenomena vodenih površina na odaslani signal. Rad detaljno prikazuje razvoj tehnologije kroz tri faze uz analizu doprinosa svake te opisuje smjernice budućeg razvoja tehnologije. Naposljetku, prikazani su proizvodi satelitske altimetrije dostupni za primjenu u geodetske svrhe kao što su modeli anomalija ubrzanja sile teže, dubina, trendova srednje promjene razine mora i drugi.
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