Tomislav Bašić

Eocene to present subduction of southern Adria mantle lithosphere beneath the Dinarides

We modeled global positioning system measurements of crustal velocity along a N13°E profile across the southern Adria microplate and south-central Dinarides mountain belt using a one-dimensional elastic dislocation model. We assumed a N77°W fault strike orthogonal to the average azimuth of the measured velocities, but we used a constrained random search algorithm minimizing misfit to the velocities to determine all other parameters of the model. The model fault plane reaches the surface seaward of mapped SW-verging thrusts of Eocene and perhaps Neogene age along the coastal areas of southern Dalmatia, consistent with SW-migrating deformation in an active fold-and-thrust belt. P-wave tomography shows a NE-dipping high-velocity slab to ∼160 km depth, which reaches the surface as Adria, dips gently beneath the foreland, and becomes steep beneath the Dinarides topographic high. The thrust plane is located directly above the shallowly dipping part of the slab. The pattern of precisely located seismicity is broadly consistent with both the tomography and geodesy; deeper earthquakes (down to ∼70 km) correlate spatially with the slab, and shallower earthquakes are broadly clustered around the geodetically inferred thrust plane. The model fault geometry and loading rate, ages of subaerially exposed thrusts in the fold-and-thrust belt, and the length of subducted slab are all consistent with Adria-Eurasia collision involving uninterrupted subduction of southern Adria mantle lithosphere beneath Eurasia since Eocene time.

A New Geopotential Model Tailored to Gravity Data in Europe

The European north-south GPS traverse was established to control and improve the European geoid. Comparisons of GPS and levelling data with different geoid computations show a strong slope (1.5 m/700 km) between Denmark and Norway. This slope was suspected to be caused by bad quality of the up to now available 6′ × 10′ gravity values for Scandinavia. Therefore an updated set of 0.5° × 0.5° mean free-air gravity anomalies was calculated for Scandinavia. The new geopotential model (IFE88E2) has been calculated using this new set of 0.5° × 0.5° mean free-air gravity anomalies merged with other available 0.5° × 0.5° mean values for Europe. The calculation of the tailored model, complete to degree and order 360, is based on the OSU86F coefficient set, that was used as a start model. The RMS value of the differences between the 6715 mean values and the model derived values decreased from 15.8 mgal to 6.0 mgal for OSU86F resp. IFE88E2. The magnitude of residual point free-air anomalies relative to OSU86F and IFE88E2 were evaluated in 1495 points in Scandinavia. The RMS values of the differences were 23.4 mgal and 18.5 mgal respectively. Especially comparisons of the two models with GPS/levelling data in Europe show an improved accuracy of the IFE88E2 model. The RMS value of the differences relative to OSU86F is 0.774 m and decreases to 0.322 m for IFE88E2. Furthermore, the slope between Denmark and Norway has almost disappeared.

Accuracy validation and comparison of global digital elevation models over Croatia

Accuracy assessment of digital elevation models (DEMs) plays an important role in facing their use in geoscience applications. This study investigates the vertical accuracy of most recently published versions of global DEMs over Croatia: 1 arc-minute global relief model (ETOPO1), Global 30 Arc-Second Elevation (GTOPO30), SRTM30+, Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010), Altimeter Corrected Elevations 2 DEM (ACE2 DEM), Shuttle Radar Topography Mission GDEM (SRTM GDEM), and Advanced Spaceborne Thermal Emission and Reflection GDEM (ASTER GDEM). Geodetic ground control points (benchmarks) allowed the comparison in terms of vertical accuracy. Additionally, the differences between models in the identical points were determined and analysed after adjusting the models to the same resolution. The results have yielded information about the overall accuracy of models; the accuracy depending on height, land cover, and slope; presence of large and systematic errors; and mutual agreement between the models. Overall vertical accuracies according to the root mean square error over Croatia are: ETOPO1 27.6 m, GTOPO30 21.6 m, SRTM30+ 21.3 m, GMTED2010 7.4 m, ACE2 DEM 4.5 m, SRTM GDEM 3.8 m, and ASTER GDEM 7.1 m. The highest accuracy was shown by SRTM GDEM version 3, which is far better than the previously released versions. All models have proved to be worse in the rough and forest areas, whereas in flat and barelands, new-generation global DEMs SRTM GDEM, and ASTER GDEM are highly accurate.

A new, more accurate geoid for Croatia

Abstract A new geoid for the entire territory of the Republic of Croatia has been computed using point gravity data, ERS-2 satellite altimetry data, GPS/Levelling data, digital terrain models as well as the global geopotential model EGM96. The calculation of geoid undulations is accomplished by the collocation technique in a well-known remove-restore procedure. Taking benefit of the new gravity and altimetry data resulted in a significantly more accurate geoid model for Croatian land and sea territory in comparison to prior solutions, and to the more recent European EGG97 geoid. The obtained geoid surface should be useful for different purposes, particularly in the precise height definition using modern GPS technology. The application of this surface in modelling efforts of Adriatic Sea bathymetry from satellite altimetry is also planned.

Empirical Research of Interpolation Methods in Distortion Modeling for the Coordinate Transformation between Local and Global Geodetic Datums

Conformal coordinate transformations very often are not accurate enough to be used for the coordinate transformations between local and global geodetic datums because of the inhomogeneity of the spatial data in different geodetic datums. Therefore, distortion modeling is used to improve the accuracy of the coordinate transformations. This paper presents empirical research on distortion modeling methods used to improve the coordinate transformation process from local to global geodetic datum and vice versa. Various models of distortion shifts in different grid resolutions were computed, evaluated, and compared with the official Croatian model of distortion shifts. Tested modeling methods are inverse distance to a power, kriging, minimum curvature, modified Shepard’s method, natural neighbor, nearest neighbor, polynomial regression, radial basis function, triangulation with linear interpolation, moving average, local polynomial, and least-squares collocation. Distortion model performance was evaluated using summary statistics derived from the back-interpolation for the independent control spatial data set. The present paper proposes the most appropriate method(s) of distortion modeling for the Croatian case and gives brief instructions on possible coordinate transformation improvements of the official Croatian coordinate transformation.

Empirical comparison of the Geodetic Coordinate Transformation Models: a case study of Croatia

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.

Analysis of Recent Global Geopotential Models Over the Croatian Territory

Independent quality control of the national geoid model HRG2000 was performed using 65 control points, obtained through the realization of EUVN and EUVN_DA projects and the Croatian fundamental gravity network. Ellipsoidal heights and positions of the control points are precisely determined by GNSS measurements while the geodetic heights are obtained by geometric levelling.

CROATIAN GEOMAGNETIC REPEAT STATIONS NETWORK

Prikazana je uspostava mreže primarnih sekularnih geomagnetskih tocaka na teritoriju Republike Hrvatske. Tocke za istraživanje sekularne varijacije projektirane su sukladno preporukama Coordination Committee for Common European Repeat Station Surveys, kriterijima International Association of Geomagnetism and Aeronomy – IAGA te iskustvima europskih zemalja. Konacne lokacije sekularnih tocaka izabrane su evaluacijom kriterija na samom terenu. U tu svrhu razvijene su i testirane metode određivanja gradijenata totalnog intenziteta ukljucujuci potrebnu programsku podrsku. Iz ispitivanja razlicitih materijala uslijedio je izbor kamene stabilizacije. Tocke mreže stabilizirane su ukopavanjem stabilizacije standardnim geodetskim postupcima. Status svake tocke mreže dokumentiran je obrascima Položajnog opisa i Geomagnetskih parametara.

Improved Geoid Solution for Slovenia and a Part of Croatia

At the Faculty of Geodesy, University of Zagreb, the necessary preparations have been made in the past few years for a new gravity field determination for the territories of Slovenia and Croatia. Now we present the results for an improved astrogeodetic geoid in these areas, which is, we hope, at the subdecimeter level of accuracy at least.

Towards the new Croatian terrestrial reference frame based on CROPOS - preliminary results

Since the establishment of CROPOS, almost seven years have passed. Initial and also the last adjustment CROPOS network was carried out in 2008 using only seven 24h session data in GPS Week 1503 (ETRF2000 R05 ; e2008, 83). In the recent period there have been significant changes - Croatian State Geodetic Administration (CSGA) signed an agreement on the exchange of data of national positioning systems neighboring countries: Slovenia (SIGNAL), Hungary (GNSSnet.hu), Montenegro (MontePOS), Federation of Bosnia and Herzegovina (FBiHPOS) and Republika Srpska (SRPOS). This paper presents the results of long-term stability of coordinates of CROPOS stations through absolute comparison of ETRF2000 coordinates from initial adjustment with the combined networked solution of CROPOS and nearby positioning systems, calculated on the basis of 1463 daily solutions for the time span of four years.