Papers by Alexandru Călin
At this time, when marine and river navigation intensifies, it is necessary detailed knowledge of... more At this time, when marine and river navigation intensifies, it is necessary detailed knowledge of the water bottom topography of the river navigable channel and marine coastal areas. Sonar sounding systems, multibeam ecosounders systems or those using interferometry, is investigating ways water bottom topography, to identify sedimentary deposits or to achieve the necessary studies hydrotechnical constructions. The importance of bathymetric measurements is noted in several projects implemented in Romania, presented in this paper. Keywords—bandwidth, beamwidth, depth, echosounder, seafloor, signal, SAS interferometry, Danube Delta
This article presents a general way of the possibility to investigat to the bottom of rivers or s... more This article presents a general way of the possibility to investigat to the bottom of rivers or sea. Measuring the response time of rising sound sonar, multibeam ecosounders systems or interferometric methods of investigation of water bottom provides precise or less precise information about topography underwater fauna or sedimentary deposits required in many human activities. Are presented here and several such projects in Romania where the bathymetry have an important role. Key-Words: signal, echosounder, bandwidth, depth, seafloor, SAS interferometry, Danube Delta
Usually, the engineering survey applications are carried on in all the realization stages which c... more Usually, the engineering survey applications are carried on in all the realization stages which concern construction objectives based on a local three-dimensional geodetic network. When these networks are lying on a small surface, the problem is treated trivially, but correctly, by choosing a local coordinate system which widely meets the requirements regarding the accuracy and the configuration of these projects. Another problem for the geodetic specialist appears in case of large range works and especially in case of works that are developing, mainly, in one cardinal direction. In this situation it is necessary to choose and adopt a specific projection system, so that the deformation coefficient of the linear values induced by the chosen projection system tends to the value of 1. To reach this desideratum it is necessary to develop a local projection system, chosen in such way that in the points of the extended line barycentre, the linear deformations induced by the system are nul...
Landslides Study Analyses by Digital Terrain Models
13th SGEM GeoConference on INFORMATICS, GEOINFORMATICS AND REMOTE SENSING, 2013
Study regarding the use of the vertical deviation from Romanian historical astro-geodetic network in the geoid model development on the national territory
Romanian Astronomical Journal, 2016
Astro-geodetic platform for high accuracy geoid determinat ion
In many situations the ortophotos are necessary in GIS. Geometric requirements like fixed geometr... more In many situations the ortophotos are necessary in GIS. Geometric requirements like fixed geometry and homogenity for an ortophoto makes it a good choice as input data. These images have long history and still require a higher demand. Althrough ortophoto production for large urban areas using standard algorithms have problems like: shifts and occlusions which are a drawback if someone adds vector data; incomplete and imprecise orto-rectification because of the incomplete data in DHM and others. Using DSM and considering additional images in order to eliminate occlusions it is possible to generate a true-ortophoto without problems mentioned before. In this paper some aspects in true-ortophoto and improved DHM production will be discussed.
Environmental Engineering and Management Journal, 2016
This paper present first results of a study, on the determination and use of the deviations of th... more This paper present first results of a study, on the determination and use of the deviations of the vertical for obtaining an accurate geoid in Romania, as a future goal. For the beginning, the study occurred on a limited area of about 22000 km 2 in the south part of Romania, including the capital Bucharest. We used data from three different sources: historical astro-geodetic deviations of the vertical (before 1990), deviations derived from two global geoid models (Gravity field and steady-state Ocean Circulation Explorer-GOCE and Earth Gravitational Model 2008-EGM2008) and present astro-geodetic deviations. Present deviations was obtained using three different instruments, one astronomical and two geodetic. Inside of the study we perfect a new procedure for the determination of the astro-geodetic vertical deviation, adapted for modern geodetic instruments. The results and comparisons made offers insight into the possibilities of obtaining and using vertical deviations, as well as an estimate of their quality in terms of precision and accuracy.
arXiv: Applications, 2018
The paper demonstrates the application of statistical based methodology for the analysis of the v... more The paper demonstrates the application of statistical based methodology for the analysis of the vertical deviation angle. The studied data set contains astro-geodetic observations. The Principal Component Analysis and the Multiple Linear Regression models are embedded within a bootstrap procedure, in order to overcome the difficulties related to data correlation, while taking advantage of all the information provided. The methodology is applied on real data. The obtained results indicate that the pressure, the temperature and the humidity are variables that may influence the measure of the vertical deviation.
Aspects of Geodetic Practice in the Area of Vrancioaia Geodynamic Micropolygon
This paper presents aspects of the organization and development of geodetic practice organized by... more This paper presents aspects of the organization and development of geodetic practice organized by the Department of Geodesy and Photogrammetry of the Faculty of Geodesy Bucharest. Since 2006, in the Vrancea area were accomplished the necessary conditions for the good performance of the geodetic practice including geometric levelling, directions and distance measurements, satellite measurements. The existing geodynamic micropolygon in the area was completed with a geodetic network allowing proper development of the mentioned types of measurements already mentioned. In parallel with specific educational activities conducted, the observations results contributes to geodynamic phenomena research in the Vrancea area.
The studies of the hydrographic basins areas are an import activity regarding the prevention of t... more The studies of the hydrographic basins areas are an import activity regarding the prevention of the natural disasters. The geodetics works supposed to determine the digital elevation model to be used then in hydraulic analyses applications. A crucial support , not only for the GNSS determinations but also for the LiDAR and orthophotomap production is represented by the model of the quasigeoid for the studied area that can be used for the conversion of the ellipsoidal altitudes determined with GNSS technology into the national altimetric reference system. In this paper is presented a study case for the modelling of the quaisgeoid in the Prut-Barlad hydrographical basin area using the geometric method. There were made GNSS static observations and precise leveling measurements for the points of the thickening network. An application in Matlab software was developed for the correction of the European quasigeoid model EGG97.
International Journal of Remote Sensing, 2019
In Bucharest, new subway tunnels are under construction since 2011. The whole project of extendin... more In Bucharest, new subway tunnels are under construction since 2011. The whole project of extending Bucharest underground infrastructure is due to be finished by 2030. The M-5 artery has been under construction since 2011 and ongoing. In December 2015, dewatering procedures in one of the metro stations caused serious damage to the surface infrastructure above, which subsided and partially collapsed in some locations. This paper relies on multitemporal interferometry techniques to characterize displacement patterns of the ground surface above M-5 beltway between 2014 and 2018, and presents the capacity of Sentinel-1 satellite imagery to detect potential hazards in urban environments. Two stacks of Synthetic Aperture Radar (SAR) images acquired between October 2014 and October 2018 by the Sentinel-1 A and B satellites on ascending and descending orbits have been processed using the Delft Persistent Scatterer Interferometry algorithm (DePSI). The results indicate atypical acceleration in velocities starting in November 2015, prior to the described events, and manifesting until April 2016, when the ground was completely stabilized. The displacement trends and velocity values in the area of the Eroilor underground station were successfully validated using the groundbased Global Navigation Satellite Systems (GNSS) technique.
InSAR validation based on GNSS measurements in Bucharest
International Journal of Remote Sensing, 2016
ABSTRACT This research aims to complex validate radar displacement products over Bucharest based ... more ABSTRACT This research aims to complex validate radar displacement products over Bucharest based on Global Navigation Satellite System or GNSS. Validation was represented by the comparison of the recent TerraSAR-X (TSX) displacement results with field GNSS data. For this purpose, 24 and 27 high-resolution images acquired from the TSX satellite between 2011 and 2014 were processed by Permanent Scatterer Inteferometry (PSI) and Small BASeline Subset (SBAS) – interferometric techniques using synthetic aperture radar (SAR) images. The images were selected from a larger pool of SAR images, after consulting weather databases, which helped eliminate the images acquired under adverse weather conditions. GNSS locations were cross-checked on high-resolution optical images and 21 ground points (including three permanent stations) were selected. All these points were (1) characterized by high coherence on radar images; (2) were on the ground; (3) were situated in large vacant spaces; and (4) far away from radar obstacles such as trees. A major challenge in achieving the research goal was to overcome the lack of permanent stations at the ground level within the area of Bucharest. Instead of permanent stations, our team designed and installed forced centring systems that remained stable over time, eliminating the instalment errors of GNSS receivers. The line-of-site (LOS) components derived from GNSS data have been compared with those of the SAR scatterers closest to the GNSS markers (never coinciding). For each location, the vertical reading was projected in the LOS of the SAR sensor. These readings were compared with the displacement values determined at the locations of permanent scatterers (PSs) within 100 m from the GNSS nodes, by eliminating all scatterers on buildings. The comparison has shown a good agreement.
The paper presents some aspects regarding development of an astrogeodetic mobile platform, which ... more The paper presents some aspects regarding development of an astrogeodetic mobile platform, which will allow geoid determination or geoid validation by astrogeodetic leveling. The scope is to provide real time vertical deviation at a satisfactory precision and low cost by astronomical and geodetic measurements. The mobile platform for astro-geodetic observations consists in a suitable geodetic instrument, CCD micro-camera and GPS time receiver, all these devices as a whole, being controlled by a portable PC. The proposed method includes measurements/observations procedures, data acquisition and adjustment algorithms, instruments and adjacent devices integrated into a platform, automations and results analyses and interpretation.
Based on the previous geological and geophysical information a special network for geodynamic mon... more Based on the previous geological and geophysical information a special network for geodynamic monitoring of the Romanian territory has been designed and achieved. The network consists of three lines crossing the major lithosphere contacts: the Tornquist-Teisseyre Zone (TTZ) separating the East European Plate from the Intra-Alpine Microplate (IaP), Peceneaga-Camena Fault, as the boundary between EEP and Moesian Microplate (MoP), and the Trans-Getica Fault (TGF) between MoP and IaP. The fourth line is crossing the Vrancea active geodynamic area located in the bending area of East Carpathians. The project INDEGEN (grant CEEX-2 MENER no. 732/2006-2008) started in 2006 with a duration of three years, managed by the Institute of Geodynamics of the Romanian Academy in co-operation with other scientific organizations: Technical University for Civil Engineering – Faculty of Geodesy, University of Bucharest, Geological Institute of Romania, and National Institute for Earth Physics. The main t...
This paper presents aspects of the organization and development of geodetic practice organized by... more This paper presents aspects of the organization and development of geodetic practice organized by the Department of Geodesy and Photogrammetry of the Faculty of Geodesy Bucharest. Since 2006, in the Vrancea area were accomplished the necessary conditions for the good performance of the geodetic practice including geometric levelling, directions and distance measurements, satellite measurements. The existing geodynamic micropolygon in the area was completed with a geodetic network allowing proper development of the mentioned types of measurements already mentioned. In parallel with specific educational activities conducted, the observations results contributes to geodynamic phenomena research in the Vrancea area.
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Papers by Alexandru Călin