Applicability of Cost-Effective GNSS Sensors for Crustal Deformation Studies

The geodetic monitoring of the continuous crustal deformation in a particular region has traditionally been the prerogative of the scientific communities capable of affording high-price geodetic-class instruments to track the tiny movements of tectonic plates without losing precision. However, GNSS technology has been continuously and rapidly growing, and in the last years, new cost-efficient instruments have entered the mass market, gaining the attention of the scientific community for potentially being high-performing alternative solutions. In this study, we match in parallel a dual-frequency low-cost receiver with two high-price geodetic instruments, all connected to the same geodetic antenna. We select North-East Italy as testing area, and we process the data together with the observations coming from a network of GNSS permanent stations operating in this region. We show that mm-order precision can be achieved by cost-effective GNSS receivers, while the results in terms of time series are largely comparable to those obtained using high-price geodetic receivers.

Updating the subsidence map of Emilia-Romagna region (Italy) by integration of SAR interferometry and GNSS time series: the 2011–2016 period

The analysis of the vertical movements of the soil in the Po River plane of the Emilia-Romagna Region (Italy) was updated through an interferometric analysis referred to the 2011–2016 time-span. This activity is a continuation of previous studies on the state of knowledge of vertical soil movements in the same area, analyzed firstly by levelling and GNSS and more recently by SAR interferometry for the periods 1992–2000, 2002–2006, 2006–2011, on behalf of the Emilia-Romagna Region. The survey area analysed was approximately 13 300 km2, which corresponds to the territory of the regional plain. The interferometric dataset was calibrated through the use of velocity time series of several permanent GNSS stations. Among the 36 stations analysed, 22 were included in the study area: 16 were used for the calibration and 6 as check points). The velocities required for the calibration of the SAR analysis were calculated in the period following the important seismic events that struck the territory of the Emilia Romagna Region in May 2012. The interferometric analysis was carried out by TRE ALTAMIRA using the SqueeSAR™ technology. In particular, in order to update the interferometric dataset to 2016, it was necessary to perform a joint processing of the available RADARSAT-1 data and of the data acquired by the RADARSAT-2 satellite using a specific operating mode of the SqueeSAR™ algorithm known as stitching; this approach allowed the joint processing of images acquired in the same geometry by these two satellites. The study of the time series of the GNSS permanent stations used to provide the velocity datum to the interferometric analysis, is described, and the results of the SqueeSAR™ interferometric processing are reported. Statistical analyses on the spatial distribution and the type of scatterers have been performed during the screening and validation procedures of the dataset, and for the identification and removal of the outliers. Finally, the resulting map is described in order to analyse the measured soil movements with respect to the results obtained in past analyses, and the possible geological and human-induced causes, which could have produced them.

GNSS measurements for ground deformations detection around offshore natural gas fields in the Northern Adriatic Region

The study aims to evaluate ground deformations in a vast area characterized by the coexistence of intense anthropic activities and offshore natural gas production. Onshore subsidence can be studied by GNSS, InSAR, high precision leveling and extensometers that provide broad datasets for a fully integrated description of the phenomenon. At present, seafloor subsidence monitoring cannot be carried out by high precision leveling, and GNSS is the only reliable method, implemented by means of permanent stations installed on offshore hydrocarbon production facilities. In the Northern/Central Adriatic Sea gas production platforms, GNSS data are recorded since more than 15 years, allowing to estimate not only the average subsidence of the platform/seafloor, but also possible velocity variations due to underground fluids withdrawal. This study shows the comparison of 22 offshore GNSS permanent stations located in the study area. Raw data have been processed with two different software packages (GIPSY-OASIS and GAMIT-GLOBK) based on different approaches and considering different boundary conditions of geodetic and/or modeling nature. Main results point out the high accuracy of the GNSS technology considering also the impact of data processing. Finally, at selected permanent stations we also performed a comparison of results obtained by GNSS, InSAR and high precision leveling.

Radar Corner Reflector installation at the OCA geodetic Observatory (France)

<p>Geodetic observatories play a fundamental role in the determination of the International Terrestrial Reference System releases. They host several geodetic permanent instruments whose coordinates can be determined at the centimeter level or better. They comprise Global Navigation Satellite System (GNSS) permanent antenna/receivers, Satellite Laser Ranging (SLR) stations, Very Long Baseline Interferometry (VLBI) telescope and Doppler Orbitography Integrated by Satellite (DORIS) beacons. The Calern site of the Observatoire de la Côte d’Azur (OCA) is an example of such a multi-technique site located in the South of France. It hosts a DORIS beacon, a SLR/LLR station and two GNSS permanent stations.</p><p> </p><p>In the process of determining coordinates of geodetic instruments in a unified reference frame, the relative positions of the instruments at co-location sites are integrated in the ITRF combination. Thanks to the additional measurements obtained from local surveys, it is possible to determine global biases between coordinates determined by individual space geodetic techniques, and express them in the same reference system. An additional fundamental assumption of the combination process is that stations located on the same site do not move with respect to each other. Spaceborne Synthetic Aperture Radar Interferometry (INSAR technique), is an interesting tool to evaluate that hypothesis as it allows measuring ground displacements in the line of sight of the satellite,  and has been used only occasionally in the past for this purpose,. Notably, the Persistent Scatterer (PS) Interferometry enables determining time series of ground displacements on particular scatterers exhibiting phase stability in a stack (or series ?) of SAR images. To ensure the existence (or presence ?) of such PS, artificial corner reflectors can be installed.</p><p> </p><p>We present the procedure that we adapted from Parker et al. (2007) to install and validate the installation of a corner reflector at OCA observatory, close to the currently operating GNSS, SLR and DORIS stations, specifically designed for Sentinel-1 satellite. An initial local tie survey was carried out to assess the stability of the reflector through time.</p>

Ground displacement of the 6 July 2019 Ridgecrest earthquake from the GNSS permanent stations

The Eastern California earthquake (also known as the Ridgecrest earthquake) occurred at 03:19:53 (UTC) on the 6th of July, with a moment magnitude of 7.1. Over the region, there is an accurate network of GNSS permanent stations. Precise determination of displacements of these stations will provide important information to better understand the structure and scope of the earthquake, contributing to faster and more accurate earthquake prediction. In this paper, we used precise point positioning with ambiguity resolution to determine the co-seismic displacements of 25 GNSS stations around the epicenter for the day of the earthquake. The processing results show that the affected area being more than 100 km centered around the earthquake epicenter with the largest value being approximately 0.6 m.

MONITORING SEISMIC DISPLACEMENTS USING GNSS DATA WITH PPP METHOD

The Precise Point Positioning (PPP) analysis method adapted for monitoring coordinate displacements from GNSS permanent stations data. One week period data were analyzed covering the Samothrace strong earthquake event of 6.8M. The sample data were processed with Bernese v5.2 PPP engine and with the online web platform of JPL which uses the GIPSY/OASIS v6.3 software package. Also, for validation purposes the output results were compared with those derived by network analysis by means of the GAMIT processing software of MIT. Our experiments proved the ability to measure dynamic seismic related coordinate variations at sub-centimeter level using the PPP algorithm. But this is efficient when strong earthquakes occurs and for stations close to epicenter.

Investigation of Changes of the Kinematic Parameters of Antarctic Tectonic Plate Using Data Observations of Permanent GNSS Stations

The paper describes a modified algorithm of determination of the Euler pole coordinates and angular velocity of the tectonic plate, considering the continuous and uneven distribution of daily measurements of GNSS permanent stations. Using developed algorithm were determined the mean position of Euler pole and angular velocity of Antarctic tectonic plate and their annual changes. As the input data, we used the results of observations, collected on 28 permanent stations of the Antarctic region, within the period from 1996 to 2014.

Civil Engineering and Building Service Topographic Permanent Landmarks Network. Spatial Coordinate Optimization

Sustainable development is a modern concept of adaptation conditions for achieving objectives that respond simultaneously to at least three major requirements: economic, social and environmental. Achieving sustainable development cannot be accomplished without a change of mentality of people and without communities able to use resources rationally and efficiently. For an efficient application programs surveying topography discipline the students have imagined and created a network of local topographic permanent terminals required for reporting the rectangular coordinates of applications. In order to obtain more accurate values of these coordinates we have made several types of measurements that will be presented in detail in this work. The aim of this paper is to optimize the locating terminals coordinates of the points of our faculty, initially determined using GPS technology. Additional measurements were performed in an interval of one year using a total station. Considering that four previously determined terminal network points were placed between the relatively tall buildings, it was decided that it could be better to determine their spatial coordinates using the classical planimetric surveying method. To this end, the coordinates of the two reference points were located and determined near this network with the help of GPS technology in an area with good visibility. In order to determine the coordinates of the two reference points GNSS Permanent Stations National Network was used through the RTK method: RTCM (Radio Technical Commission for Maritime Services). The measurements were using GPS SOUTH S82T, whose field book has the implemented software transcomputation real-time geographic coordinates in STEREO-70 coordinate system. The network of permanent GNSS stations used the fixed station IASI_2.3 and the virtual station RO_MAC_3.1_GG. The solutions for the new determined points were fixed, the determination’s accuracy ranging between 0.034-0.010 meters. Following these two rounds of measurements of the locating terminals coordinates of the network points of the faculty using GPS technology combined with the classical planimetric surveying method, we got a new set of coordinates with a higher degree of determination accuracy after averaging the results.

The Study of Seasonal Changes of Permanent Stations Coordinates based on Weekly EPN Solutions

Daily and weekly coordinates solutions of GNSS permanent stations operating within EPN network allows to track long-term changes of coordinates caused e.g. by the local and global movements of tectonic plates. They are therefore an excellent tool for testing stability and repeatability of stations position. The article presents an analysis of coordinates changes of selected reference stations based on weekly EPN solutions. In addition the author proposes parameters of approximating function by assuming an existence of periodic, annually repeatable trend. The author performed also an independent fitting function for two different periods of two ITRF frames of routine time analysis and reprocessing.