Praćenje mijenjanja razine mora pomoću GNSS tehnologije - pregled nedavnih pokušaja

Sea level is traditionally observed with tide gauges (TG). These measurements are relative to the Earth’s crust. To improve the understanding of sea level changes it is necessary to perform measure - ments with respect to the Earth’s center of mass. This can be done with satellite techniques. Global Navigation Satellite System (GNSS) is a tool that can solves several hundred kilometers vectors with centimeter level of accuracy and can measure point height changes relative to the reference ellipsoid WGS84 which is centred at the actual center of mass of the Earth. Although in the past two decades GNSS were used in almost every field of geodetic measurements, it is still almost not in use in the field of sea level monitoring. Attempts of using GNSS equipped buoys for the determination of precise sea level (at centimeter level) were successful and suggest that GNSS is capable of replacing the conventional tide gauges. A review of recent efforts made on observing sea level variations using data from a GNSS receivers were presented here. Furthermore, presented review resulted in a conclusion that the use of a GNSS based Tide Gauge (GNSSTG) system for the determination of sea level changes is possible,and that its accuracy level (averaged) is equal to a float based tide gauge. More than that, an absolute change of sea level should be easier to be determined using GNSSTG system.Razina mora se tradicionalno promatra s mareografima (TG). Ova mjerenja se odnose na Zemljinu koru. Kako biste poboljšali razumijevanje promjena razine mora potrebno je izvršiti mjerenja s obzirom na središte Zemlje mase. Takva mjerenja se provode pomoću sateliteskih tehnika (metoda).Globalni navigacijski satelitski sustav (GNSS) je alat koji može izmjeriti nekoliko stotina kilom -etara vektora s razinom točnosti do u centimetar, te može izmjeriti visinu točke promjene u odnosu na referentnog elipsoida WGS84 koji je usmjeren na stvarni centar Zemljine mase.Iako se u posljednja dva desetljeća GNSS upotrebljava u gotovo svakom području geodetskih mjerenja, ipak još uvijek gotovo da nije u uporabi u području praćenja razine mora. Pokušaji primjene plutača opremljenih GNSS-om za određivanje precizne razine mora (na razini centimetara) bili su uspješni, a ukazuju na to da GNSS može zamijeniti konvencionalne mareografe. Pregled posljednjih promatranja promjena razine mora u kojima se koriste podaci iz GNSS prijemnika su prikazane u ovom radu. Nadalje, predstavljeni pregled u ovom radu rezultirao je zaključkom da se korištenje GNSS temelji na mareografskom (GNSSTG) sustavu za određivanje promjena razine mora, a da je njegova točnost razine (u prosjeku) jednaka plutajućem plovku mareografa. Štoviše, apsolutna promjena visine trebala bi se lakše moći odrediti pomoću GNSSTG sustava

On the Effect of Antenna Calibration Errors on Geodetic Estimates: Investigation on Zero and Double Difference Approaches

This paper addresses an approach to assess the impact of phase centre correction errors of selected receiving antennas in the Polish ASG-Eupos network using GNSS processing strategies such as zero differencing and double differencing. The objective is to characterise the nature of the error patterns of GNSS receiver antennas and to understand their impact on GNSS derived integrated water vapour and geodetic estimates. A semi-analytical approach for characterising variants of error patterns is applied. Differences of up to +12 mm between type-mean and individual receiver antenna calibrations of current antenna models on the ionosphere-free linear combination are identified for repeatable pattern deformations. The analyses show that repeatable effects on tropospheric estimates of up to 8 mm – which corresponds to approx. 1.2 kg/m2 – occur even though only 5 mm variations were applied to the pattern. The results of our analysis show a strong correlation with the type of error patterns that affect the estimates differently. Due to the complex relationship between datum settings, processing strategy, baseline orientation and satellite sky distribution, artefacts in GNSS processing models and their effects must to be modelled in order to achieve a better understanding in the context of GNSS networks and GNSS meteorology

Impact of BeiDou Observations on the Accuracy of Multi-GNSS PPP in a Function of Observing Session Duration within Europe—Analysis Based on Open-Source Software GAMP

This study aims to verify whether the open-source software may provide Precise Point Positioning (PPP) with high accuracy. In this way, we address a question on the potential usability of open-source software for PPP analysis. On 31 July 2020, the full constellation of BeiDou satellites (SV) was announced. Over the European area, however, the number of visible BeiDou SVs is significantly smaller than in Asian-Pacific regions. Additionally, the system is in a modernization process, which may result in difficulties in utilizing its full potential. Ten days of multi-GNSS data were processed using the open-source software GAMP to determine how the accuracy of a derived three-dimensional PPP coordinates depends on observation session length and satellite systems used. The time series of position components of selected EUREF Permanent Network (EPN) stations generated from sub-daily (30 min and longer) solutions were analyzed. The obtained results prove that adding BeiDou observations, even in the case of using an incomplete constellation, leads to visible improvements, which can be observed both in the reduction of differences between estimated and true coordinates, as well as in the reduction of the standard deviation (SD). Improved accuracy caused by adding BeiDou data is especially noticeable for short observation sessions (in the range of 0.5 to 2.0 h) and in the case of a joint solution with GLONASS or Galileo observations. Finally, the open-source software GAMP proved to be a useful tool for multi-GNSS data processing and analysis

SHORT STATIC GPS/GLONASS OBSERVATION PROCESSING IN THE CONTEXT OF ANTENNA PHASE CENTER VARIATION PROBLEM

So far, three methods have been developed to determine GNSS antenna phase center variations (PCV). For this reason, and because of some problems in introducing absolute models, there are presently three models of PCV receiver antennas (relative, absolute converted and absolute) and two satellite antennas (standard and absolute). Additionally, when simultaneously processing observations from different positioning systems (e.g. GPS and GLONASS), we can expect a further complication resulting from the different structure of signals and differences in satellite constellations. This paper aims at studying the height differences in short static GPS/GLONASS observation processing when different calibration models are used. The analysis was done using 3 days of GNSS data, collected with three different receivers and antennas, divided by half hour observation sessions. The results show that switching between relative and absolute PCV models may have a visible effect on height determination, particularly in high accuracy applications. The problem is especially important when mixed GPS/GLONASS observations are processed. The update of receiver antenna calibrations model from relative to absolute in our study (using LEIAT504GG, JAV_GRANT-G3T and TPSHIPER_PLUS antennas) induces a jump (depending on the measurement session) in the vertical component within to 1.3 cm (GPS-only solutions) or within 1.9 cm (GPS/GLONASS solutions)

Dual Receiver EGNOS+SDCM Positioning with C1C and C1W Pseudo-Range Measurements

The paper presents an approach to the simultaneous use of SDCM and EGNOS corrections for two GNSS receivers placed at a constant distance. The SDCM and EGNOS corrections were applied for two GPS code measurements on L1 frequency: C1C and C1W. The approach is based mainly on the constrained least squares adjustment, but for the horizontal and vertical coordinates, the Kalman Filter was applied in order to reduce pseudo-range noises. It allows for obtaining a higher autonomous accuracy of GPS/(SDCM+EGNOS) positioning than when using only the GPS/EGNOS or GPS/SDCM system. The final dual-redundant solution, in which two SBAS systems were used (EGNOS+SDCM) and two GPS pseudo-ranges (C1C+C1W) were present, yielded RMS errors of 0.11 m for the horizontal coordinates and 0.25 m for the vertical coordinates. Moreover, the accuracy analysis in the developed mathematical model for the determined 3D coordinates with simultaneous use of EGNOS and SDCM systems proved to be much more reliable than using only a single EGNOS or SDCM system. The presented approach can be used not only for precise navigation, but also for some geoscience applications and remote sensing where the reliable accuracy of autonomous GPS positioning is required

SHORT STATIC GPS/GLONASS OBSERVATION PROCESSING IN THE CONTEXT OF ANTENNA PHASE CENTER VARIATION PROBLEM

So far, three methods have been developed to determine GNSS antenna phase center variations (PCV). For this reason, and because of some problems in introducing absolute models, there are presently three models of PCV receiver antennas (relative, absolute converted and absolute) and two satellite antennas (standard and absolute). Additionally, when simultaneously processing observations from different positioning systems (e.g. GPS and GLONASS), we can expect a further complication resulting from the different structure of signals and differences in satellite constellations. This paper aims at studying the height differences in short static GPS/GLONASS observation processing when different calibration models are used. The analysis was done using 3 days of GNSS data, collected with three different receivers and antennas, divided by half hour observation sessions. The results show that switching between relative and absolute PCV models may have a visible effect on height determination, particularly in high accuracy applications. The problem is especially important when mixed GPS/GLONASS observations are processed. The update of receiver antenna calibrations model from relative to absolute in our study (using LEIAT504GG, JAV_GRANT-G3T and TPSHIPER_PLUS antennas) induces a jump (depending on the measurement session) in the vertical component within to 1.3 cm (GPS-only solutions) or within 1.9 cm (GPS/GLONASS solutions)