BeiDou Global Navigation Satellite System (BDS-3) was formally commissioned to provide satellite navigation services worldwide in 2020. It not only has the normal positioning, navigation and timing (PNT) functions, but also provides several kinds of featured services. The paper  focuses on the featured services of BDS-3 and their applications in various geoscience fields. First, the featured services of BDS-3 and their performances are introduced. Then different application examples are described and analyzed based on the Geostationary Orbit (GEO) satellite-based featured services and Middle Earth Orbit (MEO) satellite-based featured services. Finally, some possible improvements to BDS in the future are discussed.

How to cite: Yang, Y., Ren, X., Xu, T., and Sun, B.: Featured Services of BDS-3 with Applications in Geoscience, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17041, https://doi.org/10.5194/egusphere-egu23-17041, 2023.

Due to the correlation between coordinates, atmospheric delays, and ambiguities, Precise Point Position with Ambiguity Resolution (PPP-AR) needs a long convergence time (around 20 min) to achieve cm-level accuracy. With the help of precise external atmospheric products, PPP-AR convergence time can be reduced to a few minutes or even instantaneously. However, a stable and continuous data transmission in real-time communication could be challenging in more expansive areas due to the massive amount of correction information from dense networks. In addition, data interruptions and switching reference stations also could cause discontinuity or anomalies in the real-time correction information. By combining both wide-area fitting functions and regional un-modeled corrections, we present an integrated hierarchical augmentation method, which could ensure reliable and precise positioning with less communication burden. The first level of the hierarchical model includes the satellite-wise slant ionospheric delay and tropospheric Zenith Wet Delay (ZWD) wide-area fitting models, which provides an essential correction with few model coefficients covering a larger area. Moreover, the residual unmodeled errors and phase residuals can be provided optionally, according to the communication capability and the user’s requirement. The newly developed augmentation mode extends from the current wide-area low-precision to the hierarchical-precision service, which relieves the communication burden and greatly reduces the dependence on the distribution of reference stations. We evaluate our model in the European region, using 103 EUREF Permanent Network (EPN) stations with 200 km station-spacing as modeling stations and 84 stations as external validation. The precision of the wide-area ionospheric and tropospheric delay models are 4.5 cm and 1.3 cm, respectively. With only the wide-area correction information, an convergence time (to 10 cm) of 2 and 3 minutes can be achieved for the horizontal and vertical components, respectively. Based on the magnitude of wide-area unmodeled errors, the optional unmodeled correction broadcast volume can be saved by 40-50% with respect to the legacy interpolation mode. Moreover, instantaneous ambiguity fixing within one to two epochs (1 min) can be achieved if the unmodeled residuals are exploited. Therefore, the proposed hierarchical augmentation mode satisfies different positioning demands of wide-area with low resource utilization.

How to cite: Cui, B., Wang, J., Jiang, X., Li, P., Ge, M., and Schuh, H.: An integrated hierarchical wide-area augmentation for real-time GNSS positioning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3580, https://doi.org/10.5194/egusphere-egu23-3580, 2023.

Over the past decades, Precise Point Positioning (PPP) has become a well-established technique for determining the user's position with the signals of Global Navigation Satellite Systems (GNSS). PPP is characterized by applying precise satellite products (orbits, clocks, and biases) and accurately modeling a wide range of error sources to estimate the user's position. This way, a position accuracy at the centimeter or even millimeter level is accomplished. However, the convergence time until the coordinates have reached this accuracy is well known as the primary concern of PPP. In that regard, PPP with integer ambiguity resolution (PPP-AR) has proven as an effective way to dramatically reduce the convergence time of PPP, especially in the east coordinate component.

Currently, the so-called Orbit Exchange (ORBEX) format is under revision. Its main philosophy is larger flexibility for the description of the satellite state than in different existing formats. Besides other advantages, the ORBEX format can provide information on the satellite orientation in attitude records. Several Analysis Centers have started to provide such data in addition to their satellite orbits, clocks, and biases. Consequently, the PPP user can accurately calculate the satellite orientation instead of relying on the usually adopted IGS convention.

Since the satellites' orientation is essential for accurately modeling several error sources and recovering the integer property of the phase ambiguities, the performance of PPP is usually improved by using accurate satellite attitude information. This contribution illustrates the effect of attitude data on ambiguity fixing, convergence time (time to first fix), and coordinate accuracy in several test cases. Especially, satellite eclipse seasons are investigated. The PPP calculations are performed with our software raPPPid, the PPP module of the Vienna VLBI and Satellite Software (VieVS PPP).

How to cite: Glaner, M. F. and Weber, R.: Enhancing PPP-AR with satellite attitude data from ORBEX files, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11735, https://doi.org/10.5194/egusphere-egu23-11735, 2023.

GNSS/A is a proven method to localize seafloor geodetic stations and, thus, to monitor seafloor tectonic phenomena. This approach combines GNSS positioning of a surface platform with acoustic ranging between this platform and acoustic beacons on the sea bottom, with the objective to localize the beacons in a global frame within a centimeter or so. As part of the FOCUS project, a network of seafloor stations was deployed offshore Sicily in Italy, at about 1900 meters depth. It was surveyed from a small autonomous surface vehicle (ASV) equipped with two GNSS receivers. Here we present the post-processing applied to the GNSS surface navigation data in order to reduce the uncertainty budget of the GNSS/A algorithm. We found significant discrepancies between GNSS receivers in terms of signal degrading effects (multipaths, cycle slips, signal interruptions). We also found that GNSS antennas are less subject to these effects when mounted on an ASV rather than on the main vessel mast. The correlation found between solution accuracy and signal degrading effects potency turned out to be inadequate to predict the former knowing the latter. Then, we compared the accuracy of kinematic solutions from three GNSS PPP-AR post-processing packages to a few/several centimeters level. From our analysis, we find that the best accuracy was reached using the CSRS-PPP service.

How to cite: Lenhof, E., Royer, J.-Y., Ballu, V., Sakic, P., Poitou, C., Beauverger, M., Coulombier, T., Dausse, D., Jamieson, G., Morvan, P.-Y., and Gutscher, M.-A.: Comparison of GNSS PPP-AR packages for post-processing seafloor geodetic data., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15254, https://doi.org/10.5194/egusphere-egu23-15254, 2023.

A GNSS data set was recorded for ionosphere sounding on the German research icebreaker Polarstern during the expedition of MOSAiC (Multidisciplinary Observatory for the Study of the Arctic Climate). The GNSS setup comprised a multi-GNSS high-rate (50 Hz) receiver and a multiband GNSS antenna at right-handed polarization. During the one-year expedition (Sep. 2019 to Oct. 2020) the ship drifted with ice floes over the Arctic Ocean for studying the Arctic climate. In addition, the drift gave an excellent opportunity to collect GNSS data for ionosphere sounding over the central Arctic (at lat. > 85° N). More than five months the ship was drifting in the central part of the Arctic where data from permanent GNSS stations are not available. Nearest stations are all located further south. These measurements aboard Polarstern provide ideal conditions to study scintillations induced by disturbances in the Arctic ionosphere (e.g. by polar patches). The coincidence of the expedition period (2019/20) and solar minimum is a small drawback for the study. It limits the probability of strong scintillations in the observations. So, the question arises whether the precision of GNSS phase measurements on a ship is high enough to detect phase scintillations at solar minimum.

The standard deviation of detrended phase samples (phase scintillation index) is derived with 30 s resolution for each GNSS link to quantify disturbance. The study focuses in a first approach on GPS data and high elevation angles (> 30°) as these rays propagate rather vertically and stay in the central Arctic with ionospheric piercing points (assumed at 350 km) not far from the ship location (roughly: horizontal distance < 600 km). Three categories of disturbance are identified in this elevation range:

• Phase index baseline of about 0.1 +/- 0.05 rad, that is the lower limit for this ship-based setup
• Phase index anomalies from 0.15 to 0.4 rad (and more) that are found in constant directions on the ship (constant relative bearing) and can be attributed to disturbance of ship multipath/shadowing (by mast and chimney) affecting the field-of-view in these directions
• Phase index anomalies between 0.15 and 0.2 rad, that occur around local noon at the given high latitudes and can be identified as weak scintillations due to ionospheric disturbance in the cusp region (at the convergence of geomagnetic field lines)

Compared to a typical ground-based station operating in the Arctic, the ship-based measurements present a rather high baseline index level that is already in the weak scintillation range. The difference between baseline and the cusp-related scintillations is rather small. Parameters (latitude, elevation angle and local time of the observation) are considered to identify the ionospheric scintillations. Furthermore, anomalies induced by ship multipath disturb the scintillation detection and need to be identified and masked out based on relative bearing limits. We conclude that ship-based GNSS is precise enough to detect Arctic phase scintillations even at the minimum of the solar cycle if proper analysis is conducted.

How to cite: Semmling, M., Berdermann, J., Sato, H., Fohlmeister, F., Kriegel, M., and Hoque, M.: Are ship-based GNSS measurements precise enough to detect ionospheric phase scintillation at solar minimum?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9866, https://doi.org/10.5194/egusphere-egu23-9866, 2023.

Ionospheric disturbances can negatively impact the accuracy, continuity, availability, and integrity of Global Navigation Satellite Systems (GNSS) based services. Therefore, reliable description and characterization of these disturbances are essential to guarantee an adequate level of safety for GNSS-based systems, susceptible to strong spatial gradients and rapid changes in electron density along the receiver-satellite path (slant total electron content, STEC).

This study aims to compare various indices that describe the current condition and intensity of ionospheric disturbances using GNSS observations from approximately 350 reference stations in Europe. The indices studied include the Gradient Ionospheric Index (GIX), the Sudden Ionospheric Disturbance Index (SIDX), and the Rate Of Tec Index (ROTI). The study focuses on selected geomagnetic storms and compares the results for different latitude zones (30-45°N, 45-60°N, and 60-75°N). The results show that the behaviors of the investigated indices differ in each case and are strongly dependent on the ionospheric storm propagation mechanism and associated with actual space weather and geo-physical conditions. The study also examines the relationships between the analyzed indices and GNSS positioning results using absolute and differential approaches and code pseudorange and carrier phase-based results. In addition, a comparison with vertical protection error (VPE) and vertical protection level (VPL) for selected EGNOS Ranging and Integrity Monitoring Stations is included.

How to cite: Nykiel, G., Cahuasquí, J. A., Hoque, M., and Jakowski, N.: Comparison of GIX, SIDX and ROTI ionospheric indices and their relationships with GNSS positioning results, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9450, https://doi.org/10.5194/egusphere-egu23-9450, 2023.

In GNSS analysis, tropospheric modelling is done in the form of Zenith Hydrostatic Delay (ZHD), which can be empirically computed from surface pressure and temperature, and Zenith Wet Delay (ZWD), which is estimated together with the other unknown parameters.  Analysis methods based on undifferenced GNSS code- and carrier-phase observations like Precise Point Positioning (PPP), which can achieve millimeter-accurate positioning results, provide therefore also time-series of ZWD, which can be used for meteorologic applications. However, due to receiver noise and system characteristics like cycle-slips the accuracy as well as the precision of such ZWD estimates is limited. Thus, we propose a novel approach for sites, which have several receivers connected to a single antenna or which are separated horizontally by only a few meters. For such sites, one can simultaneously process multi-frequency GNSS data by fusing observations from several receivers, while estimating a common ZWD parameter.

For this purpose, we have implemented a PPP algorithm based on an Extended Kalman Filter (EKF) approach, which has the advantage that ZWD estimates are available in real-time for meteorologic applications. We demonstrate that those combined ZWD estimates are superior to single receiver estimates in term of precision and accuracy. For the latter measure, we make use of a GNSS hardware simulator and show that the RMS between the simulated and estimated ZWD significantly decreases when having two or more receivers at that site. Based on real-data we show that this concept provides less noisy ZWD estimates which agree better with physical properties of the local wet refractivity field.

Moreover, we demonstrate that fusing data from several receivers by estimating a common ZWD parameter improves also positioning accuracy and precision, in particular in the up-component. In order to properly combine observations from geodetic-grade and low-cost GNSS receivers, we present our adaptive Kalman filter approach, which adjusts the observation noise covariance matrix automatically during processing. The presentation concludes with an outlook on the usage of this approach for larger networks and answers the question how arrays of low-cost GNSS receivers can compete against geodetic-grade GNSS hardware in term of providing ZWD estimates for meteorology.

How to cite: Wang, R., Hobiger, T., Marut, G., and Hadas, T.: Improving GNSS meteorology by fusing measurements of multi-receiver sites on the observation level, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3364, https://doi.org/10.5194/egusphere-egu23-3364, 2023.

The high-rate GNSS has been proven to be an effective tool to describe moderate and strong natural earthquakes, whereas the much less addressed application is monitoring anthropogenic earthquakes, such as mining tremors, where the noise and displacements have similar values. Although the anthropogenic events have small magnitudes (usually below 4.5), they also have much shallower epicentres (depths up to 1-2 km). Therefore, the vibrations they cause are often felt and may have a dangerous impact on the ground, structures and infrastructure nearby.

Here we show that with the high-rate multi-constellation GNSS observations (GPS+Galileo), we can reliably detect the low-magnitude shallow anthropogenic earthquakes and characterise them in terms of displacements and velocities. Our filtering procedure is based on multiresolution analysis and successfully retrieves the small signal of ground vibrations. We analysed five mining tremors with magnitudes of 3.4-4.0 and presented the results from high-rate GNSS position changes calculated parallel with the PPP and variometric approach. The accuracy was very few millimetres for displacements and 1-2 cm/s for velocities. We obtained satisfying correlations with seismological data in correlation, peak values comparison and earthquake first epoch determination. Finally, considering the high-rate GNSS positioning noise level, we demonstrate the capacity to resolve the dynamic displacements from high-rate GNSS at the epicentral distance of about 7-8 km.

How to cite: Kudłacik, I., Kapłon, J., Fortunato, M., Kaźmierski, K., and Crespi, M.: GNSS-seismology for anthropogenic earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11547, https://doi.org/10.5194/egusphere-egu23-11547, 2023.