Search

Accurate Low Earth Orbit satellite (LEO) orbits are essential for many applications, such as for assessing the change in current global mean sea level, or solving the ground coordinates and velocities of tracking system networks such as the DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite). Maneuvers are required for any remote sensing satellite to maintain the reference orbit. The presence of orbit maneuvers poses a challenge for Precise Orbit Determination (POD). At present, most maneuver analysis is conducted using the reduced-dynamic POD approach thus making it impossible to separate specific forcing effects, such as atmospheric drag or maneuver acceleration, from the generic empirical acceleration parameters used in the approach to absorb remaining errors. Therefore, this paper adopts the dynamic model method to better evaluate maneuver accelerations estimated from HY2C and HY2D DORIS/RINEX data. And, we focus on the determination of highly accurate HY2C and HY2D orbits over spans which can include maneuver events. In the course of this study, a maneuver model strategy is developed, and we use the DORIS/RINEX data of HY2C and HY2D satellites to validate the method, and to show it is reliable. Our analysis results are: (1) The standard deviations of DORIS residuals for HY2C and HY2D satellites are respectively 0.45 mm/s and 0.43 mm/s, and these residual values have no significant fluctuations and systematic errors. (2) In the case when there are no DORIS tracking data over the maneuver period, extending the period by 30 s to include tracking will improve orbit accuracy sufficiently to even satisfy altimetry requirements. (3) Based on the developed maneuver model strategy, the radial orbit differences can achieve about 1.70 cm, that can satisfy high precision altimetry requirements of HY2C and HY2D satellites. (4) When the model strategy is used on days containing no orbit maneuvers, the average RMS (root mean square) of radial orbit differences for these days is 1.60 cm, which shows that our maneuver model strategy is also reliable. [ABSTRACT FROM AUTHOR]

We have developed a new multi-GNSS data pre-processing software "RINGO" that provides various features including editing, quality checking, clock jump correction, higher order ionosphere correction, conversion of BINEX and RTCM files, and an interactive viewer for RINEX files. The recent increase in number of GNSS satellites has made GNSS data more complex; however, the software available to pre-process them is very limited. RINGO is a command line tool capable of handling multi-GNSS data, including GPS, QZSS, GLONASS, Galileo, and other systems in RINEX 2.xx, 3.0x, and 4.00 formats, which allows users to easily manage the multi-GNSS data observed at continuously operating reference stations. We present algorithms and applications for each RINGO feature. The results of the quality check feature were compared with results estimated by other existing software packages. Our results agreed well with those of the TEQC software. With RINGO, users can easily pre-process multi-GNSS data without combining multiple tools, and the software will contribute to the popularization of the latest RINEX format. [ABSTRACT FROM AUTHOR]

It is critical to evaluate the reliability of using free online processing software for Global Navigation Satellite System post-processing since the advancement of GNSS gives satellite navigation customers all over the world great benefits. AUSPOS, IBGE, Magic GNSS, CSRS-PPP, and open-source software are some of the online processing solutions being evaluated for accuracy in this study. GNSS observations from IGS were used to conduct field observations using RINEX 3 data from three stations, with an observation duration of 30 seconds. After data acquisition, it was processed with online and free software that made use of GPS, GPS, and GLONASS. When compared to coordinates obtained from reference stations, the relative differences and correctness of the coordinates generated by each piece of software were then evaluated. coordinates in the ITRF14 reference for the X, Y, and Z directions. Online GNSS processing services may be used with greater accuracy for engineering and geodetic applications and are simple to use without the need for GNSS data processing expertise. [ABSTRACT FROM AUTHOR]

Precise position information available from smartphones can play an important role in developing new location-based service (LBS) applications. Starting from 2016, and after the release of Nougat version (Version 7) by Google, developers have had access to the GNSS raw measurements through the new application programming interface (API), namely android.location (API level 24). However, the new API does not provide the typical GNSS observations directly (e.g., pseudorange, carrier-phase and Doppler observations) which have to be generated by the users themselves. Although several Apps have been developed for the GNSS observations generation, various data analyses indicate quality concerns, from biases to observation inconsistency in the generated GNSS observations output from those Apps. The quality concerns would subsequently affect GNSS data processing such as cycle slip detection, code smoothing and ultimately positioning performance. In this study, we first investigate algorithms for GNSS observations generation from the android.location API output. We then evaluate the performances of two widely used Apps (Geo++RINEX logger and GnssLogger Apps), as well as our newly developed one (namely UofC CSV2RINEX tool) which converts the CSV file to a Receiver INdependent Exchange (RINEX) file. Positioning performance analysis is also provided which indicates improved positioning accuracy using our newly developed tool. Future work finding out the potential reasons for the identified misbehavior in the generated GNSS observations is recommended; it will require a joint effort with the App developers. [ABSTRACT FROM AUTHOR]

The Global Navigation Satellite System (GNSS) is a well-known and fundamental tool for crustal monitoring projects and tectonic studies, thanks to its high coverage and the high quality of the data they provide. In particular, at slowly convergent margins, where deformation rates are of the order of a few millimetres per year, GNSS monitoring proves to be beneficial in detecting the diffuse deformation responsible for tectonic stress accrual. Its strength lies in the high precision achieved by GNSS permanent stations, especially when long-term data and stable structures are available at the stations. North-eastern Italy is a tectonically active region located in the northernmost sector of the Adria microplate, slowly converging with the Eurasia plate, characterized by low deformation rates and moderate seismicity. It greatly benefits from continuous and high-precision geodetic monitoring, since it has been equipped with a permanent GNSS network providing real-time data and daily observations over 2 decades. The Friuli Venezia Giulia Deformation Network (FReDNet) was established in the area in 2002 to monitor crustal deformation and contribute to the regional seismic hazard assessment. This paper describes GNSS time series spanning 2 decades of stations located in north-eastern Italy and surroundings as well as the outgoing velocity field. The documented dataset has been retrieved by processing the GNSS observations with the GAMIT/GLOBK software ver10.71, which allows calculation of high-precision coordinate time series, position and velocity for each GNSS station by taking advantage of the high-performance computing resources of the Italian High-Performance Computing Centre (CINECA) clusters. The GNSS observations (raw and standard RINEX – Receiver INdependent EXchange – formats) and the time series estimated with the same procedure are currently daily continued, collected and stored in the framework of a long-term monitoring project. Instead, velocity solutions are intended for annual updates. The time series and velocity field dataset documented here are available on Zenodo (10.5281/zenodo.8055800, Tunini et al., 2024). [ABSTRACT FROM AUTHOR]

The Geodetic Observatory Pecný (GOP) analysis center of the International DORIS Service (IDS) has participated in the ITRF2020 IDS DORIS data reprocessing. This participation followed previous contributions for the ITRF2014 and ITRF2008. The processing standards have changed since the ITRF2014 realization, in particular by switching to data processing based on RINEX observation files, keeping compatibility with the recent operational version of the IERS2010 conventions and with the IDS recommendations. The orbit parametrization and various models have been updated to reach the recent highest standards. The analysis strategy is completely independent of the auxiliary information from the data provider such as quality indicators and center of mass corrections. Several testing campaigns have been performed to optimize the strategy. Jason-1 data have been completely excluded, while SPOT-5 data have fully contributed. A specific strategy for handling the South Atlantic Anomaly was applied for the satellites SPOT-5 and Jason-3. When compared to the GOP solution for ITRF2014, changes in modeling and processing strategy resulted in several significant improvements in the solution statistics and the series of estimated parameters as the stability of the scale and the scattering of the translation series. The analysis of the WRMS of the station position residuals confirmed improvements in particular between mid-2002 and mid-2008 (reduction by more than 1 mm) and after mid-2008 (reduction by about 3 mm). The decrease of the standard deviations in the estimated pole coordinate series reaches 40 percent after adding of Jason-2 in mid-2008. [ABSTRACT FROM AUTHOR]

Global Navigation Satellite Systems are well-known fundamental tools for crustal monitoring projects and tectonic studies, thanks to the high coverage and the high-quality data. In slow convergent margins, in particular, where the deformation rates are of the order of few mm/yr, the GNSS monitoring is beneficial to detect the diffused deformation which is responsible for the tectonic stress accrual. Its strength is the high precision reached by GNSS permanent stations, particularly if long span-data and stable monuments are available at all the stations. North-East Italy is a region which can take the most from continuous and high-precision geodetic monitoring, since it is a tectonically active region located in the northernmost sector of the Adria microplate, slowly converging with the Eurasia plate, but characterised by low deformation rates and moderate seismicity. Furthermore, this region is equipped with a permanent GNSS network providing real-time data and daily observations over two decades. The Friuli Venezia Giulia Deformation Network (FReDNet) was established in the area in 2002 to monitor crustal deformation and contribute to the regional seismic hazard assessment. This paper describes GNSS time series spanning two decades of stations located in the NE-Italy and surroundings, as well as the outcoming velocity field. The documented dataset has been retrieved by processing the GNSS observations with the GAMIT/GLOBK software ver10.71, which allows calculating high-precision coordinate time series, position and velocity for each GNSS station, and by taking advantage of the high-performance computing resources of the Italian High-Performance Computing Centre (CINECA) clusters. The GNSS observations (raw and standard RINEX formats) and the time series estimated with the same procedure are currently daily continued, collected and stored in the framework of a long-term monitoring project. Instead, velocity solutions are planned to be updated annually. The time series and velocity field dataset documented here is available at https://doi.org/10.13120/b6aj-2s32 (Tunini et al., 2023). [ABSTRACT FROM AUTHOR]

The present study analyzes the GNSS time series obtained between the years 2017 and 2022 for the calculation of absolute and residual rates of Ecuador in 10 stations (ABEC, CUEC, ECEC, EPEC, FOEC, GZEC, MUEC, PLEC, RIOP, SEEC, TPC) of the continuous monitoring REGME network. Considering that the latest studies refer to periods 2012–2014 and Ecuador is located in an area of high seismic activity, it is important to update the GNSS rates. The RINEX data were provided by the Military Geographic Institute of Ecuador, the governing institution of geoinformation in that country; for processing, GipsyX scientific software was used with a PPP mode, considering 24 h sessions, and high precision was achieved. For the analysis of time series, the SARI platform was used. The series was modeled using a least-squares adjustment, which delivered the velocities for each station in the three local topocentric components. The results were contrasted with other studies, obtaining interesting conclusions as the presence of abnormal post-seismic rates stands out due to the high rate of seismic occurrence in Ecuador, and reaffirms the idea of a constant update of velocities for the Ecuadorian territory and the inclusion of the stochastic factor in the analysis of GNSS time series, since it can affect the ability to obtain the final GNSS velocities. [ABSTRACT FROM AUTHOR]

Monitoring of the periglacial environment is relevant for many disciplines including glaciology, natural hazard management, geomorphology, and geodesy. Since October 2022, Rock Glacier Velocity (RGV) is a new Essential Climate Variable (ECV) product within the Global Climate Observing System (GCOS). However, geodetic surveys at high elevation remain very challenging due to environmental and logistical reasons. During the past decades, the introduction of low-cost global navigation satellite system (GNSS) technologies has allowed us to increase the accuracy and frequency of the observations. Today, permanent GNSS instruments enable continuous surface displacement observations at millimetre accuracy with a sub-daily resolution. In this paper, we describe decennial time series of GNSS observables as well as accompanying meteorological data. The observations comprise 54 positions located on different periglacial landforms (rock glaciers, landslides, and steep rock walls) at altitudes ranging from 2304 to 4003 ma.s.l. and spread across the Swiss Alps. The primary data products consist of raw GNSS observables in RINEX format, inclinometers, and weather station data. Additionally, cleaned and aggregated time series of the primary data products are provided, including daily GNSS positions derived through two independent processing tool chains. The observations documented here extend beyond the dataset presented in the paper and are currently continued with the intention of long-term monitoring. An annual update of the dataset, available at 10.1594/PANGAEA.948334 ,​​​​​​​ is planned. With its future continuation, the dataset holds potential for advancing fundamental process understanding and for the development of applied methods in support of e.g. natural hazard management. [ABSTRACT FROM AUTHOR]

The aim of this work is to explore, for the first time in Poland, the possibility of determining Earth's crust movements from permanent observations at selected permanent stations using the GipsyX software for a period of 8 years (2011--2018) in the ITRF2014 reference frame. The data used in this work are from 15 Aktywna Sieć Geodezyjna (ASG)-EUPOS stations from 2011 to 2018, which are also European Permanent Network (EPN) stations. The stations Borowa Góra, Borowiec, Józefosław, Lamkówko, and Wroclaw are also International Global Navigation Satellite Systems (GNSS) Service (IGS) stations. Daily data, rinex files, for these stations have been made available for this work by the Main Office of Surveying and Cartography. The calculations were made using the GipsyX software in the ITRF14 reference frame. The tests performed have shown that daily solutions from 8-year-long time series give secular trends with an accuracy of 0.01 mm/yr. Our results suggest that there are small differences in horizontal and vertical velocities and in the accuracy estimated between our and EPN solutions. At some stations, for example, Łódź, the differences are much larger. The impact of additional GNSS observations on the accuracy of determination of horizontal and vertical movements of the Earth's crust shows a submillimeter accuracy in computed coordinates of stations even at a relatively small time interval. It means that multi-GNSS Precise Point Positioning (PPP) processing can be used in the future for the estimation of geodynamic processes. [ABSTRACT FROM AUTHOR]

More than 66% of the Nepalese population has been actively dependent on agriculture for their day-to-day living. Maize is the largest cereal crop in Nepal, both in terms of production and cultivated area in the hilly and mountainous regions of Nepal. The traditional ground-based method for growth monitoring and yield estimation of maize plant is time consuming, especially when measuring large areas, and may not provide a comprehensive view of the entire crop. Estimation of yield can be performed using remote sensing technology such as Unmanned Aerial Vehicles (UAVs), which is a rapid method for large area examination, providing detailed data on plant growth and yield estimation. This research paper aims to explore the capability of UAVs for plant growth monitoring and yield estimation in mountainous terrain. A multi-rotor UAV with a multi-spectral camera was used to obtain canopy spectral information of maize in five different stages of the maize plant life cycle. The images taken from the UAV were processed to obtain the result of the orthomosaic and the Digital Surface Model (DSM). The crop yield was estimated using different parameters such as Plant Height, Vegetation Indices, and biomass. A relationship was established in each sub-plot which was further used to calculate the yield of an individual plot. The estimated yield obtained from the model was validated against the ground-measured yield through statistical tests. A comparison of the Normalized Difference Vegetation Index (NDVI) and the Green–Red Vegetation Index (GRVI) indicators of a Sentinel image was performed. GRVI was found to be the most important parameter and NDVI was found to be the least important parameter for yield determination besides their spatial resolution in a hilly region. [ABSTRACT FROM AUTHOR]

The large amount of data that are available for ionospheric studies using the GPS TEC method, as well as the need to take into account complex atmospheric dynamics, create certain difficulties in automating the process of searching and recognizing traveling ionospheric disturbances generated by different sources. To automate the process of detecting wave disturbances, numerical criteria for assessing the level of the wave disturbance signal were proposed. The signal-to-noise ratio calculated by the proposed method was used as one of such criteria. This work contains a description of the developed software system that implements the proposed methodology and allows the loading of RINEX files and processing, analyzing, and visualizing total electron content data. [ABSTRACT FROM AUTHOR]

Here we test the capability of the Broadcast Ephemeris Message, in both its GPS-like (Keplerian ellipse with secular and periodic perturbations) and Glonass-like (numerical integration of a 9D state vector) formats, to reproduce a corresponding precise ephemeris. We start from a daily Rinex 3.04 navigation file for multiple GNSS and the corresponding SP3 precise orbits computed by CNES (Centre National d'Etudes Spatiales) for GPS, Glonass, Galileo and CODE (Center for Orbit Determination in Europe) for Beidou, and compute broadcast ECEF coordinates and clocks. The pre-fit discrepancies are converted by least squares to corrections to the broadcast ephemeris parameters in two-hour consecutive arcs (for GPS, Galileo and Beidou) and to a set of seven Helmert parameters for the entire day, to align in origin, orientation and scale to the common GNSS IGS14 Reference Frame. The test cases suggest that the Broadcast Ephemeris Message, complemented with Reference Frame information, can reproduce the precise ephemeris and clocks with centimetric accuracy for intervals at least equal to the respective validity times, typically 2 h. The broadcast ephemeris of Glonass consists of three initial positions and velocities at epoch, three constant Lunisolar accelerations for the satellite position, and of three polynomial coefficients for the satellite clock. The 9D vector of state is numerically integrated to generate position and velocity data within the validity time (0.5 h) of the message. To test the capability of this model to reproduce the corresponding values of a precise ephemeris, the 9D vector of state and clock polynomials are adjusted until the rms (root mean squared spread) of the post-fit residuals relative to a precise orbit (CNES's in our case) is minimum. We show in one example (one satellite for one day) that the Glonass type of message can reproduce a precise ephemeris and clock with a rms spread of 0.025 m over one-hour arcs. Volume computations on one month of data with all available satellites confirm the test results. For GPS, Glonass, Galileo and Beidou, the best fitting clock values predicted by our second order polynomials, based on a 15 min sampling, are shown to fit the corresponding high rate clocks (30 s sampling) of MGEX with zero bias and a rms spread of 0.062 ns (GPS G01), 0.023 ns (Galileo E01), 0.43 ns (Glonass R01), 0.086 ns (Beidou C07) and 0.086 ns (Beidou C12). Modifications to the GPS-like message structure and Glonass algorithm are proposed to increase the validity time by including the effect of the 3rd zonal harmonic of the Earth's gravity field. The potential of the RTCM messages for broadcasting the improved navigation message is reviewed. [ABSTRACT FROM AUTHOR]

Robust autonomous driving, as long as it relies on satellite-based positioning, requires carrier-phase-based algorithms, among other types of data sources, to obtain precise and true positions, which is also primarily true for the use of GNSS geodetic receivers, but also increasingly true for mass-market devices. The experiment was conducted under line-of-sight conditions on a straight road during a period of no traffic. The receivers were positioned on the roof of a car travelling at low speed in the presence of a static jammer, while kinematic relative positioning was performed with the static reference base receiver. Interference mitigation techniques in the GNSS receivers used, which were unknown to the authors, were compared using (a) the observed carrier-to-noise power spectral density ratio as an indication of the receivers' ability to improve signal quality, and (b) the post-processed position solutions based on RINEX-formatted data. The observed carrier-to-noise density generally exerts the expected dependencies and leaves space for comparisons of applied processing abilities in the receivers, while conclusions on the output data results comparison are limited due to the non-synchronized clocks of the receivers. According to our current and previous results, none of the GNSS receivers used in the experiments employs an effective type of complete mitigation technique adapted to the chirp jammer. [ABSTRACT FROM AUTHOR]