The Workshop will comprise 10 scientific sessions (see list below) including oral and poster presentations, as well as splinter meetings for the different IGS working groups.
Summary: In this session, we seek contributions from the IGS analysis centers on improvements to analysis methods and models that they are exploring and on experiences with the transition to IGS14. Of interest are presentations of new orbit modeling and analysis efforts, generation of historical PPP clock and orbit products in IGS14, and other modeling improvements that are likely to increase the quality of IGS products.
Summary: Released in January 2017, the new IGS antenna calibration file (igs14.atx) provides phase center offset (PCO) and variation (PCV) parameters for almost 200 GNSS satellite transmitting antennas and more than 300 geodetic station receiver antennas. The most relevant changes to igs14.atx compared to the previous version, igs08.atx, are the realigned radial offsets (z-PCOs) for the GPS/GLONASS constellation and the integration of additional receiver antenna calibration results from robotic field measurements, bringing the total number of absolutely calibrated ground antennas in the global IGS tracking network to more than 90 percent. However, despite these promising developments, igs14.atx still has several known shortcomings, including the failure to account for the azimuth dependence of the phase center position of certain transmit antennas (GPS Block II/IIA/IIR/IIF, Galileo IOV), failure to support antenna group delay patterns, the lack of satellite antenna PCVs for emerging GNSS systems (BeiDou, Galileo, QZSS, IRNSS), the lack of phase center corrections for the new GNSS signals (GPS L5, GLONASS G3), and the presence of site-specific multipath near-field effects altering the tabulated phase center parameters. Accordingly, the antenna session is open to submissions related to a wide range of antenna- and igs14.atx-oriented topics, including but not limited to new results in the following areas:
- GNSS/multi-GNSS ground antenna calibrations systems
- Investigation of in-situ calibrations of antenna installations
- Benefits of individual calibrations of GNSS ground antennas
- Benefits of azimuthal satellite antenna PCVs
- Importance of group delay patterns, particularly related to integer ambiguity resolution
- Estimation of satellite antenna PCOs and PCVs for the new GNSS signals and constellations
- Use of current and future spaceborne missions in low, medium, and high Earth orbit for consistent in-situ calibration of all GNSS antennas, ground and space
- Multipath mitigation and interference suppression
Careful treatment of measurement biases in legacy and new signals is crucial for combined analysis of multiple GNSS. Contributions presenting results and processing concepts for the modeling, determination, or calibration of biases are invited. This includes:
- code and code-phase receiver biases in GPS, GLONASS and new constellations,
- the handling of biases in single-receiver ambiguity resolution,
- line bias variations,
- absolute, or observable-specific bias concepts,
- results concerning long-term stability or combination of biases.
To use the nomenclature of the new Bias-SINEX Format Version 1.00 is suggested. In addition, the field of GNSS biases may be extended to site-specific biases that may vary between each contributing GNSS, such as GNSS-specific station coordinate deviations. Contributions building on data and products from the IGS MGEX project are specifically encouraged.
Infrastructure, Data Centers and Formats
Summary: The backbone of all IGS products will continue to be having state-of- the-art formats, data centers, and infrastructure that can cope and adapt to the increasing need for greater accuracy, reliability and speed, which are critical to serve the scientific community in their IGS data and product requirements. This session will present the latest developments in how the IGS has been adapting its infrastructure, its data centers, and data formats to better fulfill the goals of the IGS, its members, and its global user community.
Ionosphere & Troposphere
Summary: Total Electron Content (TEC) is important because of the dispersive effect it has on any trans-ionospheric radio signals which leads to a frequency dependent delay and refraction of the signals. Space geodetic techniques such as GNSS (ground- and satellite-based), DORIS, VLBI, satellite altimetry or the GPS radio occultation missions can provide valuable information on the electron density. The potential for ionospheric sensing using these techniques has improved considerably over the last few years. The ionosphere session will be a forum for discussing a) algorithms and models for processing, calibrating and improving the precision of TEC measurements, b) possible improvements of the IGS ionospheric products, c) occultation measurements, d) applications of TEC measurements products. The session also includes a summary of the activities of the IGS Ionosphere Working Group.
The troposphere session will include presentations related to GNSS-based troposphere delay: computation/distribution of estimates, research into mapping functions and models, applications of troposphere estimates, comparison with other methods, impact of troposphere delay estimates on timing or positioning, and other topics.
Multi-GNSS & Constellation Monitoring
Summary: This session solicits contributions related to the joint processing of legacy and new (BeiDou, Galileo, QZSS, NavIC) navigation satellite systems as well as GNSS performance monitoring. Topics may include – but are not limited to – the generation of multi-GNSS orbit, clock, and bias products, their use in precise multi-GNSS applications (positioning, atmospheric monitoring, etc.), and the evaluation of GNSS performance indicators such as signal-in-space range accuracy, user range error, and availability. Contributions shall be closely related to IGS activities in the field and results from the MGEX Pilot Project as well as the recently launched IGMA-IGS Joint Trial Project on GNSS Performance Monitoring are specifically encouraged.
Summary: Modelling accurately GNSS satellites orbits remains an important issue for the quality of IGS products. The surface force models are probably the most important sources of differences between analysis centers products (effect of SRP models and attitude, albedo models, modelling methods like bow and wings, semi-empirical, empirical...). This is also related to different parametrization strategies for empirical parameters. The use of different constellations will change the errors characteristics observed in the results (draconitic effects...), so the impact of the different constellation dynamic characteristics has to be considered (geometry, planes, inclination, period...). The length of the solved arcs is also an issue to be addressed to achieve multi-constellation consistent solutions, using for example longer arcs than the usual daily solutions. The inclusion of LEO satellites in the global GNSS constellation solutions could change some characteristics of the GNSS solutions errors. Any contribution related to these topics is welcome.
Summary: The IGS Real Time Service (RTS) was formally launched in April 2013. This consists of GNSS data and products that are streamed from IGS data centres and are openly available to subscribed users with latencies of a few seconds.
The session will focus on aspects of the RTS and its potential evolution, including the core infrastructure of GNSS receiver networks, data centres and analysis and combination centres and on the scientific and public service applications (e.g. precise positioning, atmospheric modelling, disaster monitoring, time transfer) that make use of the service. Emphasis will be given on techniques and processes that improve the accuracy and reliability of the service to the user and on addressing the challenges of multi-GNSS processing for AC and user solutions. These include the need for accurate satellite modelling and early identification of orbit problems to minimise the effect of orbit prediction errors, understanding the impact of biases on multi-signal multi-constellation solutions and the latest advances in the user Precise Point Positioning (PPP) algorithms.
Summary: GNSS play a fundamental role in the elaboration and dissemination of the International Terrestrial Reference Frame (ITRF), in the monitoring of the Earth's rotation and in the study of geophysical ground deformations. However, GNSS-derived station positions and Earth Orientation Parameters are known to be affected by systematic and random errors of various types and origins. This session therefore welcomes contributions related to the characterization, understanding and mitigation of these errors, but also to the interpretation and modelling of the geophysical signals present in GNSS station position time series.
Besides improvements in the GNSS reference frame products and their geophysical interpretation, this session is additionally intended to discuss potential improvements in the construction of the ITRF (i.e., handling of non-linear station motions, handling of the systematic and random errors in the technique contributions) and in the implementation of the ITRF by the IGS (i.e., how to best ensure the alignment of the IGS products to the ITRF datum).
Summary: IGS products are being used for an increasingly broad diversity of scientific applications. The benefits of using IGS products include accuracy, robustness, consistency, stability, standardization, and traceability in reference systems and time standards. Moreover, many applications benefit retrospectively when IGS completely reprocesses of its entire dataset with improved reference systems, models, estimation strategies, algorithms, and calibrations. Scientific applications that benefit from IGS comprise an exponentially growing list, including reference frame realization, Earth rotation, plate tectonics, plate boundary deformation, the earthquake cycle, seismology, glacial isostatic adjustment, sea level monitoring, low Earth orbiter positioning, time transfer, weather forecasting, climate monitoring, ionospheric science, atmospheric sounding, tsunami early warning, terrestrial water storage, snow depths, soil moisture, vegetation monitoring, and fundamental physics experiments. For this session, we solicit presentations on scientific applications that use IGS products (either combination products or Analysis Center products). We particularly encourage presentations that trace the quality of the science outcomes to the quality of IGS products, and identify how future science may be improved by either new or improved IGS products.
Summary: Precision clocks and frequency standards are both critical to the operation of all GNSS. The IGS Clock Products and its associated working group were established in 2003 after considerable joint work between the IGS and BIPM that investigated time and frequency comparisons using GPS phase and code measurements. Early goals of this joint work included: installation of geodetic timing receivers at timing laboratories, inclusion of tracking station clocks in the formal IGS products, and development of methods for accurate instrument calibration for precision timing applications.
The IGS clock products now contributes to and participates in the IGS rapid and final clock combinations. Clock estimates and statistics are generated monthly and the IGS reference time is steered to UTC(k) laboratories daily. Future clock products will consist of solutions and estimates for clocks across many GNSS constellations.
A specific topic of interest is the need for interoperability of these many GNSS that have become available. The 11th meeting of the International Committee on GNSS (ICG) has stressed the importance of determining GNSS time offsets between systems to maintain the interoperable service provision.
For this session, we solicit presentations on the applications of the IGS products for timing research and development including but not limited to:
- links between the IGS and the time laboratories participating to UTC;
- IGS clock products and their assessment;
- use of IGS clock products for time and frequency transfer;
- calibration of geodetic time receivers;
- GNSS clock performance and development; and,
- assessment of GNSS system time offsets and the interoperability of GNSS systems.