Sub-Commission 4.4

GNSS Integrity and Quality Control

Chair: Pawel Wielgosz (Poland)
Vice-Chair: Jianghui Geng (China)
Secretary: Grzegorz Krzan (Poland)

Terms of Reference

GNSS constellation is rapidly developing by growing the number of satellites and available signals and frequencies. In addition to two already operational GPS and GLONASS systems, the new Galileo and BDS systems achieved initial operational capabilities. Both GPS and GLONASS are currently undergoing a significant modernization, which adds more capacity, more signals, better accuracy and interoperability, etc. In addition, a rapid development in the mass-market GNSS chipsets has to be also acknowledged.
These new developments in GNSS provide opportunities to create new high-precision GNSS technologies and applications and also to open new research areas. This, however, results in new challenges in multi-GNSS data processing, which primarily concern the positioning integrity and reliability. Recognizing the central role of GNSS in providing high accuracy positioning information, SC4.4 will foster research activities that address integrity, quality control and relevant applications of GNSS in case of multi-constellation and multi-frequency environment. SC4.4 will coordinate activities to deliver practical and theoretical solutions for engineering and scientific applications. Among those applications there are structural and ground deformation monitoring, precise navigation, GNSS remote sensing, geodynamics, etc.
SC4.4 will also encourage strong collaboration with the IAG Services (primarily IGS) as well as with relevant entities within scientific and professional sister organizations (FIG, IEEE and ION).

The major objective of SC4.4 is to promote collective research on GNSS Integrity and Quality Control methods and their novel applications to facilitate timely dissemination of scientific findings, to stimulate strong collaborations among researchers and international organizations and the industry.

Program of Activities
• to identify and investigate important scientific and technical issues in GNSS integrity and quality control methods and their applications,
• to stimulate strong collaborations among researchers,
• to organize international conferences and workshops,
• to promote the use reliable GNSS techniques and products in interdisciplinary scientific research and engineering applications.
Working and Study Groups of Sub-Commission 4.4

WG 4.4.1: Integrity monitoring and quality control of Precise Positioning

Chair: Ahmed El-Mowafy (Australia)
Vice-Chair: TBD

Global Navigation Satellite Systems (GNSS) are the prime source of precise position information for a variety of applications including autonomous driving, precision agriculture, road charging, deformation monitoring and civil aviation. For such applications that even small errors can incur serious consequences like loss of human lives, wrong legal decisions and damage to infrastructure, the provided position information needs to be of high level of reliability. On the other hand, any positioning platform, either based on standalone- or augmented-GNSS, is subject to a series of vulnerabilities, e.g. interference and carrier phase cycle-slips, which can dramatically deteriorate the reliability of the position solutions. As such, it is crucial to have proper ‘Quality Control’ mechanisms in place for timely detection of hazardous faults, thus warranting the reliability. The constituent components of a quality control procedure will vary depending on the positioning sensors in use and the precision and reliability requirements. This will in turn raise the need for a thorough research into factors contributing to the quality of a positioning platform as well as their interactions, so as to enable the development of optimal application-dependent quality control procedures.

The main objectives of this working group are:
• to carry out an in-depth analysis of the factors affecting the positioning reliability and precision for different observational models,
• to derive optimal statistical testing regimes that are capable of handling multiple alternative hypotheses about the underlying model,
• to characterize the link between statistical testing and parameter estimation exercised in data processing so as to develop rigorous quality control frameworks for evaluating the reliability of the position solutions,
• to disseminate the developed algorithms and numerical results through journals and conference proceedings.

WG 4.4.2: Geophysical Applications of High-Rate GNSS
Chair: Brendan Crowell (USA)
Vice-Chair: TBD

The proliferation of high-rate Global Navigation Satellite System (GNSS) data has enabled advances in geophysical monitoring well beyond the original intent of such systems. It has been well demonstrated that models of large and rapid deformation events, such as earthquakes and volcanic eruptions, are improved considerably by including high-rate GNSS observations because of the ability to directly track ground motions from strong shaking out to the permanent offsets. Likewise, the models of the impacts of these events (i.e. ground motions, tsunami predictions) are improved for applications such as early warning and rapid response. In addition to direct measurements of the deformation field, high-rate GNSS can offer additional applications in weather forecasting, space weather through ionospheric tracking, and environmental probing with GNSS reflectometry. High-rate GNSS observations can also be applied to engineering seismology problems such as long-period peak ground motions and can help determine the post-event resiliency of engineered structures. The use of this data for geophysical operations is still in its infancy, and robust algorithms, especially for the quality control and reliability assessment of high-rate GNSS, are required to be developed to ensure future use.

The primary objectives for this working group are:

• Objectively characterize the limitations of high-rate GNSS data and determine avenues for improvement,
• Determine the roadblocks to greater adaptation of high-rate GNSS methods,
• Identify stakeholders outside the group that would benefit from high-rate GNSS data, such as monitoring agencies,
• Improve global access to high-rate GNSS data and methodologies.

WG 4.4.3: Reliability of Low-cost & Android GNSS in navigation and geosciences
Chair: Jacek Paziewski (Poland)
Vice-Chair: TBD

Nowadays, we may observe a rapid development in the mass-market GNSS chipsets including those which are used in smart devices. A real milestone on the way to the introduction of smartphones into location-based applications was the introduction of Android Nougat 7 OS and, therefore making their GNSS raw observations accessible to the general public. This in turn, induced a development of algorithms enhancing the accuracy of positioning with mass-market devices. Hence, now it is feasible to determine the position with low-cost GNSS chipset with a degree of precision which was previously achievable only by survey-grade receivers with advanced processing algorithms.
This working group will endeavor to address and investigate issues related to the usage of low-cost receiver and smartphone GNSS observations to navigation, positioning and selected geoscience applications. It will also cooperate and provide input to SG4.1.x.
The main research will focus on the following objectives:
• To perform a comprehensive characterization of low-cost receiver/smartphone signal quality, including carrier-to-noise density ratio and measurement noise,
• To identify and investigate of the anomalies present in smartphone observables,
• To assess the low-cost receiver/smartphone GNSS positioning performance,
• To develop of novel processing algorithms addressing low-cost receiver/smartphone GNSS observables characteristics,
• To call out new geophysical applications based on GNSS smartphone signals.

JSG 4.4.4: Assessment and validation of IGS products and open-source scientific software (Joint WG between IAG and IGS)

Chair: Yidong Lou (China)
Vice-Chair: TBD

High-precision GNSS applications require not only the high-accuracy GNSS products but also the high-precision software. The IGS (International GNSS Service) has been maintaining public available high-quality products for decades, including the GNSS satellite ephemerides, geocentric coordinates of IGS tracking stations, earth rotation, atmospheric parameters and biases, to satisfy the objectives of a wide range of scientific research and applications, which has greatly benefited the GNSS community. With the modernization of GPS and GLONASS and the in-service of Galileo, Beidou and QZSS, the precision and timelines of IGS products are continuously improved and types are under expansions. On the other hand, however, we seldom have credible open-source high-precision scientific software for enormous users. The open-source of more high-precision/scientific software can significantly boost the utilization of IGS products in the scientific community and promote the popularization of GNSS in high-precision applications. Although a few software packages have been open sourced recently, they may be far from enough to demonstrate their applicability in high-precision applications, and questions like how the performance of these current open-source software is and what kinds of applications they can satisfy remain unclear. This study group is therefore set up mainly to investigate the performance of different software comprehensively, improve their capability through international coordination, encourage the open-source of more professional software, and bridge the IAG and IGS regarding the applications of IGS products in diverse fields.

The main objectives of this working group are:
• to investigate the performance and reliability of different open-source scientific software comprehensively, so as to provide important references to users for choosing the most suitable software in different applications
• to provide a platform to facilitate the communications between the developers and users of the open-source high-precision/scientific software, so as to promote the improvement of algorithms and potential scientific application.
• to collect and disseminate information of open-source high-precision/scientific software for the scientific community,
• to act as a bridge between the IAG and IGS regarding the applications of the high-precision IGS products in diverse fields.

WG 4.4.5: Spoofing and Interference of GNSS

Chair: Lakshay Narula (
Vice-Chair: ??

Description TBD