International Association of Geodesy


SC 4.4: Applications of Satellite and Airborne Imaging Systems




SC 4.1

SC 4.2

SC 4.3

SC 4.4


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Terms of Reference

Multi-GNSS Constellation is rapidly growing extending the number of satellites and available signals/frequencies. In addition to two already operational GPS and GLONASS systems, the new Galileo and BDS systems are under construction. Both GPS and GLONASS are currently undergoing a significant modernization, which adds more capacity, more signals, better accuracy and interoperability, etc.  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. Recognizing the central role of GNSS in providing high accuracy positioning information, the SC4.4 will foster research that address standards, theory and applications of Multi-GNSS Constellation. SC4.4 will coordinate activities to deliver practical and theoretical solutions for engineering and scientific applications and also will stimulate strong collaboration with the IAG Services (IGS) as well as with relevant entities within scientific and professional sister organizations (FIG, IEEE and ION).



Steering Committee

Chair: Pawel Wielgosz (Poland)

Vice-Chair: Yang Gao (Canada)

Secretary: George Liu (China)





The major objective of SC4.4 is to promote collective research on Multi-Constellation GNSS methods and technologies 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 Multi-Constellation GNSS applications,

·       to stimulate strong collaborations among researchers,

·       to organize international conferences and workshops,

·       to promote the use of multi-GNSS techniques and products in interdisciplinary scientific research and engineering applications;



SG 4.4.1: Integrity Monitoring for Precise Positioning"

Chair:              Ahmed El-Mowafy (Australia).

Vice-Chair:     Aboelmagd Noureldin (Canada).




The use of GNSS for real-time precise positioning, defined here as positioning at cm to sub-meter accuracy level, relays on GNSS signals that have well-known vulnerabilities and the use of supplementary systems to calibrate measurement biases. In addition, when working in urban environment or in case of a break in receiving the reference station data, GNSS need to be integrated with other sensors such IMU and speed sensors. For a user, such as driverless cars, intelligent transport systems (ITS) and UAVs, with such vulnerabilities and mixture of systems, integrity monitoring is important for protection from faults and to alert the user in case that the system cannot reach the target performance.

This Study Group (SG) will endeavour to research and develop a framework, including theory and algorithms, for integrity monitoring of precise positioning in a number of applications.  It will include precise positioning from GNSS in a stand-alone mode, e.g. in Precis Point Positioning (PPP), Real-Time Kinematic (RTK) or Network RTK processing, and when being integrated with other sensors such as IMU and speed sensors. The study group will carry out its work in close cooperation with other IAG and integrity monitoring groups, as well as via linkages with relevant scientific and professional organizations such as IGS, FIG, IEEE and ION. The SG will document the body of knowledge in the proposed field and present such knowledge at symposia and workshops.


WG 4.4.1 "Biases in Multi-GNSS data processing"

Chair: Xingxing Li (Germany)
Vice-Chair: Jan Dousa (Czech Republic)




To address and investigate issues related to the various biases in multi-GNSS data processing. The main research focus will include the definition and mathematical representation of various biases in multi-GNSS, their spatiotemporal characters and the related mechanism, precise bias modeling and the estimability, the development of rigorous multi-GNSS algorithms, to improve positioning performance and to enhance computational efficiency (especially for real-time orbit and clock determination) through proper bias estimation and correction. The continuous effort is to tightly integrate multi-GNSS signals together through precise determination and application of the biases for the best positioning performance.



WG 4.4.2: Integer Ambiguity Resolution for Multi-GNSS PPP and PPP-RTK”

Chair: Xiaohong Zhang (China)

Vice-Chair: Sue Lynn Choy (Australia)




To study the methodology of integer ambiguity resolution for Multi-GNSS PPP and investigate issues and problems of Multi-GNSS PPP related to ambiguity initialization time, success rate, accuracy and reliability etc. The research will focus on the following areas: the development of methods and algorithms for integer ambiguity resolution in Multi-GNSS precise point positioning; the development of new ionospheric correction model to speed up PPP ambiguity initialization time, and the real-time implementation and standardization of PPP-based Multi-GNSS RTK systems. The working group will carry out its work in close cooperation with other IAG groups  to promote the use of multi-GNSS techniques and products in interdisciplinary scientific research and engineering applications