Implementing the International GNSS Service 2021+ Strategic Plan: Vision and Use Cases
Authors: Craddock Allison B. , Oyola-Merced Mayra I. , Martire Léo , Santiago Ashley 
Published: August 2022

&lt;p&gt;For almost thirty years, the International Global Navigation Satellite System (GNSS) Service (IGS) has carried out its mission to advocate for and provide freely and openly available high-precision GNSS data and products.&lt;/p&gt;
&lt;p&gt;The IGS is an essential component of the IAG&amp;#8217;s Global Geodetic Observing System (GGOS), where it facilitates cost-effective geometrical linkages with and among other precise geodetic observing techniques, including: Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), and Doppler Orbitography and Radio Positioning Integrated by Satellite (DORIS). These linkages are fundamental to generating and accessing the International Terrestrial Reference Frame (ITRF).&amp;#160; As it enters its second quarter-century, the IGS is evolving into a truly multi-GNSS service, and at its heart is a strong culture of sharing expertise, infrastructure, and other resources for the purpose of encouraging global best practices for developing and delivering GNSS data and products all over the world.&lt;/p&gt;
&lt;p&gt;The IGS 2021+ Strategic Plan was developed by the IGS Governing Board with the help and support of the Central Bureau, and guided by extensive community feedback and discussions. It presents a forward-looking strategy addressing the role of IGS as facilitator, incubator, coordinator, and advocate working towards three major goals in service to our community and beyond. We will present how the plan focuses on maintenance and enhancement of its leadership role within the broader GNSS community, as societal demands for GNSS products and services continues to grow. Central to the goals and objectives are the complementary roles of the IGS as a collaborative research program, as well as an operational service.&lt;/p&gt;
&lt;p&gt;This presentation will be supported by two use cases on advocacy for novel applications &amp;#8211; and unanticipated benefits &amp;#8211; of GNSS data and products for understanding and modeling two types of disaster risk: tsunami and wildfires. We will discuss how the IGS Central Bureau has been identifying these advocacy opportunities and incubating preliminary research for the benefit of our geodetic community as well as science and society. Finally, alignment of these use cases to major international frameworks such as the United Nations Sustainable Development Goals and Sendai Framework for Disaster Risk Reduction will be introduced.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Use Case 1: GNSS-Enhanced Natural Hazards Early Warning System through Near-Real-Time High-Rate Ionospheric Monitoring&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;L&amp;#233;o Martire&lt;sup&gt;1,2&lt;/sup&gt;;&lt;/strong&gt; Siddharth Krishnamoorthy&lt;sup&gt;1&lt;/sup&gt;; Panagiotis Vergados&lt;sup&gt;1&lt;/sup&gt;; Xing Meng&lt;sup&gt;1&lt;/sup&gt;; Larry J. Romans&lt;sup&gt;1&lt;/sup&gt;; B&amp;#233;la Szil&amp;#225;gyi&lt;sup&gt;1&lt;/sup&gt;; Angelyn W. Moore&lt;sup&gt;1&lt;/sup&gt;; Attila Komj&amp;#225;thy&lt;sup&gt;1&lt;/sup&gt;; Yoaz E. Bar-Sever&lt;sup&gt;1&lt;/sup&gt;; Allison B. Craddock&lt;sup&gt;1,2&lt;/sup&gt;&lt;/p&gt;
&lt;p&gt;&lt;em&gt;&lt;sup&gt;1&lt;/sup&gt;&lt;/em&gt;&lt;em&gt; NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA&lt;/em&gt;&lt;/p&gt;
&lt;p&gt;&lt;em&gt;&lt;sup&gt;2&lt;/sup&gt;&lt;/em&gt;&lt;em&gt; International GNSS Service Central Bureau; Pasadena, California, USA&lt;/em&gt;&lt;/p&gt;
&lt;p&gt;Natural hazards &amp;#8211; such as earthquakes, tsunamis, or volcanic eruptions &amp;#8211; have devastating human and economic consequences. Early detection and characterization of such threatening events lead to timely evacuations, which are critical for significantly reducing casualties and economic cost. However, traditional warning systems (&lt;em&gt;e.g.&lt;/em&gt;, seismometers or ocean buoys) are challenging to deploy and maintain in remote areas and in the open ocean, leading to limited coverage. By monitoring the effects of such natural hazards in the ionosphere, Global Navigation Satellite Systems (GNSS) measurements can be a valuable and inexpensive augmentation to existing early warning systems.&lt;/p&gt;
&lt;p&gt;Natural hazards release energy into the Earth&amp;#8217;s atmosphere in the form of acoustic-gravity waves, which can propagate up to the ionosphere. The resulting travelling ionospheric disturbances (TIDs) can be detected using GNSS signals, through the computation of the integrated total electron content (TEC) along the lines of sight between GNSS receivers and satellites. The global distribution of ground-based GNSS receivers, constantly tracking multiple GNSS constellations (GPS, Galileo, GLONASS, BeiDou, and others), provides excellent spatial and temporal coverage worldwide, including in areas of limited coverage by existing warning systems.&lt;/p&gt;
&lt;p&gt;An operational example of such methods is developed by NASA&amp;#8217;s Jet Propulsion Laboratory: the GNSS-based Upper Atmospheric Real-time Disaster Information and Alert Network (GUARDIAN). Using dual-frequency GNSS data from JPL&amp;#8217;s Global Differential GPS (GDGPS) network, its architecture computes TEC time series in near-real-time. As part of the GDGPS network, 78 stations around the Pacific Ring of Fire monitor the four main GNSS constellations: GPS, Galileo, GLONASS, and BeiDou. The resulting data stream is output with minimum latency to an upcoming user-friendly public website, benefitting the general public and scientific community. Furthermore, as a first step towards a prototype early warning system, an inverse modelling framework using ensemble modelling has been implemented to extract tsunami wave characteristics (such as tsunami wave heights) from the observed TIDs.&lt;/p&gt;
&lt;p&gt;Three main arguments make ionospheric monitoring a viable augmentation to early warning systems: (1) GNSS-based measurements typically cover a range of up to 1200 km around each ground receiver, (2) the ionosphere reacts relatively early to natural hazards thanks to a rapid atmospheric propagation (from 8 to 40 minutes from surface to ionosphere), and (3) the magnitude of TEC perturbations is often directly correlated to the events themselves (&lt;em&gt;e.g.&lt;/em&gt;, for tsunami waves). Furthermore, these elements are particularly valuable in regions where the installation and maintenance of conventional instruments can be tedious, expensive, or even physically impossible.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Use Case 2: Transdisciplinary Application of Global Navigation Satellite System (GNSS) Radio Occultation to Characterize Atmospheric Hazards and Model Systemic Risk&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Mayra Oyola-Merced&lt;sup&gt;1&lt;/sup&gt;&lt;/strong&gt;, Allison B. Craddock&lt;sup&gt;2,3&lt;/sup&gt;, Chi Ao&lt;sup&gt;2&lt;/sup&gt;, Olga Verkhoglyadova&lt;sup&gt;2&lt;/sup&gt;&lt;/p&gt;
&lt;p&gt;&lt;em&gt;&lt;sup&gt;1&lt;/sup&gt;&lt;/em&gt;&lt;em&gt; University of Wisconsin-Madison; Madison, Wisconsin, USA&lt;/em&gt;&lt;/p&gt;
&lt;p&gt;&lt;em&gt;&lt;sup&gt;2&lt;/sup&gt;&lt;/em&gt;&lt;em&gt; NASA Jet Propulsion Laboratory, California Institute of Technology; Pasadena, California, USA&lt;/em&gt;&lt;/p&gt;
&lt;p&gt;&lt;em&gt;&lt;sup&gt;3&lt;/sup&gt;&lt;/em&gt;&lt;em&gt; International GNSS Service Central Bureau; &lt;/em&gt;&lt;em&gt;Pasadena, California, USA&lt;/em&gt;&lt;/p&gt;
&lt;p&gt;Atmospheric data collected from Earth observation satellites is increasingly used by decision makers in both public and private sectors to define, characterize, measure, and assess airborne pollutants. This data can be processed into information supporting improved air quality forecasting, modeling, and monitoring of long-term trends.&lt;/p&gt;
&lt;p&gt;Despite this broad potential benefit to global health and well-being, the strategies and atmospheric retrievals from these satellites are not optimized for air quality applications. Furthermore, spaceborne sampling and estimation of important features of the lower atmosphere, where most emissions and pollutant plumes occur, is inherently difficult. Where lower atmosphere measurements from traditional satellite platforms are limited or highly biased, transdisciplinary Global Navigation Satellite System (GNSS) radio occultation (RO) techniques provide a new approach. GNSS-RO yields datasets with the accuracy, stability, and precision required for global assessments and other research applications.&lt;/p&gt;
&lt;p&gt;This case study focuses on applying data derived from GNSS-RO satellite data to determine distributions of pollutants and emissions during the 2020 California Fire Season in North America. This satellite technique coupled with aerosol concentration information from observations and weather models can help develop tools to study air quality on a global scale. This study specifically addresses how future observing systems with higher spatio-temporal coverage of RO, could help in the management and mitigation of these hazards. The use of GNSS RO measurements to track progress on SDG 11 (11.6.2), as well as indicators for Sendai Framework Targets F and G, will be presented.&amp;#160;&lt;/p&gt;