JSG T.36

Introduction

Global Navigation Satellite Systems Radio Occultation (GNSS-RO) have become an important technique to globally sound the Earth’s atmosphere from space. This technique overcomes some of the main limitations of ground-based remote sensing instruments, increasing the amount of tropospheric and ionospheric data measured over the oceans and under sampled regions.

Up until few years ago, GNSS-RO observations were mainly supported by expensive satellite missions (e.g. COSMIC-1), which implies also considerably high operational costs. A great opportunity was brought in the field by nanosatellites, which are a satellite of low mass and size, usually under 500 kg. These satellites can significantly reduce the large economic cost of launch vehicles and the costs associated with construction.

In recent years, commercial RO providers (e.g., Spire Global) shifted the paradigm and started operationally producing GNSS-RO data from CubeSats in Low Earth Orbit (LEO). This data was demonstrated to be comparable in quality to larger satellite constellations (e.g., COSMIC-1), but with a denser spatial and temporal coverage. The new paradigm proposed by these commercial companies is that nanosatellites, especially in large numbers, may be more beneficial than using fewer, larger satellites in tasks such as gathering scientific data.

Independent assessments of these commercial data quality were carried out by JPL, UKMO, ESA, NOAA, and NRL, which convinced the international RO community that commercial data are ready to be assimilated by NWP centres and used by scientists to investigate different research topics.

Often, these nanosatellites carry different scientific payloads collecting a large amount of different data (e.g., GNSS-POD solutions, GNSS top ionosphere TEC observations), that could be exploited for several scientific investigations. Furthermore, contemporary technological advances of other low-cost sensors (e.g., in-situ atmospheric sensors, MEMS accelerometers and gyros) opens new opportunity and problems, first of all related to data fusion, validation and sensor integration. Spire will share data samples (e.g., podGps, atmPhs, podTec, atmPrf) within the members of the study group, in order to promote the development of new algorithms and methodologies for remote sensing of the Earth.

It is clear that this unprecedented dense coverage of troposphere and ionosphere sounding enabled by commercial GNSS-RO CubeSats and dense network of ground-based GNSS receivers represents a great opportunity for future investigations in Earth sciences. This brings the attention to the methodological point of view in order to exploit their full potential and extract the best information. This is the reason why it is worth opening a focus on dense troposphere and ionosphere sounding using GNSS-RO and ground-based GNSS techniques within ICCT.

Objectives

• To realize inventories of:
  • commercial and publicly available GNSS-RO and ground-based GNSS observations, with a distinction between troposphere and ionosphere observations, and a classification based on the different acquisition parameters (e.g., sampling rate, vertical or temporal resolution, altitude range of acquisition, tracking mode),
  • present and wished applications of dense troposphere and ionosphere sounding for science and engineering, with a special concern to the estimated physical quantities (e.g., temperature, pressure and TEC), in order to focus on related problems (still open and possibly new) and draw future challenges.
• To address known problems related to dense troposphere and ionosphere sounding using GNSS-RO observations as (not an exhaustive list): atmospheric anomalies detection, localization and classification; revision and refinement of inversion techniques; temporal variability of receivers DCBs and evaluation of their impact in the calibrated process; data quality assessment and validation; outlier detection and removal; in-situ sensors evaluation, cross-calibration and integration.
• To describe the different analytical and physical implication of combining observations collected with different observational geometries, such as: ground-based receivers tracking signals transmitted by GNSS satellites in MEO and GEO orbits; space-based receivers tracking GNSS signals at different elevation angles (from positive to negative and vice versa). Furthermore, investigate the different ways of combining together these remote sensing observations to retrieve fundamental atmospheric parameters, and disentangle the spatial and temporal variability of the atmosphere.

Program of activities

• To organize a session at the forthcoming Hotine-Marussi symposium 2022.
• To convene at international conferences such as IAG/IUGG, EGU, AGU.

Membership

Giorgio Savastano (Luxembourg), chair
Matthew Angling (UK)
Elvira Astafyeva (France)
Riccardo Biondi (Italy)
Mattia Crespi (Italy)
Kosuke Heki (Japan)
Addisu Hunegnaw (Luxembourg)
Alessandra Mascitelli (Italy)
Giovanni Occhipinti (France)
Michela Ravanelli (Italy)
Eugenio Realini (Italy)
Lucie Rolland (France)
Felix Norman Teferle (Luxembourg)
Jens Wickert (Germany)