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THE ESA/ESOC NAVIGATION SUPPORT OFFICE ACTIVITIES FOR THE  IONOSPHERE

1    INTRODUCTION

First investigations to establish ionosphere maps from GPS dual-frequency data collected with the International GNSS Service (IGS) global ground station network began at ESOC in 1993: Mathematical models, initially for a single layer approach to represent the ionosphere, were worked out, including the design and development of dedicated software, from scratch. At the end of 1995 a prototype version of this new IONosphere MONitoring Facility (IONMON) software was ready. This prototype version was quasi-operationally used since 1996 and became, after some further upgrades, fully operational as IONMON Version 1 in 1998. Already IONMON Version 1 offered, apart from single layer approaches, a first Chapman Profile-based 3D model.

Since 1999 efforts were undertaken to extend the 3D Chapman Profile approach to a multilayer 3D ionosphere model. Also this work included the development of comprehensive new mathematical models and software. This IONMON Version 2 is available since March 2008. In addition to TEC derived from dual-frequency IGS/GPS data (the inclusion of data from other GNSS systems is principally possible), IONMON Version 2 needs observed electron density profiles, e.g. from COSMIC and other sources such as ionosondes, for its 3D processing. IONMON Version 2 combines profile functions, describing the vertical structures of the ionosphere, with surface functions to represent the horizontal variation of key profile parameters, like maximum electron densities and their heights.

In order to stabilize the IONMON Version 2 fits, currently efforts are undertaken to supplement the system with a background model combined with an observation data assimilation.

For a detailed description of the IONMON system see IONMON Webpage.

2   CONTRIBUTIONS TO THE IGS WITH DAILY TEC MAPS

Since June 1998, ESOC contributes with final IONMON products to the IGS Ionosphere Working Group and since spring 2004 with rapid products. Global TEC & RMS maps are produced in a global IONEX grid with a 2-hours time resolution on routine operational basis in final (11 days latency) and rapid (1 day latency) mode. For the routine operational processing, IONMON Version 1 is still used. The global vertical Total Electron Content (vTEC) is represented as single layer with spherical harmonics. In addition to the spherical harmonic coefficients for the vTEC, a set of daily satellite & station Differential Code Biases (DCBs) is estimated. In a test phase, vTEC maps are currently also produced with 1-hour time resolution, in parallel to the 2-hours processing. In future, the 1-hour vTEC maps will replace the 2-hours vTEC maps as official IGS ionosphere product. Currently, tracking data from about 300 globally distributed IGS tracking sites are processed operationally per day.

Figure 1 displays an example 15 minutes resolution vTEC film produced with IONMON Version 1.

Tec Animation displaying ionosphere computed with IONMON

3    FUTURE TASKS

The major future task will be the routine production of 3D pictures of the ionosphere. IONMON Version 2 is still in an experimental phase. Currently preparations are undertaken to supplement IONMON Version 2 with a background model and an observation data assimilation procedure. At the same time this data assimilation shall also enable Real-Time applications. In addition to ground-based observation data, also spaced-based observables recorded on Low Earth Orbit (LEO) spacecraft shall be included into the data assimilation. For the current status of IONMON Version 2 and the planned extensions and upgrades see IONMON Webpage.

4    DEDICATED STUDIES/ PROJECTS / SPECIAL ACTIVITIES

Besides the routine processing and delivery of global vTEC maps to the IGS since 1998, several special activities / projects / studies about different ionosphere-relevant aspects have been performed at ESOC’s Navigation Support Office in the past:

1998 – 2002: IGS Ionosphere Working Group Chairmanship

2003: Automatic Gain Control (AGC) Fluctuations Working Group

2009: ESA Technical Research Programme (TRP) Study: “GNSS Contribution to Next Generation Global Ionospheric Monitoring”

2010: In-house support to ESA’s Soil Moisture and Ocean Salinity (SMOS) mission

2010: In-house support to the Herschel/Planck mission

2010: Prediction of ESOC vTEC maps and, in a test phase, combination of predicted vTEC maps for a new IGS predicted ionosphere product

2011: IONMON Version 1 as ESA asset for ESA’s Space Situational Awareness (SSA) programme

5    CONCLUSIONS

ESOC’s Navigation Support Office commenced its activities in the area of the ionosphere in 1993. After having established the IONosphere MONitoring Facility (IONMON) system from scratch, routine delivery of ionospheric vertical Total Electron Content (vTEC) maps began in 1998. Since then, the IONMON system and products have continuously been improved and enhanced. Currently the major efforts are undertaken into the direction of 3D modelling and Real-Time processing.

In parallel to the regular tasks for the IGS, several dedicated activities and projects have been conducted in the recent years, such as:

–         Investigation of signal fluctuations observed on Cluster and other ESA spacecraft

–         Study of future GNSS-based ionosphere models

–         In-house support to SMOS and other ESA missions

–         Delivery of IONMON Version 1 as ESA asset to ESA’s Space Situational Awareness (SSA) programme