Assessment of rst Real-Time IGS global VTEC maps

Abstract

The assessment of the first Real-Time (RT) IGS global VTEC maps computed by DLR and UPC, against JASON-1 (during 2011) and JASON-2 altimeter VTEC measurements (2012), is presented in this work. Indeed, within the International GNSS Service (IGS), Associate Analysis Centres (ACC) produce specialized or derived products. Two examples of Real-time ACCs are the Universitat Politecnica de Catalunya (UPC) and the German Aerospace Center (DLR). They have participated in the IGS Real Time Pilot Project (RTPP) and continue to collaborate on the development of a combined global IGS RT-VTEC product. This collaboration is occurring under the umbrella of the IGS Ionosphere Working group (IGS Iono-WG) currently lead by the University of Warmia and Mazury in Olsztyn, Poland. RT-VTEC information is used to support earth observation missions and space weather monitoring and forecast. RT-VTEC information can improve single-frequency positioning on a global scale and in smaller regions where the ionosphere may be well sounded. RT-VTEC information is known to improve RTPPP accuracy results for single-frequency users. Through the use of iono-geodetic techniques, phase quality dual-frequency RTPPP results are being improved by reducing the convergence time for phase ambiguity fixing. The JASON comparisons are considered pessimistic for the overall global VTEC product accuracy because the land-based tracking stations are generally located quite far from the location of the JASON measurements. The importance of a reliable globally distributed and su�ciently dense real-time GNSS tracking network will be shown. Moreover the RT-VTEC results are quite compatible with the rapid and final IGS VTEC maps for a significant fraction of time. These results suggest that it may be feasible to combine real-time VTEC products from several centres into a robust IGS real- time IONO product. Additional work to compare both solutions is underway with the goal of �nding optimal ways to assess and combine these products into an IGS RT- VTEC product. Future efforts will include working with RTCM to ensure that the IGS RT-VTEC product is compatible with ionosphere correction information proposed for the RTCM-SSR standard