The IGS Ionosphere Working Group (Iono-WG) was established by the IGS
Governing Board on
28 May 1998 and commenced working in June 1998. The working group's main activity is
the routine provision of ionosphere Total Electron Content (TEC) maps with a 2-hours time
resolution and of daily sets of GPS satellite (and receiver) hardware differential code bias (DCB)
values. The computation of these TEC maps and DCB sets is based on the routine evaluation of
GPS dual-frequency tracking data recorded with the global IGS tracking network.
Currently four IGS Ionosphere Associate Analysis Centers (IAACs) contribute with their ionosphere products to the Iono-WG activities (CODE, ESA, JPL and UPC1).
Once per week their ionosphere final products are compared with a dedicated comparison algorithm. This comparison/combination algorithm was worked out and coded in 1998 from scratch. In the meantime the original comparison/combination algorithm was upgraded with new weights computed from the results of external self-consistency validations. The weekly comparisons are done with this new approach since August 2001. Furthermore, the IAACs TEC maps are routinely validated with TOPEX altimeter data since July 2001.
The official status of final IGS ionospheric product was obtained in the IGS Governing Board meeting held at Nice, April 2003, after the presentation of the combined TEC maps performance in a dedicated report.
The final IGS global maps, computed with a latency of about 11 days and with the resolution of 2 hours x 5 deg. x 2.5 deg. in UT x Longitude x Latitude, are stored in ionex format. They can be downloaded from the official server (CDDISA at GSFC/NASA) (being the IGS and IAAC ionex files stored in the corresponding year and day subdirectories) and or from the combination center server, presently UPC (the IGS ionex file is contained in the corresponding YYDOY subdirectory, being YY the year and DOY the day). Please refer to the IGS Central Bureau server in order to have a more complete information of the different available products and the corresponding directories structure in the IGS servers, such as CDDIS and IGN.
The generation of a rapid IGS product (with a latency of less than 24 hours) started in December 2003 (by using an automatic software coded from scratch), following the suggestion of the IGS GB during the meeting at Nice, in April 2003. The corresponding rapid combined global TEC maps (with the same resolution than the final ones, i.e. 2 hours x 5 deg. x 2.5 deg. in UT x Longitude x Latitude) can be accessed from the official rapid IGS server (CDDISA at GSFC/NASA) and from the original server at UPC (please notice the the corresponding rapid IGS ionex files igrgDOY0.YYi.Z, for year YY and day of year DOY, are stored in subdirectories for the year YEAR and day DOY). The corresponding validation with JASON TEC is automatically performed, and included in the corresponding IONEX file header, before to deliver such file with less than 24 hours of latency. There are also additional information in the UPC server such as plots representing the comparison with JASON TEC and movies which are stored in a provisional format which can change during the next weeks.
Since 2004 the four active ionospheric (CODE, ESA, JPL and UPC) analysis centers have delivered their rapid VTEC maps, and the performance since August 2004 is just slightly worst (5-10%) than the final maps. These results have deserved the official status in the IGS Governing Board meeting held at Vienna, 24 April 2005 (see Iono IGS WG report presented there to see some performance details).
Presentations on behalf of the IGS Ionosphere WG:
