[IGSMAIL-8654] New proposed ionospheric RT-RMS corrections transmitted in CAS product streams

[wangningbo at aoe.ac.cn]

Author: Ningbo Wang (AIR/CAS)

Dear colleagues,

Following the release of the IGS-SSR Format Version 1.00 standard in 2020 and its broad adoption by the GNSS community, potential extensions of the IGS-SSR format have been discussed and agreed within the IGS Real-Time Committee (RTC). These extensions include the introduction of satellite APC and attitude information, the global ionospheric accuracy information, and regional atmospheric corrections together with corresponding quality indicators, as announced during the 2024 Bern Workshop.

In the IGS-SSR V1.00, RT-VTEC information is represented and transmitted using a spherical harmonic expansion, which is a well-established standard within the GNSS community. To complement this information, we proposed an update (or amendment) to current IGS-SSR V1.00 to include the RT-RMS message. In our understanding, this information is highly requested by the users, as it provides a formal precision indicator of the provided RT-VTEC corrections. 

Similar to the RT-VTEC representation, the proposed RT-RMS information is described using spherical harmonics (up to degree and order 15, with up to four layers). Global ionospheric VTEC is disseminated via IGS-SSR message type 201, while the corresponding RT-RMS information is transmitted using IGS-SSR message type 202. Detailed message definitions are provided in the accompanying documentation (“Proposal of New IGS-SSR Ionospheric RMS Message”). Together, message types 201 and 202 enable the dissemination of global RT-VTEC corrections together with their associated accuracy information.

Over the past few months, the proposed IGS-SSR ionospheric RT-RMS message has been added into CAS generated real-time correction streams, using a temporally adopted "Message Number 202". The following product streams can be accessed via the IGS BKG caster (products.igs-ip.net:2101)

IONO01CAS1: global ionospheric RT-VTEC and RT-RMS information;
SSRC01CAS1: G+E+C orbit, clock, code and phase bias, together with global RT-VTEC and RT-RMS information.

where IONO00CAS1 provides ionospheric corrections only, and SSRC01CAS1 also provides additional orbit, clock, code and phase bias corrections. Internal validation of the proposed ionospheric RT-RMS information has been completed at CAS, and a methodological paper describing the approach has been submitted to Space Weather.

In addition to access via the IGS BKG caster, interested users can also apply for accounts through CAS regional data center of the IGS at https://igs.bdsmart.cn

Should you encounter any issues while testing the RT-RMS information, or if you have specific requirements or questions, please do not hesitate to contact us directly via email (wangningbo at aoe.ac.cn). You feedback is highly appreciated!

With best regards,
Ningbo Wang
On behalf of CAS Team 



Ningbo WANG, Ph.D Associate Professor
Aerospace Information Research Institute (AIR)
Chinese Academy of Sciences (CAS)
No 9 Dengzhuang South Road
Beijing China

Tel (+86) 186 7401 0516
e-mail wangningbo at aoe.ac.cn
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