Galileo HAS corrections vary from ones, recieved via E6B signal

[vladyslav.v.kerker@…]

A discrepancy has been observed in the Galileo High Accuracy Service (HAS) orbit corrections when comparing data distributed via BNC Ntrip Caster against data received directly from the Galileo E6B Signal-in-Space (SIS).

The issue affects the radial component of the orbit corrections. The streams recieved through BNC show a measurable offset in the radial component (orbit correction) compared to the same data, recieved via SIS. This affects whole Galileo constellation (~8-10cm offset) and several GPS satellites (~65-70cm offset). Two files with corrections are attached.
Thank you in advance.
With regards,
Vladyslav Kerker.

[vladyslav.v.kerker@…]

HAS Corrections, recieved via SIS and BNC.

[vladyslav.v.kerker@…]

HAS Corrections, recieved via BNC.

[stuerze]

Dear Vladyslav Kerke,

Thank you very much for this interesting observation. Especially the differences with respect to GPS would explain the sometimes very poor PPP results using both, GPS+Galileo HAS corrections.

Nevertheless, do you think, it is really a problem of BNC? BNC only decodes the RTCM messages provided by EUSPA:
​https://www.gsc-europa.eu/galileo/services/galileo-high-accuracy-service-has/internet-data-distribution

Maybe you should contact the provider of the Internet based Galileo HAS corrections with your observations. Perhaps with a current example from 2026?

Best regars, Andrea

[vladyslav.v.kerker@…]

Dear Andrea,
Thank you for your responce. I contacted EUSPA and their responce suggests that the GPS offset may be related to Inter-System Bias between GPS and Galileo.
After conducting more tests, I am almost certain that the problem is not related to ISB.
The 70cm offset is present only in GPS BLOCK III satellites. Moreover, it is not only present in HAS correction stream but also in SSRA00BKG1, SSRA03IGS1 (files attached) and, as I suspect, every SSR correction source that includes GPS BLOCK III satellites. BLOCK 3 includes following satellites: G20, G04, G18, G23, G14, G11, G28, G01. For each of those satellites, Radial orbit correction sits at -0.7m, while for other GPS Blocks there is no such offset.
My personal guess is that BNC may be using outdated ANTEX file when forming corrections, which contains incorrect or outdated Phase Center Offset values (PCO) for GPS BLOCK 3. I would kindly ask you to check it.
Thank you for your time,
Vladyslav Kerker.

[vladyslav.v.kerker@…]

IGS RTS corrections

[vladyslav.v.kerker@…]

BKG Corrections

[anonymous]

Dear Vladyslav,

Thank you for your analysis.

You are right, we are responsible for SSRA00BKG1 and SSRA03IGS1 but NOT for SSRA00EU0.

Nevertheless, SSRA streams are related to APC, which means Antenna Phase Center Offset. And SSRC streams are related to CoM, which means Centre of Mass.

Hence, the ANTEX file is used only in case of the generation of SSRC streams. Maybe this is the difference, you see?

𝑿_𝐶𝑜𝑀 = 𝑿_𝐴𝑃𝐶 − 𝑨_(𝐵𝑜𝑑𝑦𝐹𝑖𝑥𝑒𝑑_𝐸𝐶𝐸𝐹) ∗ 𝑷𝑪𝑶_(𝑟𝑒𝑓_𝑓𝑟𝑒𝑞)

Best regards, Andrea

[vladyslav.v.kerker@…]

Dear Andrea
Thank you for your responce. After more communication with EUSPA, it turns out that Galileo HAS IDD corrections are refferred to a different APC (L1/E1 for GPS/GAL) than SIS (E1/E5 pair for GAL, L1/L2 for GPS). That is the sole reason for the difference I observed.
I am thankful to you for prompt responces, even though the BNC software is working perfectly fine and there was no reason to open a bug ticket at all!
Have a nice day,
Vladyslav Kerker.

[stuerze]

Dear Vladyslav,

Thank you very much for this exlanation.

Do you know, why they are using a different APC for Galileo HAS IDD than for SiS?

Best regards, Andrea.

[vladyslav.v.kerker@…]

Dear Adnrea
It is stated in IGS State Space Representation (SSR) Format document (​https://files.igs.org/pub/data/format/igs_ssr_v1.pdf). At page 6, citing:
"If the SRP (Satellite Reference Point) is not the CoM, the SRP for orbit corrections is the antenna phase center (APC) of the reference frequency as listed in Table 2." Table 2 provides following reference points:
GPS L1
GLONASS G1
Galileo E1
SBAS L1
BDS B1-2
QZSS L1
NavIC/IRNSS L5

As for Galileo HAS Signal-in-Space, I suspect that those corrections are referred to iono-free APC to simplify processing chain, as the service is designed for real-time PPP, where user would anyway form iono-free combinations to eliminate first-order ionosphere.

With regards,
Vladyslav.