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hirokawa / cssrlib

Python Toolkit for satellite-based open PPP/PPP-RTK services
MIT License
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satellite pcv/pco correction issue in pppssr #47

Open howiie11 opened 3 months ago

howiie11 commented 3 months ago

I find that there is satellite pcv/pco correction for measurement in zdres function in pppssr.py . But I think normally we do not correct PCO for satellites in ssr mode as the orbit correction(dx,dy,dz) is based on broadcast ephmeris.

Is there any problem?

Best regards.

AndreHauschild commented 3 months ago

Thanks for your comment. In principle you are right: the corrected satellite positions after applying SSR corrections are in the antenna phase center (APC) so the user does not need to apply additional offsets. However, the various signals on different frequencies have different antenna phase centers. In the past, where only dual-frequency signals have been available, it has been the standard to use the iono-free combination of the two APCs. This approach reaches its limitations with the availability of three (and more) signals and the un-combined approach for PPP. Modern SSR standards (like IGS-SSR) therefore refer to a single-frequency APC and the users then needs to apply APC difference corrections depending on the signals they process. The implementation in pppssr.py does exactly this by first applying the APC correction to translate back to the CoM and then apply the individual signal APC corrections depending on the user's signals.

howiie11 commented 3 months ago

Many thanks for your information, I will look into it more carefully