I was thinking more about how to get RTCM corrections to the Healy in the Arctic using NTRIP.
First, while the folks at C&C Technologies did not see a commercial interest in developing a capability to transmit their globally corrected GPS service via internet for Arctic operations, it seems to me, now that the oil industry is looking at drilling on the Arctic shelf, C&C might reconsider. Moreover, with the advent of NTRIP, it would be trivial for them to provide. So we should revisit this.
Second, it might be possible to provide it on our own. UNAVCO provides lots of NTRIP sources and data products. Here is a link to GPS streaming data from UNAVCO. So, how might this work? Consider the types of corrections one must make to raw GPS observables.
Of these, IGS now provides ultra-rapid (predicted) satellite orbital corrections that are quite good (sufficient for cm level positioning). These can be found here.
Clock corrections are also predicted by IGS (same link). However others have estimated clock corrections by assimilating GPS observations from several regional reference stations – perhaps to greater accuracy.
Ionospheric delay correction can be corrected for by a dual-frequency receiver because the first-order correction can be estimated from the fact that the delay is frequency dependent. Alternatively, folks like JPL predict ionospheric delay globally. However I think they provide this information for commercial entities and so it is probably not universally available. There are probably other real-time sources – something to research.
Regarding tropospheric delay, the largest component is the dry. This can be modeled for sub-cm accuracy with a local measure of atmospheric pressure (and maybe temperature). Healy has a full met system logging these values in real time. The dry does not change rapidly – on the order of hours to days, therefore only periodic pressure measurements would be required. Alternatively, the International Arctic Buoy Program provides real-time met sensor data that could be used for this purpose.
The wet component of the tropospheric is about ¼ the magnitude of the dry (the latter being about 2m, the former being about 50 cm) and is much more variable (hours to days). This would be hard to estimate without a local reference GPS station. However in the Arctic the cold temperatures do not support lots of water vapor – it is very dry. Therefore it is likely that this correction could be omitted without significant error.