Wondering what the complication would be of utilizing signals in RTK that are set to unhealthy??ÿ Should be mitigated by the use of a local reference base correct?
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I'm certainly not an expert on this, but would worry that if a satellite is marked unhealthy its clock setting or the orbit data might be sufficiently wrong to give you an error that varies as the satellite moves overhead.?ÿ I think testing sometimes uses different modulation codes, so your receiver might not see its timing the same way as a healthy satellite.?ÿ Read the overview in this document for a sense of timing problems
http://iopscience.iop.org/article/10.1088/1755-1315/37/1/012013/pdf
Comparing to two receivers that receive that satellite among others, and using the vector between them for your work, will tend to reduce, but perhaps not totally cancel such errors.
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I would not use satellites flagged as unhealthy.
I would not use satellites flagged as unhealthy.
Why?
Some seem to only be set as unhealthy because they've not yet been "blessed".
That is correct, new satellites are monitored for some period of time to ensure that they're behaving correctly before they're set healthy. Significant clock or orbital error translates directly to pseudorange error which is going to affect your ability to get a good solution. I'm no expert either, but?ÿI would think that depending on how?ÿmany satellites you're tracking a significant enough error in the pseudorange is going to either impart a large ?ÿerror in the autonomous position or make it impossible to calculate a valid intersection of the ranges. I would also think that most modern day GNSS receivers would be smart enough to recognize the outlier and throw it out of the solution.
Assuming the bird is in reality healthy then sure, it's going to be useful, but you have no real way of knowing that. And in any case, there are enough of them up there that there's no reason to take the risk. The RTK solution is an infinitely complex mathematical model and I would think that the old axiom "garbage in, garbage out" would apply.
I'd like to hear the opinion of someone truly knowledgeable on the subject.
Satellites? as in which constellations?
GPS satellites are seldom set unhealthy unless they have actual problems or are in the process of adjusting their orbit, which implies no valid ephemeris position. Older satellites may be up there hat are set unhealthy and are in fact being ignored but they could be called back into service. Other constellations I pay little attention to, so no comment.
I might use an unhealthy satellite in special circumstances if I could confirm it's location from at least 3 surrounding base locations, but hey if it is set unhealthy a CORS is going to ignore it. RTK is based on the assumption that the satellite is where it says it is. If you use multiple CORS they can fix the satellite based on geometry from the whole set to the satellite, but that is dependent on having common observations, which you will not have.
For research purposes colleges use unhealthy satellites quite often, but they are not in the for profit business.
Paul in PA
The question was mostly because there's 4 additional Galileo undergoing commissioning, but you also have the 19 Beidou at the link below.?ÿ These are in an orbit that doesn't benefit the US as much, but using planning software shows that there are times in the day where I'll see 7 of the 19
https://en.wikipedia.org/wiki/List_of_BeiDou_satellites
The fact that there's 19 of them and one was launched a year ago leads me to believe that they're just waiting for a milestone to flip the switch.?ÿ It could also be because they're upgrading the ground segment for ephemeris tracking??ÿ I know just about enough about this to be dangerous...I'm going to turn them all on and ignore health with my R10 base rover.?ÿ My thoughts are it will either obviously hurt or help...I do a lot of LOD stakeout in very challenging terrain.?ÿ 2' is good enough, and getting the project done with GNSS opposed to a total station is money in my pocket!?ÿ 🙂
