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pseudorange VS carrier phase observables GPS
Posted by geodesist on November 17, 2018 at 4:30 pmHello,
Could i know please, why the carrier phase is more precise than the pseudorange measurement ?
Thanks
geodesist replied 5 years, 5 months ago 3 Members · 6 Replies- 6 Replies
I don’t think the question is meaningful as stated. I think pseudoranges are estimates of the range obtained from any features of the GPS signal, and you are probably thinking of measurements depending on the C/A code.
C/A code pseudoranges are measured from a 1.023 megabit per second signal, thus having a length of 300 meters, and if you can determine the timing on that to, for instance, 1% then you have an uncertainty of 3 meters no matter what other corrections you apply.
The L1 carrier is at 1575.42 MHz, thus having a wavelength of 19 cm. The receiver can track that to some small percentage, thus having less uncertainty than the uncertainty in the other corrections such as tropo and ionospheric. The carrier pseudoranges are usually computed from the doppler rate of carrier change in order to avoid the need for a super-precise receiver clock.
If someone has a better answer, I will defer to them.
.Thank you very much for your excellent explanation.
Please, do you have a simplified explanation of the the Integer Ambiguity.
Yours Sincerely
When the receiver locks on to the carrier, all 19-cm-long cycles look alike to it and it initially has no indication of how many cycles N, N+1, N+2, etc. are traveling between the satellite and the receiver. It must resolve that ambiguity by trying for a solution (picking N) where multiple satellite signals will agree on the position.
.Thank you
So we fix, initially, this ambiguity. Please, if yes (how we fix it)?
The integer ambiguity refers to the un-measurable number of wavelengths transmitted by the satellite before the receiver starts logging. There is one integer unknown per frequency for each satellite from the receiver.
The French text shows what I wrote. The continuous SV signal is captured hen the receiver locks on. We want the whole number of wavelengths.
The correct determination of the integer unknowns yields a strong solution as fewer parameters are computed. If the wrong integers are fixed a poor solution will result.
The paper linked here discusses the issue: https://link.springer.com/article/10.1007/s0019001001
The LAMBDA method is a favorite.
A better worde explanation is: https://www.gpsworld.com/clarifying-the-ambiguities/
HTH,
DMM
Thank you so much..
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