Difference: PreprocessingUsingDiscFixApp (r4 vs. r3)

Question

Dear GPSTk,

I am a ph.d student from University of New South Wales. Now I am using GPSTk tools for my research work.

I want to preprocess my RINEX files, which are obtained from the Gravity Recovery and Climate Experiment (GRACE) mission. However, some error occurs showing 'Unknown or unsupported RINEX version' when using the 'DiscFix' app. Then I modify the version into 2.1.1, finally it runs successfully and valid results are generated. However, I feel a little strange about the debiased carrier phase measurements in the new observation file. In comparison with the values in the old file, both L1 and L2 change in about 100 cycles. It looks good with the smoothed code measurements which do not fluctuate a lot (just several decimetres) . Are the results trustful? How can I make them verified?

Hope that you can give me some suggestions. Much appreciated! Ian YANG

-- IanYANG - 01 Apr 2013

Answer

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Hi Ian,

About the RINEX file problem, from the information I have found, it looks as if the RINEX files from the GRACE mission are RINEX 2.20 files. The DiscFix app has not been updated to handle RINEX files greater than 2.10 (apparently 2.11 also works, possibly due to the minor changes outside of additional GNSS system support), which is why you are receiving an error when using the app prior to the version modification. Since DiscFix does not error out with the new modified RINEX file, its data can be trusted.

In reference to the debiased carrier phase measurements in your output observation file, it sounds like DiscFix worked correctly, and the measurements in the old observations file were biased by 100 cycles, hence the difference in the new observations file.

We are happy to see that GPSTk has been of assistance to your research work.

-- BryanParsons - 08 Apr 2013

Dear Dr. Bryan,

Thanks for your response. I still have some more questions.

I know that in app DiscFix debiasing technique is used, which is a process of subtracting the weighted average of the carrier phase observables from the carrier phase observables and adding the weighted average code observables. How can I know about the specific value of the weight here? Should I refer to the *.cpp file for more details? I think after the debiasing, the geometry-free combination of the carrier phase observables can represent the TEC, right?

And for the code smoothing method, how do you set the coefficient which controls the effective length of the Hatch filter in time?

Thanks and regards, Ian

-- IanYANG - 09 Apr 2013 No such template def TMPL:DEF{PROMPT:supportquery}

First and foremost, I have not attained a PhD, so no Dr. formality is needed. Though, thanks for the consideration.

"How can I know about the specific value of the weight here?"

~Actually, there is no weight, its just the bias (pseudo-range subtracted from the phase) added to the phase.

"I think after the debiasing, the geometry-free combination of the carrier phase observables can represent the TEC, right?"

~Yes

"And for the code smoothing method, how do you set the coefficient which controls the effective length of the Hatch filter in time?"

~There is actually no hatch filter, as the smoothing code is the same code used in the de-biasing phase.

Hope that helps.

-- BryanParsons - 12 Apr 2013 No such template def TMPL:DEF{PROMPT:supportquery}

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