Custom Query (104 matches)

First message from Loukis:

Attached is a spreadsheet with the results of a manual reconstruction of the clocks for two GLONASS satellites and comparison against the batch files. The following are noted:

1. There is a bias in the DLR results which is constant for both satellites
   
2. The BKG and CNES results are very close for R02 (non-zero drift term) but significantly different for R01 (zero drift term). The BKG difference for R01 is very large.
   
3. The GMV results for R02 are closer than for R01, but still different.
   

My suspicion is that there is a problem in using the GLONASS brdc drift term (or a misunderstanding on my part). In any case I am attaching extracts of the BNC decoded CLK files, the batch clock files that are submitted by the ACs, the reconstructed clock files that I generated and the brdc file for the relevant epoch (from CDDIS). Please note that the results I generated (gma, bka, cna, dla) are in exact agreement with the manual reconstruction in the spreadsheet. Also, the GPS results are very close, showing that the GPS satellites are properly encoded and decoded.

Files attached

Test results from Andrè Hauschild:

1. I can confirm a 400ns (=120m) offset, which is identical for all GLONASS satellites, which corresponds to the GPS-GLONASS system time offset.
   
2. After removing this offset, the batch and SSR clocks are virtually identical (~1mm level differences).
   

I conclude from these findings, that your way and my way of converting from RTCM-SSR to SP3 are consistent.
The 400ns-offset for all GLONASS sats shows up, because the clocks in my batch and my SSR solution refer to different system times. I could remove this offset, but I do not believe it does any harm (SPP/PPP users should estimate separate GPS and GLONASS clocks in any case), so I would prefer not having to make a software update. However, please let me know your thoughts on this!

Concluding remarks from Loukis:
Andre’s response reinforces my suspicion that there is an issue in the BNC encoding for GLONASS clocks where the drift term is non-zero.

I have a suspicion that the degradation of the GLONASS ephemeris may have been corrupting the RTCM MSM GLONASS measurements and would like to ask if this is something you are aware of. The reason I am asking is because I had problems with solutions involving MGEX GLONASS observations but the solutions based on IGS-sourced RINEX files and conventional RTCM streams from the RTS appeared to behave well. Is there a reliance on the GLONASS ephemeris within the RTCM MSM encoding software that could be affected by the corrupted messages?

message from fgnievinski@…:

There are a few issues when saving RINEX observation files, though.

(a) Two mandatory header lines are missing (RINEX version 3.02):

"GLONASS SLOT / FRQ #" "GLONASS COD/PHS/BIS"

(b) The default skeleton includes observation codes that could benefit from some improvement, as follows:

(b.1) C5, D5, L5, S5 are invalid, as they lack the third character, denoting the attribute (tracking mode or channel); most commonly it's "X", thus C5X, D5X, L5X, S5X.

(b.2) The modernized GPS L2 signal ("L2C") is being reported under observation codes C2C, D2C, L2C, S2C. Actually, the "C" attribute is reserved for the C/A signal (as in C1C, D1C, L1C, S1C), whose transmission in the L2 band remains a technical possibility (according to Table 3-III, "Signal Configuration", of the GPS ICD), even in pre-modernized or legacy GPS satellites, although as far as I know it is very rare. The L2C signal normally is reported under C2X, D2X, L2X, S2X.

(b.3) The legacy GPS L2 signal ("L2-P(Y)") is being reported under observation codes C2P, D2P, L2P, S2P. This is only true when anti-spoofing is disabled, which again is very rare. Under encrypted broadcast, observation codes C2W, D2W, L2W, S2W are employed for civilians (and C2Y, D2Y, L2Y, S2Y for military receivers).

(b.4) In summary, may I suggest the following new default GPS observation codes:

G 20 C1C L1C D1C S1C C1W L1W D1W S1W C2X L2X D2X S2X C2W SYS / # / OBS TYPES

L2W D2W S2W C5X D5X L5X S5X SYS / # / OBS TYPES

These correspond to the majority of stations, see, e.g.: <​http://www.bernese.unibe.ch/publist/2013/post/SL_euref2013_rinex3.pdf>