Report of the GPS calibration trip among NIMT, NMIM, and VMI in 2017

Transcription

1 Report of the GPS calibration trip among NIMT, NMIM, and VMI in 2017 Y. Huang, T. Chiu, H. Lin and C. Liao 2017 ATF, CSIR-NPL, India November 25, 2017

2 Calibration for time transfer UTC(k) UTC(j) GPS Receiver UTC(k) GPST Reading: 15 ns GPS Receiver UTC(j) GPST Reading: 10 ns [UTC(k) UTC(j)] = 5 ns + internal delay internal delay The calibration is to determine the value of the internal delays

3 The GPS Receiver Readings GPST REF GPST-REF Reference delay, d GPST to k-th SV, d k GPST k-th GPS SV Geometry delay, ρk c Ionosphere, I k reading: Pseudorange τ k Troposphere, T k Internal (antenna), d Antenna cable, d GPS Receiver t Internal (receiver), d REF (e.g. UTC(k))

4 Model of the pseudorange ρ k : geometry distance d: total delay (ANT, INT and REF) τ k = d k + ρk c + Ik + T k + d + t REFGPS τ k : pseudorange atmosphere effects t REFGPS : time difference satellite clock offset

5 Common view and common clock: put two stations together τ L k = d k + τ T k = d k + x L k c x T k c + I k + T k + d L + t REFGPS + I k + T k + d T + t REFGPS GPS SV k x L k x T k GPST => τ k T τ k L x T k k x L = d c T d L Raw (common lock) difference Local Traveling REF

6 Raw (common clock) Difference Obtained from broadcasted navigation data τ T k τ L k x T k x L k c = d T d L pseudoranges: readings of the two receivers differential calibration: given one, compute the other This can be done by taking the difference between two CGGTTS data

7 Raw Difference from CGGTTS INT DLY = ns (GPS C1), ns (GPS P1), ns (GPS P2) CAB DLY = 0.0 ns REF DLY = 0.0 ns REF = UTC(TL) CKSUM = FF CAL_ID = xxxx-2017 Traveling receiver SAT CL MJD STTIME TRKL ELV AZTH REFSV SRSV REFSYS SRSYS DSG IOE MDTR SMDT MDIO SMDI MSIO SMSI ISG FR HC FRC CK hhmmss s.1dg.1dg.1ns.1ps/s.1ns.1ps/s.1ns.1ns.1ps/s.1ns.1ps/s.1ns.1ps/s.1ns G02 FF L1C FF RAW T = REFSV T + MDIO T + MDTR T + INTDLY T + CABDLY T REFDLY T ================================================================================================================================== INT DLY = ns (GPS C1), ns (GPS P1), ns (GPS P2) CAL_ID = CAB DLY = 0.0 ns REF DLY = 0.0 ns REF = UTC(TL) CKSUM = FF Local receiver SAT CL MJD STTIME TRKL ELV AZTH REFSV SRSV REFSYS SRSYS DSG IOE MDTR SMDT MDIO SMDI MSIO SMSI ISG FR HC FRC CK hhmmss s.1dg.1dg.1ns.1ps/s.1ns.1ps/s.1ns.1ns.1ps/s.1ns.1ps/s.1ns.1ps/s.1ns G02 FF L1C FF RAW L = REFSV L + MDIO L + MDTR L + INTDLY L + CABDLY L REFDLY L d T d L = RAW T RAW L

8 BIPM Calibration TL registered an ID Advised by NMIA(Australia), TL is in charge of the G2 calibration activity among NIMT(Thailand), NMIM(Malaysia) and VMI(Viet Nam) The trip: Taiwan->Thailand->Malaysia->Viet Nam->Taiwan Six months $8,000 for shipment (no CARNET)

9 GPS receivers in TL Ashtech Z12T (Reference, code: TLT1) NMIA Topcon/Javad Euro-80 (Traveling, code: TRVL) Cal_ID: Use time interval counters to link the UTC(k) and the time base inside the receiver

10 Traveling standard: TRVL To reduce the uncertainty, we ask the labs to use the same PPS cable (RG-58, 10m) to directly connect their UTC(k)

11 Long-term stabilities According to the BIPM guidelines, the receiver must demonstrate sufficient stability over a time period comparable with the campaign Reference receiver AU01 Data provided by NMIA MJD C1 INTDLY / ns

12 RAWDIF / ns Time Deviation / s RAWDIF in NIMT E C E C1, median = ns MJD 0.1ns 1.0E E E E E E+06 Averaging Time / s Visited receiver: NMIA Topcon/Javad Euro-80 (code: MTTO) The stability cannot reach 0.1 ns due to the salt-and-pepper noise

13 RAWDIF / ns Time Deviation / s RAWDIF in NMIM 0 1.0E C1-6 C1, median = ns MJD 1.0E E E E E E+06 Averaging Time / s Visited receiver: NMIA Topcon/Javad Euro-80 (code: LSM1)

14 RAWDIF / ns Time Deviation / s RAWDIF in VMI E C E C1, median = ns MJD 1.0E E E E E E+06 Averaging Time / s Visited receiver: NMIA Topcon/Javad Euro-80 (code: VM )

15 Time Deviation / s RAWDIF, Topcon receivers 1.0E E E ns MTTO LSM1 VM 1.0E E E E E E+06 Averaging Time / s TDEV of MTTO cannot down to 0.1 ns even we measured for 30 days Therefore, MTTO dominates the ua

16 RAWDIF / ns Time Deviation / s RAWDIF in NMIM E C1, median = ns P1, median = ns P2, median = ns 1.0E C1 P1 P MJD 1.0E E E E E E+06 Averaging Time / s Visited receiver: Septentrio PolaRx2eTR (code: LS2P)

17 RAWDIF / ns Time Deviation / s RAWDIF in VMI E C1, median = ns P1, median = ns P2, median = ns 1.0E C1 P1 P MJD 1.0E E E E E E+06 Averaging Time / s Visited receiver: Septentrio PolaRx3eTR (code: VM12)

18 RAWDIF / ns RAWDIF / ns RAWDIF in TL, closure C1, median = ns P1, median = ns P2, median = ns Misclosure of P2: 1.1 ns C1, median = ns P1, median = ns P2, median = ns MJD MJD The variation of RAWDIF (misclosure) is the largest components in the ub

19 Uncertainty Budget Unc. Value C1/P1 (ns) Value P2 (ns) Value P1-P2 (ns) Value P3 (ns) Description u a (T V) RAWDIF (traveling visited) u a (T R) RAWDIF (traveling reference) Misclosure u b, observed misclosure Systematic components related to RAWDIF u b, Position error at reference u b, Position error at visited u b, Multipaths at reference u b, Multipaths at visited Link of the Traveling system to the local UTC(k) u b, REFDLY T (at ref lab) u b, REFDLY T (at visited lab) Link of the Reference system to its local UTC(k) u b, REFDLY R (at ref lab) Link of the Visited system to its local UTC(k) u b, REFDLY V (at visited lab)

20 Results in the Circular T Date h UTC AUG 29 SEP 3 SEP 8 SEP 13 SEP 18 SEP 23 SEP 28 Uncertainty/ns Notes MJD ua ub u Laboratory k [UTC-UTC(k)]/ns NIMT (Pathumthani) NMLS (Sepang) VMI (Ha Noi) Only VMI modified the header of their CGGTTS, so they got the improvement As well, they got a time step. Date h UTC SEP 28 OCT 3 OCT 8 OCT 13 OCT 18 OCT 23 OCT 28 Uncertainty/ns Notes MJD ua ub u Laboratory k [UTC-UTC(k)]/ns NIMT (Pathumthani) NMLS (Sepang) VMI (Ha Noi) (4) (4) VMI : Time step of UTC(VMI) of about 25 ns on MJD due to calibration

21 Some observations Misclosure is the largest component in the uncertainty table A shorter traveling time may avoid this The biggest variation dominate the uncertainty for all labs To measure the ionosphere delay more accurately, the P1/P2 of Topcon receiver are required to calibrate

22 Summary One lab per trip is recommended Duties and rights are clear for the lab To minimize the aging of the traveling equipment To shorten the calibration period Thanks to Michael and Louis of NMIA for their technical support, and PTB for the financial support