GPS link calibrations in support of CCTF-K001.UTC

Project Description

CCTF 2009 passed Recommendation 2 which states that BIPM will continue to study the characterization of GNSS equipment in use for establishing the time links between institutes contributing with their clocks to TAI. BIPM will concentrate on some selected laboratories world-wide. The RMOs are requested to support this activity by organization of calibration campaigns linking institutes whose equipment has been or will be characterized by BIPM with other institutes.
It is planned to:

  •  identify current needs of EURAMET laboratories,
  •  identify suitable equipment,
  •  organize bilateral or multilateral campaigns of visits with one laboratory acting as the pilot, and
  •  report results to BIPM in a format which shall be developed in joint work of members of the CCTF WG on the MRA, and BIPM.

Progress Report 2019-09-30

Since its beginning in the year 2011, ROA has supported the coordination of the EURAMET TC-TF Project 1156, to study the characterization of GNSS equipment of the contributing institutes to TAI. Starting that year, a GPS calibration campaign was organized between three contributing laboratories: ROA (Spain), PTB (Germany) and INRIM (Italy). The time transfer results were achieved by using the P3 method and the carrier phase PPP comparison techniques.

The GPS calibration was carried out in differential mode or link calibration, where the GPS units involved in each lab and the travelling receiver were operated using common clock signals over a near zero baseline.
During 2011 and 2012, the campaign was repeated, and in 2012 two other laboratories were included in the calibration trip: NPL (United Kingdom) and OP (France).

In 2014, as a result of the CCTF recommendation of collaboration between the BIPM and the RMOs for GNSS equipment calibration, some National Metrology Institutes (NMIs) and Designated Institutes (DIs), were selected to be Group 1 (G1) laboratories, to function as regional nodes for the GPS calibrations. The mission of these Laboratories, once calibrated by BIPM, were to perform and lead new calibration campaigns between Group 2 (G2) laboratories, under the responsibility of RMOs.

PTB, OP and ROA are the only G1 laboratories in Europe. Since then, ROA has conducted several GPS G1 to G2 calibration campaigns in the frame of the EURAMET 1156 Project, involving some G2 laboratories (other NMI, DI or research institutes, non G1 laboratories, irrespective of their nature):

- Cal_Id=1011-2016: ROA, BIM (Bulgaria), DMDM (Serbia), IMBH (Bosnia & Herzegovina), UME (Turkey), BOM (FYR Macedonia), INRIM
- Cal_Id=1014-2017: ROA, NPL, SMD (Belgium)
- Cal_Id= 1020-2017: ROA, SASO (Saudi Arabia)
- Cal_Id= 1101-2017: JV (Norway)
- Cal_Id= 1015-2019: NPL, UFE (Czech Republic) – (ongoing)

Similarly, PTB has undertaken several campaigns since 2016:

- CAL_Id=1012_2016: DLR, METAS, BEV, VSL
- CAL_Id= 019_2016: ESTEC
- CAL_Id=1015_2017: DTAG
- CAL_Id=1016_2017: BKG (Geodetic Obs. Wettzell, IFAG)
- CAL_Id=1102_2017: UFE
- CAL_Id=1014_2018: FTMC, GUM, AOS
- CAL_Id=1018_2018: NMISA
- CAL_Id=1011_2019: IMBH
- CAL_Id=1012_2019: DTAG (ongoing)
- CAL_Id_1013_2019: NMIB, SIQ (scheduled start late September 2019)

In addition, LNE-SYRTE (OP) has undertaken several calibration campaigns since 2016:

- CAL_Id =1101-2016: CNES
- CAL_Id=1013-2016: INRIM, SP
- CAL_Id=1018-2017: ORB
- 2017: LNE-LTFB (in the context of French metrology for accredited laboratories)
- CAL_Id=1015-2018: CNES
- CAL_Id=1012-2018: LUX
- CAL_Id=1014-2019: INRIM, RISE (in progress)

LNE-SYRTE is grateful to PTB and ROA for having taken the largest part of the EURAMET G1/G2 calibrations over this period.

The calibration campaigns were carried out in differential mode with closure, where the travelling system served as a transfer between all systems visited during the trip and the reference receiver. They were labelled with a calibration identifier (Cal_ID) to enable the process yielding the results to be traced. The Cal_ID is used to report calibration information in Section 5 of Circular T, and the results are available on the BIPM website (via the "Current files" tab):

https://www.bipm.org/jsp/en/TimeCalibrations.jsp