SuperK OD-DAQ - GPS subsystem

HGB, updated 15 Sep. 2009

Two Global Positioning System (GPS) receivers are mounted inside the radon hut near the entrance to the Atotsu tunnel to the SuperK tank. Their purpose is to receive time-of-year data with approx. 100 nsec absolute accuracy from the worldwide GPS satellite network, provided by the US Naval Observatory (USNO) Master Clock. The antennae are mounted on top of the radon hut roof, picking up the satellite signals and transmitting them to the receiver via coax cables.

The receivers then each transfer the time information via a dual 2km optical fiber cable through the car tunnel to the inside of the mine. There, the signals are picked up by an interface board in the OD-DAQ VME crate in the center hut on top of the SuperK tank. The primary receiver (TrueTime XL-DC) uses an "IRIG-B" pulse code (commonly used for military applications) for the optical data transfer which contains the time of the year in DDD:HH:MM:SS format along with status information. For the secondary receiver (Motorola UTPlus Oncore), a UW-made interface module is multiplexing the serial time/position/status data (Motorola Oncore format) with the 1PPS synchronization pulse before it is converted to optical pulse code.

Inside the VME crate, the optical pulses are de-converted to digital electrical signals and then decoded. The TrueTime IRIG-B code is used for synchronizing and conditioning an internal clock in the TrueTime VME-SG module with the GPS time in order to achieve 100 nsec accuracy. The serial Motorola Oncore data is buffered for direct access at the VMEbus by the ODDAQ computer (sukant). The 1PPS pulses of the two optical signals are decoded and then used as calibration triggers for the Local Time Clock module and Rubidium Clock. The high-resolution time information then can be picked up through the VMEbus for further use with the ODDAQ online software.

GPS Ant. XL-DC MOTRCVR Rubidium RS232VME VME-SG FI-VME LTC5 Fifos Bit3 sukant RadonSys VMEcrate backgrnd

GPS system block diagram

Hardware documentation links:
  1. GPS synchronized time and frequency receiver: TrueTime model XL-DC product description (177k pdf)
  2. VME interface module for the XL-DC receiver: TrueTime model VME-SG (38k pdf)
  3. Backup GPS receiver: Motorola UT Plus Oncore
  4. NEW!   Rubidium Frequency Standard: SRS PRS10 (user manual)
  5. Outer Detector Electronics
  6. IRIG-B code infos
  7. Measurement of 2km optic fiber delay time (12/15/98):
    10.008 µsec +/- 2 nsec
  8. The K2K GPS System

Operation and software help:

  1. Outer Detector Data Acquisition (ODDAQ) Online Software
  2. The Super-Kamiokande UTC Clock System (J. George, R. J. Wilkes, H. Berns, revised 3/11/98)
  3. How to swap the TrueTime GPS receiver in the radon hut [Aug.31, 1999, due to GPS-rollover bug in our 1995 model].
  4. SuperK GPS Shift Help Guide.
  5. NEW!   Super-K GPS system satellite tracking monitor (updated hourly).
  6. Super-K GPS system 1PPS/data performance monitor (updated hourly).

Position measurements and maps:

  1. Geographical Location and Orientation of Superk (J.Wilkes, 8/24/96)
  2. Maps of the SuperK location:
  3. Our GPS receiver surveys at the radon hut position:
    • August 1996, after 90,000 of 3D-fixes with TrueTime XL-DC:
      Latitude: North 36o 24' 31.2''
      Longitude: East 137o 18' 30.5''
      Altitude: 389 meters (WGS84)
      Estimated errors: +/- 10 meters horizontally, +/- 20 meters vertically
    • May/June 1998 survey for testing backup GPS receiver:
      TrueTime XL-DC:
      450000 of 3D-fix samples      		 Latitude: North 36o 24' 31.20''
      Longitude: East 137o 18' 30.50''
      Altitude: +389.4 meters (WGS84)
      Motorola VP Oncore
      (with TAC32 software):
      399737 of 3D-fix samples      		 Latitude: North 36o 24' 31.159''
      Longitude: East 137o 18' 30.253''
      Altitude: +408.74 m (WGS84)
      +373.35 m (MSL) (*)
      (*): Mean Sea Level geoid correction = -35.39 m
      Estimated errors: +/- 4 meters horizontally, +/- 8 meters vertically.
    • The antenna position offset to the tunnel mouth centerline was measured as:
      17.6 meters along roadway centerline extended
      8.1 meters perpendicular to extended centerline
      5.2 meters above level of centerline at tunnel mouth
  4. Calculation of SuperK tank center location with above 1998 survey data and projection of Mining Co. maps:
    Latitude: North 36o 25' 32.282'' +/- 0.460'' (14.2 meters)
    Longitude: East 137o 18' 37.224'' +/- 1.673'' (41.6 meters)
    Altitude: 374 meters (MSL) +/- 40 meters

KEK / SuperK reports about GPS

  1. " Precision Positioning of SuperKamiokande with GPS for a Long-Baseline Neutrino Oscillation Experiment" (6.2MB pdf) by H.Noumi et al., KEK Internal 96-17, March 1997.
  2. "Alignment and Control of Neutrino Beam towards SuperKamiokande" (700kB pdf) by H.Noumi et al., Draft, 31 Jan. 2000.
  3. "GPS clock calibration using an atomic clock" (233kB pdf) by S.Yamada et al, Draft, Dec. 1999.
{click on photo(s) for full size}

GPS Antennas GPS antennas mounted on north side of the radon hut (2/99)

GPS Antennas (zoomed) closer look at the GPS antennas (2/99)

TrueTime XL-DC Receiver Primary GPS receiver: TrueTime model XL-DC

MOTRCVR module Secondary (backup) GPS receiver: MOTRCVR module box with Motorola UT Plus Oncore (2/99)

GPS system in radon hut GPS system shelf in radon hut (1/03)

SK GPS receivers rear sides cabling detail of both receivers at rear side (2/99)

ODDAQ VME crate ODDAQ VME crate in SuperK Center Hut (2/99)