Research Global Positioning System

Short Name or Variable Name
GPS

GPS position and velocity reported at 20 samples per second from the Novatel BESTPOS and BESTVEL logs. GPS time is extracted from these logs and converted to UTC time based on the Novatel TIME log. The TIME log, as well as the NMEA GPGGA and GPRMC logs, are recorded once per minute.

Model: Novatel OEM628

Measurements Provided: Aircraft GPS position and Earth-relative velocity.

Measurement Characteristics: 

  • Overall estimate of uncertainty: For TerraStar-c, fully converged,  Horizontal accuracy = 4 cm (RMS), 5 cm (95%). Vertical Accuracy = 6.5 cm (RMS). Without TerraStar but with WAAS/SBAS corrections the horizontal accuracy is typically 0.6 m. If neither is available the accuracy specification is 1.2 m horizontal.
  • TerraStar corrections often will not be available near the poles, as the TerraStar transmitting satellites are in a geosynchronos orbit. The basic GPS accuracy is degraded near poles due to the satellite orbits. 
  • Response time: Recorded at 20 samples per second since January 2022
  • Other measurement characteristics (comments on signal/noise, bias limits, etc): Can dropout on sharp turns, accuracy is degraded near the poles and during times of ionospheric disturbances. TerraStar may not be available near the poles. TerraStar coverage maps are available at https://www.novatel.com/products/terrastar-gnss-corrections/terrastar-coverage-map/

History of Significant Changes: 

2008-August: Updated C-130 receiver firmware to 2.312. Changed pulse-per-second output to positive polarity.

2008-December: Updated GV firmware to 3.500.

2014 - Moving to the OEM628 in FlexPak6 receivers.

2016: Firmware version 6.730.

2021: Added GLONASS constellation to receivers in addition to GPS constellation.

2022: Increased UDP update rate to 20 Hz, added TIME log, reduced RS232 NMEA logs to 1/minute.

Lead Contact
Patrick Veres
Typical Sampling Rates
20 samples per second