GPS Satellite Ephemerides / Satellite & Station Clocks



Type Accuracy Latency Updates Sample Interval
Broadcast orbits ~100 cm real time -- daily
Sat. clocks ~5 ns    RMS
~2.5 ns SDev
Ultra-Rapid (predicted half) orbits ~5 cm real time at 03, 09, 15, 21 UTC 15 min
Sat. clocks ~3 ns    RMS
~1.5 ns SDev
Ultra-Rapid (observed half) orbits ~3 cm 3 - 9 hours at 03, 09, 15, 21 UTC 15 min
Sat. clocks ~150 ps RMS
~50 ps SDev
Rapid orbits ~2.5 cm 17 - 41 hours at 17 UTC daily 15 min
Sat. & Stn. clocks ~75 ps RMS
~25 ps SDev
5 min
Final orbits ~2.5 cm 12 - 18 days every Thursday 15 min
Sat. & Stn. clocks ~75 ps RMS
~20 ps SDev
Sat.: 30s
Stn.: 5 min

Note 1: Orbit accuracies are 1D mean RMS values over the three XYZ geocentric components. IGS accuracy limits, except for predicted orbits, are based on comparisons with independent laser ranging results and discontinuities between consecutive days. The precision is better.

Note 2: The accuracy (neglecting any contributions from internal instrumental delays, which must be calibrated separately) of all clocks is expressed relative to the IGS timescale, which is linearly aligned to GPS time in one-day segments. The standard deviation (SDev) values are computed by removing a separate bias for each satellite and station clock, whereas this is not done for the RMS values.



GLONASS Satellite Ephemerides



Type Accuracy Latency Updates Sample Interval
Final ~3 cm 12 - 18 days every Thursday 15 min


Geocentric Coordinates of IGS Tracking Stations



Type Accuracy Latency Updates Sample Interval
Final positions horizontal 3 mm 11 - 17 days every Wednesday weekly
vertical 6 mm
Final velocities horizontal 2 mm/yr 11 - 17 days every Wednesday weekly
vertical 3 mm/yr


Earth Rotation



Polar Motion (PM) Polar Motion Rates (PM rate) Length-of-day (LOD)

Type Accuracy Latency Updates Sample Interval
Ultra-Rapid (predicted half) PM ~200 µas real time at 03, 09, 15, 21 UTC daily integrations at 00, 06 12, 18 UTC
PM rate ~300 µas/day
LOD ~50 µs
Ultra-Rapid (observed half) PM ~50 µas 3 - 9 hours at 03, 09, 15, 21 UTC daily integrations at 00, 06, 12, 18 UTC
PM rate ~250 µas/day
LOD ~10 µs
Rapid PM ~40 µas 17 - 41 hours at 17 UTC daily daily integrations at 12 UTC
PM rate ~200 µas/day
LOD ~10 µs
Final PM ~30 µas 11 - 17 days every Wednesday daily integrations at 12 UTC
PM rate ~150 µas/day
LOD ~10 µs

Note 1: 100 µas = 3.1 mm of equatorial rotation; 10 µs = 4.6 mm of equatorial rotation.

Note 2: The IGS uses VLBI results from IERS Bulletin A to partially calibrate for LOD biases over 21-day sliding window, but residual time-correlated LOD errors remain.



Atmospheric Parameters



Type Accuracy Latency Updates Sample Interval
Final tropospheric zenith path delay 4 mm < 4 weeks weekly 2 hours
Ultra-Rapid tropospheric zenith path delay 6 mm 2-3 hours every 3 hours 1 hour
Final ionospheric TEC grid 2-8 TECU ~11 days weekly 2 hours;
5 deg (lon) x 2.5 deg (lat)
Rapid ionospheric TEC grid 2-9 TECU <24 hours daily 2 hours;
5 deg (lon) x 2.5 deg (lat)


IGS Final products (IGS) 
The IGS Final products have the highest quality and internal consistency of all IGS products. They are made available on a weekly basis, by each Friday, with a delay up to 13 (for the last day of the week) to 20 (for the first day of the week) days. The IGS Final products are the basis for the IGS reference frame and are intended for those applications demanding high consistency and quality.


IGS Rapid products (IGR) 
The IGS Rapid products have a quality nearly comparable to that of the Final products. They are made available on a daily basis with a delay of about 17 hours after the end of the previous observation day; i.e., the IGS Rapid products are released daily at about 17:00 UTC. For most applications the user of IGS products will not notice any significant differences between results obtained using the IGS Final and the IGS Rapid products.


IGS Ultra-rapid products (IGU) 
To reduce the age of the prior, discontinued Predicted orbits, the IGS started the Ultra-rapid products officially week 1087 in November 2000 (see IGSMAIL-3088) . Like the former IGS Predicted products, the Ultra-rapid products are available for real time and near real time use. The Ultra-rapid products are released four times per day, at 03:00, 09:00, 15:00, and 21:00 UTC. (Until week 1267 they were released twice daily.) In this way the average age of the predictions is reduced to 6 hours (compared to 36 hours for the old IGS Predicted products and 9 hours for the twice-daily Ultra-rapids). The shorter latency should lead to significantly improved orbit predictions and reduced errors for user applications. Contrary to all other IGS orbit products the IGS Ultra-rapid orbit files contain 48 hours of tabulated orbital ephemerides, and the start/stop epochs continuously shift by 6 hours with each update. All other orbit products contain strictly the 24 hours from 00:00 to 23:45. The first 24 hours of each IGS Ultra-rapid orbit are based on the most recent GPS observational data from the IGS hourly tracking network. At the time of release, the observed orbits have an initial latency of 3 hours. The next 24 hours of each file are predicted orbits, extrapolated from the observed orbits. The orbits within each Ultra-rapid product file are, however, continuous at the boundary between the observed and predicted parts. Normally, the predicted orbits between 3 and 9 hours into the second half of each Ultra-rapid orbit file are most relevant for true real time applications.

Please include the IGS logo and citation in all websites, presentations, publications, or posters that use IGS data, products, or services. IGS is a service of IAG.