GPS-only Analysis Products

Figures and Statistics from the IGS Rapid GPS Orbit Combination

Orbit and clock comparison figures

The WRMS plots below show the Weighted RMS (mm) of the individual AC orbit solutions with respect to the IGS Rapid (IGR) products. The Clock Std Dev and Clock RMS plots show the standard deviations (ps) and RMS (ps) of the individual AC clock solutions with respect to the IGS Rapid products. The Std Dev values are computed by removing a separate bias for each satellite/station clock, whereas this is not done for the clock RMS values. In the case where one uses these products with carrier phase data and estimates an ambiguity parameter for each station-satellite pair (such as for precise point positioning), the satellite clock biases will be absorbed by the ambiguity parameters, so the Std Dev statistics are appropriate. In other applications where no station-satellite bias parameter is estimated or where the underlying satellite time scale itself is of interest, then probably the RMS statistics are more suitable. For display purposes, the daily clock Std Dev and RMS values from the Rapid combination summaries are weekly averaged.

On 11 April 2014, this webpage was updated to include following comparisons:

• IGR and the observed part (IGA) of the 00h IGS Ultra-rapid product
• IGR and the real-time part of the IGS Ultra-rapid product (denoted here as IGU**)
• IGR and the IGS Real-time streams (denoted here as IGC**)

Note that IGC** are 24h SP3 files each containing four 6h segments (hours 4 thru 10) from each update interval of the IGS RT streams. The comparison with IGR is done daily over the full 24h of each IGC SP3. IGU** consists of 4 separate comparisons to IGR done each day over the first 6h of each IGS Ultra-rapid product.

The IGS Ultra-rapid orbit prediction errors grow with the sqrt(2). Each 6h segment within the 24h IGC file has a latency of 4 hours. The WRMS orbit differences between IGU** and IGC** for the first few weeks of this comparison are consistent with the errors for hours 4-10 of the IGS Ultra-rapid orbit predictions.

ERP comparison figures

The next plots show the difference between individual AC Rapid ERP solutions and the IGS Final product. The differences are shown for X-, and Y-pole, X-, and Y-pole rate, and LOD (length of day).

For the X-, and Y-pole figure the individual series are shifted by 1 mas.
For the X-, and Y-pole rate figure the individual series are shifted by 4 mas/day.
For the LOD figure the individual series are shifted by 0.2 ms/day.

AC Rapid ERP differences w.r.t. IGS Finals

Orbit transformation results per AC

The next plots show the weekly averages of the Helmert translation, rotation, and scale parameters for the individual AC solutions with respect to the IGS Rapid products.
“igu” is the 24 hours predicted orbit.

The next plots show the daily Helmert scale, translation, and rotation parameters for the individual AC orbit solutions separately, with respect to the IGS Rapid products.

The translations are shifted by 50 mm. The rotations are shifted by 1 mas.
“igu” is the 24 hours predicted orbit.

Scale/Translations from:

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Figures and Statistics from the IGS Final GPS Orbit Combination

Orbit and clock comparison figures

The WRMS plots below show the Weighted RMS (mm) of the individual AC orbit solutions with respect to the IGS Final products. The Clock Std Dev and Clock RMS plots show the standard deviations (ps) and RMS (ps) of the individual AC clock solutions with respect to the IGS Final products. The Std Dev values are computed by removing a separate bias for each satellite/station clock, whereas this is not done for the clock RMS values. In the case where one uses these products with carrier phase data and estimates an ambiguity parameter for each station-satellite pair (such as for precise point positioning), the satellite clock biases will be absorbed by the ambiguity parameters, so the Std Dev statistics are appropriate. In other applications where no station-satellite bias parameter is estimated or where the underlying satellite time scale itself is of interest, then probably the RMS statistics are more suitable. For display purposes, the daily clock Std Dev and RMS values from the Final combination summaries are weekly averaged.

Starting on 19-Aug-2012 (GPS Week 1702; mjd=56158), the IGS Finals products switched from being based on weekly SINEX integrations to being based on daily ones.

ERP comparison figures

The next plots show the difference between individual AC Final ERP solutions and the IGS Final product. The differences are shown for X-, and Y-pole, X-, and Y-pole rate, and LOD (length of day).

For the X-, and Y-pole plots the individual series are shifted by 0.5 mas for recent data and 1 mas for historic data.
For the X-, and Y-pole rate plots the individual series are shifted by 2 mas/day for recent data and 4 mas/day for historic data.
For the LOD plots the individual series are shifted by 0.2 ms/day.

AC Final ERP differences with IGS Finals

Orbit transformation results per AC

The next plots show the weekly averages of the Helmert translation, rotation, and scale parameters for the individual AC orbit solutions, with respect to the IGS Final products, compared to each other.

The next plots show the daily Helmert scale, translation, and rotation parameters for the individual AC orbit solutions separately, with respect to the IGS Final products. The orbit rotation plots also show associated polar motion (PM) offsets to check for rotational consistency (-dPMy with RX; -dPMx with RY). Recall that small AC SINEX rotational offsets were applied in the orbit combination process to all the AC orbit and PM values in order to align them consistently to the current IGS reference frame.

The translations are shifted by 50 mm. The rotations are shifted by 1 mas.

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Figures and Statistics for Broadcast Orbits wrt IGS Rapid Orbits

Orbit and clock comparison figures

The WRMS plots below show the Weighted RMS (m) of the Broadcast orbits (brd) with respect to the IGS Rapid product. The Clock Std Dev and Clock RMS plots show the standard deviations (ns) and RMS (ns) of the Broadcast clocks with respect to the IGS Rapid product. The Std Dev values are computed by removing a separate bias for each satellite clock, whereas this is not done for the clock RMS values. For Broadcast orbits and clocks, normally the RMS statistic is more suitable. Note that the intentional degradation of the GPS clock signals by Selective Availability (SA) was discontinued at midnight EDT on 01 May 2000, GPS Week 1060, Day 1 (or 04:00 UTC on 02 May). Since that change, civilian GPS users can obtain positioning and timing determinations that are more accurate than before by about a factor of up to ten. Clock statistics before Week 1060 are not shown here.

Orbit transformation results

The next plots show the weekly averages of the Helmert translation, rotation, and scale parameters of the Broadcast orbits with respect to the IGS Rapid products.

Figures and Statistics for Precise Point Positioning (PPP)

PPP Strategy:

A Precise Point Positioning (PPP) is performed using the ERPs, SP3 orbits, and satellite clocks from the IGS Final/Rapid combination as well as from the individual contributing Analysis Centers. Clocks and RINEX observations are decimated to 5-min intervals.

The PPP is done on a daily basis for each of the available stations defining the IGS Reference Frame (about 232 for IGS08/IGb08). For each set of AC orbits, ERPs, and satellite clocks, a PPP solution is done in three steps. Step 1 involves fitting the satellite positions from the SP3 orbit files to the extended CODE (6+9) orbit model using the associated ERPs in the ECF->Inertial transformation. Step 2 involves preprocessing of the clocks and RINEX observations to detect and eliminate clock jumps and cycle slips. Step 3 is the data reduction with iterative post-fit cleaning; outliers in the phase residuals are taken to be greater than 25 mm and outliers in the code residuals are taken to be greater than 2.5 m. A-priori modeling of the tropospheric delay is done using the Global Mapping Function (GMF) and Global Pressure and Temperature (GPT) model. Prior to 11 April 2013, The Niell Mapping Function (NMF) and standard meteorological data were used. The products from each AC are processed separately; this way the cleaning for one AC has no effect on the results for the other ACs.

Helmert transformations are performed between the global network compiled from the PPP results and both the IGS Reference Frame and the IGS combined SINEX solution. The Helmert transformation parameters and station residual statistics are given over the past 7 days. North, east, up residuals (after the Helmert transformation) for each of the stations are presented including its mean and standard deviation over the past 7 days.

The PPP results give a measure of the internal consistency for each set of AC clocks, orbits, and ERPs. Over time, the PPP analysis also reveals information about the stability of station coordinates and the realization of a given reference frame.

Starting on 19-Aug-2012 (GPS Week 1702; mjd=56158), the IGS Finals products switched from being based on weekly SINEX integrations to being based on daily ones. Associated with this switch is a change to comparing with daily SINEX files, instead of a weekly one. The switch began impacting the Rapid PPP starting on 05-Sep-2012 (GPS Week 1704, day 3; mjd=56175).

Software:
Bernese GNSS Software v. 5.2, Developed by the Astronomical Institute of the University of Bern, Switzerland
(Bernese v. 5.0 was replaced on 11 April 2013)

PPP using Rapid Orbits and Clocks

PPP using Final Orbits and Clocks

All AC and IGR/IGS results in one plot for each component.

Figures for the individual ACs (and IGR/IGS)

Transformation parameters from the SINEX combinations are included for comparison.

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Rapid PPP

station repeatabilities referenced to

Final PPP

station repeatabilities referenced to