Wuhan Combination Center
Established: 2024
Mailing List:
Charter
The Wuhan Combination Center (WCC) was formally approved by the IGS Governing Board (GB) in 2024. It aims at providing combined high-precision and highly-reliable multi-GNSS satellite products. The priorities of the WCC include: (1) The WCC serves as a backup combination institution; (2) The WCC incorporates the MGEX or demonstration products into the combination; (3) The WCC combined products contain all-frequency code/phase biases to avoid day-boundary discontinuity.
The tasks of the WCC are: (1) The WCC will focus on combining orbit, clock, and code/phase bias products, covering ultra-rapid, rapid, and final product lines; (2) Combined products for GPS, GLONASS, and Galileo will be released initially and BDS/QZSS will be introduced later; (3) PPP-AR validation will be carried out to monitor the quality and reliability of combined products. The WCC will enhance the consistency, interoperability, and reliability of AC-specific GNSS products, addressing the challenges in areas such as time and frequency transfer, geodesy, and satellite positioning.
Goals
1.Towards stable GPS, GLONASS, Galileo and BDS/QZSS orbit/clock/bias product combination over all frequencies.
2.Ensure a minimum availability of 95% for ultra-rapid and rapid combined products, and over 99% for final combined products.
3.Cross-validate both OPS and MGEX products.
4.Facilitate PPP-AR by integrating phase bias products into the combination process.
5.Ensure day-boundary continuity of combined products to deliver more stable services for time and frequency transfer.
6.Disseminate combined products to the GNSS community to support geodetic, geophysical, and timing applications.
Combination and analysis of ultra rapid products
The ultra rapid orbit/clock/bias products provided by different ACs are combined and evaluated.
These products are accessed from the CDDIS archive (https://cddis.nasa.gov/archive/gnss/products/) and the corresponding ACs are listed in the following table.
In the pipeline |
|---|
Orbit combination results
For the methods used in the orbit combination, please refer to the tabs Resources.
All the products in the table are included in the combination except for the IGS products, which is used for comparison.The GNSS ultra rapid clock products are combined with a sampling interval of 300 s. All the results are presented on a weekly basis, with a latency of one week.
Product integrity
The integrity of satellite orbit products for each AC is calculated as the percentage of the number of effective epoch relative to the total number of epoch.
The combined weight
The orbit combination employs an satellite-wise weighting method in which the weight assigned to a specific product depends on its consistency in relation to the combined orbit.
ACs’ transformation parameters
The differences in satellite orbits, relative to the combined orbit coordinate frame for each AC, are expressed in terms of seven parameters.
Clock/bias combination results
For the methods used in the clock and bias combination, please refer to the tabs Resources.
All the products in the table are included in the combination except for the IGS products, which is used for comparison. The combined orbit products are used as reference orbit, and the reference attitude is generated by the open source software GROOPS. The GNSS ultra rapid clock products are combined with a sampling interval of 300 s. All the results are presented on a weekly basis, with a latency of one week.
The combined weight
The clock combination employs an iterative weighting method in which the weight assigned to a specific product depends on its residuals in relation to the combined clock.
The weekly clock/bias RMSE
The clock/bias RMSE refers to the daily RMSE of clock/bias for each AC with respect to the combined integer clock, which reflects the precision of clock and bias combination and the consistency between individual ACs. Each grid represents a satellite on a particular day. Blank grids mean unavailable products and a slash inside means an outlier excluded from the combination. The line chart below shows the satellite clock outlier rate per day for each AC, with gray block indicating that relevant satellite clocks do not participate in the comparison. The statistics at the bottom indicate the overall RMSE of AC clock/bias for this week.
The accumulated clock/bias RMSE
The accumulated clock/bias RMSE refers to the daily RMSE of clock/bias for all the ACs with respect to the combined integer clock, which reflects the change of the combined accuracy over time. The line chart below shows the overall RMSE for each constellation.
Combination and analysis of rapid products
The rapid orbit/clock/bias products provided by different ACs are combined and evaluated.
These products are accessed from the CDDIS archive (https://cddis.nasa.gov/archive/gnss/products/) and the corresponding ACs are listed in the following table.
In the pipeline |
|---|
Orbit combination results
For the methods used in the orbit combination, please refer to the tabs Resources.
All the products in the table are included in the combination except for the IGS products, which is used for comparison.The GNSS rapid clock products are combined with a sampling interval of 300 s. All the results are presented on a weekly basis, with a latency of one week.
Product integrity
The integrity of satellite orbit products for each AC is calculated as the percentage of the number of effective epoch relative to the total number of epoch.
The combined weight
The orbit combination employs an satellite-wise weighting method in which the weight assigned to a specific product depends on its consistency in relation to the combined orbit.
ACs’ transformation parameters
The differences in satellite orbits, relative to the combined orbit coordinate frame for each AC, are expressed in terms of seven parameters.
Clock/bias combination results
For the methods used in the clock and bias combination, please refer to the tabs Resources.
All the products in the table are included in the combination except for the IGS products, which is used for comparison. The combined orbit products are used as reference orbit, and the reference attitude is generated by the open source software GROOPS. The GNSS rapid clock products are combined with a sampling interval of 30 s. All the results are presented on a weekly basis, with a latency of one week.
The combined weight
The clock combination employs an iterative weighting method in which the weight assigned to a specific product depends on its residuals in relation to the combined clock.
The weekly clock/bias RMSE
The clock/bias RMSE refers to the daily RMSE of clock/bias for each AC with respect to the combined integer clock, which reflects the precision of clock and bias combination and the consistency between individual ACs. Each grid represents a satellite on a particular day. Blank grids mean unavailable products and a slash inside means an outlier excluded from the combination. The line chart below shows the satellite clock outlier rate per day for each AC, with gray block indicating that relevant satellite clocks do not participate in the comparison. The statistics at the bottom indicate the overall RMSE of AC clock/bias for this week.
The accumulated clock/bias RMSE
The accumulated clock/bias RMSE refers to the daily RMSE of clock/bias for all the ACs with respect to the combined integer clock, which reflects the change of the combined accuracy over time. The line chart below shows the overall RMSE for each constellation.
PPP-AR validation
The GPS/Galileo/BDS data with a sampling interval of 300 s from 10 globally distributed stations are processed for PPP-AR in a static mode with the PRIDE PPP-AR software. The fixing rate and position precision of each single constellation solution are presented in the figure below. IGS daily SINEX products are used as reference solution. “CMBr” stands for the combined rapid products.
Combination and analysis of final products
The final orbit/clock/bias products provided by different ACs are combined and evaluated.
These products are accessed from the CDDIS archive (https://cddis.nasa.gov/archive/gnss/products/) and the corresponding ACs are listed in the following table.
In the pipeline |
|---|
Orbit combination results
For the methods used in the orbit combination, please refer to the tabs Resources.
All the products in the table are included in the combination except for the IGS products, which is used for comparison.The GNSS final clock products are combined with a sampling interval of 300 s. All the results are presented on a weekly basis, with a latency of three weeks.
Product integrity
The integrity of satellite orbit products for each AC is calculated as the percentage of the number of effective epoch relative to the total number of epoch.
The combined weight
The orbit combination employs an satellite-wise weighting method in which the weight assigned to a specific product depends on its consistency in relation to the combined orbit.
ACs’ transformation parameters
The differences in satellite orbits, relative to the combined orbit coordinate frame for each AC, are expressed in terms of seven parameters.
Clock/bias combination results
For the methods used in the clock and bias combination, please refer to the tabs Resources.
All the products in the table are included in the combination except for the IGS products, which is used for comparison. The combined orbit products are used as reference orbit, and the reference attitude is generated by the open source software GROOPS. The GNSS final clock products are combined with a sampling interval of 30 s. All the results are presented on a weekly basis, with a latency of three weeks.
The combined weight
The clock combination employs an iterative weighting method in which the weight assigned to a specific product depends on its residuals in relation to the combined clock.
The weekly clock/bias RMSE
The clock/bias RMSE refers to the daily RMSE of clock/bias for each AC with respect to the combined integer clock, which reflects the precision of clock and bias combination and the consistency between individual ACs. Each grid represents a satellite on a particular day. Blank grids mean unavailable products and a slash inside means an outlier excluded from the combination. The line chart below shows the satellite clock outlier rate per day for each AC, with gray block indicating that relevant satellite clocks do not participate in the comparison. The statistics at the bottom indicate the overall RMSE of AC clock/bias for this week.
The accumulated clock/bias RMSE
The accumulated clock/bias RMSE refers to the daily RMSE of clock/bias for all the ACs with respect to the combined integer clock, which reflects the change of the combined accuracy over time. The line chart below shows the overall RMSE for each constellation.
PPP-AR validation
The GPS/Galileo/BDS data with a sampling interval of 300 s from 10 globally distributed stations are processed for PPP-AR in a static mode with the PRIDE PPP-AR software. The fixing rate and position precision of each single constellation solution are presented in the figure below. IGS daily SINEX products are used as reference solution. “CMBf” stands for the combined rapid products.
Last Updated on 25 Feb 2025 14:55 UTC