Wuhan Combination Center
Established: 2024
Chair: Jianghui Geng
Mailing List: Wuhan Combination Center 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 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.
ID |
Rapid | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| name | system | orbit | clock | attitude | code bias | phase bias | ||||
| COD | COD0OPSRAP | GRE | 300 s | 30 s | 30 s | GE (OSB) | GE (OSB) | |||
| EMR | EMR0OPSRAP | GR | 900 s | 300 s | ||||||
| ESA | ESA0OPSRAP | GR | 300 s | 30 s | ||||||
| GFZ | GFZ0OPSRAP | GRE | 300 s | 300 s | ||||||
| GRG | GRG0OPSRAP | GRE | 300 s | 30 s | 30 s | GE (OSB) | GE (OSB) | |||
| HUS | HUS0MGXRAP | GRE | 300 s | 30 s | 30 s | GRE (OSB) | GE (OSB) | |||
| IGS | IGS0OPSRAP | G | 900 s | 300 s | ||||||
| JGX | JGX0OPSRAP | GRE | 300 s | 30 s | ||||||
| JPL | JPL0OPSRAP | GRE | 300 s | 30 s | 30 s | |||||
| WUM | WUM0MGXRAP | GRE | 300 s | 30 s | 30 s | GRE (OSB) | GE (OSB) | |||
| Note: a. GRE stand for GPS, GLONASS and Galileo respectively. b. OSB stands for observable specific bias, IRC stands for integer recovery clock. |
||||||||||
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.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.
Orbit combination weight
The orbit combination employs an ACs-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.
The weekly orbit RMSE
The orbit RMSE refers to the daily RMSE of orbit for each AC with respect to the combined orbit, which reflects the precision of orbit 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 statistics at the bottom indicate the overall RMSE of AC orbit for this week.
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.
Clock/bias combination 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 clock/bias Allan Deviation
Modified Allan Deviation (MDEV) is used to characterize the frequency stability and noise properties of the clock. Red and blue colors indicate the original product and the product after the day-boundary alignment process, respectively, the smaller the MDEV, the better the stability of the clock products.
Day boundary discontinuity
Day boundary discontinuity refers to the difference between the clock at 24:00:00 and its counterpart the next day at 00:00:00. The image shows the cumulative day boundary discontinuity of the WCC products to date to reflect the overall continuity of the WCC.
PPP-AR validation
The GPS/Galileo 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. “WCC” stands for the combined 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.
ID |
Final | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| name | system | orbit | clock | attitude | code bias | phase bias | 24:00 epochs | |||
| COD | COD0OPSFIN | GRE | 300 s | 30 s | 30 s | GE (OSB) | GE (OSB) | CLK&SP3 | ||
| ESA | ESA0OPSFIN | GRE | 300 s | 30 s | SP3 | |||||
| GFZ | GFZ0OPSFIN | GRE | 300 s | 30 s | ||||||
| GRG | GRG0OPSFIN | GRE | 300 s | 30 s | 30 s | GE (OSB) | GE (OSB) | CLK&SP3 | ||
| HUS | HUS0MGXFIN | GRE | 300 s | 30 s | 30 s | GE (OSB) | GE (OSB) | CLK&SP3 | ||
| IGS | IGS0OPSFIN | G | 900 s | 30 s | ||||||
| JGX | JGX0OPSFIN | GRE | 300 s | 30 s | SP3 | |||||
| JPL | JPL0OPSFIN | GE | 300 s | 30 s | 30 s | CLK&SP3 | ||||
| Note: a. GRE stand for GPS, GLONASS and Galileo respectively. b. OSB stands for observable specific bias. c. HUS is used for detecting gross errors and comparison. |
||||||||||
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.The GNSS final orbit products are combined with a sampling interval of 300 s. All the results are presented on a weekly basis, with a latency of two weeks.
Orbit combination weight
The orbit combination employs an ACs-wise and constellation-specific 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.
The weekly orbit RMSE
The orbit RMSE refers to the daily RMSE of orbit for each AC with respect to the combined orbit, which reflects the precision of orbit 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 statistics at the bottom indicate the overall RMSE of AC orbit for this week.
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 two weeks.
Clock/bias combination 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 clock/bias Allan Deviation
Modified Allan Deviation (MDEV) is used to characterize the frequency stability and noise properties of the clock. Red and blue colors indicate the original product and the product after the day-boundary alignment process, respectively, the smaller the MDEV, the better the stability of the clock products.
Day boundary discontinuity
Day boundary discontinuity refers to the difference between the clock at 24:00:00 and its counterpart the next day at 00:00:00. The image shows the cumulative day boundary discontinuity of the WCC products to date to reflect the overall continuity of the WCC.
PPP-AR validation
The GPS/Galileo 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. “WCC” stands for the combined products.
Last Updated on 13 May 2025 11:51 UTC