GNSS ATMOSPHERIC ESTIMATION WITH FEDERATED IONOSPHERIC FILTER

• US 20120092213A1
• Filed: 05/26/2011
• Published: 04/19/2012
• Est. Priority Date: 08/19/2008
• Status: Active Grant

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Chen, Xiaoming
• Granted Patent: US 9,091,757 B2
• Time in Patent Office: Days
• US Class Current: 342/26.A
• CPC Class Codes: G01S 19/32 Multimode operation in a single same satellite system, e.g. GPS L1/L2
• CPC Class Codes: G01S 19/44 Carrier phase ambiguity resolution; Floating ambiguity; LAMBDA [Least-squares AMBiguity Decorrelation Adjustment] method

Abstract

Methods and apparatus are presented for estimating environmental parameters from GNSS signals in real time. Some embodiments estimate a float solution using a federated ionospheric filter. Some embodiments fix ambiguities for improved estimates.

Claims

1. A method of processing GNSS signal data to estimate environmental parameter values, comprising

obtaining GNSS data collected at a plurality of stations distributed over a region from signals received from GNSS satellites over multiple epochs,

obtaining a satellite differential code bias (DCB) per satellite, and

estimating a receiver differential code bias per station and a value of total electron content (TEC) per station per satellite from the GNSS data and the satellite differential code biases using a federated ionospheric filter.

2. The method of claim 1, further comprising

applying a geometric filter to estimate from the GNSS data a set of values for atmospheric parameters comprising at least one of:

(i) a zenith total delay per station, (ii) a zenith total delay per station and a set of tropospheric gradients per station, and (iii) a slant total delay per station per satellite,

obtaining meteorological data for locations within the region, and

determining values over the region for at least one of;

(1) integrated precipitable water vapor (IPWV) and (2) tropospheric slant wet delay, from the set of values for atmospheric parameters and from the meteorological data.

3. The method of claim 1, wherein obtaining a satellite differential code bias per satellite comprises one of (i) retrieving a satellite differential code bias per satellite from an external source, and (ii) computing a satellite differential code bias per satellite from GNSS data collected at a network of reference stations.

4. The method of claim 1, wherein estimating a value of total electron content per station per satellite comprises

estimating values for ionospheric model parameters and for a stochastic ionospheric delay term per satellite per station in the federated ionospheric filter, and

determining the value of total electron content per station per satellite from the estimated values for the ionospheric model parameters and the stochastic ionospheric delay terms.

5. The method of claim 1, wherein applying a federated ionospheric filter comprises:

for each satellite,

applying to the GNSS signal data an ionospheric subfilter to estimate values for local states representing parameters unique to that satellite and values for common states representing parameters common to all receivers,

providing values for the common states and associated statistical information to a master filter; and

preparing updated estimates for the local states when updated values for the common states are provided by the master filter; and

applying to the values for the common states and the associated statistical information a master filter to estimate updated values for the common states, and to provide the updated values to the ionospheric subfilters.

6. The method of claim 5, wherein the states unique to the satellite comprise:

a set of parameters characterizing ionosphere across the region, a stochastic ionospheric delay term per station per satellite, and an integer ambiguity per station per satellite.

7. The method of claim 5, wherein the states common to all satellites comprise a receiver differential code bias per station.

8. The method of claim 5, further comprising:

resetting states in the master filter to zero with infinite variance before any observation update at each epoch, and then applying the decorrelated observations from each subfilter to the master filter

9. The method of claim 1, wherein the value of total electron content per station per satellite comprises a value mapped to vertical.

10. The method of claim 2, wherein obtaining meteorological data comprises obtaining surface meteorological data for locations within the region.

11. The method of claim 2, wherein obtaining meteorological data comprises obtaining radiosonde temperature data for locations within the region.

12. The method of claim 1, wherein elapsed time between obtaining the GNSS data and determining values over the region for total electron content is no more than about five seconds.

13. The method of claim 2, wherein elapsed time between obtaining the GNSS data and determining values over the region for total electron content and at least one of integrated precipitable water vapor and tropospheric slant delay is no more than about five seconds.

27. A computer program product comprising:

a computer usable medium having computer readable instructions physically embodied therein, the computer readable instructions when executed by a processor enabling the processor to perform the method of claim 1.

14. Apparatus for processing GNSS signal data to estimate environmental parameter values, comprising a federated ionospheric filter adapted to estimate a receiver differential code bias per station and a value of total electron content (TEC) per station per satellite from satellite differential code biases and the GNSS signal data.

15. The apparatus of claim 14, further comprising:

a geometric filter adapted to estimate from the GNSS data a set of values for atmospheric parameters comprising at least one of;

(i) a zenith total delay per station, (ii) a zenith total delay per station and a set of tropospheric gradients per station, and (iii) a slant total delay per station per satellite, and

an atmospheric watch module to determine values over the region for at least one of (1) integrated precipitable water vapor and (2) tropospheric slant wet delay, from the estimated values for atmospheric parameters and from meteorological data for the region.

16. The apparatus of claim 14, further comprising an element to obtain a code bias per satellite by one of (i) retrieving a code bias per satellite from an external source, and (ii) computing a code bias per satellite from GNSS data collected at a network of GNSS reference stations.

17. The apparatus of claim 14, comprising:

a module to estimate values for ionospheric model parameters and for a stochastic ionospheric delay term per satellite per station, and

a module to determine the value of total electron content per station per satellite from the estimated values for the ionospheric model parameters and the stochastic ionospheric delay terms.

18. The apparatus of claim 14, wherein the federated ionospheric filter comprises:

an ionospheric subfilter for each satellite adapted to

estimate values for local states representing parameters unique to that satellite and values for common states representing parameters common to all receivers, from the GNSS signal data and a satellite differential code bias,

provide values for the common states and associated statistical information to master filter; and

prepare updated estimates for the local states when updated values for the common states are provided by the master filter; and

a master filter adapted to estimate updated values for the common states from the values for the common states and the associated statistical information, and to provide the updated values to the ionospheric subfilters.

19. The apparatus of claim 18, wherein the states unique to the satellite comprise:

a set of parameters characterizing ionosphere across the region, a stochastic ionospheric delay term per station per satellite, and an integer ambiguity per station per satellite.

20. The apparatus of claim 18, wherein the states common to all satellites comprise a receiver differential code bias per station.

21. The apparatus of claim 18, wherein the federated ionospheric filter is operative to reset states in the master filter to zero with infinite variance before observation update at each epoch, and then to apply the decorrelated observations from each subfilter to the master filter.

22. The apparatus of claim 14, wherein the value of total electron content per station per satellite comprises a value mapped to vertical.

23. The apparatus of claim 14, wherein the meteorological watch module is adapted to use surface meteorological data for locations within the region as at least a subset of the meteorological data.

24. The apparatus of claim 14, wherein the meteorological watch module is adapted to use radiosonde sounding data as at least a subset of the meteorological data.

25. The apparatus of claim 14, wherein elapsed time between obtaining the GNSS data and determining values over the region for total electron content is no more than about five seconds.

26. The apparatus of claim 14, wherein elapsed time between obtaining the GNSS data and determining values over the region for total electron content and at least one of integrated precipitable water vapor and tropospheric slant wet delay is no more than about five seconds.