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Data-Replay Analysis of LAAS Safety during Ionosphere Storms

Data-Replay Analysis of LAAS Safety during Ionosphere Storms. Young Shin Park , Godwin Zhang, Sam Pullen, and Per Enge Stanford University. ION GNSS 2007 Session E1 Paper # 5 September 26 , 2007. This research was supported by the FAA LAAS Program Office.

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Data-Replay Analysis of LAAS Safety during Ionosphere Storms

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  1. Data-Replay Analysis of LAASSafety during Ionosphere Storms Young Shin Park, Godwin Zhang, Sam Pullen, and Per Enge Stanford University ION GNSS 2007 Session E1 Paper # 5 September26, 2007 This research was supported by the FAA LAAS Program Office

  2. Iono. Anomaly from JPL IGS/CORS Data (20 Nov. 2003; 20:15 – 21:00 UT) Severely anomalous ionosphere behavior poses a threat to LAAS user integrity. 11/20/2003, 20:15:00 UT 11/20/2003, 21:00:00 UT Courtesy of Seebany Datta-Barua

  3. Ionosphere Impact on a LAAS User Simplified Ionosphere Wave Front Model: a wave front ramp defined by the “slope” and the “width” Front Speed Front Slope LGF IPP Speed Front Width Airplane Speed LAAS Ground Facility Courtesy of Jiyun Lee

  4. Simulation Iono. Slope 425 375 15 68 Elevation Iono. Anomaly Database Ionosphere Anomaly Threat Model • LAAS Mitigations • CCD Monitor • Sigma/P-value inflation • (VPLinf > VAL) LAAS Impact Simulation 5km DH Separation Pierce Point Plucker Method (Jiyun Lee, 2006) Worst-Case VPE (MIEV) Wedge Sweeper Method (Ming Luo, 2005)

  5. Simulation vs. Data-Replay Analysis Pick Actual Iono. Data for Pair of CORS Stations (> 23 km apart) Iono. Anomaly Database Ionosphere Anomaly Threat Model Compute Actual Unsmoothed DGPS Range Errors • LAAS Mitigations • CCD Monitor • Sigma/P-value inflation • (VPLinf > VAL) VPL > VAL Compute Histogram of VPE over Time and Subset Geometry LAAS Impact Simulation 5km DH separation Pierce Point Plucker Method (Jiyun Lee, 2006) Worst-Case VPE (MIEV) Worst-Case VPE Wedge Sweeper Method (Ming Luo, 2005)

  6. Validated Iono. Gradients on SVN 26 (20 Nov. 2003; 20:49 ~ 21:17 UT in OH-MI) 425 ZOB1 * 360 300 345 Ionosphere Front 240 300 150 Data from the Ohio/Michigan Cluster of CORS stations on November 20, 2003; 9 Pairs of CORS Stations

  7. Data-Replay Analysis Procedure Differential GPS (DGPS) Pseudorange (One station: static LAAS user) Corrections from LGF (The other station: LAAS reference facility) Compute Corrected Pseudorange All viable subset geometries: All in view + N-1 + N-2 Compute Vertical Position Error (VPE) Geometry Screening by checking VPL_H0 - VAL (far away) = 43.35 m - VAL (DH) = 10 m Worst-Case VPE

  8. WOOS-GARF (74.5 km) USER 425 360 ZOB1 * LGF Ionosphere Front 345 300 240 150

  9. Subset of OH/MI Stations that Saw Similar Ionosphere Behavior on 11/20/2003 35 30 25 20 15 10 5 0 0 50 100 150 200 250 300 350 Data from 7 CORS Stations, SVN 38 Initial upward growth;slant gradients ~ 60 – 120 mm/km Sharp falling edge; slant gradients ~ 300 - 330 mm/km from previous work Slant Iono Delay (m) Slant Iono Delay (m) “Valley” with smaller (but still anomalous) gradients WAAS Time (minutes from 5:00 PM to 11:59 PM)

  10. VPE for All-in-view(WOOS-GARF; 74.5 km) 241 data 200 bins No. of Occurrence VPE (m) UT (hour) Vertical Position Error 37 m Sharp falling edge at 9 PM ; Max. error occurs when the max. gradient occurs, as expected.

  11. VPE for All-in-view + N-1 + N-2(WOOS-GARF; 74.5 km, VAL = 43.35 m) , VAL = 43.35 m , VAL = 43.35 m No. of Occurrence VPE (m) Vertical Position Error UT (hour) 91 m One subset geometry that we can’t get rid of with VAL = 43. 35 m

  12. VPE for All-in-view + N-1 + N-2(WOOS-GARF; 74.5 km, VAL = 10 m) , VAL = 10 m , VAL = 10 m VPE (m) No. of Occurrence UT (hour) Vertical Position Error 62 m The worst-case VPE screened by VAL = 10 m is smaller than the one screened by VAL = 43.35 m, as expected.

  13. ERLA-GALB (23.5 km) 425 360 Ionosphere Front 345 300 240 150 USER 300 LGF Smaller maximum ionosphere gradient, Smaller separation

  14. VPE for All-in-view(ERLA-GALB; 23.5 km) VPE (m) No. of Occurrence UT (hour) Vertical Position Error 9 m

  15. VPE for All-in-view + N-1 + N-2 (ERLA-GALB; 23.5 km, VAL = 43.35 m) , VAL = 43.35 m , VAL = 43.35 m VPE (m) No. of Occurrence UT (hour) Vertical Position Error 40 m Before 9 PM; - Driven by a bad geometry - Big gap to worst-case VPE

  16. VPE for All-in-view + N-1 + N-2(ERLA-GALB; 23.5 km, VAL = 10 m) , VAL = 10 m , VAL = 10 m VPE (m) No. of Occurrence Vertical Position Error UT (hour) 18 m

  17. Summary: Worst-Case VPENov. 20, 2003 UT in OH-MI Worst-Case VPE vs. Separation, Nov. 20, 2003 in OH-MI VAL = 43.35 m LS for VAL = 43.35 m VAL = 10 m LS for VAL = 10m Worst-Case VPE LS fit for VAL = 43.35 m VAL = 43.35 m VAL = 10 m LS fit for VAL = 10 m Separation from Reference to User

  18. Validated Iono. Gradients (29Oct. 2003; 21:00 UT in NC) LILL-RALR (45.9 km) USER RALR 256 278 LGF SNFD LILL Ionosphere Front 177 FAYR Data from the North Carolina Cluster of CORS stations on October 29, 2003; 3 Pairs of CORS Stations

  19. Ionosphere Behaviorbetween LILL and RALR (45.9 km) Ionosphere front is moving very fast.

  20. VPE for All-in-view(LILL-RALR; 45.9 km) 241 data 200 bins No. of Occurrence VPE (m) UT (hour) Vertical Position Error 8 m

  21. VPE for All-in-view + N-1 + N-2(LILL-RALR; 45.9 km, VAL = 43.35 m) No. of Occurrence VPE (m) UT (hour) Vertical Position Error 18 m

  22. VPE for All-in-view + N-1 + N-2(LILL-RALR; 45.9 km, VAL = 10 m) No. of Occurrence VPE (m) UT (hour) Vertical Position Error 18 m

  23. Conclusions • Objective of this work • To complement the results of worst-case simulations • To provide an alternative depiction, based on actual data, of the impact of specific validated ionosphere anomalies on LAAS users • Comparison with the result of simulation • Despite very large separations between CORS stations and the lack of a moving user, worst-case VPE and VPE histograms are similar (to first order) to those given by simulation methods • Roughly linear increase of VPE versus separation is as expected • Reduction in worst case VPE when VAL is reduced to 10 meters matches the impact of geometry screening when implemented in simulation • Our Results, while not a one-to-one comparison, support the notion that Cat I iono. analysis is sober and is probably conservative

  24. Backups

  25. Outline • Introduction • Procedure for Data-Replay Analysis • Data • Results • Conclusion

  26. Iono. Anomaly from JPL IGS/CORS Data (20 Nov. 2003; 20:15 – 21:00 UT) Severely anomalous ionosphere behavior poses a threat to LAAS user integrity. 11/20/2003, 20:15:00 UT 11/20/2003, 21:00:00 UT Courtesy of Seebany Datta-Barua

  27. Backgrounds • Local Area Augmentation System (LAAS) • Designed to insure the integrity of broadcast pseudorange corrections by monitoring of measured satellite pseudoranges within the LAAS Ground Facility (LGF). • In order to maximize LAAS availability in the presence of ionosphere anomalies • Ming Luo: Wedge Sweeper Methodology • M. Luo, et al, “LAAS Study of Slow-Moving Ionosphere Anomalies and Their Potential Impacts,” Proceedings of ION GNSS 2005, Long Beach, CA, Sept. 13-16, 2005, pp. 2337-2349. • Jiyun Lee: Pierce Point Plucker Method • Fixed Sigma_vig inflation, Real–Time Sigma_vig inflation • J. Lee, M. Luo, et al, “Position-Domain Geometry Screening to Maximize LAAS Availability in the Presence of Ionosphere Anomalies,” Proceedings of ION GNSS 2006, Fort Worth, TX, Sept. 26-29 , 2006, pp. 393-408 .

  28. Simulation Iono. Slope 425 375 15 68 Elevation Iono. Anomaly Database Ionosphere Anomaly Threat Model • LAAS Mitigations • CCD Monitor • Sigma/P-value inflation • (VPLinf > VAL) LAAS Impact Simulation 5km DH Separation Ionosphere Front Pierce Point Plucker Method (Jiyun Lee, 2006) Worst-Case VPE (MIEV) Wedge Sweeper Method (Ming Luo, 2005)

  29. Data Used in Data-Replay Analysis • Data from the Ohio/Michigan cluster of CORS stations on November 20, 2003 • Data from the North Carolina cluster of CORS stations on October 29, 2003 • Over 10 independent station pairs with separations from 23 to 75 km

  30. LILL-RALR (45.9 km) USER RALR 256 278 LGF SNFD LILL Ionosphere Front 177 FAYR Data from the North Carolina Cluster of CORS stations on October 29, 2003; 3 Pairs of CORS Stations

  31. Summary: Worst-Case VPEOct. 29, 2003 20:00~22:00 UT in NC Worst-Case VPE vs. Separation, Oct. 29, 2003 in NC VAL = 43.35 m LS for VAL = 43.35 m VAL = 10 m LS for VAL = 10m Worst-Case VPE Only three points Separation from Reference to User

  32. Validated Iono. Gradients on SVN 26 (20 Nov. 2003; 20:49 ~ 21:17 UT in OH-MI) 425 360 ZOB1 * 150 200 240 Ionosphere front 100 345 300 70 240 130 225 230 150 250 25 300

  33. SIDN-KNTN (59.1 km) Discovered from work in Early Jan. (Group 1) August (Group 2) November (Group 3) 425 ZOB1 * 150 200 360 240 Ionosphere front USER 100 345 300 70 240 LGF 130 225 230 150 250 25 300

  34. VPE for All-in-view 241 data 200 bins 20 m

  35. VPE for All-in-view + N-1 + N-2 (VAL = 43.35 m) 75 m

  36. VPE for All-in-view + N-1 + N-2 (VAL = 10 m) 47 m

  37. N-2 VPE for GARF and GUST (75Km)Nov. 20, 2003 20:00 – 22:00 Eliminated PRNs

  38. GARF-GUST (75.3 km) Discovered from work in Early Jan. (Group 1) August (Group 2) November (Group 3) LGF USER 360 150 200 240 100 345 300 70 240 130 225 230 150 250 25 300

  39. VPE for All-in-view 241 data 200 bins

  40. VPE for All-in-view + N-1 + N-2 VAL = 43.35 m

  41. WOOS-GARF (74.5 km) Discovered from work in Early Jan. (Group 1) August (Group 2) November (Group 3) USER 360 150 200 240 LGF 100 345 300 70 240 130 225 230 150 250 25 300

  42. VPE for All-in-view 241 data 200 bins

  43. VPE for All-in-view + N-1 + N-2 VAL = 43.35 m

  44. VPE for All-in-view + N-1 + N-2 VAL = 10 m

  45. ZOB1-GARF (51.2 km) Discovered from work in Early Jan. (Group 1) August (Group 2) November (Group 3) USER 425 LGF ZOB1 * 150 200 360 240 100 345 300 70 240 130 225 230 150 250 25 300

  46. VPE for All-in-view 239 data 200 bins

  47. VPE for All-in-view + N-1 + N-2 VAL = 43.35 m

  48. VPE for All-in-view + N-1 + N-2 VAL = 10 m

  49. FREO-LSBN (73.6 km) Discovered from work in Early Jan. (Group 1) August (Group 2) November (Group 3) 425 ZOB1 * 150 200 360 240 USER 100 345 300 70 240 LGF 130 225 230 150 250 25 300

  50. VPE for All-in-view 241 data 200 bins

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