1. © David Last, University of Wales, Bangor 31st Annual Convention & Technical Symposium International Loran Association 27-30 October, 2002 Washington, DC, USA New ways of looking at Loran-C ASFs Professor David Last Dr. Paul Williams University of Wales

2. © David Last, University of Wales, Bangor

4. NELS ASF mapping - principles Calculate ASFs using most sophisticated computer models Measure values precisely at fewest data points Adjust modelled values to fit measured data Model gives detail, measurements remove biases Results validated by measurement programme

5. © David Last, University of Wales, Bangor

6. Photo: Norwegian Tourist Board

7. © David Last, University of Wales, Bangor

11. Sylt ASFs

12. © David Last, University of Wales, Bangor Lessay ASFs

13. © David Last, University of Wales, Bangor

17. Location of October 2001 Sea Trials

18. Green: GPS Black: Loran, with and without modelled ASFs

19. Green: GPS Black: Loran with modelled ASFs

20. Green: GPS. Black: Loran with modelled ASFs. Orange: Loran with measured ASFs.

21. Green: GPS. Black: Loran with modelled ASFs. Orange: Loran with measured ASFs.

22. Non-precision approach to Oslo Gardermoen

23. © David Last, University of Wales, Bangor Variations of Sylt ASF around Oslo Gardermoen airport (Values in μs; 0.1μs=30m pseudorange)

24. © David Last, University of Wales, Bangor 439ns =132m 625ns = 187m ASF changes from airfield values over 10km and 20km

25. © David Last, University of Wales, Bangor ASF changes from airfield values with height

26. © David Last, University of Wales, Bangor ASF seasonal changes Due to ground conductivity changes Greatest over freeze/thaw paths Temperate areas: 40-70m pseudorange (2-sigma) Ignore seasonal variations in temperate areas Northern Scandinavia: +/-100m pseudorange max Publish updated values here in AIRAC cycle

27. From: Tech Center Factsheets, US Federal Aviation Administration

28. Figure: Locus Inc. Landing at Atlantic City. Green: GPS. White: Satmate Loran with airfield ASFs

29. Figure: Locus Inc. Flying in Chesapeake Bay area, using ASFs from Atlantic City, 200km away

30. Figure: Locus Inc.

32. © David Last, University of Wales, Bangor Photo: Norwegian Tourist Board