© david last, university of wales, bangor 31st annual convention & technical symposium...
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© David Last, University of Wales, Bangor
31st Annual Convention & Technical SymposiumInternational Loran Association
27-30 October, 2002Washington, DC, USA
New ways of looking at Loran-C ASFs
Professor David LastDr. Paul WilliamsUniversity of Wales
© David Last, University of Wales, Bangor
© David Last, University of Wales, Bangor
© David Last, University of Wales, Bangor
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
© David Last, University of Wales, Bangor
© David Last, University of Wales, Bangor
Photo: Norwegian Tourist Board
© David Last, University of Wales, Bangor
© David Last, University of Wales, Bangor
.'
AB
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© David Last, University of Wales, Bangor
© David Last, University of Wales, Bangor
© David Last, University of Wales, Bangor
Sylt ASFs
© David Last, University of Wales, Bangor
Lessay ASFs
© David Last, University of Wales, Bangor
Mode of operation ASF needed?
Repeatable No
Single-chain, hyperbolic Yes. “TD ASFs” OK
Cross-chain YesStand-alone Loran receiver
Master-independent Yes
Land mobile tracking Yes. At base station OK.
Positions integratedYes. GNSS ASFs OK for
short distances.Integrated Loran-GNSS
receiverPseudo-ranges integrated Yes
Aircraft landing or ship entering harbour Yes. Single ASF value OK.
© David Last, University of Wales, Bangor
Mode of operation ASF needed?
Repeatable No
Single-chain, hyperbolic Yes. “TD ASFs” OK
Cross-chain YesStand-alone Loran receiver
Master-independent Yes
Land mobile tracking Yes. At base station OK.
Positions integratedYes. GNSS ASFs OK for
short distances.Integrated Loran-GNSS
receiverPseudo-ranges integrated Yes
Aircraft landing or ship entering harbour Yes. Single ASF value OK.
© David Last, University of Wales, Bangor
Mode of operation ASF needed?
Repeatable No
Single-chain, hyperbolic Yes. “TD ASFs” OK
Cross-chain YesStand-alone Loran receiver
Master-independent Yes
Land mobile tracking Yes. At base station OK.
Positions integratedYes. GNSS ASFs OK for
short distances.Integrated Loran-GNSS
receiverPseudo-ranges integrated Yes
Aircraft landing or ship entering harbour Yes. Single ASF value OK.
© David Last, University of Wales, Bangor
Mode of operation ASF needed?
Repeatable No
Single-chain, hyperbolic Yes. “TD ASFs” OK
Cross-chain YesStand-alone Loran receiver
Master-independent Yes
Land mobile tracking Yes. At base station OK.
Positions integratedYes. GNSS ASFs OK for
short distances.Integrated Loran-GNSS
receiverPseudo-ranges integrated Yes
Aircraft landing or ship entering harbour Yes. Single ASF value OK.
© David Last, University of Wales, Bangor
Location of October 2001 Sea Trials
Green: GPS Black: Loran, with and without modelled ASFs
Green: GPS Black: Loran with modelled ASFs
Green: GPS. Black: Loran with modelled ASFs.Orange: Loran with measured ASFs.
Green: GPS. Black: Loran with modelled ASFs.Orange: Loran with measured ASFs.
Non-precision approachto Oslo Gardermoen
© David Last, University of Wales, Bangor
Variations of Sylt ASF around Oslo Gardermoen airport(Values in μs; 0.1μs=30m pseudorange)
© David Last, University of Wales, Bangor
439ns =132m 625ns = 187m
ASF change (ns) – 10km from airfield
ASF change (ns) – 20 km from airfield
Station Airfield ASF (μs)
N S E W N S E W Sylt 2.474 126 16 266 -439 201 -37 625 -425 Vaerlandet 4.216 107 -179 72 -133 -281 -383 188 -599 Bø 5.798 -56 96 -6 140 -327 152 250 -455
ASF changes from airfield values over 10km and 20km
© David Last, University of Wales, Bangor
Gardermoen ASF variations with height
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0200
400
600
800
1000
Height (m)
AS
F (
us
)Bo Sylt Vaerlandet
ASF changes from airfield values with height
© 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
From: Tech Center Factsheets, US Federal Aviation Administration
Figure: Locus Inc.
Landing at Atlantic City. Green: GPS. White: Satmate Loran with airfield ASFs
Figure: Locus Inc.
Flying in Chesapeake Bay area, usingASFs from Atlantic City, 200km away
Figure: Locus Inc.
Figure: Locus Inc.
© David Last, University of Wales, Bangor
Photo: Norwegian Tourist Board
Photo: Norwegian Tourist Board