© david last, university of wales, bangor 31st annual convention & technical symposium...

© 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

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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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400

600

800

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Height (m)

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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