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Loran Integrity Performance Panel Analysis of ASF for RNP 0.3 Sherman Lo, Stanford University International Loran Association Boulder, CO, Nov 3-7, 2003.

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Presentation on theme: "Loran Integrity Performance Panel Analysis of ASF for RNP 0.3 Sherman Lo, Stanford University International Loran Association Boulder, CO, Nov 3-7, 2003."— Presentation transcript:

1 Loran Integrity Performance Panel Analysis of ASF for RNP 0.3 Sherman Lo, Stanford University International Loran Association Boulder, CO, Nov 3-7, 2003

2 Loran Integrity Performance Panel 2 Additional Secondary Factors Additional Secondary Factor (ASF) QDelay in propagation time due to traversing heterogeneous earth relative to sea water path QMajor source of error for Loran navigation Why are we studying this? QNeed to understand effects of ASF to meet aviation requirements QIntegrity: Bound the worst case Haven’t we been here before? Hasn’t this been studied before?

3 Loran Integrity Performance Panel 3 Aviation Requirements HAL Integrity: Does our protection level bound position error Requirement: % ( ) Availability: How often is the solution valid for RNP 0.3 Requirement: > 99.9% (HAL = 556 m) Continuity: Is solution available for entire approach if initially available Requirement: > 99.9% (150 sec) HPL

4 Loran Integrity Performance Panel 4 Calculating HPL  i is the standard deviation of a normal distribution that overbounds the randomly distributed errors QSNR, transmitter jitter  i an overbound for the correlated bias terms Q Correlated temporal ASF  i an overbound for the uncorrelated bias terms QUncorrelated ASF temporal errors, ASF spatial error PB is a position domain overbound QASF spatial error

5 Loran Integrity Performance Panel 5 Temporal & Spatial Effects ASF is modeled in two components: temporal & spatial. ECD is can be modeled similarly though with other components (transmitter effects, etc.)   1 ECD 1  2 ECD 2  3 ECD 3  4 ECD 4  5 ECD 5  6 ECD 6  7 ECD 7  8 ECD 8  N ECD N Varies temporallyVaries spatially

6 Loran Integrity Performance Panel 6 Average ASF Value At Calibration Point x o Provided At Aircraft Location User ASF will differ from provided ASF Variation of ASF User has an average ASF ASF look up table is to be provided to user (at each calibration pt) ASF used by receiver (rx ASF) Difference from rx ASF from using a different location Difference from rx ASF from seasonal changes

7 Loran Integrity Performance Panel 7 One Important Concept … Assumption: Time of Transmission (TOT) QEliminate effect of SAM QOtherwise SAM induced changes need to be accounted for when using TOA TOT control eliminates a potential source of error QWhile the SAM may reduce the actual error, since we do not know its effects, we have to assume it does not TOT aids in reducing bound on ASF Results in better availability, continuity

8 Loran Integrity Performance Panel 8 Data Collection TOA and TOT monitors; FAATC/JJMA/USCGA flight tests USCG data from transmitters, SAM (TINO, etc.) TOT Master TOT Monitor TOA Monitor Spatial ASF

9 Loran Integrity Performance Panel 9 Temporal ASF

10 Loran Integrity Performance Panel 10 Historical ASF Variation (Temporal)

11 Loran Integrity Performance Panel 11 Temporal ASF Model ASF N,mean = mean ASF used by the receiver  TOA N (t) is the TOA relative to the nominal for the Nth signal (transmitter) at time t d N,land are the relative amplitudes for the time varying components depending on distance (initially assumed known)  TOA(t) are the common time varying components that have different amplitudes for different signals (propagation) c(t) are the common time varying components that have the same amplitudes for different signals (mainly clock error)  N (t) are what remains after taking out the correlated part of the TOAs (residual error)

12 Loran Integrity Performance Panel 12 Monitor Data Raw Data “Decimated” Data

13 Loran Integrity Performance Panel 13 Modeling at Sandy Hook (Not Using Caribou)  TOA(t) c(t)  Car (t)  max

14 Loran Integrity Performance Panel 14 Modeling at Sandy Hook (Not Using Nantucket)  TOA(t) c(t)  Nan (t)  max

15 Loran Integrity Performance Panel 15 Temporal ASF at Other Locations MonitorNum Stations  TOA (All Sta) Residual Error (All Sta) Cape Elizabeth, ME Sandy Hook, NJ Annapolis, MD*

16 Loran Integrity Performance Panel 16 Conclusions on Temporal ASF Bound on Temporal ASF Variations is a significant factor in the HPL QShould be worst in NEUS Important to divide temporal ASF into correlated and uncorrelated contributions QCorrelated error does not need to be treated in the worst possible manner Current values used (NEUS) Q1000 ns/Mm (correlated) Q300 ns (uncorrelated) QAre these values adequate for integrity? QCan we do better with another model?

17 Loran Integrity Performance Panel 17 Spatial ASF

18 Loran Integrity Performance Panel 18 Spatial ASF – Cape Elizabeth from Nantucket (D. Last, P. Williams)

19 Loran Integrity Performance Panel 19 Comparison of Spatial ASF Data vs. Model (G. Johnson) Greg Johnson will present more about this next!

20 Loran Integrity Performance Panel 20 HPL Contribution from Position Domain

21 Loran Integrity Performance Panel 21 Cape Elizabeth Spatial ASF Bounds SituationRadius (nm)Bound PD (m) Cape Elizabeth nominal Cape Elizabeth: 1 loss Cape Elizabeth: 1 loss include Nantucket Cape Elizabeth: 2 loss Cape Elizabeth: 2 loss include Nantucket

22 Loran Integrity Performance Panel 22 Bounds for Spatial ASF LocationTerrain TypeNumber Sta Nom PD (m)1 Loss PD (m) 10 nm20 nm10 nm20 nm Cape Elizabeth, MECoast Destin, FLCoast Grand Junction, COMountain Point Pinos, CACoast, Mountain Spokane, WAMountain Plumbrook, OHInterior Bismarck, NDInterior Little Rock, ARInterior

23 Loran Integrity Performance Panel 23 Conclusions on Spatial ASF Bound on Spatial ASF Variations is a significant factor in the HPL QShould be worst in mountainous and coastal regions Position Domain Bound used QAllows the incorporation of correlation QLimits allowable station sets Current values used Q120 m (PD) for interior QGood for up to 20 km with 1-2 station(s) missing QHow much an inflation factor is necessary?

24 Loran Integrity Performance Panel 24 Availability & Continuity Bound on ASF variations allows calculation of HPL Q Need bound for noise, transmitter error Availability occurs when: Q Pass Cycle Resolution Test Q HPL < HAL (556 meter) Continuity occurs when: Q Initially Available Q Available over next 150 seconds

25 Loran Integrity Performance Panel 25 Caveats Models dependent on many assumed values QErrors (ASF, tx, noise) QNoise QAlgorithm (Cycle, etc.) QStation availability Need to aggregate for all scenarios Q interference, early skywave, different noise levels QOnly one case shown: 99% noise level, etc. Weighted by assumed regional ASF variations, etc. RESULTS SHOWN ARE NOT FINAL NOR NECESSARILY REPRESENTATIVE

26 Loran Integrity Performance Panel 26 Test Case: Availability

27 Loran Integrity Performance Panel 27 Test Case: Continuity

28 Loran Integrity Performance Panel 28 Conclusions … Need to bound ASF – largest error source QTOT reduces error to be bounded QSeparate ASF into temporal & spatial Temporal ASF QSeparate into correlated & uncorrelated terms Spatial ASF QUse position bound QBounds can be very high on coast, mountain Have tools in place so that once we have results for all hazards, the continuity and availability can be quickly determined Story is not complete – more to come

29 Loran Integrity Performance Panel 29 Acknowledgements Federal Aviation Administration QMitch Narins – Program Manager Contributors QBob Wenzel, Ben Peterson QProf. David Last, Paul Williams QGreg Johnson, CAPT Richard Hartnett, FAATC QLT Dave Fowler, LT Kirk Montgomery The views expressed herein are those of the presenter and are not to be construed as official or reflecting the views of the U.S. Coast Guard, Federal Aviation Administration, or Department of Transportation.


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