1. Avionics Engineering Center Characterization of Atmospheric Noise in the Loran-C Band Presented to the International Loran Association (ILA-32) November 6, 2003 Boulder, CO Manish Lad Frank van Graas, Ph.D. David Diggle, Ph.D. Curtis Cutright

2. Avionics Engineering Center Outline Data Processing Overview Flight Test Results  “Quiet (normal conditions)” data collected in Ohio  “Thunderstorm” data collected in Florida Conclusions

3. Avionics Engineering Center Flight Data Collection Equipment King Air C-90 B Aircraft LORADD-DS DataGrabber Novatel OEM4 GPS receiver WX-500 StormScope Apollo 618 (Loran receiver) Data collection PC King Air C-90B

4. Avionics Engineering Center Wire vs. Loop Antenna Gain Theoretically, the dual-loop antenna has a 3-dB gain advantage over the wire antenna Exact gain difference depends on the antenna installation Gain = 0 dB Gain = 3 dB Note: SNR results are determined at the output of the antenna.

5. Avionics Engineering Center Processing Collected Data Read Loran-C data Identify and remove CW interference Remove Thunderstorm bursts Read GPS data Identify and remove Loran-C chains Calculate signal-to-noise ratio Characterize atmospheric noise

6. Avionics Engineering Center Loran-C Data Processing Overview Noise distribution Collected dataFind filter coefficients Bandstop filters GPS Time, Position Noise Sequence Track transmitters Signal power Remove pulses that are above noise floor Noise power Calculate SNR Loran Processor Noise Characterization

7. Avionics Engineering Center Removal of CW and Thunderstorm Bursts Detect CW 2-sec data block Filter the CW from 2 second data block Bank of band-pass filters 1-500 Hz 501-1000 Hz 1001-1500 Hz 199.5-200KHz Calculate bandstop filter coefficients Sampled data at 400 kSamples/sec Calculate Energy in bins Remove bins with Energy above a set threshold Integrate PCI’s for identifying different chains

8. Avionics Engineering Center Loran processor Compute average noise power obtained after removal of pulses Integrate signal as per PCI of chain Identify Master and secondaries Remove Loran-C pulses that are above noise floor Compute signal power for each station Calculate SNR for master and secondaries Chain information Antenna position Calculate the noise distribution Signal after removal of CWs and Thunderstorm Bursts (if present)

9. Avionics Engineering Center Flight Test Data Results obtained for different data sets under diverse atmospheric conditions (clear and Thunderstorm) Data collected in Ohio: NEUS chain Data collected in Florida: SEUS chain

10. Avionics Engineering Center Flight Test Results Normal conditions Athens, Ohio Collected on August 13, 2003

11. Avionics Engineering Center Ground Path (Athens, Ohio) Flight test trajectory near Athens, Ohio

12. Avionics Engineering Center E–field Data Example: Time Domain Note: Signal Amplitude is in A/D levels

13. Avionics Engineering Center E–field Data Example (Cont’d) Before and after processing the 2-second data chunk

14. Avionics Engineering Center E-field Noise Statistics (Athens, Ohio) Noise Distribution Number of samples

15. Avionics Engineering Center E-field Noise Statistics (Cont’d) Calculated and Gaussian cdf cdf Cumulative probability (1-cdf)

16. Avionics Engineering Center H–field Data Example (Athens, Ohio)

17. Avionics Engineering Center H–field Data Example (Cont’d) Before and After Processing the 2-second data chunk

18. Avionics Engineering Center H-field Noise Statistics (Athens, Ohio) Noise Distribution Number of samples

19. Avionics Engineering Center H-field Noise Statistics (Cont’d) Calculated and Gaussian cdf (1-cdf)cdf Cumulative probability

20. Avionics Engineering Center Results (Athens, Ohio) Antenna SNR M (avg) Seneca, NY SNR Z (avg) Dana, IN Wire (E-field) 10.513.3 Loop (H-field) 12.413.2 SNR measurements (average of 326 seconds) at the output of the antenna for NEUS chain

21. Avionics Engineering Center Flight Test Results Daytona Beach, Florida Collected in the Vicinity of Thunderstorms on August 14, 2003

22. Avionics Engineering Center Ground Path (Daytona Beach, FL) Flight test trajectory near Daytona Beach, FL

23. Avionics Engineering Center E-field Data Example (Daytona Beach, FL) Note: Dynamic range of data collection equipment is 96 dB (16 bits) Signal Amplitude Number of samples (2 seconds of data)

24. Avionics Engineering Center E-field Data Example (Cont’d) Before and After Processing the 2-second data chunk

25. Avionics Engineering Center Number of samples (2 seconds of data) Signal Amplitude E-field Data Example (Cont’d)

26. Avionics Engineering Center Before and After Processing the 2-second data chunk E-field Data Example (Cont’d)

27. Avionics Engineering Center E-field Data Example (Cont’d)

28. Avionics Engineering Center E–field Noise Statistics (Daytona Beach, FL) Noise Distribution Number of samples

29. Avionics Engineering Center E–field Noise Statistics (Cont’d) Calculated and Gaussian cdf (1-cdf)cdf Cumulative probability

30. Avionics Engineering Center H–field Noise Statistics (Daytona Beach, FL) Noise Distribution Number of samples

31. Avionics Engineering Center H–field Noise Statistics (Cont’d) Calculated and Gaussian cdf (1-cdf)cdf Cumulative probability

32. Avionics Engineering Center Results (Daytona Beach, FL) AntennaSNR M (avg) Malone, FL SNR Y (avg) Jupiter, FL Wire (E-field) 7.78.7 Loop (H-field) 9.212.5 SNR (average of 326 seconds) measurements at the output of the antenna for SEUS chain

33. Avionics Engineering Center Flight Test Results Palm Coast, Florida Collected in the Vicinity of Thunderstorms on August 14, 2003

34. Avionics Engineering Center Ground Path (Palm Coast, FL) Flight test trajectory near Palm coast, FL

35. Avionics Engineering Center E–field Noise Statistics (Palm Coast, FL) Noise Distribution Number of samples

36. Avionics Engineering Center E–field Noise Statistics (Palm Coast, FL) Calculated and Gaussian cdf (1-cdf)cdf Cumulative probability

37. Avionics Engineering Center H–field Noise Statistics (Palm Coast, FL) Noise Distribution Number of samples

38. Avionics Engineering Center H–field Noise Statistics (Palm Coast, FL) Calculated and Gaussian cdf (1-cdf)cdf Cumulative probability

39. Avionics Engineering Center Results (Palm Coast, FL) AntennaSNR M (avg) Malone, FL SNR Y (avg) Jupiter, FL Wire (E-field) 12.615.2 Loop (H-field) 13.818.4 SNR (average of 326 seconds) measurements at the output of the antenna for SEUS chain

40. Avionics Engineering Center Conclusions SNR at the output of Loop (H-field) antenna is generally greater than the SNR at the output of Wire (E-field) antenna by 2-3 dB Noise distribution  Core of distribution looks Gaussian  Tail probabilities are much larger than Gaussian with an equivalent rms value (looks like 3- sigma) Data collected from both the antennas closely match in the calculated cdf of the noise

41. Avionics Engineering Center Acknowledgements Federal Aviation Administration (FAA)  Mitch Narins (Loran Program Manager) Reelektronika B.V.  Dr. Durk van Willigen, Wouter Pelgrum King Air Crew  Bryan Branham, Jay Clark

42. Avionics Engineering Center Questions ?