Manish Lad Frank van Graas, Ph.D. David Diggle, Ph.D. Curtis Cutright

Avionics Engineering CenterAvionics 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


Outline

• Data Processing Overview

• Flight Test Results “Quiet (normal conditions)” data

collected in Ohio“Thunderstorm” data collected in Florida

• Conclusions


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 PCKing Air C-90B


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.


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


Loran-C Data Processing Overview

Noise distribution

Collected data Find 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


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

2ix

2ix

1-500 Hz

501-1000 Hz

2ix

2ix

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


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)


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


Flight Test Results

Normal conditions

Athens, Ohio

Collected on August 13, 2003


Ground Path (Athens, Ohio)

Flight test trajectory near Athens, Ohio


E–field Data Example: Time Domain

Note: Signal Amplitude is in A/D levels


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


E-field Noise Statistics (Athens, Ohio)

Noise Distribution

Number of samples

1010 to


E-field Noise Statistics (Cont’d)

Calculated and Gaussian cdf

cdf

Cumulative probability

(1-cdf)

100 to010 to


H–field Data Example (Athens, Ohio)


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


H-field Noise Statistics (Athens, Ohio)

Noise Distribution

1010 to

Number of samples


H-field Noise Statistics (Cont’d)


100 to010 to

(1-cdf)cdf



Results (Athens, Ohio)

AntennaSNR M (avg)

Seneca, NY

SNR Z (avg)

Dana , IN

Wire

(E-field)10.5 13.3

Loop

(H-field)12.4 13.2

SNR measurements (average of 326 seconds) at the output of the antenna for NEUS chain


Flight Test Results

Daytona Beach, Florida

Collected in the Vicinity of Thunderstorms on August 14, 2003


Ground Path (Daytona Beach, FL)

Flight test trajectory near Daytona

Beach, FL


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)


E-field Data Example (Cont’d)Before and After Processing the 2-second data chunk


Number of samples (2 seconds of data)

Signal Amplitude

E-field Data Example (Cont’d)


Before and After Processing the 2-second data chunk





E–field Noise Statistics (Daytona Beach, FL)

Noise Distribution

1010 to

Number of samples


E–field Noise Statistics (Cont’d)Calculated and Gaussian cdf

100 to010 to

(1-cdf)cdf



H–field Noise Statistics (Daytona Beach, FL)

Noise Distribution

1010 to

Number of samples


H–field Noise Statistics (Cont’d)Calculated and Gaussian cdf

100 to010 to

(1-cdf)cdf



Results (Daytona Beach, FL)

Antenna SNR M (avg)

Malone, FL

SNR Y (avg)

Jupiter, FL

Wire

(E-field) 7.7 8.7

Loop

(H-field) 9.2 12.5

SNR (average of 326 seconds) measurements at the output of the antenna for SEUS chain


Flight Test Results

Palm Coast, Florida

Collected in the Vicinity of Thunderstorms on August 14, 2003


Ground Path (Palm Coast, FL)

Flight test trajectory near Palm coast, FL


E–field Noise Statistics (Palm Coast, FL)

Noise Distribution

1010 to

Number of samples


E–field Noise Statistics (Palm Coast, FL)


100 to010 to

(1-cdf)cdf



H–field Noise Statistics (Palm Coast, FL)

Noise Distribution

1010 to

Number of samples


H–field Noise Statistics (Palm Coast, FL)


100 to010 to

(1-cdf)cdf



Results (Palm Coast, FL)

Antenna SNR M (avg)

Malone, FL

SNR Y (avg)

Jupiter, FL

Wire

(E-field) 12.6 15.2

Loop

(H-field) 13.8 18.4

SNR (average of 326 seconds) measurements at the output of the antenna for SEUS chain


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 distributionCore of distribution looks GaussianTail 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


Acknowledgements

• Federal Aviation Administration (FAA)Mitch Narins (Loran Program Manager)

• Reelektronika B.V.Dr. Durk van Willigen, Wouter Pelgrum

• King Air CrewBryan Branham, Jay Clark


Questions ?

Documents

Manish Lad Frank van Graas, Ph.D. David Diggle, Ph.D. Curtis Cutright