A Preliminary Study of Loran-C Additional Secondary Factor (ASF) Variations International Loran Association 31st Annual Convention And Technical Symposium October 27-30, 2002

10/30/02USCGA-JJMA Presentation for ILA-312 Authors  CAPT Richard Hartnett  US Coast Guard Academy  Gregory Johnson  John J. McMullen Assoc. Inc.  Peter Swaszek  University of Rhode Island  Mitchell J. Narins  US Federal Aviation Administration

10/30/02USCGA-JJMA Presentation for ILA-313 Outline  Introduction  Methodology of Data Collection  Error Sources and Bounds  August Flight Tests  Highlights of ASF Corrected Loran data  Conclusions  Future work

10/30/02USCGA-JJMA Presentation for ILA-314 Introduction  Concept:  LORAN-C as “the” backup for GPS  NPA – RNP 0.3  Obvious issues: accuracy, availability, integrity, and continuity  USCGA Goal: Improve our understanding of those variations in TOA that could be mitigated (ASFs)

10/30/02USCGA-JJMA Presentation for ILA-315  This report:  Report on flight tests (August 2002) to collect concurrent LORAN and WAAS GPS position data (equipment, methodology, variation characteristics)  From ground data estimate TOA ASF in the vicinity of an intended approach  (post-)Process some approach flight data to determine feasibility of 1/6 NM accuracy using local correction

10/30/02USCGA-JJMA Presentation for ILA-316 Data Collection Methodology  Use USCGA PC-104 TOA ASF Measurement System  Run receiver in reference mode at a known location (surveyed or DGPS/WAAS position)  Save TIC and RAW TOA, SNR, ECD measurements for each station at 2 sec. intervals  Collect data over 1-2 hr period  Post-process to calculate ASF’s at 2 sec. intervals  ASF, SNR, and ECD are used to determine if ASF is valid  Average ASF’s over the 2 hr period

10/30/02USCGA-JJMA Presentation for ILA-317 TOA ASF Measurement System H-field antenna Novatel OEM-4 WAAS GPS PC-104 Rcvr 1 PPS DS-345 Signal Generator 10 MHz 12.8 MHz2 Channels RF Save to disk: TIC, RAW TOA, ECD, SNR, etc.

10/30/02USCGA-JJMA Presentation for ILA-318 PC-104 Based TOA ASF Measurement System  CPU board, Gatefield DSP board, oscillator board (opt), Power and I/O boards  Provide stabilized clock frequency  12.8 MHz from Cesium clock stabilized signal source  GPS 1PPS signal  H-field antenna  Two crossed loops

10/30/02USCGA-JJMA Presentation for ILA-319 ASF Calculation (TIC + Raw TOA - Rcvr Delay - Emission Delay - Predicted TOA ) mod 200 μsec = EDC + ASF

10/30/02USCGA-JJMA Presentation for ILA-3110 ASF Definition  Define TOA ASF as the additional propagation delay due to a non-seawater path  Need to separate out system timing errors from ASF value  Need to know exactly when stations transmit, relative to UTC (use GPS 1 PPS as time reference).  Master: existing TTM equipment  Secondary: LSU/PIG installed TOTM equipment  Difference between measured and calculated TOA is ASF + time offsets

10/30/02USCGA-JJMA Presentation for ILA-3111 Nantucket TOTM  Secondary TOTM data for time period of flight tests (Julian days , 2002)  X-axis = hours starting from midnight of first day  Y-axis = offset from UTC in ns

10/30/02USCGA-JJMA Presentation for ILA-3112 Carolina Beach TOTM

10/30/02USCGA-JJMA Presentation for ILA-3113 ASF Measurement Error Sources  Timing Errors  Master and Secondary  Receiver Errors  1 PPS stability  Sampling resolution  Receiver tracking accuracy  Receiver calibration  Cross-coupling in H-field antenna

10/30/02USCGA-JJMA Presentation for ILA-3114 Error Bounds Error Source Notes Error bounds Master timingTOTM equip.Unknown, 23 hr avg. only Secondary timingPIG/LSU TOT monitors2/4 minute samples, vary +/- 50 ns 1 PPS stabilityUniversal Counter referenced to Cesium +/- 1 ns for Novatel OEM-4 PowerPak Sampling resolution12.8 MHz+/- 39.1ns resolution Tracking accuracySNR dependent~20 ns for strong signal Receiver calibrationFixed offsetApprox. 100 ns Loop cross-couplingFixed offset for given heading +/- 145 ns

10/30/02USCGA-JJMA Presentation for ILA-3115 Loop cross-coupling Nantucket Carolina Beach Seneca Caribou Dana Variation in TOAs as aircraft antenna is rotated 720 degrees.

10/30/02USCGA-JJMA Presentation for ILA-3116 Loop cross-coupling Close-up of Nantucket data from previous slide

10/30/02USCGA-JJMA Presentation for ILA-3117 Ohio University King Air

10/30/02USCGA-JJMA Presentation for ILA-3118 CG Equipment on King Air

10/30/02USCGA-JJMA Presentation for ILA-3119 August 2002 Flight Test Date Location and Airport Designator 21 Aug Hyannis, MA (HYA) 22 Aug Sandy Hook, NJ (BLM) 26 Aug Cape Elizabeth, ME (PWM) 27 Aug Bay Bridge area (W29) Mayport, FL (CRG) 28 Aug Plumbrook, OH (5A1) Westerly, RI (WST) 29 Aug FAA Tech Ctr (ACY)

10/30/02USCGA-JJMA Presentation for ILA-3120 Flight routes Dana Malone Carolina Beach Seneca

10/30/02USCGA-JJMA Presentation for ILA August, 9960 Data

10/30/02USCGA-JJMA Presentation for ILA August, 8970 Data

10/30/02USCGA-JJMA Presentation for ILA August, 5930 Data

10/30/02USCGA-JJMA Presentation for ILA /22 BLM TOA Distributions

10/30/02USCGA-JJMA Presentation for ILA /27 W29 TOA Distributions

10/30/02USCGA-JJMA Presentation for ILA-3126 Portland ME, 26 Aug 02 Loran (red), Corrected Loran (green) and DGPS (blue) positions during approach to Portland, PWM. Corrected Loran is the raw TOA’s corrected with measured ASF values, ED offsets, and Master TOT offsets.

10/30/02USCGA-JJMA Presentation for ILA-3127 Portland ME, 26 Aug 02 Radial error measured from WAAS GPS position

10/30/02USCGA-JJMA Presentation for ILA-3128 Conclusions  ASF collection procedure:  Methodology works  Further resolution of error sources  Sample flight tests:  TOA All-In-View receiver (with timing corrected and static, local ASF correction) provided <1/6 NM accuracy on approaches (to 20 miles out)  Potential for LORAN to achieve RNP 0.3

10/30/02USCGA-JJMA Presentation for ILA-3129 Future Work  Examine spatial and temporal ASF variations  Daily data collection at USCGA (multi-week)  Collect additional spatial data in December and January  Receiver improvements  Increase sampling rate to 25.6 MHz to increase resolution  Resolve receiver calibration  Apply ASF corrections to Locus receiver TOAs

10/30/02USCGA-JJMA Presentation for ILA-3130 Acknowledgments  Christian Oates, George Sanders, Ken Dykstra  JJMA, Inc.  Dave Diggle, Brian Branham, Jamie Edwards  Ohio University  Ben Peterson  P.I.G.  USCG Loran Support Unit  USCG NAVCEN