1 EARLY SKYWAVE EXAMPLES FROM U.S. COAST GUARD PRIMARY CONTROL MONITOR SET DATA KIRK MONTGOMERY, U.S. COAST GUARD NAVIGATION CENTER BOB WENZEL, BOOZ, ALLEN, HAMILTON ILA 32 NOVEMBER 2003

2 Previous Work ….. THE CLEAREST EXAMPLES OF A PROBLEM HAVE COME FROM THE VERY NORTHERN LATITUDES Ad Hoc examinations done by the U.S. Coast Guard, but little documentation in the literature A series of papers done on the early 1990’s regarding Alaska stations, most notably the Port Clarence signal:  ILA 22’s “Port Clarence Skywave Interference Study” by Ben Peterson et al (Oct. 1993)  ILA 23’s Analysis of High Latitude Loran-C Abnormalities in Alaska by David Watkins’ (Nov. 1994)  ILA 23’s Effects of Geomagnetic Activity on Skywave Interference by Al Arsenault (Nov. 1994)

3 Previous Work ….. OF THE RECEIVER PERFORMANCE STANDARDS AT THE TIME OF THESE STUDIES, ONLY ONE INDICATED EARLY SKYWAVE PROBLEMS WERE PARTICULARLY SEVERE SourceModeMin. SW Delay (usec)SW/GW Ratio RTCA/FAAAviation35+ 6 db db db db db RTCM/USCGMaritime db db Transport CanadaMaritime db db The USCG Monitor receiver of the time could meet all the above, though the 32.5 usec/+12 db requirement is very challenging.

4 The path from Port Clarence to Fairbanks is predominantly east-west in central Alaska

5 Previous Work ….. THE “ALASKA PAPERS OF THE 1990’S” SHOWED THE RECEIVERS OF THE TIME HAD PROBLEMS For the Port Clarence signal at Fairbanks, Ben estimated he was seeing skywave delays as short as about 28 usec ** In a particular case featuring a +6 db skywave at a delay of just under 30 usec*** the Austron 5000 ECD had moved about usec from the nominal, a JET receiver was showing a change of about – 3.2 usec Dave Watkins wasn’t equipped to measure the skywave, but he showed Austron 5000 ECD variations in the Tok signal, as monitored at Kodiak, of about 5 usec BY THE END OF THE YEAR 2000, THE COAST GUARD HAD REPLACED THE AUSTRON 5000 RECEIVERS WITH THE LOCUS LRSIIID RECEIVERS WHICH SHOW ABOUT THE SAME – OR SLIGHTLY BETTER PERFORMANCE

6 Recent Observations ….. LET’S FOLCUS ONLY ON JANUARY FIRST, LET’S LOOK AT THE “BLINK RECORD” By themselves, these 6 incidents are significant because they average about 3- hours in duration. 18 hours of blink over a 31-day period yields only a 97.6% availability for this baseline, that month.

7 Pause ….. WENZEL STATEMENT: I STARTED THIS EFFORT UNCONVINCED CROSS-RATE SKYWAVES EFFECTS HAD BEEN ELIMINATED IN PAST STUDIES Dave Watkins, for example, was more interested in correlating abnormalities with solar activity – for control purposes There were some coincidences, but there were nearly as many questions Even Ben’s instrumentation suffered from a few problems that can now be greatly reduced: - Port Clarence was broadcasting with an AN/FPN-42 transmitter which has “a complicated signal” after the peak - “Due to several pulse building evolutions at Port Clarence and other factors, we no longer consider our groundwave template accurate.”

8 Pause ….. BEN RECENTLY RAN LRSIIID RECEIVER SIMULATOR TESTS. THEY SHOWED THE FOLLOWING RESULTS FROM A 0 DB (IN-PHASE) SKYWAVE

9 Recent Observations ….. STICKING WITH JANUARY 2002, HERE ARE THE ECD AND TD PLOTS

10 Recent Observations ….. HERE’S A BLOW-UP OF THE 1 JANUARY INCIDENT

11 Recent Observations ….. HERE’S SOME MORE ALASKA DATA – FROM JANUARY 2002

12 Recent Observations ….. HERE’S A FINAL EXAMPLE OF ALASKA DATA – JANUARY

13 Recent Observations ….. WHAT ABOUT ELSEWHERE? THE MAGNETIC LATITUDE OF THE NORTHEAST IS GREATER THAN THAT OF THE NORTHWEST, U.S. The markers occur during the first 5 “incidents noted in Alaska They show the times when the Port Clarence ECD variations were notable. The Sandy Hook shows no perceptible phase variations. However, there are notable ECD indications, though they don’t perfectly align with the Alaska times.

14 Recent Observations ….. HERE’S A CLOSER LOOK AT THE INCIDENT ON THE EVENING (GMT) OF THE 10 TH

15 Recent Observations ….. A SEARCH OF THE SPACE ENVIRONMENTAL CENTER’S DATA FOR “VERY ENERGETIC” SOLAR EVENTS DIRECTED OUR ATTENTION TO APRIL 2001 The ECD is out of Tolerance for much of the first 2-3rds of the month. The following slides show more detail of this month.

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20 CONCLUSIONS There is strong evidence of extreme early skywave interference along this long path in Alaska These events are initiated by high energy solar activity. Unlike “classical” skywave, the effects are visible during the day, and disappear at night. High performance receivers like the Austron 5000 and the Locus LRSIIID easily meet RTCA and RTCM Mops However, under these Alaska anomalies which feature delays 10 usec or more less than previously spec’d, even these “monitor grade” receivers show effects that must be called “unusable” We’d need special monitor equipment to nail down the exact delay/amplitude of the skywaves Similar ECD effects, somewhat attenuated, can be seen in very long baselines in the NEUS chain. Phase changes were not discernible in the small number of NEUS records examined.