# Presentation: 365845

## Effective HF Communications: Synergy of Good Engineering Practice, Optimum System Resources, and Timely Space Weather Information with an Emphasis on Polar ProblemsJohn M. Goodman and John W, BallardRadio Propagation Services Inc.

- 3rd Meeting of the Cross Polar Trans-East Air Traffic Management Provider’s Working Group
- April 26, 2007

## RPSI Background & Technology

- RPSI was formed in 1998 by John Ballard and John Goodman to focus on radio communication performance assessment and forecasting, with an emphasis on HF communications and broadcasting systems.
- Using Dynacast® technology, patented by Ballard and Goodman, RPSI has embarked on an aggressive campaign to provide greatly improved communication predictions through incorporation of real-time information to update climatological models such as VOACAP.
- Dynacast technology is comprised of a suite of prediction methods or tools that have the following common features:
- a suitable ionospheric median model
- an update source or sources
- a set of proprietary algorithms for modification of the median model based upon the update sources
- a application program that provides a tailored output for the customer

## Who are our customers?

- GLOBALink/HF frequency management services for ARINC, Inc.
- HF Frequency management  for Gannet Communications (i.e., Radio Iceland)
- Antenna design and frequency management support for a land-mobile HF messaging service (company proprietary)
- HF Frequency management support for maritime-mobile services (company proprietary)
- Antenna analysis and propagation analysis for Antarctica (NSF and USN-SPAWAR)
- Significant military users of HF

## Why is RPSI making this Presentation?

- There is a potential for tremendous vulnerability of HF communications for aircraft flights over the pole. But it need not be so. We can help!
- RPSI has a  technical approach that has the best chance of accurately forecasting HF propagation conditions for polar flights under benign and disturbed conditions
- We think that the airlines can use our Dynacast® forecasting service as a way to circumvent or mitigate against poor communications in the high latitude environment.
- We have also examined some of the infrastructure and spectrum issues and would like to outline our conclusions

## Who are we ?

- Principals within RPSI are scientists, engineers, and aviators.
- HF communication is our specialty
- We are experts in ionospheric propagation, and the impact of disturbances on system performance
- We specialize in ionospheric nowcasting, forcasting and prediction
- We are regular contributors at scientific meetings and colloquia
- We have close ties with TCI/BR Communications, an HF engineering firm of some repute. [TCI is now a wholly-owned subsidiary of Dielectric Inc.]

## Our Relationship with NOAA/SEC

- RPSI is a vendor of HF Communications services and products, with specialities in the following activities:
- Real-time frequency management
- Performance forecasting and prediction
- Optimization of HF networks and spectrum
- HF antenna specification
- Ionospheric measurements using sounders
- RPSI is also a customer of Space Weather services, like many of the audience. We have a good relationship with NOAA-SEC, the primary source of such data. We take the very best that NOAA has to offer and build tailored products for our customers.

## NOAA-SEC Policy for Improving Customer Service by Fostering a Vendor Industry: (excerpt from SEC web site)

*“**Excellent customer service provided by industry enhances all space weather services and benefits the customer. SEC would like for vendors to provide tailored customer services, while SEC focuses on improving generic, environmental nowcasting and forecasting services. Vendor-provided tailored services are vital to improving service, as SEC finds less and less time to meet individual user needs.”*
- “*Vendors are expected to create products tailored to specific end users; SEC will not compete with vendors in the area of tailored products.”*

## R&D Highlights

- Patented processes for near-real time insertion of space weather (and ionospheric) data to improve HF communication system performance: 2 patents and a 3rd pending
- Orchestrated unique chirpsounder study for comprehensive synoptic view of global HF communications (so-called Northern Experiment)
- RPSI (and TCI) studies led to ITU-R Recommendations specifying of RPSI chirpsounder approach as a preferred method for updating adaptive HF communication systems
- Evaluated optimal communication frequencies and radio ground station locations for voice communication services in support of the ARINC/FAA GLOBALink/HF communication system
- Evaluated the optimal communication topology and communication assets required to support LDOC and ATS communications in over-the-pole applications

## R& D Highlights (Cont.)

- Evaluated communication strategies in support of the U.S. Navy/NSF communication requirements in Antarctica. This included antenna and propagation capabilities
- RPSI has evaluated the HF communication segment of a proposed CONUS land-mobile communication system for civilian use.
- Developed a methodology whereby space-weather data could be exploited to evaluate the impact of geomagnetic storms and related phenomena on HF communication performance
- Currently RPSI is the sole provider of Active Frequency Tables to ARINC in support of the GLOBALink/HF operations.
- Currently RPSI is the sole provider of High Frequency transmission frequency predictions for Gannet Communications (e.g., Iceland Radio) in its polar coverage areas
- RPSI also provides near-real time frequency predictions for global maritime mobile applications, taking geomagnetic storm impacts on the ionosphere into account

## Background

- Northern Experiment: 1994-1996
- Over-the-Pole Experiment: 2001
- Numerous studies leading to publications dealing with adaptive HF and dynamic frequency management (1997-2006)
- ITU-R Rec. F.1337, Geneva, 1997
- A number working papers (e.g. RTCA, AEEC, ICAO/WGE, etc.; 1990s-present)

## The Northern Experiment

- Chirpsounder data were obtained continuously at a number of receiving stations, including (but not limited to) the following: Churchill, Reykjavik, St. Johns, Henrico (NC). Each of these stations served as the “clusterhead” of a star network comprised of four diverse paths. Over 28 paths were analyzed from 1994-1996.
- The data we obtained were derived from so-called ionograms, and the output included SNR versus frequency from 3-30 MHz. Sampling rates were typically twice per hour for each designated path, but the cadence was often faster. The spectral resolution was 100 Hz and the amplitude resolution was 1⁄2 dB.
- It was possible to conduct “Thought” experiments with the data. We looked at the sensitivity of SNR (and communication reliability) to the number of available paths and frequencies.

## Slide 12

## General Remarks

- The NE experiment taught us a number of things about the value of diversity. From the data sets we were able to evaluate the improvement in performance as the number of frequencies and stations increased.
- While much of the NE data were not in the polar environment, there were sufficient transauroral and polar data to arrive at some preliminary conclusions concerning the optimal communication architecture (i.e., topology and spectrum)
- While we could not examine the phenomenon of PCA in 1994-1996 (as no PCA occurred in the period), we have notional solutions to this effect.
- To confront ionospheric variability and the limitations it imposes, it is necessary to have as many frequencies and stations as possible, a pretty obvious fact.

## Sample HF Performance Estimates under Specified Conditions

- We can specify the typical reliabilities that can be achieved for specified numbers of independent bands (viz., 1,2,4,8) and independent paths (viz., 1,2,3,4).
- The available bands are specified a priori, and quasi-dynamic frequency selection is employed to derive the “best” band.
- Static frequency selection is employed (i.e., predictions) to derive the “best” frequency

## Sample Reliability Estimates (Continued)

- By data sorting, we can also examine the impact of storms and other phenomena. The list includes:
- Sunspot number
- Season
- Time-of-Day
- Phenomenological conditions
- Magnetic activity
- Sunspot epoch
- PCA, aurora, etc.

## Sample Reliabilities for Mid- Latitude Paths

|  | #Paths | 1 | 2 | 3 | 4 |
| --- | --- | --- | --- | --- | --- |
| #Bands |  |  |  |  |  |
| 8 |  | 90 | 95 | 99 | 100 |
| 4 |  | 85 | 90 | 95 | 99 |
| 2 |  | 70 | 85 | 90 | 95 |
| 1 |  | 50 | 70 | 85 | 90 |

*time-averaged over all conditions*
*isolated “storm” days can have significant lower reliabilities*
*Quasi-dynamic freq. Mgmt.*
*Representative system properties and voice circuits*

## Reliabilities for High Latitude Paths

|  | #Paths | 1 | 2 | 3 | 4 |
| --- | --- | --- | --- | --- | --- |
| #Bands |  |  |  |  |  |
| 8 |  | 85 | 90 | 93 | 95 |
| 4 |  | 75 | 80 | 90 | 93 |
| 2 |  | 55 | 70 | 80 | 90 |
| 1 |  | 35 | 55 | 75 | 85 |

*time-averaged over all conditions*
*isolated “storm” days can have significant lower reliabilities*
*Quasi-dynamic freq. Mgmt. (optimal frequency specification)*
*Representative system properties and voice circuits*

## Slide 18

## Slide 19

## Sensitivity to Disturbances

- There are definite differences between Disturbed and Non-Disturbed conditions.
- The following slide indicates the extent to which the flight path (and the region through which it transits) will control the relative communication efficiency. (No surprises here, but the graph quantifies the effect.)
- The graph represents a situation for which dynamic frequency management is employed and all aeronautical mobile bands are available for selection over 4 paths.

## Availability Difference between Disturbed and Non-disturbed Conditions

## Sensitivity to Path Selection

- It is obvious that if one were to limit the number of available bands for exploitation, one could use path diversity to partially compensate for this limitation. But care is required.
- No amount of path diversity can fully compensate for wide-ranging instances of  non-selective fading (i.e., PCA) unless path alternatives have control points that lie outside the zone of PCA.
- Path diversity means what it says. If the paths do not optimize around a set of spaced (independent) frequencies then the path diversity gain is somewhat muted. (Hence if an A/C is equidistant from each ground station serving it, path diversity gain is reduced.)

## General Comments on Polar Region HF System Topology and Spectrum

- Best strategy is to locate ground stations within 1-hop of the aircraft. (d < ~ 4000km)
- Ground station distribution should subtend a substantial distribution of ranges from 500 km to 3500 km, enabling a defacto range of independent frequencies at the OWFs
- Three-to-five ground stations are optimum, and these stations should be located either within the polar cap or near the poleward edge of the auroral oval. Midlatitude locations and locations within the trough would not be recommended.
- The distributions should be distributed rather uniformally (in azimuth) with respect to the geomagnetic pole

## Issues of Spectrum

- It can be shown that dynamic frequency management is a viable method for achieving the highest possible communication reliabilities.
- Unless an adequate number of diverse frequency bands are available, dynamic frequency management cannot reach its potential.
- The NE data analysis shows that as the number of aeronautical-mobile bands become increasingly populated, the communication reliability increases monotonically. (There is a point where the frequency band diversity gain begins to saturate, and this depends on other factors such as magnetic storminess, region of operation, time of day, etc. )
- The polar region is a special case. It is bounded by a number of circumpolar features that render it unique.

## Spectrum Issues (cont.)

- HF communication within the Polar Cap can be excellent. F-region variability is generally less pronounced.
- Noise levels are reduced within the polar region, suggesting the utility of lower portions of the HF band, everything else being equal. This is because the region is partially protected from terrestrial noise (atmospherics) by the auroral curtain. This is fortunate since the MOFs are generally smaller in the Polar Cap than other regions.
- RPSI has taken measurements over the polar path between Svalbard and Barrow and it shows the existence of some rather striking variabilities in propagating spectrum. This is decidedly different from the rather featureless ionograms that have been observed in the past ... or inferred from ionograms.  Above-the-MUF frequencies are routinely observed in local wintertime. The availability of frequencies in the 22-28 MHz region might be used to mitigate against absorption effects such as PCA.

## Special Circumstances in the Polar region

- While propagation can be excellent at high latitudes, the impact of disturbances can be dramatic whenever they do occur. In fact disturbance effect can be much more severe during period of magnetic activity. (This has been shown in an earlier slide)
- A major determinant of communication impairment is magnetic activity, a phenomenon that accompanies auroral activity.
- Polar Cap absorption is also a serious issue. It has been shown that sporadic E propagation (at the higher bands) could serve to mitigate PCA absorption Thus high band availability should be considered.

## Observations of High-Band and Above-the-MUF Propagation

- Preliminary Evaluation of the Svalbard-to-Barrow Path by RPSI in December 2000
- Other previous studies

## Nature of RPSI Experiment

- The Svalbard-to-Barrow path is ~ 1840 nautical miles or ~ 3400 km. The midpath of the ray trajectory is near the geographic North Pole.
- A Chirpsounder transmitter was deployed to Svalbard (78N, 15E), and a receiver was deployed to Barrow, Alaska (71N, 157W).
- Oblique-incidence ionograms were obtained at Barrow and automatically uploaded to the RPSI Web site via the Internet.

##          Anticipated Ionograms 

- We expected ionograms to look like the following. They exhibit a high-ray/low-ray pattern, typical of 1-hop F2 layer propagation. In addition, see that the so-called MOF (shown by the dotted line in the lower curve), or maximum observable frequency, is around 14.5 MHz. This is within the margin of error of propagation models in use today (i.e., VOACAP and ICEPAC). We observe this pattern is not always observed

## Actual IonogramsAbove-the-MUF Example #1

- For many instances, the ionograms display quite a different pattern, with MOFs much greater than would be predicted by typical models. Below we provide a number of examples.

## Above-the-MUF Example #2

## Above-the-MUF Example #3

## Observed MOF Values aT Barrow:

- The VOACAP MUFs are ~16 MHz; and the ICEPAC MUFs are ~18 MHz irrespective of local time (or Universal Time) We see the observed values are generally higher.

## Other Studies

- Ken Davies [1], in his book, concludes that some of the deleterious effects of PCA can be ameliorated by nature itself. Since PCA generally occurs at solar maximum the OWFs are relatively higher. This would tend to reduce the impact of PCA which is a LOF enhancement effect.
- Herman and Penndorf [2]  suggest that F-region morphology is not correlated with PCA. {This could be exploited, but RTCE would be needed. JMG}
- Bartholomew [3] observed that the propagation bandwidth was twice that which is predicted. He suggests that sporadic E is the cause. He suggests that this facet may be exploited to compensate for PCA.
- TCI/BR (now RPSI) discovered systematic above-the-MUF signals over a path between Churchill and Iqaluit during Northern Experiment [1994-1996].

## Northern Experiment Observations:Iqaluit-Churchill: 4-7-95; Ap=100

## References

- Davies, K., 1990, *Ionospheric Radio*, Peter Perigrinus, London.
- Herman, J.R., and R.B. Penndorf, 1964, “Reception of Midlatitude Transmissions in Northern Canada”, in *Arctic Communications*, edited by Landmark, NATO-AGARD, Pergamon Press
- Bartholomew, R.R., “Some Results of an Oblique-Incidence Pulse Sounding HF (4-64 MHz) Experiment between Andoya, Norway, and College Alaska, in *Oblique Ionospheric Radio Propagation* edited by T.B. Jones, AGARDOgraph 13, Technivision, Slough, UK.
- Goodman, J. and T. Wendel, 1997, “Benefits in the Utilization of Frequencies above 22 MHz for HF Data Link Communication”, AMCP/WG-E Meeting, Colorado Springs, WP#15

## CONSEQUENCE

- Predictions used by frequency planners are typically based upon static models that are poorly defined in the polar regions.
- Our results show a consistent above-the-MUF component of propagation during wintertime. (That is, frequencies higher than predictions).
- These RPSI results correspond to oblique paths that are actually measured, while planning models are based upon archived ionospheric data (from VIS instruments) requiring oblique path predictions to be calculated.
- _Result_: Planners will have a tendency to ignore the potential of higher frequencies (observed by RPSI) that may be suitable to carry traffic.
- _Consequence_: Lower frequencies may propagate but the circuit reliabilities are smaller due to increased signal absorption at lower frequencies, as well as increased noise and interference.
- _Bottom Line_: HF voice and data service for over-the-pole flights may be disadvantaged through lack of access of higher bands or sub-optimal frequency selection.

## Conclusion

- RPSI has instrumented a transpolar path from Svalbard to Barrow Alaska. The system is currently in standby, but could be restarted within several months. This exhibits some fascinating features of the arctic communication path.
- We don’t claim to have the full explanation for all features we have observed, but our observations of above-the-MUF signals are hard to dispute. Our preliminary conclusions are fully consistent with other observations and earlier accounts (i.e., Davies, Penndorf, etc.)
- In practical communication terms, we often find excess bandwidth above the values predicted by standard codes.
- This excess bandwidth can be exploited to achieve considerably higher reliabilities.
- Real-time frequency management through Dynacast®  has the potential to identify the existence of above-the-MUF modes of propagation.

## Dynacast Forecasting for Over-the-pole Routes

## RPSI’s Specialized IDETM Inputs Pertinent to Over-the Pole Problems

- The Problems
- Trough Effects
- Auroral Effects
- Polar Cap Effects
- Frequency Constraints
- Radiation hazards
- The Solutions
- Monitor S-T data sets
- Filter out inconsistencies and produce accurate maps of the ionosphere
- Exploit RPSI’s polar monitoring capabilities (i.e., Chirpsounder assets, as available)

## Dynamic Frequency Management Advantages over Pure Predictions

- Note: Pure predictions do not include forecasting elements such as current geophysical and ionospheric data that can be used to update climatological models
- Update strategies are numerous. RPSI has patented Dynacast®, a method for updating the ionosphere using sounder data. (More on this aspect of our work later.)
- Dynacast compensates for variability as exhibited on the next slide.

## Advantage of RTCE over Predictions

## Improvements in Dynacast® Technology

- RPSI is continually investing in new approaches and algorithms that have the potential for improving service
- We have an IR&D program whereby Northern Experiment data is exploited to test new concepts of assessment and forecasting
- We are involved in discussions with scientists at Government agencies (viz., NOAA) indicating how they can improve their service to the public, so that we, in turn, can improve our service to the airlines.

## Sketch of Forecasting Methodologywith an emphasis on the polar air corridor problem

- In its most advanced system architecture, RPSI monitors its Svalbard-to-Barrow sounder path to ascertain the temporal behavior of radio propagation and to assist in developing trendlines (i.e., forecasts). This path corroborates the existence of Polar Cap Absorption (i.e., high energy protons) and its growth.
- RPSI examines the variation of the ionosphere based upon its Integrated Dynacast® Environment (i.e., IDE). This assists in defining the equatorward boundary of the auroral oval in terms of ionospheric conditions. We compare IDE picture with satellite images. The IDE package includes:
- Evaluation of the impact of geomagnetic storms through exploitation of a storm model driven by magnetic activity indices.
- Monitoring the solar photon (i.e., x-ray and EUV) and corpuscular (i.e., high energy particles and solar wind plasma) flux from national resource satellites and other relevant data from NOAA-SEC. This aids in determination of SID effects and PCA absorption over requisite paths
- Combination of all of this information to arrive at forecasts of communication performance for over-the-pole flights.
- RPSI has developed a client-server scheme whereby radio operators, dispatch, and other users can have convenient access to frequency-station pairs ranked in accordance with reliability of linking, and based upon all available information.

## Applying the RPSI Technology for Polar Routes

- RPSI has developed techniques that can provide airlines with a capability to evaluate communication efficacy in advance of takeoff (viz., forecasts).
- RPSI has developed techniques that could address near real-time frequency management decisions.(i.e., nowcasts and nearcasts).

## The Proposed RPSI Solution

- RPSI uses all available data, including RPSI polar soundings and unique IDE-Dynacast algorithms for HF communication performance assessment to provide the following:
- Assessments of the best propagating bands to be used for specified polar flight paths and plans. (i.e., best frequencies and stations)
- Assessments for an entire flight plan are provided with a cadence of 1 hour along the specified flight trajectories (but subject to customer need)
- RPSI has a near-real time solution based upon an active client-server architecture (i.e., Nowcast). *(We are now testing this with a maritime-mobile customer for non-polar circuits.)*
- For the Forecast mode, the performance assessment data files could optionally be provided in advance of the projected flight by between ~ 1 hour and 24 hours. (i.e., paper or data file).

## We will summarize what needs to be done and why to improve Polar HF Voice

- The Polar Regions are very different and quite difficult. Presenting great uncertainty and variability, but ...
- It is possible to have high availabilities at high latitudes, under the conditions specified (i.e., a full complement of frequencies, sufficient stations, and quasi-dynamic frequency management)
- The TCI/BR* Northern Experiment* showed long-term average availabilities of ~ 0.99 were sometimes possible.
- Including PCA events, the long-term averages for the polar region are of the order of ~ 95%, still a very high figure.

## To succeed we need:

- Adequate ground stations (four or more within 3,000 km of the flight routes)
- Adequate spectrum (at least eight aeronautical bands at each station, and higher frequencies for Polar operation
- A technique to manage the network by measuring propagation and thereby choosing station/frequency pairs that work.

## Problems Facing Polar LDOC Are  RATHER Acute

- Twelve Service Providers—All too distant
- Forty-three frequencies, but no guidance for the Pilot.

## The pilot’s task in making a good LDOC link is unnecessarily difficult

- Twelve Service Providers
- Forty-three frequencies
- Pilot initiated
- He has to choose the best, or very nearly the best station/frequency
- The pilot needs help

## REMEMBER: THERE is substantial unrecognized and useful spectrum

## The help can be based on measurements 

## The RPSI Frequency Management Service

- Start with parameterized Polar Models
- Continually adjust the model with direct ionospheric measurements (as available) and  Space-Wx information
- With the adjusted model, compute reliabilities from all providers at all frequencies to specified “waypoints” along track, taking system characteristics into account
- Tabulate a ranked list of “best” frequency-station pairs at each waypoint
- Provide information to customer

## RPSI Frequency Management Service

- Plan is provided before departure, at departure and before VHF coverage is lost.
- Techniques have been in service for more than six years providing ARINC with an Active Frequency Table for the GLOBALink/HFDL system
- Service is available now

## RESULTS FROM LDOC CONNECTIVITY TESTSUSING RPSI DYNACAST® SPECTRUM MANAGEMENT SOFTWARE

**	**_Purpose_
- Operational evaluation of RPSI Dynacast software to provide pilots with list of LDOC frequency-station pairs ranked by probability of success.
- In Short: Does it Work?

## Method

- Utilized Continental airlines flights from EWR to HNL, to GUM, to HKG, to GUM, to HNL, terminating at IAH.
- All possible frequency-station pairs for ARINC facilities in NYC, SFO, Hawaii, Guam and Bolivia were computed before flight for each expected time of crossing of each 5 degree increment of longitude,
- the ranked list of the best ten choices was presented to the airborne ARINC RO.

## Method (Continued)

- All 10 pairs were tried sequentially at each longitude crossing, in order of ranking,
-  Quality was noted by both the airborne and ground based ROs.
- Ranking algorithm considered all relevant physical, temporal and geomagnetic factors including those related to storm periods.

## Results

- 29 contacts or 63% of tries succeeded on the first attempt, generally in less than a minute.
- 10 contacts, or 21.7% of tries succeeded on the second attempt, generally in under two minutes.
- 5 contacts, or 10.9% of tries succeeded on the third attempt, generally in under three minutes.
- 2 contacts, or 4.4% of tries succeeded on the fourth attempt, generally in under four minutes.

## Results (Continued)

- Dynacast and test protocol showed regions where good communications was not physically possible.
- GUM-HKG-GUM lacked adequate station diversity and spectrum.  Lowest frequencies were above the MUF, and we had only one station, with suspect antennas. Reliabilities were in the 6-20% range.

## Results (continued)

- Thus all attempts to contact in four minutes or less among the population expected to connect reliably (46 tries) were successful.  There was one case where a radio failed, and another case where the radio was operationally occupied.  There were 8 attempts where forecast probabilities were generally below 65% and results were correspondingly poor.  Each of these eight cases is amenable to engineering remedy.

## Implications regarding ATS

- This test was directed toward LDOC services
- We maintain that substantial benefits to ATC services are also indicated
- Conventional wisdom is that ATC operators are so skilled that real-time guidance would not help

## Implications for ATS (Cont.)

- The best an ATC operator can do is to approach the climatological median of ionospheric behavior. Many operators, with long experience, do approximate this capability.
- However, this is where quasi-dynamic storm modeling and related ionospheric measurements can be of considerable benefit. They allow us to approach reality and not rely on history alone.
- For Example: We examined the errors of the climatological median and of the storm model vs. actual ionospheric measurements at 11 northern ionosonde stations during the most stressed 24 hour period of the April 5-9, 2000 storm. (We have used both the NOAA-SEC storm model and the RPSI version developed for use with propagation assessments.)

## Implications for ATS (Cont.)

- The stations were:
- Thule
- Millstone
- Boulder
- Rostov
- Narssaruaq
- Moscow
- Novosibirisk
- Sofia
- Rugun
- Chilton
- Tortosa

## Implications for ATS (Cont.)

- The electron density frequently dropped to 40% of the climatological prediction. How well did geomagnetic storm model corrections do?
- We found the following:
- The average error for the climatological model for foF2 (i.e., URSI-88) was much larger than the resultant error after it was corrected for modeled storm behavior (viz., 2.9 times the error).
- It is clear that the wise use of the storm model would be of immense value in providing stable, reliable HF service during storms.
- Hence ATS can also be assisted

## Conclusions (Cont.)

- The spectrum management tools provided by Dynacast can be of substantial assistance in both LDOC and ATC services

## Modern HF Spectrum Management for Air Transport Services

## The Problem

- HF LDOC is pilot-initiated and requires the pilot to choose one of a few station-frequency pairs which can support adequate voice service from a large number of candidate choices.
- The difficulty in making a successful choice is caused by the variability of HF Radio Propagation which the pilot is powerless to assess.

## The Problem (CTD.)

- The result is a poor level of service, pilot frustration and inclination to avoid the medium.
- Yet in-flight events demanding support from dispatch will always be with us.

## The Solution

- We have developed a computationally efficient way to model all possible HF communication paths from all service providers using all assigned frequencies and rank the frequency-station pairs by reliability.
- The inputs are Date, UT, Lat. Lon. (All from GPS) SSN and recent and expected magnetic activity (from Dispatch).
- The execute time is about 3.5 seconds on a Windows Lap-Top.

## Screen Display Summary

- The client module requires a minimal number of inputs indicated conveniently on the screen
- Other essential parameters are inserted at the server location, and are invisible to the user.
- The client display is summarized in the following four slides

## Initial server display prior to the insertion of desired data

***Initial server display prior to the insertion of desired data***

## Server display following insertion of data (SSN, Lat, Lon); Set, Run. 1st 10 ranks.

## Server display following insertion of data (SSN, Lat, Lon); Set, Run. 2nd 10 ranks.

## Server display following insertion of data (SSN =100). 1st 10 ranked pairs shown

## Evaluation of the Svalbard-to-Barrow Path

- Radio Propagation Services
- Feb. 1, 2001

## Nature of Experiment

- The Svalbard-to-Barrow path is ~ 1840 nautical miles or ~ 3400 km. The midpath of the ray trajectory is near the geographic North Pole.
- A Chirpsounder transmitter was deployed to Svalbard (78N, 15E), and a receiver was deployed to Barrow, Alaska (71N, 157W).
- Oblique-incidence ionograms were obtained at Barrow and automatically uploaded to the RPSI Web site via the Internet.
- The sampled data period is Dec. 1-6, 2000

##          Anticipated IonogramsWe expected ionograms to look like the following. They exhibit a high-ray/low-ray pattern, typical of 1-hop F2 layer propagation. In addition, see that the so-called MOF (shown by the dotted line in the lower curve), or maximum observable frequency, is around 14.5 MHz. This is within the margin of error of propagation models in use today (i.e., VOACAP and ICEPAC). We find that this pattern is not generally observed.

## Actual IonogramsAbove-the-MUF Example #1For many instances, the ionograms display quite a different pattern, with MOFs much greater than would be predicted by typical models. Below we provide a number of examples.

## Above-the-MUF Example #2

## Above-the-MUF Example #3

## Observed MOF Values at Barrow:The VOACAP MUFs are ~16 MHz; and the ICEPAC MUFs are ~18 MHz irrespective of local time (or Universal Time)We see the observed values are generally higher.

## CONSEQUENCES

- Predictions used by frequency planners are typically based upon static models that are poorly defined in the polar regions.
- Our results show a consistent above-the-MUF component of propagation. (That is, frequencies higher than predictions).
- These RPSI results correspond to oblique paths that are actually measured, while planning models are based upon archived ionospheric data (from VIS instruments) requiring oblique path predictions to be calculated.
- _Result_: Planners will have a tendency to ignore the potential of higher frequencies (observed by RPSI) that may be suitable to carry traffic.
- _Consequence_: Lower frequencies may propagate but the circuit reliabilities are smaller due to increased signal absorption at lower frequencies, as well as increased noise and interference.
- _Bottom Line_: HF voice and data service for over-the-pole flights may be disadvantaged through lack of access of higher bands or sub-optimal frequency selection.

## Conclusions

- RPSI has instrumented a path from Svalbard to Barrow Alaska. This exhibits some fascinating features of the arctic communication path at HF.
- We don’t claim to have the full explanation for all features we have observed, but observational conclusions are hard to dispute.
- We often find excess bandwidth above the values predicted by standard codes.
- This excess bandwidth can be exploited to achieve considerably higher reliabilities.
- Real-time frequency management through Dynacast®  has the potential to identify the existence of above-the-MUF modes of propagation.
- RPSI has an operational plan of attack and is proposing to launch an interim service in this calendar year.

## Svalbard to Barrow Soundings

- December 01, 2000
- 12-hour Period: 0355-1605 UT
- AP  = 6
*Radio Propagation Services, Inc*

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