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Effect of Antenna Length

Effect of Antenna Length. Effectively no change in length scale of fluctuations - resolution changes from 12.5m to 4.0838m when antenna changes from 27.55m to 9m. - little power included in PSDF between length scales associated with this change in resolution.

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Effect of Antenna Length

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  1. Effect of Antenna Length • Effectively no change in length scale of fluctuations • - resolution changes from 12.5m to 4.0838m when antenna changes from 27.55m to 9m. • - little power included in PSDF between length scales associated with this change in resolution. • Synthetic aperture increases linearly with antenna length • - more large scale fluctuations across aperture for smaller antenna. • Little effect upon point spread function however • - in fact, PSF statistics improve slightly for shorter antenna.

  2. Boreal Location (17E, 65N) 06:00 Orbit d = 27.55m d = 9m Phase (rad) across aperture Point Spread Function

  3. Boreal Location (17E, 65N) 18:00 Orbit d = 27.55m d = 9m Phase (rad) across aperture Point Spread Function

  4. Equatorial Location (115E, 2S) 06:00 Orbit d = 27.55m d = 9m Phase (rad) across aperture Point Spread Function

  5. Equatorial Location (115E, -2N) 17:00 Orbit d = 27.55m d = 9m Phase (rad) across aperture Point Spread Function

  6. Equatorial Location (115E, 2S) 18:00 Orbit d = 27.55m d = 9m Phase (rad) across aperture Point Spread Function

  7. Equatorial Location (115E, -2N) 19:00 Orbit d = 27.55m d = 9m Phase (rad) across aperture Point Spread Function

  8. Equatorial Location (115E, -2N) 20:00 Orbit d = 27.55m d = 9m Phase (rad) across aperture Point Spread Function

  9. Effect of Antenna Length Effect upon statistics when moving from 27.55m to 9m antenna (06:00 orbits, 99th CkL percentile, 100 realisations): * Not enough admissible realisations for meaningful statistics, included for completeness

  10. Effect of CkL Confidence Interval Key parameter dictating level of ionospheric disturbance is CkL, which is proportional to the variance of phase fluctuations. WBMOD returns CkL values as confidence intervals of log-normal distribution. To date, worked with 99th percentile as worst case scenario – 99% of time, will be better than this. What is the effect upon the metrics as this confidence interval varies? Considered the following percentiles: 50th, 75th, 90th, 95th, 99th.

  11. Boreal Location (17E, 65N) 06:00 Orbit 9m antenna

  12. Effect of CkL Confidence Interval 80% of sample PSFs still admissible for 95th percentile Rapid deterioration in all metrics and number of admissible samples beyond 95th percentile, as seen. Resolution fairly stable right up to 90th percentile Decrease in radiometric height to about 70% at 90th percentile, and to 55% by 95th percentile. Increasing geometric distortion with percentile – large jump to 99th percentile most likely due to anomalous peak recognition in software, rather than true physical effect.

  13. Effect of CkL Confidence Interval on Choice of Local Time • Previous considerations based on 99th percentile showed that: • - High levels of scintillation in Boreal zone for all LTs • - Little variation with LT with the exception of equatorial zone, where orbit with LT later than 07:40 encountered high levels of post-dusk scintillation Are these conclusions valid for lower percentiles? We consider the variation of the CkL percentiles with LT since this is the main driver for scintillation.

  14. Boreal Location (17E, 65N) 75th Percentile, 21/06/01 (Solar max), look angle of 25 log10 CkL log10 CkL Local Time at Equator Dawn Local Time at Equator Dusk Approx 1-2% variation in log10 CkL (2-5% variation in CkL) from earliest to latest orbits, decreasing from night to day side. Not significant in effect on PSF.

  15. Boreal Location (17E, 65N) Qualitatively similar for all percentile values. Local time has relatively little effect on CkL levels in Boreal zone. Main effect is overall levels of CkL, not variation with LT.

  16. Equatorial Location ( 115E, -2N) 75th Percentile, 21/06/01 (Solar max), look angle of 25 log10 CkL log10 CkL Local Time at Equator Local Time at Equator Dusk: rapid increase for orbits with LT later than 19:40, but ~1.5% in magnitude so not significant for 75th percentile Dawn: steady decrease in CkL, about 10% variation but low overall levels so little effect on PSF.

  17. Equatorial Location ( 115E, -2N) 90th Percentile, 21/06/01 (Solar max), look angle of 25 log10 CkL log10 CkL Local Time at Equator Local Time at Equator Dawn node: approx 10% change, but low levels of CkL so unimportant from point of view of PSF. Dusk node: much greater increase (~12%) beyond 19:40, coupled with significant levels of CkL.

  18. Equatorial Location ( 115E, -2N) CkL variation with LT for dawn orbits of little significance for all percentiles due to low overall CkL levels. Dusk orbits exhibit a sudden increase in CkL at 19:40 for all percentiles, magnitude of increase greater for higher percentiles.

  19. Conclusions For Boreal locations: - change in CkL with LT insignificant - high levels of CkL are the key factor here - accepting a lower percentile reduces these levels - increased lieklihood of exceedance however For Equatorial locations: - larger variation in CkL with LT for dawn nodes, but overall levels of CkL low so little effect on PSF - for dusk nodes, significant increase in CkL for orbits with LT later than 19:40 - The magnitude of this post-dusk increase greater for higher percentiles: more PSF distortion - Dusk orbits later than 19:40 should be avoided, due to reduced likelihood of acceptable CkL levels

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