Transcript .ppt

Making sense of
SuperDARN elevation:
Phase offset and variance
Pasha Ponomarenko, Jan Wiid, Sasha Koustov,
and Jean-Pierre St.-Maurice
University of Saskatchewan, CANADA
4 August, 2016
SuperDARN Workshop, 29 May - 3June 2011,
Hanover, US
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Abstract
The vertical angle of arrival of HF signals contains very important information about the
propagation modes and ionospheric conditions. However, despite being routinely
registered by SuperDARN radars, elevation angles are rarely utilised. The main reason
for that is the apparent unreliability of these data, which frequently appear to be
unrealistic. At SuperDARN’2010 we attributed the problem to an inadequate phase
calibration that fails to account for certain phase shifts in the radar hardware. However, a
following detailed analysis of the experimental data and statistical modelling revealed
that the presence of “strange” elevation components could be fully explained by
accounting for the statistical distribution of phase fitting errors. In essence, a
combination of this distribution with the very non-linear phase-elevation relationship
leads to a two-pi wrap-around of the phase that results in an artificial population of
echoes at very high elevation angles.
4 August, 2016
SuperDARN Workshop, 29 May - 3June 2011,
Hanover, US
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Outline
Introduction
Apparent problems
Phase calibration
Fitting error effects
Conclusions
4 August, 2016
SuperDARN Workshop, 29 May - 3June 2011,
Hanover, US
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Definition and importance
• Elevation angle – vertical angle of arrival of
HF signal
h
n <1
n=1
x
• Diagnostic importance:
– HF propagation mode
– ionospheric plasma density (Secant Law)
4 August, 2016
SuperDARN Workshop, 29 May - 3June 2011,
Hanover, US
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SuperDARN Interferometry
d
  cos
d
Ψ
1
 cos
Ψ max
1


d
2π
Ψ  kd , Ψ max  kd
max
d  k  Ψ max  2
4 August, 2016
SuperDARN Workshop, 29 May - 3June 2011,
Ψmax
Hanover,
US
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Elevation vs phase shift
4 August, 2016
SuperDARN Workshop, 29 May - 3June 2011,
Hanover, US
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Suspiciously high values
4 August, 2016
SuperDARN Workshop, 29 May - 3June 2011,
Hanover, US
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Split phase distribution?
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SuperDARN Workshop, 29 May - 3June 2011,
Hanover, US
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All ranges @ multiple frequencies
4 August, 2016
SuperDARN Workshop, 29 May - 3June 2011,
Hanover, US
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Phase offset?
4 August, 2016
SuperDARN Workshop, 29 May - 3June 2011,
Hanover, US
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Phase calibration
4 August, 2016
SuperDARN Workshop, 29 May - 3June 2011,
Hanover, US
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Calibrated elevation
4 August, 2016
SuperDARN Workshop, 29 May - 3June 2011,
Hanover, US
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Still does not look right...
4 August, 2016
SuperDARN Workshop, 29 May - 3June 2011,
Hanover, US
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What about phase fitting errors?
   0     
p()
σ
0
0

Δ
4 August, 2016
SuperDARN Workshop, 29 May - 3June 2011,
Hanover, US
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One-sigma fitting error from data
median  8 deg
mean  6 deg
4 August, 2016
SuperDARN Workshop, 29 May - 3June 2011,
Hanover, US
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Modelling: phase variance effect
4 August, 2016
SuperDARN Workshop, 29 May - 3June 2011,
Hanover, US
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So, SOME flipping is OK!
Limited
Calibrated
Raw   7
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SuperDARN Workshop, 29 May - 3June 2011,
Hanover, US
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Concluisons
If after phase calibration the maximum of
the phase distribution at any given range
does not flip over to the high elevation
end, the elevation data should be OK.
Now, how can we utilise elevation?
See the follow-up talk on Wednesday!
4 August, 2016
SuperDARN Workshop, 29 May - 3June 2011,
Hanover, US
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