lyra occultations meeting 2011/05/05. lyra: occultations lyman α herzberg aluminum zirconium euvuv...
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LYRA occultations
Meeting 2011/05/05
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LYRA: Occultations
Lyman α
Herzberg
Aluminum
ZirconiumEUV UV
Vis
(IR ?)
Lyman α: very sensitive to Visible and InfraRed
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LYRA: Occultations
• Resonant scaterring of Lyman α
• Lyman α emission from missiles or spacecraft trails ?(Hicks et al, 1999)
• Sublimation of meteorites ? (Infrared emission)
• Infrared emission from the earth atmosphere ?
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LYRA: Degradations ?
Lyman α Channel
≈ 19%
Spectral Change: more sensitive to visible light ?
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LYRA: Occultations
Difference in ionospheric density between nights and days
Comparison with a model of extinction during Sunset/Sunrise needed
Descending phase
Ascending phase(Aluminum)
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• First simulation with– Uniform solar emission I=I(λ)– Absorption coefficient independent of temperature
and averaged over the spectral range of each channel=> very restrictive hypothesis considering the large bandwidth of the channels
– Onion peeling (concentric layers) model of Earth atmosphere
– No scattering, no banding of the photon trajectory due to refraction
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Problem:Full-sun radiometer => a traditional onion peeling would limit the resolution to 25 km
Alternative: to divide the sun into parallel horizontal layer and evaluate the extinction of each level separately BUT needs a high signal to noise ratio for the measures to be differentiated
Earth
Observer
Earth
Observer
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Channel Components
6-20 nm O, O2, N2
17-80 nm O, O2, N2
120-123 nm O2
190-222 nm O2, O3
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LYRA pre-flight spectral responsivity(filter + detector, twelve combinations)
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Next steps
• Use an absorption cross-section varying with the wavelength
• Introduce a non-uniform solar irradiance (limb-darkening / brightening)
• Compare with PREMOS data• Check the impact of extended wavelength
ranges on Ly model + include the soft X-ray into Al and Zr
=> might involve new species
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Oscillations in occultations
• See David’s PDF• Only in Zr channel?
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Annexes
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Forward model
2
0
2/
0
2
1
2
0
2/
0
2
1
),,()cos()sin()(
),,()(exp),,()cos()sin()(
)(
IddQd
rNIddQd
rT iii
C
1. σ* = mean of σ one channel
2.
3. variable change€
I(λ ,θ ,ψ ) ≈ I1(λ )I(θ ,ψ ) ≈ I1(λ )
2
2
2
2
2
2
2
2
1
1
1
1
)(
)()(exp
y
y
y
yiii
Mddy
MdyNdy
T
2
22
2
1
),()(
y
yIM
, with
cossin
cos
y
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Results
Zr Al
Ly Hz
We have retrieved the extinction coefficients in each LYRA channel for optical thicknesses from 0.01 to 10.
BUT we miss information to separate the components.
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