LYRA occultations
Meeting 2011/05/05
LYRA: Occultations
Lyman α
Herzberg
Aluminum
ZirconiumEUV UV
Vis
(IR ?)
Lyman α: very sensitive to Visible and InfraRed
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 ?
LYRA: Degradations ?
Lyman α Channel
≈ 19%
Spectral Change: more sensitive to visible light ?
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)
• 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
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
Channel Components
6-20 nm O, O2, N2
17-80 nm O, O2, N2
120-123 nm O2
190-222 nm O2, O3
LYRA pre-flight spectral responsivity(filter + detector, twelve combinations)
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
Oscillations in occultations
• See David’s PDF• Only in Zr channel?
Annexes
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
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.
Top Related