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.