1. LYRA occultations Meeting 2011/05/05

2. LYRA: Occultations Lyman α Herzberg Aluminum Zirconium EUVUV Vis (IR ?) Lyman α: very sensitive to Visible and InfraRed

3. 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 ?

5. LYRA: Degradations ? Lyman α Channel ≈ 19% Spectral Change: more sensitive to visible light ?

6. 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)

7. 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

8. 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

9. ChannelComponents 6-20 nmO, O 2, N 2 17-80 nmO, O 2, N 2 120-123 nmO2O2 190-222 nmO 2, O 3

11. LYRA pre-flight spectral responsivity (filter + detector, twelve combinations)

13. 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

14. Oscillations in occultations See David’s PDF Only in Zr channel?

15. Annexes

16. Forward model 1.σ* = mean of σ one channel 2. 3.variable change, with

17. 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.