LYRA occultations Meeting 2011/05/05
LYRA: Occultations Lyman α Herzberg Aluminum Zirconium Vis (IR ?) EUV UV 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 Descending phase Ascending phase (Aluminum) Difference in ionospheric density between nights and days Comparison with a model of extinction during Sunset/Sunrise needed
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
Observer Earth Earth 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 Observer
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?
, with Forward model • σ* = mean of σ one channel • variable change
Al Zr Hz Ly Results 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.