Title: An Optimal Estimation Spectral Retrieval Approach for Exoplanet Atmospheres
1An Optimal Estimation Spectral Retrieval Approach
for Exoplanet Atmospheres
- M.R. Line1, X. Zhang1, V. Natraj2, G. Vasisht2,
P. Chen2, Y.L. Yung1 - 1California Institute of Technology
- 2Jet Propulsion Laboratory, California Institute
of Technology - EPSC-DPS 2011, Nantes France
Line et al. in prep
2Goals
- Find a robust technique for retrieving
atmospheric compositions and temperatures from
exoplanet spectra - Determine the number of allowable atmospheric
parameters that can be retrieved from a given
spectral dataset
3Method Optimal Estimation (Rodgers 2000)
xa- prior state vector Sa - prior uncertainty
matrix
4Forward Model F(x)
- Parmentier Guillot 2011 Analytical TP
- ?v1,?v2, a, ?IR ,Tirr , Tint
- Constant with Altitude Mixing Ratios
- H2O, CH4, CO, CO2, H2, He
- Reference Forward Model (http//www.atm.ox.ac.uk/R
FM/) - -HITEMP Database for H2O, CO, CO2
- -HITRAN Database for CH4
- -H2-H2, H2-He Opacities (from A. Borysow)
5HD189733b Jacobian
6HD189733b Retrieval
A priori State Retrieved State Retrieved State
(Hi Res)
?20.86
DOF 5
7Degrees of Freedom and Information Content
FINESSE
NICMOS
8Conclusions
- Rodgers optimal estimation technique can provide
a robust retrieval of exoplanetary atmospheric
properties - Quality of the retrieval of each parameter can be
determined - Knowledge of the Jacobian, Information content,
and degrees of freedom can aid future instrument
design
9Synthetic Data Test
Model Atmosphere Tirr1220 K fH20.86 Tint100
K fHe0.14 ?v1410-3 cm2g-1 fH2O510-4 ?v241
0-3 cm2g-1 fCH4110-6 a0.5 fCO310-4 ?IR
110-2 cm2g-1 fCO2110-7
Instrumental Specs R40 at 2µm (??0.05
µm) S/N10
10Synthetic Data Jacobian
11Synthetic Data Retrieval
?20.01
DOF 6
12Method Optimal Estimation(Rodgers 2000)
Minimize Cost Function from Bayes
Likelihood that data exists given some model
Prior Information
y - measurement vector x - true state vector -
retrieved state vector xa- prior state
vector F(x)Kx-forward model K -Jacobian
matrix Se- data error matrix Sa - prior
uncertainty matrix S-retrieval uncertainty matrix
Degrees of Freedom
Information Content