Kinetic Temperature Retrievals from MGS TES Bolometer Measurements:
Current Status and Future Plans
A.A. Kutepov, A.G. Feofilov, L.Rezac
July 28, 2009, NASA GSFC
Outline
• Theoretical approach, algorithm
• Application to real retrievals: problems.
• Methods of solution: separating detectors, re-calibration, etc
• Other possible methods
• Conclusions and future plans
Thermal Emission Spectrometer on MGS Satellite
Spectrometer• Michelson interferometer; spectral range: 1700 – 200 cm-1 (6 – 50 m); spectral sampling: ~5 or ~10 cm-1
Bolometer• Bolometric thermal radiance channel (5.1 – 150 m)• Solar reflectance channel (0.3 – 2.9 m)• Spectral range: 5.1 – 150 m• Tangent heights range: 0~100 km• Single detector FOV: 13 km, however:• 3x2 array of detectors scanned in overlapping steps provide 1-5 km vertical resolution
Array ofdetectors
Bolometric instrumental functionand contributions to signal
Non-LTE in CO2: vibrational temperatures
Forward Radiative Transfer
modelFeedback scheme:
T’(z) = F{Imeas(z), Isimul(z)}
Corrected T(z)
P0 from TES SpectrometerInitial guess for T(z)
Iterations
Non-LTE model
Measured radiance I(z)
Imeas(z) ~ Isimul(z) ?Retrieved T(z)
CO2 populations
I simul(z
)
Imeas(z)
Forward fitting algorithm
Numerical simulation of retrieval process
Real life
• Daytime signal has an unknown pedestal. Moreover, 10m radiance is non-thermal. Considering only nighttime retrievals.
• Straightforward interpretation of nighttime bolometric data produces unrealistic data.
• Calibration of TES bolometer using integrated TES spectrometer.
• Even re-calibrated TES bolometer radiances do not lead to temperature retrievals that would qualitatively agree with the current understanding of Martian atmosphere’s physics.
• Illustrations of these issues will follow.
Examples of day- and nighttime bolometric signals
Day- and nighttime simulations
Very first nighttime temperature retrievals. Ls=0.
Possible reasons?
• Non-LTE issues: not important below ~80km altitude.• Atomic oxygen or KV-T(CO2-O) rate: can not change the signal at 50-60km to be 2-3 times larger while the radiance from 100km remains negligible.• Insufficient number of levels and transitions: tested.• Line parameters uncertainties: this is very unlikely for the fundamental bands.• Offsets in P0 leading to changes in P(z): varied by ~30%, didn’t help.• Possible signal issues: - twilight/night: only “pure night” cases selected - sporadic spikes: filtered out - differences between detectors (gain, latitudinal coverage): checked. Even if we take the “best” detector, it doesn’t help. - absolute values verification: need extra source of information.
Spectral TES as a reference dataset for calibration
Average of the above
Average of the above
Bolometer Spectrometer conversion (by M.Smith)
We are interested in this part
Bolometer Spectrometer conversion tables
Bolometer Spectrometer conversion tables
“Best achievement”: temperature distribution for Ls=0
Comparing with other measurements
TES Spectrometer
Ls=0
MCS Ls=330
Even less realistic: temperature distribution for Ls=90
Reasons for retrieving increased T
Possible ways of solving the problem
• Continue further attempts of re-calibrating bolometer.
• Switch to spectrometer and work with integrated signal.
Questions:
• What do we call an “integrated spectrometer”?
• Will the integrated spectrometer go above 60km?
• How good are MGS TES limb retrievals compared to retrievals from nadir observations?