kinetic temperature retrievals from mgs tes bolometer measurements: current status and future plans...
TRANSCRIPT
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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
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Outline
• Theoretical approach, algorithm
• Application to real retrievals: problems.
• Methods of solution: separating detectors, re-calibration, etc
• Other possible methods
• Conclusions and future plans
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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
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Bolometric instrumental functionand contributions to signal
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Non-LTE in CO2: vibrational temperatures
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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
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Numerical simulation of retrieval process
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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.
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Examples of day- and nighttime bolometric signals
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Day- and nighttime simulations
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Very first nighttime temperature retrievals. Ls=0.
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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.
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Spectral TES as a reference dataset for calibration
Average of the above
Average of the above
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Bolometer Spectrometer conversion (by M.Smith)
We are interested in this part
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Bolometer Spectrometer conversion tables
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Bolometer Spectrometer conversion tables
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“Best achievement”: temperature distribution for Ls=0
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Comparing with other measurements
TES Spectrometer
Ls=0
MCS Ls=330
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Even less realistic: temperature distribution for Ls=90
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Reasons for retrieving increased T
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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?