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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 of detectors
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Bolometric instrumental function and contributions to signal
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Non-LTE in CO 2 : vibrational temperatures
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Forward Radiative Transfer model Feedback scheme: T’(z) = F{I meas (z), I simul (z)} Corrected T(z) P 0 from TES Spectrometer Initial guess for T(z) Iterations Non-LTE model Measured radiance I(z) I meas (z) ~ I simul (z) ? Retrieved T(z) CO 2 populations I simul (z) I meas (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, 10 m 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. L s =0.
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Possible reasons? Non-LTE issues: not important below ~80km altitude. Atomic oxygen or K V-T (CO 2 -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 P 0 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
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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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“Best achievement”: temperature distribution for L s =0
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Comparing with other measurements TES Spectrometer L s =0 MCS L s =330
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Even less realistic: temperature distribution for L s =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?
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