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?