thermophysics with themis
Post on 03-Jan-2022
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Thermophysics with THEMIS
• Background• THEMIS daytime infrared images
– Comparison with visible images• THEMIS nighttime infrared images
– Proxy for qualitative thermal inertia• THEMIS thermal inertias
– Comparison with TES and Mini-TES data
Background• Surface
temperatureaffected by:
– Solar radiation ontothe surface
– Albedo – thermalenergy absorbed orreflected
– Conductivity of thesurface material
– Presence of CO2 ice
THEMIS Daytime IR• During the day surface temperature is
primarily a function of:– Surface albedo– Topography– Thermal inertia
• Poor time to derive thermal inertia• Good proxy for morphology and
context for THEMIS and MOC visibleimages
• Absolute accuracy: ~1° K
I06353020M0201821MSSS/JPL/NASA
Pasteur Crater
8 km
Day IR
THEMIS Visible
MOC Visible
4.8 kmV10422009
185 240
300 m
THEMIS Nighttime IR• Surface temperature at night dominated by:
– Thermal inertia - Physical nature of thesurface, such as particle size
– Effects of albedo and topography have largelydissipated
• Qualitative thermal inertia – band 9– High signal to noise– Fairly transparent to the atmosphere
• Most images are acquired between 4.5-5 H– CO2 frost may be present
• Absolute accuracy – ~4º K
PasteurCrater
I063
5302
0
8 km
Day IR
V10422009
THEMIS Visible
Night IR
I086
4401
2
8 km
185 240 150 195
4.8 km
Thermal Inertia• I = (ρkc)1/2
ρ – bulk density (kg m-3) k – conductivity (J kg-1 °K-1 ) c – specific heat (J s-1 °K-1 m-1)• Units of J m-1 °K-1 s-1/2
• Measure of the resistance of a material to achange in temperature
Thermal Inertia Method• Use thermal model developed by H. H. Kieffer
– Ls, latitude, local time from spacecraft ephemeris– TES-derived albedo (8ppd)– MOLA-derived elevations (128 elem. per degree)– TES-derived dust opacity (2 ppd) every 30° Ls
• Radiance at 12.57 µm (Band 9) is convertedto brightness temperature, correcting for driftand wobble of the spacecraft.
• Interpolate upon a 7-D look-up table
Comparison with Orbital Data - TES
• Differences inthermal inertias areprimarily due todifferences insurface temperature– Differences are
roughly the sameas THEMISuncertainty
– This differencedoes not changethe scientificinterpretation of thegeology
• Thermal models results used for TES and THEMISagree within 3°K
Fergason et al., in prep.
Comparisonwith Surface
Measurements -MER
Fergason et al., in submission
THEMIS and Mini-TES Thermal Inertia
0
500
1000
1500
0 10 20 30 40 50 60 70 80
Spirit - Gusev Landing Site Number
Th
erm
al In
ert
ia
Mini-TES Thermal Inertia THEMIS Thermal Inertia
250 430J/m2Ks1/2
Arabia Terra
• Blue – dust– TI: 60-85
• Green –sand– TI: 210-250
• Red –resistiveoutcrops– TI: 400-435
J/m2Ks1/224 430
M0310925NASA/JPL/MSSS
1 km
16 km
I01229007
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