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Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity Laboratory
Facing the heat –Obtaining near infrared real
emissivity spectra at Venus surface temperatures
J. Helbert, A. „grill master“ Maturilli, N. Müller DLR
Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity Laboratory
3
2
1
4Coconoma Tesserea
Mylitta F
luctu
s
Boala Corona
Quetzalpetlatl Corona
Otygen Coronae
Jord Corona
Cavillaca
FluctusJuturna
Fluctus
Helbert, Müller et al. GRL 2008
What actually are the red and blue materials
on the surface??
Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity LaboratoryThe answers can only come from laboratory work• Now that we got data which might indicate
compositional differences, we need to understand better how to classify composition from only three channels
• In Berlin we have started to set up a new Planetary Emissivity Lab which will allow to measure the wavelength range from 1-50μm for samples at high temperature (>700K)
• This will cover the surface windows observable by VIRTIS
• However it will operate under vacuum and will not be able to reach more than (Earth) ambient pressure
Hashimoto and Sugita, 2003
Still it should be good to confirm – or improve – this plot
Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity Laboratory
Checklist for high temperature emissivity measurements
2. Heat your sample to at least 400°C2a. Do not heat your spectrometer or
chamber to 400°C
3. Find a reliable calibration working in the same temperature range with a known emissivity below 3 μm
1. Build and characterize a setup that allows measurements with a good signal to noise ratio for emissivity measurements at 1 μm For characterisation see Maturilli et al. 2008
4. Put everything in a nice looking box
Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity Laboratory
Lets turn up the heat – and keep everything else cold!
Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity LaboratoryCharacterisation of thermal behavior
460.6°C – standard dev 3.1°C
Helbert and Maturilli, 2009
Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity Laboratory
Playing with Quartz in the mid-infrared –Not good for Venus but always a good test case
• There is a clear change of the spectral behaviour with temperature
• No shift of the position of the emissivity maximum or the reststrahlen band is observed
• The shape of the reststrahlen band changes significantly
• We see a shift in the position of the transparency features
The problem: Our calibration source could not go beyond 175°C
Helbert and Maturilli 2009
Maybe not completely useless for Venus after all…
Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity Laboratory
A „cold“ 175°C calibration source does not help with measurements for VEX VIRTIS
While the raw data shows a good signal for hot samples the „cold“ blackbody can not be measured…
Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity LaboratoryLinearity of the response function
Helbert and Maturilli, 2009
Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity Laboratory
Evaluating a possible calibration source
Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity Laboratory
With this blackbody we could finally try to calibrate our emissivity measurements
Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity LaboratoryWe were getting close already in Dec
Cu
rrent lim
it of u
sable S
/N ratio
„VIR
TIS
“ win
do
ws
Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity LaboratoryThe next step is only days away –The planetary simulation chamber
• Vacuum(!?!)
• Internal calibration sources
• Induction heating
• A lot of temperature sensors
• Automatic sample transport system
• All components are separately tested
• Easily adaptable!
Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity Laboratory
Getting the last items done – BBQing a new blackbody coating
Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity LaboratoryManufacturing and testing is finished
Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity LaboratoryAutomatic sample transport system
Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity LaboratoryNew sample cups
• Higher thermal stability• A modified version with a
window can be used to measure (and transport) weathered samples in a Venus-like atmosphere
Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity LaboratoryConclusions
• Obtaining emissivity measurements for samples at 500°C is a tricky task, but we managed (see Helbert et al. 2009)
• Obtaining emissivity measurements at 1μm for samples at 500°C is a very tricky task
• We are getting close, however we can not yet give any indication for the „red“ or „blue“ material
• Once the basic setup is working we need to perform extensive tests• Then the fun part begins:
– Selection of analog materials
– Characterisation of changes in the materials
– Characterisations of mixtures
– Test of different hypothesis for the interpretation of VIRTIS data
– Support for future missions and instrument development
• Finally - include the temperature as another parameter in the Berlin Emissivity Database (Maturilli et al. 2008)
Jörn
Hel
bert
joer
n.he
lber
t@dl
r.de
Planetary Emissivity Laboratory
SurVenTIS – Surface of Venus Thermal Imaging System
10°-15° wide angle optics
Filter wheelCCD/CMOS detector 256x256
Electronics box
Wheel drive
• Basic design idea is a CCD imager with a filter wheel
• Proposed filter
1.02 µm + 0.85, 0.90, 1.10, 1.18 µm
Surface imaging
1.31 µmCloud imaging – cloud correction for surface imaging
0.77 µmConstrain albedo vs. absorption
0.65 µmFe3+ band, oxidation state of the surface
Neutral
„Grayscale imaging“ – cloud morphology and public outreach
Black Flatfielding and calibration
VIRTISMass of 31kg
SurVenTISMass > 1kg