jörn helbert joern.helbert@dlr.de planetary emissivity laboratory facing the heat – obtaining...

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