Jörn Helbert 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 Helbert Planetary Emissivity Laboratory Coconoma Tesserea Mylitta Fluctus Boala Corona Quetzalpetlatl Corona Otygen Coronae Jord Corona Cavillaca Fluctus Juturna Fluctus Helbert, Müller et al. GRL 2008 What actually are the red and blue materials on the surface??

Jörn Helbert Planetary Emissivity Laboratory The 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 Helbert Planetary Emissivity Laboratory Checklist for high temperature emissivity measurements 2. Heat your sample to at least 400°C 2a. 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 Put everything in a nice looking box

Jörn Helbert Planetary Emissivity Laboratory Lets turn up the heat – and keep everything else cold!

Jörn Helbert Planetary Emissivity Laboratory Characterisation of thermal behavior 460.6°C – standard dev 3.1°C Helbert and Maturilli, 2009

Jörn Helbert 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 Helbert 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 Helbert Planetary Emissivity Laboratory Linearity of the response function Helbert and Maturilli, 2009

Jörn Helbert Planetary Emissivity Laboratory Evaluating a possible calibration source

Jörn Helbert Planetary Emissivity Laboratory With this blackbody we could finally try to calibrate our emissivity measurements

Jörn Helbert Planetary Emissivity Laboratory We were getting close already in Dec Current limit of usable S/N ratio „VIRTIS“ windows

Jörn Helbert Planetary Emissivity Laboratory The 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 Helbert Planetary Emissivity Laboratory Getting the last items done – BBQing a new blackbody coating

Jörn Helbert Planetary Emissivity Laboratory Manufacturing and testing is finished

Jörn Helbert Planetary Emissivity Laboratory Automatic sample transport system

Jörn Helbert Planetary Emissivity Laboratory New 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 Helbert Planetary Emissivity Laboratory Conclusions 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 Helbert Planetary Emissivity Laboratory SurVenTIS – Surface of Venus Thermal Imaging System 10°-15° wide angle optics Filter wheel CCD/CMOS detector 256x256 Electronics box Wheel drive Basic design idea is a CCD imager with a filter wheel Proposed filter 1.02 µm , 0.90, 1.10, 1.18 µm Surface imaging 1.31 µm Cloud imaging – cloud correction for surface imaging 0.77 µm Constrain albedo vs. absorption 0.65 µm Fe3+ band, oxidation state of the surface Neutral „Grayscale imaging“ – cloud morphology and public outreach Black Flatfielding and calibration VIRTIS Mass of 31kg SurVenTIS Mass > 1kg