The MErcury Radiometer and Thermal Infrared Imaging Spectrometer (MERTIS) is an instrument to study mineralogy and temperature distribution of Mercury surface in unprecedented quality. MERTIS was proposed in 2003 as payload of the Mercury Planetary Orbiter spacecraft of ESA-JAXA BepiColombo mission and will reach Mercury in 2026. MERTIS will map the whole surface at 500m resolution combining a push-broom IR grating spectrometer (TIS) with a radiometer (TIR) sharing the same optics, instrument electronics and in-flight calibration components for the whole wavelength range of 7-14μm (TIS) and 7-40μm (TIR). Currently we are developing and testing an ingestion, calibration and transformation pipeline for MERTIS data, from raw telemetry level data to calibrated product and high level derived product. Bepicolombo Science Ground Segment (BC-SGS or SGS) is embracing new technologies for the BepiColombo mission and follows the latest NASA/PDS format, the xml based PDS4. We adopt open source languages and well optimized libraries for the underlying processing. The data processing pipeline is fully containerized via Docker to be independent from transition between server/OSs/environment, drastically reducing the integration and testing time. Due to strict infrastructural constrains like spacecraft downlink bandwidth and onboard mass memory, the already complex observation scenario is subject to further optimizations. This complicates the reconstruction process for higher-level products like global maps of emissivity and thermal inertia.
The Planetary Spectroscopy Laboratory (PSL) of DLR in Berlin provides spectral measurements of primarily planetary analogues from the visible to the far-infrared range. PSL has supported the data analysis as well as the development and calibration of instruments for planetary missions from ESA, NASA and JAXA. For this purposes PSL provides reflection, transmission and emission spectroscopy of target materials. Currently PSL operates two identical Bruker Vertex 80V vacuum FTIR spectrometer, one spectrometer is equipped with aluminum mirrors optimized for the UV, visible and near-IR, the second features gold-coated mirrors for the near to far IR spectral range. External simulation chambers are attached to each of the instruments for emissivity measurements. The chamber at the near to far IR instruments allows emissivity measurements from 0.7-200 μm under vacuum for sample temperatures from 320K to above 900K, using an innovative induction system. The second chamber (purged with dry air and water cooled to ≤270K) allows emissivity measurements of samples with surface temperature from 290 to 420K. We measure bi-directional reflectance of samples, with variable incidence and emission angles between 13° and 85°. Samples are measured currently at room temperature and 170K, with a planned extension for temperatures below 100K. Bi-directional and hemispherical reflectance is measured under purging/vacuum conditions, covering the 0.2 to above 200 μm spectral range. Transmission of thin slabs, optical filters, optical windows, pellets, and others is measured in the complete spectral range from UV to FIR using a parallel beam configuration to avoid refraction.
The MErcury Radiometer and Thermal infrared Imaging Spectrometer (MERTIS) is a highly integrated instrument to study mineralogy and temperature distribution of Mercury’s surface in unprecedented quality. MERTIS was proposed in 2003 as payload of the Mercury Planetary Orbiter spacecraft of the joint ESA-JAXA BepiColombo mission. With the planned launch on top of an Ariane 5 in October of 2018, the mission will soon start its 7 years journey to Mercury. On its way to Mercury, BepiColombo will have 2 flybys of Venus and one of the Earth-Moon system. MERTIS will obtain data during each of these flybys – for Venus the first mid-infrared spectral data since Venera 15 in 1983. After arrival at Mercury in 2025 MERTIS will globally map the surface composition with a resolution of 500m, and study surface temperature variations providing an insight into the thermo-physical properties of the surface. To achieve this, MERTIS combines a push-broom IR grating spectrometer (TIS) with a radiometer (TIR) sharing the same optics, instrument electronics and in-flight calibration components for the whole wavelength range of 7-14 μm (TIS) and 7-40 μm (TIR), respectively. Instrument operations in the challenging environment at Mercury with power and data constraints require a sophisticated mapping scheme for the TIS observations, which also has to account for the MERTIS calibration needs. Execution of this scheme creates challenges for the operation of the instruments, data processing, and the creation of map products. Extensive onground testing and rehearsals during the Venus and Earth flybys will ensure flawless performance at Mercury.
TROTIS (TROjan asteroid Thermal Infrared multi-Spectral imager) is a high spatial-resolution thermal imaging system optimized for targets in the outer solar system with heritage from the Miniaturized Asteroid thermal infrared Imager and Radiometer (MAIR) for the AIDA mission as well as Bepi-Colombo mission's MErcury Radiometer and Thermal Infrared Spectrometer (MERTIS). TROTIS will provide unique science observations that will foster our understanding of Trojan asteroids. It will provide compositional information, thermal physical properties as well as help determine accurate shapes. In addition TROTIS can aid optical navigation, as it will be able to detect targets from any phase angle.
The Venus Emissivity Mapper is the first flight instrument designed with a focus on mapping the surface of Venus using atmospheric windows around 1 μm. After several years of development VEM has a mature design with an existing laboratory prototype verifying an achievable instrument SNR of well above 1000 as well as a predicted error in the retrieval of relative emissivity of better than 1%. With that it will provide a global map of surface composition as well as redox state of the surface by observing the surface with six narrow band filters, ranging from 0.86 to 1.18 μm. Continuous observation of Venus' thermal emission will place tight constraints on current day volcanic activity. Eight additional channels provide measurements of atmospheric water vapor abundance as well as cloud microphysics and dynamics and permit accurate correction of atmospheric interference on the surface data. A mission combining VEM with a high-resolution radar mapper such as the ESA EnVision or NASA VERITAS mission proposals will provide key insights in the divergent evolution of Venus.
The Venus Emissivity Mapper (VEM) is the first flight instrument specially designed with a sole focus
on mapping the surface of Venus using the narrow atmospheric windows around 1μm. VEM will
provide a global map of surface composition as well as redox state of the surface, providing a
comprehensive picture of surface-atmosphere interaction on Venus. In addition, continuous observation
of the thermal emission of the Venus will provide tight constraints on current day volcanic activity.
These capabilities are complemented by measurements of atmospheric water vapor abundance as well as
cloud microphysics and dynamic. Atmospheric data will allow for the accurate correction of atmospheric
interference on the surface measurements and represent highly valuable science on their own. A mission
combining VEM with a high-resolution radar mapper such as the NASA VOX or the ESA EnVision
mission proposals in a low circular orbit will provide key insights in the divergent evolution of Venus.
Based on experience gained from using the VIRTIS instrument on Venus Express to observe the surface of Venus and the new high temperature laboratory experiments, we have developed the multispectral Venus Emissivity Mapper (VEM) to study the surface of Venus. VEM imposes minimal requirements on the spacecraft and mission design and can therefore be added to any future Venus mission. Ideally, the VEM instrument will be combined with a high-resolution radar mapper to provide accurate topographic information, as it will be the case for the NASA Discovery VERITAS mission or the ESA EnVision M5 proposal.
The MErcury Radiometer and Thermal infrared Imaging Spectrometer (MERTIS) is part of the payload of the Mercury Planetary Orbiter spacecraft of the ESA-JAXA BepiColombo mission. MERTIS’s scientific goals are to infer rockforming minerals, to map surface composition, and to study surface temperature variations on Mercury. To achieve these science goals MERTIS combines a imaging spectrometer covering the wavelength range from 7-14 microns with a radiometer covering the wavelength range from 7-40 microns. MERTIS will map the whole surface of Mercury with a spatial resolution of 500m for the spectrometer channel and 2km for the radiometer channel. The MERTIS instrument had been proposed long before the NASA MESSENGER mission provided us with new insights into the innermost of the terrestrial planets. The discoveries of the MESSENGER fundamentally changed our view of Mercury. It revealed a surface that has been reshaped by volcanism over large parts of geological history. Volatile elements like sulfur have been detected with unexpectedly high abundances of up to 4%. MESSENGER imagined structures that are most likely formed by pyroclastic eruptions in recent geologic history. Among the most exciting discoveries of MESSENGER are hollows – bright irregularly shaped depressions that show sign of ongoing loss of material. Despite all this new results the MERTIS dataset remains unique and is now more important than ever. None of the instruments on the NASA MESSENGER mission covers the same spectral range or provides a measurement of the surface temperature. The MERTIS will complement the results of MESSENGER. MERTIS will for example be able to provide spatially resolved compositional information on the hollows and pyroclastic deposits – both among the most exciting discoveries by the MESSENGER mission for which the NASA mission can not provide compositional information.
The permanent cloud cover of Venus prohibits observation of the surface with traditional imaging techniques most of the visible spectral range. Venus' CO2 atmosphere is transparent in small spectral windows near 1 micron. These windows have been successfully used from ground observers, during the flyby of the Galileo mission at Jupiter and most recently by the VMC and VIRTIS instruments on the ESA VenusExpress spacecraft. Studying surface composition based on only a small number of spectral channels in a very narrow spectral range is very challenging. The task is further complicated by the fact that Venus has an average surface temperature of 460°C. Spectral signatures of minerals are affected by temperature and therefore a comparison with mineral spectra obtained at room temperature can be misleading. We report here about first laboratory measurements of Venus analog materials obtained at Venus surface temperatures. The spectral signatures show clear temperature dependence. Based on the experience gained from using the VIRTIS instrument to observe the surface of Venus combined with the high temperature laboratory experiments we have developed the concept for the Venus Emissivity Mapper (VEM). VEM is a multi-spectral mapper dedicated to the task of multi-spectral mapping the surface of Venus. VEM imposes minimal requirements on the spacecraft and mission design and can therefore added to any future Venus mission. Ideally the VEM instrument is combined with a high resolution radar mapper to provide accurate topographic data.
The Mercury Radiometer and Thermal Infrared Imaging Spectrometer MERTIS on the joint ESA-JAXA mission
BepiColombo to Mercury is combining a spectrometer using an uncooled microbolometer in a pushbroom mode with a
highly miniaturized radiometer.
A full development model of MERTIS is now available. So, after three flybys of Mercury by the MESSENGER mission
and with the Planetary Emissivity Laboratory at DLR in Berlin that can routinely obtain infrared emission spectra at high
temperatures it is a good time to review the MERTIS science requirements and the performance in perspective of our
new knowledge of Mercury.