THERMAP: a mid-infrared spectro-imager for space missions to small bodies in the inner solar system

We present THERMAP, a mid-infrared (8-16 μm) spectro-imager for space missions to small bodies in the inner solar system, developed in the framework of the MarcoPolo-R asteroid sample return mission. THERMAP is very well suited to characterize the surface thermal environment of a NEO and to map its surface composition. The instrument has two channels, one for imaging and one for spectroscopy: it is both a thermal camera with full 2D imaging capabilities and a slit spectrometer. THERMAP takes advantage of the recent technological developments of uncooled microbolometers detectors, sensitive in the mid-infrared spectral range. THERMAP can acquire thermal images (8-18 μm) of the surface and perform absolute temperature measurements with a precision better than 3.5 K above 200 K. THERMAP can acquire mid-infrared spectra (8-16 μm) of the surface with a spectral resolution Δλ of 0.3 μm. For surface temperatures above 350 K, spectra have a signal-to-noise ratio >60 in the spectral range 9-13 μm where most emission features occur

Experimental study of an uncooled microbolometer array for thermal mapping and spectroscopy of asteroids

International audienceWe report on the experimental study of the imaging and spectroscopic capabilities of an uncooled microbolometer array for space missions to small bodies in the inner solar system. The selected Nano640E (T M) device manufactured by the ULIS company (Grenoble, France) has a format of 640x480 pixels and can measure temperatures down to at least 255 K, the lower limit reached in our tests. It has a Noise Equivalent Temperature Difference (NETD) of 40.9 +/- 4.5 mK (300 K, F/0.86) and the capability to produce excellent, radiometrically calibrated images with an error of the order of 1 to 5 K depending upon the number of calibration sources. Using a set of neutral density filters, we determined the signal-to-noise ratio (SNR) of a spectrum acquired by the detector, as a function of the scene temperature, wavelength and spectral resolution. Considering an asteroid at 1 AU from the Sun, an optical system at F/0.86, a spectral resolution of 0.3 mu m and a scene temperature of \textgreater 350 K, the resulting spectrum has sufficient SNR to properly identify the main mineralogical emission features. Our results show that uncooled microbolometer arrays are very promising to acquire calibrated thermal images and mid-infrared (8-14 mu m) spectra of the surface of small bodies in the inner solar system

THERMAP: a mid-infrared spectro-imager based on an uncooled micro-bolometer for space missions to small bodies of the solar system

We report on the feasibility study of a mid-infrared (8-18 µm) spectro-imager called THERMAP, based on an uncooled micro-bolometer detector array. Due to the recent technological development of these detectors, which have undergone significant improvements in the last decade, we wanted to test their performances for the Marco Polo R ESA Cosmic Vision mission. In this study, we demonstrate that the new generation of uncooled micro-bolometer detectors has all the imaging and spectroscopic capabilities to fulfill the scientific objectives of this mission. In order to test the imaging capabilities of the detector, we set up an experiment based on a 640x480 ULIS micro-bolometer array, a germanium objective and a black body. Using the results of this experiment, we show that calibrated radiometric images can be obtained down to at least 255 K (lower limit of our experiment), and that two calibration points are sufficient to determine the absolute scene temperature with an accuracy better than 1.5 K. Adding flux attenuating neutral density mid-infrared filters (transmittance: 50%, 10%, 1%) to our experiment, we were able to evaluate the spectroscopic performances of the detector. Our results show that we can perform spectroscopic measurements in the wavelength range 8-16 µm with a spectral resolution of R~40-80 for a scene temperature <300 K, the typical surface temperature of a Near Earth Asteroid at 1 AU from the Sun. The mid-infrared spectro-imager THERMAP, based on the above detector, is therefore well suited for the Marco Polo R mission