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

Abstract

We 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 μm and a scene temperature of >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 μm) spectra of the surface of small bodies in the inner solar system.