Innovative technologies for a new generation of small satellites: New concept of a thermal infrared

Abstract

The continuous development of Earth Observation technologies has paved the way to a wide range of science and civil applications which have changed and improved our lives in many ways. Nowadays VIS, IR, SWIR and SAR payloads ensure the production of images/data characterized by very high geometrical and spectral standard even when coupled with Small Satellite S/C (<200 kg); differently, in the past 20 years only few improvements have been done in technologies and performance related to TIR optical sensors. The main technical obstacles were related to the necessity to cool down the TIR detector up to cryogenic temperature, thermal noise management, optical and mechanical complexity and reliability: these are critical issues, in contrast with small satellites' performance and budgets. ELISIR (Enhanced Leap-frog Imaging Stationary Interferometer in the InfraRed spectral Range) is a Fourier Transform Spectrometer designed by SITAEL for optical observations in the TIR region of the electromagnetic spectrum. The advanced technology onboard the instrument make it able to overcome the difficulties listed above and fill the observational gap highlighted by previous TIR instruments. ELISIR could be able to collect more than 40 spectral bands with a resolution from 120nm up to 400nm over the 8μm to 14μm wavelength range (the atmospheric window), and assuring 40m of spatial resolution. The high number of spectral bands and across-track pixels allow to classify ELISIR as a hyperspectral imaging sensor. With more bands available, a hyperspectral imager can have wider spectrum of applications and be useful to both the civilian and scientific communities. Given current trends in population growth and climate change, accurate monitoring of the Earth's greenhouse gases, freshwater resources, sea, land and atmosphere pollutants at field-to-global scales become increasingly critical. The emitted energy from the exposed terrestrial surface of the Earth can be also uniquely helpful in identifying rocks, minerals, and soils and in monitoring transient thermal phenomena crucial in premonitory clues of impending volcanoes eruptions. TIR imaging can provide accurate estimates of consumptive water use at the spatial scale of human management and time scale of vegetation growth. Three priority main families of TIR-related user products have been identified: Land surface temperature; Spectral emissivity; Sea surface temperature. The ELISIR compliance to the small-satellite platform is guaranteed by the adoption of design and development criteria as well as by the selected sensor configuration. The triangular Sagnac layout makes the sensor robust against mechanical and thermal stresses, vibrations and shocks while the absence of moving parts prevents any lens misalignments. Moreover the microbolometer technology does not require an active cooling system in favor of a lower power consumption. The result is a compact (670 × 400 × 150 mm3), low-mass (<20 kg), low-power (<50 W) payload. This TIR Payload is supposed to fly within next 3 years on SITAEL Minisatellite platform S-200.