Spectral and radiometric requirements for the airborne thermal imaging spectrometer ARES

ARES (Airborne Reflective/Emissive Spectrometer) is an airborne imaging spectrometer for remote sensing of land surfaces covering the wavelength regions 0.45–2.45 µm and 8–13 µm with 160 channels. The instrument is being built by Integrated Spectronics, financed by DLR and GFZ, and will be available to the scientific community from 2005 on. This contribution presents the design of the thermal spectrometer covering the 8–13 µm region with 32 channels of 150 nm bandwidth while a separate paper treats the instrument specifications in the solar reflective region. The spectro‐radiometric design is based on scientific requirements derived from application scenarios comprising vegetation, soils of different compositions, and mineral exploration. The corresponding emissivity spectra are input for a simulation model that calculates at‐sensor radiance spectra, resamples them with the channel‐specific response functions, adds different amounts of sensor noise to the signal, and performs a retrieval to get the corresponding noisy surface emissivity spectra. The results of the simulation study indicate that a spectral wavelength accuracy of 3 nm and a sensor noise equivalent temperature of 0.05–0.1 K are required for an accurate retrieval of emissivity spectra.