HEmispheric and spectral Imaging multi-Camera System (HELICS)

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Within the framework of the DFG Major Instrumentation Initiative „HALO-Instruments – the Expansion of the Scientific Instrumentation of the High Altitude and Long Range Research Aircraft HALO“, a novel camera system entitled "HEmispheric and spectraL Imaging multi-Camera System (HELICS)" is proposed to be developed and installed in the HALO Large Wing Pods (HLWPs). The current angular-resolving radiation instrumentation on HALO comprises devices to measure upward spectral radiance in the solar and thermal-infrared wavelength ranges with sensors that have a limited field of view (FOV). With HELICS it is planned to measure the instantaneous, two-dimensional (2-D) upward multispectral atmospheric radiance field over the entire lower hemisphere, which allows to explore the solar radiative energy budget of atmospheric and surface layers and to improve remote sensing. The technical requirements of HELICS are derived from the demand of complementing the current HALO instrumentation by a wide-FOV spectral radiance measurement system capable of observing a scene from different viewing directions. This follows the vision of upcoming satellite missions such as the EUMETSAT Multi-Viewing Multi-Channel Multi-Polarisation Imaging (3MI) instrument planned to be on board of the Meteorological Operational Satellite (MetOp) Second Generation series (launched in early 2024) and LIBERA, a continuation of the Clouds and the Earth's Radiant Energy System (CERES), with an expected launch in 2026. HELICS will consist of a set of visible (VIS) and short-wave infrared (SWIR) cameras equipped with fisheye wide-angle optics each tailored to one wavelength band to make use of the full spatial resolution of the camera sensors (about 1 MegaPixel). The full system will be self-made, consisting of commercially available and custom-made components that need to be adapted to special environmental conditions (low ambient pressure and temperature). HELICS will provide angular-resolved spectral radiance data that will be used for various applications, e.g., to investigate the radiative energy budget, and to improve and validate remote sensing methods to retrieve cloud, aerosol, and surface properties as planned for 3MI as well as to evaluate the radiance to irradiance conversion that is required to quantify the Earth's radiation budget from satellite-based observations (LIBERA). As a first application, the system is planned to be part of the still to be defined follow-up mission of HALO-(AC)³ that will study Arctic cloud and surface properties during the transition phase from polar night to polar day tentatively proposed for 2028.