EUV-PHOKA - multi-channel monitor for measurements of transmittance of solar EUV-emission in the thermosphere

EUV-Phoka is intended to record solar soft X-ray and EUV radiation (1 - 130 nm) in six spectral windows. Each channel includes a silicon photodiode AXUV-100 with a collimator and an appropriate spectral filter, a preamplifier and a voltage-to-frequency converter. The precession of the measurement by the diode is better than 1%, and the absolute accuracy is about 10 %. - In addition, there is a channel to record the visual light. EUV-Phoka will be installed onboard the 'PHOTON' satellite, which is oriented to the Sun. Occultation measurements will provide a data base to derive parameters such as neutral temperature and density profiles for theoretical and empirical modeling of the thermosphere and ionosphere in the altitude range from 100 to 450 km. During the last years many space experiments such as the YOHKOH, CORONAS-1 and SOHO missions collected solar XUV/EUV data with high spatial and spectral resolutions whereas the primary goal of EUV-Phoka is defined to determin e the spectral irradiance from the total solar disk within the broadest wavelength range by the group of PHOTON experiments.