Test of MODIS-type Cloud Mask Algorithm in Comparison with Collocated Observations by infrared-thermograph on Ground

概要

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In order to search for the end of energy spectrum of ultrahigh-energy cosmic rays (UHECR), the JEM-EUSO (Japanese Experimental Module - Extreme Universe Space Observatory) project is under preparation. In this project, atmospheric fluorescence light from the trajectory of the extensive air shower (EAS) produced by UHECR is planned to be measured by photosensors placed at the focal surface of a telescope (the fluorescence technique) on the International Space Station (ISS) and hence cloud information along the trajectory of the JEM-EUSO field of view is required. To select cloud-free pixels with about 1km spatial resolution, measurement of the brightness temperature in the infrared window region is under preparation. In this report we apply the MODIS (Moderate resolution Imaging Spectroradiometer)-type cloud mask algorithm to individual sky scenes and assign a confidence level of clear-sky between 1 and 0 to a pixel of about 1km×1km area above Fukui University of Technology (FUT), Fukui, Japan. By comparing the sky conditions observed by the infrared-thermograph (IRT) at FUT at the same time with a similar field of view, we examine to what fraction of cloud in 1km-spatial resolution, the clear-sky confidence level assigned using the MODIS-type cloud mask algorithm, is applicable.