====== All Sky Imager (ASI) ======
//Mentor: [[http://www.geomet.uni-koeln.de/en/the-institute/rg-crewell/staff-crewell/schween/|J.H. Schween]]//

===== Principle =====

We use an commercially available fish-eye surveillance camera to collect images of the sky and determine cloud amount. The camera is an [[http://www.axis.com|AXIS]] [[http://www.axis.com/global/en/products/axis-m3027-pve/| M3027-PVE Fixed Dome Network Camera]] with a common [[http://www.ovt.com/uploads/parts/OV5653.pdf|Omnivision CMOS rgb-sensor]]. Images with a resolution of 800x600 pixels (BMP format) are taken every 20sec. Every pixel above the horizon is investigated for its blue-to-red-ratio and categorized as sky (blue), thin-cloud (light-blue) or cloud (white or gray). Pixels are counted and stored as relative cloud amount as well as palette based png images. From the number of satured pixels around the sun a flag for the visibility of the sun is derived. 

The camera replaced a [[instruments:tsi:yes-tsi|YES total sky imager]] which died after some years of operation.