New optical package and algorithms for the accurate cloud cover estimation for short wave parameterization. Mikhail Krinitskiy, Alexey Sinitsyn, Sergey Gulev P.P.Shirshov Institute of Oceanology, RAS, SAIL, Moscow, Russia

The problem Short-wave parameterization by cloud cover (Alexey Sinitsyn, since 2004) – Cloud cover estimation using handy optical fish-eye camera sky images with the set of most common cloud cover estimation algorithms The package for automatic cloud cover estimation using fish-eye optical module operated by PC. + new algorithm for automatic cloud cover estimation We present now: 2 / 12

Optical package. Previous revision. - Nikon D80 10MPx - Sigma 8mm F3,5 Circular-Fisheye - View angle 180 ° х 120 ° - Projection of fisheye lens: equidistant projection - Manual shooting PROBLEMS to solve: Image resolution: 3872x2592 px -Cuts 20% of image -Requires operator assistance 3 / 12

Optical package. New revision. Lab viewMounted assembly CONTAINS: -Connected to the PC, monitoring the position and managing shooting process -No operator assistance required -Mini-computer with positioning sensors (GPS, accelerometer and others) -Hi-res. fish-eye camera 4 / 12

Optical package. New revision. SKY IMAGES: over shots in 9 days x 1920px -24-bit RGB -180  x180  view angle Observations: North Atlantic / 12

Optical package. New revision. SOFTWARE collecting sensors data communicating with the PC communicating with the outdoor set (computer & camera) monitoring positioning and managing shooting process processing sky images Outdoor part mini- computer firmware Windows-based PC software 6 / 12

Processing images: the algorithm Most common processing schemes Si = (R-B)/(R+B) ( Yamashita, Yoshimura, Nakashizuka, 2004 ) Si = R/B ( LONG and DELUISI, 1998 ) then threshold using fixed value Si m PROBLEMS to solve: -Sun disk counted as cloudy area -Cloud cover systematic underestimation (up to 2-3 Octas) -Strong thresholding value dependency of the result 7 / 12

GrIx y, px x, px Processing images: the algorithm Our improved scheme: Grayness rate Index Independent of Y Depends (negatively) only of color saturation. Highly sensitive to every gray colors (white, gray or black) 8 / 12 Cloud cover systematic underestimation – solved ( caught thin clouds ) R,G,B – color components Y – brightness of pixel

Processing images: the algorithm Our improved scheme: Sunburn effect suppression GrIx x, px source field sunburn suppressed Sun disk as cloudy area - solved Thresholding value dependency of the result - solved 9 / 12

Processing images: the algorithm Our improved scheme: SOME RESULTS yr. campaign 2010yr. campaign Cloud cover estimation (Grayness Index - based with sunburn effect suppression) Deviation of human-observed values / 12

Processing images: the algorithm Our improved scheme: SOME RESULTS Cloud cover = 31%Cloud cover = 13% Source sky image Common schemes result Our algorithm result Visual observed cloud cover: 3 (of 10) – 30% 11 / 12 AND EVEN MORE!

One more thing Lower clouds margin height: basics L L = 17,162 m H 12 / 12