User Manual - pancroma

52. Haze Reduction – Haze Optimized Transform Method________________________________________________________________The previous section discussed atmospheric physics and the Dark Area methodfor haze reduction. This Section discusses an alternative method called theHaze Optimization Transform (HOT). The HOT method was developed byZhang and others from the Canadian Center for Remote Sensing. It is based onthe premise that in clear images, the digital numbers (DNs) of the pixels in all theband files are different but highly correlated. As explained in the previous article,the blue band generally exhibits more scattering due to atmospheric haze thanthe other bands. The presence of haze decreases the correlation between theblue band and the red band, which is much less affected by haze.Zhang proposed the following: First, prepare a scatter plot of the DNs of the blueband and the DNs of the red band. Determine the best-fit line through the scatterplot using linear regression. Highly correlated pixels will tend to fall on the line.Those altered by light scattering will tend to be less correlated and will fall of theline. Zhang proposed determining the HOT number for each pixel as theperpendicular (or orthogonal) distance from the HOT line. The HOT number canthen be used to remove the haze component of each band.HOT= DN blue sinθ – DN red cosθThe concept is depicted in the diagram below.The PANCROMA TM HOT utility is a three-file method like the Dark Area method.To use it, open your three band files in the order blue, green and red by selecting145