Application of Two-Dimensional Spectral Analysis to the Quantification of Satellite Cloud Photographs

Abstract

Pictures from TIROS have revealed that cumuliform clouds over the ocean quite often occur in the form of a complex pattern with lines and cells of horizontal dimensions in the range of 20 to 100 miles and with various orientations seemingly superimposed. Gross features of these patterns such as the horizontal dimensions and orientation which are predominant over particular areas should prove very useful as indicators of the prevailing meteorological conditions. A two-dimensional extension of the familiar power spectrum analysis has been applied to the TIROS photographs. The object of the analysis is to identify and quantify the statistically preferred dimensions and orientations of the cloud patterns. Digital data are derived from the photographs by adopting a simple 5-level gray scale of cloud brightness. A Monte Carlo technique has yielded estimates of the reliability of the statistical analysis. Results from these analyses have revealed patterns which tended to be obscured by the more dominant features in addition to cloud patterns which were obvious in the original picture. The method clearly enables one to distinguish different types of cloud patterns and offers a quantification of the pictures which should aid in the interpretation and utilization of the TIROS photographs.