Use of a simple pattern recognition approach for the detection of ridge lines and stripes

Abstract

Patterns often sought in meteorological fields are ridge lines or narrow zones of relatively high or low values (e.g. stripes or bands in satellite imagery). A method for the automatic detection of such features is presented, using input fields given on regular grids. The fundamental idea is that a grid point is a plausible position for a significant line where not more than two (out of eight) neighbours exhibit better suitability to lie on that very line. Locations with three or more superior neighbours are considered unsuitable, or at least less qualified, for representing positions of the line. This criterion derives from the concept that a significant line passing through a point normally enters the latter from one of the adjacent points and leaves through another neighbour, with these two special neighbours permissibly having superior values of the appropriate test variable. It is empirically demonstrated for selected applications within the field of air mass analysis (including objective front positioning on the basis of numerical model output) that the identification of points satisfying the formulated ‘2-out-of-8’ criterion is, when linked with simple post-processing steps, sufficient to accomplish a good recognition of the sought patterns.