Entropic measure of global coherence of a fluctuating field

Two descriptions of a fluctuating field, one in configuration space and the other in mode space, are shown to reveal two distinct properties of the fi eld, local coherence and global coherence. The entropic measure of global c oherence is defined and compared with the complex degree of spectral cohere nce, which is the measure of local coherence. These two measures are demons trated for the Gaussian Schell model field.