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Ø Spatial and Temporal coherence
Spatial coherence is a concept of wave disturbance describing the correlation between periodic transmitted energy (wave signals) from one point to another,it can also be said that it is a mutual interdependence or connection of variable wave quantities of two different points a in a given instant of time,the coherence is presented as a function of distance; the function of correlation against an the absolute distance between points in question.While spatial coherence is concerned with the phase correlation of waves in different observation points, temporal coherence is coherence is entails the phase correlation of waves at a given point in space at two different instances of time.