A subrefractive fading model for microwave paths using surface synoptic meteorological data

A meteorological-based model of the subrefractive fading mechanism is developed. A previous investigation supplied refractive index gradients along a test path at various times during subrefractive fading events. The lowest (worst) signal levels corresponded to linear subrefractive gradients. These linear gradients can be considered using the relative ray curvature between the ray and the earth\´s surface, and are described simply by a parameter . Using a basic model of the meteorological process causing this subrefraction, a lower bound on can be estimated. Examples of this estimation procedure are given and compared with minimum values derived from microwave fading. A method of using these minimum values to derive subrefraction statistics is the subject of a companion paper.