Applications of angular and frequency correlation functions for detecting the characteristics of geophysical media at millimeter wavelengths

Correlation effects in the scattered field from rough surfaces, also known as the memory effect, has been studied extensively in recent years [Nitta and Asakura, 1991; Knotts et al., 1992; Ishimaru et al., 1994]. One example of this effect can be observed by illuminating a rough surface with laser light. A slight change in the direction of the incidence angle will cause a shift in the speckle pattern but the new speckle pattern still has many similarities to the original one. This technique has been used for discriminating the particle sizes at optical frequencies [Nitta and Asakura, 1991]. In this paper the authors present experimental studies of the angular and frequency correlation functions conducted at the millimeter-wave frequency. It is shown that the correlation functions in the specular direction are sensitive to the surface characteristics