DISTRIBUTION OF BACKSCATTERED INTENSITY IN THE DISTORTED BORN APPROXIMATION - APPLICATION TO C-BAND SAR IMAGES OF WOODLAND

The intensity distribution in synthetic aperture radar (SAR) images of woodland is known to depend upon imaging conditions. Whilst phenomeno logical models can be used to match observed backscatter distributions , a physical model is needed to explain their origins. Images of woodl and obtained during airborne SAR trials are analysed and shown to exhi bit non-exponential intensity distributions. Expressions are derived f or the moments of the intensity distribution using discrete scattering models based on the Born and distorted Born approximations. The predi ctions of the Born approximation are such that, at all but extremely h igh resolutions, the intensity statistics reflect only fluctuations in the number of discrete scatterers in resolution cells. In the distort ed Born approximation it is revealed that, even at modest resolutions, fluctuations in both number and cross section of objects can influenc e intensity distributions. This is shown to be a direct consequence of the incorporation of attenuation effects in the distorted Born model. The theory is applied to scattering from a model woodland canopy and shown to yield intensity moments in close agreement with observations. The consequences of the model for other scattering situations are dis cussed.