A new look at the slope correction for SAR radiometric calibration

The average SAR image power of a distributed target scene is essentially a map of radar brightness, i.e. the average radar cross section per unit image area. The latter needs to be converted to backscattering coefficient, i.e. average radar cross section per unit ground area, in order to satisfy the user community. In this paper, the authors give an exact formulation of the required surface slope correction and show that two other formulations found in the literature are only approximations. It does, however, agree with the slope correction derived from SAR interferometry. The author proposes that the slope correction is expressed as sin/spl theta//sub i/, where /spl theta//sub i/ is (not the local incidence angle) the angle between the surface normal and its projection on the image plane. The correction factor thus remains compatible with literature by redefining the angle /spl theta//sub i/.