procedure of the absolute calibration of radar scatterometer is presented. Effects of the far field criterion for the calibration are analyzed. After converting the effect of curvature of spherical wavefront and the amplitude and phase nonuniformity of the incident field to the variation of the radar cross section
the concept of effective radar cross section (ERCS) is introduced to unify the calibration formula for near field region and far field region measurement
Using the new formula
a practical near field region absolute calibration scheme is proposed. Absolute calibrations of four scatterometers of S
C
X and Ku band show the validity of the given method.