Near-field effect of extended targets on absolute calibration of microwave sensors

The near-field effect of extended target, i.e. the illuminated ground area of an active microwave sensor, is discussed. It is shown by both analysis and numerical examples that all measurements are taken in the near-field and the value of normalized backscattering coefficients are varying periodically even for a uniformly distributed scattering characteristics target while the platform altitude is increasing. In order to compensate this variation, a practical platform relocation technique is proposed