HOLOGRAPHIC SAR IMAGE-FORMATION BY COHERENT SUMMATION OF IMPULSE-RESPONSE DERIVATIVES

Based on the physical optics approximation, the radar image of a targe t can be made up from a knowledge of the monostatic backscattered fiel d or hologram for all frequencies and all aspects angles. The target i mage is the two-dimensional Fourier transform of the hologram. This is based on the same principle as conventional holography. In the near f ield the image is computed by the coherent summation of back-projected range responses which are derived from complex impulse responses. Con sequently, the image can be interpreted as a tomographic reconstructio n. If the target is within the antenna beam at each radar position in the linear SAR geometry, then the algorithm of the coherent summation of impulse response derivatives (IRD's) can be applied. Experimental r esults in the near field of a wheat field and a Peugeot 504 automobile are presented to verify the effectiveness of our method.