Image speckle contrast reduction resulting from integrative synthetic aperture imaging

Reduction of image speckle noise with the use of an integrative synthetic aperture imaging technique is studied. It is found that the Fourier inversion of the mutual intensity estimate [Appl. Opt. 30, 206-213 (1991)] yields an image intensity that corresponds exactly to the illumination of the object with partially coherent light from source optics imaging a delta-function incoherent source. An expression for the signal-to-noise ratio at an image point is derived for a large rough object with delta-function correlated amplitude reflection. A synthetic aperture system receiver of sufficiently small diameter yields image speckle with a signal-to-noise ratio (SNR) equal to 1. When the receiver and the transmitter diameters are equal, the SNR is 2 for linearly polarized speckle. The SNR continues to increase with receiver size and is linear in the diameter for large receiver-to-transmitter diameter ratios.