THE UNIFYING ROLE OF THE COARRAY IN APERTURE SYNTHESIS FOR COHERENT AND INCOHERENT IMAGING

Systems of 2-dimensional imaging arrays and apertures are considered from the point of view of their performance in the imaging of spatially incoherent as well as coherent source distributions. Such systems find applications in radar, sonar, and ultrasound imaging, as well as in applications such as seismology and radio astronomy. For the linear imaging techniques related to beamforming, and based on the Fourier transform relationship between the source distribution and the aperture plane measurements, the point spread function of the system completely characterizes its performance. This function is determined by the geometry of the physical aperture or array as well as the weighting which can be applied to measurements. We show that the introduction of the concept of the coarray, both for receive apertures in incoherent imaging and for transmit/receive systems in reflection mode coherent imaging, provides a convenient and elegant framework within which many apparently isolated techniques for point-spread function or aperture synthesis can be understood. In addition to this unifying role of the coarray for diverse techniques and for both modes of image formation, the coarray concept gives new insight into the aperture synthesis process, which allows interesting new imaging techniques to be developed, especially in coherent imaging. © 1990 IEEE