Abstract: A passive detection and imaging system employs interferometric and synthetic aperture techniques. A moving platform employs a pair of sensors which receive thermal electromagnetic radiations from an area of interest. The received signals are narrow band filtered by a bank of filters covering an extended bandwidth. Signals from similar narrow bands from different sensors are correlated. The plurality of frequencies and plurality of positions relative to the area of interest due to the platform motion enable generation of an inverse Fourier transform image which is resolvable in both azimuth and range. Separate preferred embodiments operating at microwave frequencies and optical frequencies are disclosed. An achromatic optical interferometric correlation technique is also disclosed.