Differential optical synthetic aperture radar

An imaging method from a moving platform, comprising:

• illuminating an object with an electromagnetic radiation source from an aperture of size d,
• collecting for a plurality of platform positions, a reflected radiation from the object by a first and a second sub-aperture, each sub-aperture having a predetermined width of about d/2,
• measuring a plurality of differential phases for each of the plurality of platform positions that includes, optically splitting the collected radiation by the first sub-aperture into a first and a second optical beam and optically splitting the collected radiation by the second sub-aperture into a third and a fourth optical beam,
• directing the first and the second optical beams onto a first quadrature receiver and directing the third and the fourth optical beams onto a second quadrature receiver,
• generating a pair of common in-phase (I) local oscillator reference beams and a pair of common quadrature (Q) local oscillator reference beams such that the (I) beams are directed to operationally heterodyne with the first and the third optical beams and the (Q) beams are directed to operationally heterodyne with the second and the fourth optical beams respectively,
• processing the heterodyne signals to produce a first measured phase φmj and a second measured phase φmj+1 with respect to the common local oscillator such that a phase differential φmj+1−φmj between the sub-apertures is capable of being produced,
• calculating a plurality of resultant (N) phases by summing the phase differentials at each of the platform positions according to [φj+1=φj+(φmj+1−φmj)];
• and
• processing the resultant (N) phases to produce an image having a spatial resolution corresponding to a synthetic aperture of length of about Nd/4.