The van Cittert-Zernike (VCZ) theorem and its Fourier inversion enable two and three-dimensional (3-D) images of human subjects to be obtained from cross-correlations of electric fields (arising from the subject radiometric emission) measured at distributed locations. Inverted two and 3-D images in video and still format generated by this technique using experimental data in the millimetre wave band demonstrate the feasibility of the technique. Simulations for portal security screening of subjects indicate how a 3-D millimetre wave image of a person appears as surface in 3-D space, which is what the electromagnetic properties of clothing and the human body predicts. Problems and potential solutions associated with Fourier inversion techniques applied to sources with physical extents greater than the Fresnel scale (root of range wavelength product) will be presented and discussed.
Background to the VCZ theorem is that it was discovered in the 1930’s and is a spatial Fourier transform relationship between the cross-correlations of electric fields at two arbitrary locations in space and the three dimensional continuum of spatially incoherent radiators which generate these fields. The theorem is the classical formal description of passive (Planck) radiometric emission. The theorem remained in obscurity till radio astronomers realised in the 1960’s it was a route to generating high resolution 2D images of astrophysical sources; today it generates the highest resolution images of these sources. Interests in portal security screening grew when it was realised it was a means to generating 3-D images of persons in a band where clothing was semi-transparent.