Image reconstruction from Ipswich data. III

For pt.II see ibid., vol.39, p.29-32 (1997). We describe results obtained in image reconstruction using the Ipswich data sets IPS009-IPS012. In van den Berg et al. (1995, 1997) and van den Berg and Kleinman (1996), we employed versions of the modified gradient method to reconstruct the shape, location, and index of refraction of known and unknown scatterers, both dielectric and perfectly conducting, from the measured scattered field data contained in IPS001-IPS008. In the present paper, we employ a new inversion method, the contrast source inversion (CSI) method, for the reconstructions. We include here a brief description of the method, given in greater detail in van den Berg and Kleinman. In the case of the new Ipswich experiments, we have 36 angles of incidence, equidistantly distributed around the object. The unknown scatterer is assumed to be located somewhere in a known, bounded, test domain D (taken to be square), and the scattered field is measured on a domain S (taken to be a circle) containing the test domain D in its interior. In the case of the Ipswich experiments, S was taken to be in the far zone of the scattered field, and measurements were made at 18 angles of observation, equidistantly distributed over a semicircle. For each experiment, this semicircle started with the forward-scattering angle.