The analysis of synthetic aperture radar (SAR) migration developed by Gilmore has been refined within the context of the inverse scattering problem, particularly the distorted-wave Born approximation (DWBA). The SAR migration algorithm can be deduced from the DWBA-based inversion formulation when the following assumptions are satisfied: 1) homogeneous and nonfrequency-dependent background medium; 2) the exploding source model; and 3) the well-resolved targets described by an orthogonal relation derived in this paper. In addition, the other contributions of this paper are as follows: 1) The removal of the ¿2term has been clarified by the derived orthogonal relation; 2) a scale factor that balances the near-far field has been derived; and 3) a novel SAR migration algorithm for the imaging of targets embedded in a layered medium has been proposed.

A novel real-time through-wall imaging (TWI) algorithm with autofocusing ability in the presence of wall ambiguities is proposed in this paper. The spectrum Green's function is employed to formulate the TWI algorithm, where the fast Fourier transform can be used to reconstruct the image in a very short computation time. The complex scattering process due to the presence of the wall is automatically included in the imaging formulation through the multilayer Green's function. The autofocusing is achieved by introducing a time factor in the TWI formulation to get a dynamic image at different focusing time. The image at the time instant when the defined entropy is minimized is stored as the output of the TWI result. Simulation results show that the proposed method can provide high-quality focused image in a short computation time regardless of the estimated value of the wall parameters.

The closed-form solution to the reconstruction of radiating current with a line measurement configuration is presented in this paper. The analytical result of the continuous singular value decomposition of the scattering integral operator is derived and used to analyze the imaging resolution and reconstruct the radiating component of the equivalent current density. The main four advantages of the proposed closed-form solution are as follows: 1) The reconstruction of radiating current can be achieved in a very short computation time; 2) it is quite tolerant to different levels of noises; 3) it is very easy to realize the reconstruction of radiating currents within the obstacles embedded in layered medium; and 4) the imaging resolution kernel of the scattering operator can also be derived in a closed form. Numerical simulations show the high efficiency of the proposed method for the reconstruction of radiating current.

In this paper, two new approaches are presented for the solution of electromagnetic inverse scattering problems when amplitude-only data are available. The proposed techniques are based on a customized version, which are the so-called contrast source inversion (CSI) and multiplicative regularized CSI (MRCSI) methods. In the proposed approaches, denoted as the phaseless-data (PD)-CSI and the PD-MRCSI, only the term of the cost functional concerning the mismatch between the measured and estimated field data (i.e., the data equation) has been properly redefined. Moreover, the back-projection algorithm has been modified to provide an initial solution ensuring the rapid convergence of the optimization procedures and avoid the reconstruction of false solutions. A set of representative results concerning numerical as well as experimental tests is reported to show the accuracy of the proposed amplitude-only reconstruction approaches.

Inspired by the successes of the distorted Born iterative method with full data (FD-DBIM) in the electromagnetic inverse scattering problem when the weak scattering approximation breaks down, the distorted Rytov iterative method with phaseless data (PD-DRIM) for the reconstruction of an unknown object embedded in 2-D homogeneous space is proposed when only the intensity data of the total wavefield are available. Similar to FD-DBIM, the PD-DRIM algorithm can also provide the Fre acutechet derivative and the guess solution for the iterative method naturally by updating the Green's function in every iteration step. The validation of the proposed approach is justified by the experimental tests where the scattering data are kindly provided by the Institute Fresnel in Marseille (2005).

The effects of ionospheric irregularities on spaceborne synthetic aperture radar (SAR) signal propagation with double path and multilook angle are studied in a model in which a two-frequency and two-position coherence function (TFTPCF) has been adopted for analysis. The TFTPCF is derived from the phase-screen principle. The ambiguity function based on TFTPCF has been used to analyze the effects of ionospheric turbulence on range resolution and cross resolution. The results show that, in some cases, the effects from the irregularities on SAR imaging can be very serious