Microwave Imaging

CHAPTER FIVE

Qualitative Reconstruction Methods

5.1 INTRODUCTION

In the scientific literature the term qualitative is used to denote essentially two families of reconstruction methods. In the first case it refers to approaches aimed at obtaining only some information about the scatterers under test. Such methods are generally unable to retrieve the distributions of the unknown electromagnetic parameters (e.g., dielectric permittivity, electric conductivity, magnetic permeability), but they provide information concerning only the shapes and locations of the scatterers.

In the second case, the same term is used to indicate the reconstruction methods that are based on certain approximations in scattering models (e.g., those based on Born- and Rytov-type approximations) and can then be successfully applied only if some a priori information on the unknown object is available and if the inspected objects fulfill the conditions making the approximate models valid. For example, in order to apply the Born approximation, one needs to know that the object is a weak scatterer, as discussed in detail in Chapter 4.

Despite their limited applicability, qualitative methods are of significant interest for their computational efficiency, enabling fast and robust reconstructions possible in a quite short time period. Such considerations suggest a classification of microwave imaging algorithms into two groups, namely, quantitative and qualitative methods, in order to distinguish qualitative approaches ...