|
Automated aids for SAR image interpretation are required to address both the 'data deluge' problem in surveillance applications and the 'cockpit load' problem in targeting applications. With resolutions becoming comparable to the radar wavelength, the interactions of scattering events on hard targets result in a signal which is very difficult to interpret especially simply on the basis of the signal amplitude. For this reason, there has been a significant move towards complex image analysis, spearheaded by Rihaczek [Rihaczek and Hershkowitz, Radar Resolution and Complex-Image Analysis, Artech House, 1996], who has presented strong evidence to suggest that use of the image phase is the key to understanding the complicated scatterer interactions and is hence the key to target recognition. He has introduced a 'two-scatterer algorithm' which attempts to unravel the complex signal to determine the presence of two closely spaced scatterers. He also hypothesises that the approach may be extended to multiple scatterers. In this paper, an alternative to the 'two-scatterer algorithm' of Rihaczek has been introduced which is based on a statistical model and a fitting procedure. This has allowed a theoretical analysis of the errors in estimation of scatterer parameters to be performed thus leading to an alternative definition of resolution which is applicable to complex image analysis. The new definition overcomes the inability of the traditional definition of resolution to describe the varying degree to which equidistant in-phase and out-of-phase scatterers can be distinguished. The resolution limits appear naturally from this error analysis as the result of the errors increasing rapidly as the two scatterers approach each other. A generalisation to multiple scatterers arises naturally from the formulation which offers the prospect of significantly extending the applicability of complex image analysis to the understanding of scattering from hard targets.
|
