TABLE OF CONTENTS 'Blow, bugle, blow, set the wild echoes flying. Blow bugle: answer, echoes, dying, dying, dying.'
Tennyson
Previous chapters considered point targets - so physically small that only single pairs of direct and indirect rays exist, giving definite multipath structures within the interference region. Point targets also usually have well-defined and broad (often omnidirectional) spatial target pattern maps (TPM) or radiation patterns, so their RCS does not vary much as they tilt. Although sea-waves may modulate their multipath factor, received signal is reasonably steady. In this chapter we consider how multipath affects vertically extended targets, such as ships and coastlines, whose structure extends over a wide height bracket. We shall frequently recall principles established in Chapters 5 and 6. Atmospheric and precipitation attenuations do not affect the arguments deployed in this chapter and will be ignored. We defer target roll to Chapter 10, which examines RCS values.
Vertically extended targets contain many scatterers or individual elements which combine to reflect through a height bracket extending from the waterline up to the target tip, at height j metres. This configuration introduces apparent complications which in the end turn out to allow simplification: (a) one element of the target may be in the interference region while a lower element is in the diffraction region; (b) direct and indirect rays striking low elements have different phases and amplitudes from rays hitting high elements. The element reflections combine to form the echo received at the scanner, so we cannot...
