13.1 INTRODUCTION

For an operational radar, backscatter of the transmitted signal by elements of the sea surface often places severe limits on the detectability of returns from ships, aircraft and missiles, navigation buoys, and other targets sharing the radar resolution cell with the sea. These interfering signals are commonly referred to as sea clutter or sea echo. Since the sea presents a dynamic, endlessly variable face to the radar, an understanding of sea clutter will depend not only on finding suitable models to describe the surface scattering but on knowledge of the complex behavior of the sea as well. Fortunately, a close relationship between radar and oceanography has grown up in the remote-sensing community, leading to the accumulation of a large amount of useful information about scattering from the sea and how this scattering relates to oceanographic variables.

It would seem a simple matter to characterize sea clutter empirically by direct measurement of radar returns for a wide variety of both the radar and environmental parameters that appear to affect it. Parameters relating to the radar or its operating configuration, such as frequency, polarization, cell size, and grazing angle, may be specified by the experimenter, but the environmental parameters are quite another matter for two reasons. First, it has not always been clear which environmental variables are important. For example, wind speed certainly seems to affect clutter levels, but correlation of clutter with, say, ships' anemometer readings has not been entirely satisfactory. The...