BRIGHT TARGETS IN THE COASTAL ZONE: A TOMOGRAPHIC RECONSTRUCTION APPROACH APPLIED TO ENVISAT RA-2 DATA

摘要: Usage and availability of Sea Surface Height (SSH) information from satellite radar altimeters undergo known limitations in the coastal zone, where such data are of great importance and usefulness. In fact, coastal regions are a crucial zone to be investigated and monitored, due to the high impact of sea level and circulation changes on the environmental security and the related economic and societal aspects. It is known that radar returns from the sea surface sometimes present target-like echoes (“bright targets”), especially in correspondence of particular features of the coastal zone, thus entailing a potential interference with SSH measurements. In the recent literature, the hyperbolic patterns in the radargram domain generated by such spiky echoes have been tentatively explained as resulting from flat water areas in the proximity of the coastline, but the physical mechanism which underlies their occurrence was still unclear. This work describes the experimentation of a microwave tomographic reconstruction approach applied to Envisat RA-2 waveforms, tested on selected passes over the Pianosa Island, with the aim of identifying the signal contamination sources in terms of their location and extent. The obtained results encourage the idea that the origin of such signatures is associated with particular conditions of the sea surface, which are easier to be found in the proximity of coastal closed areas such as gulfs, but presumably not limited to such circumstances.The tomographic reconstruction technique falls within the inverse scattering approaches [Colton and Kress, 1992], where the unknown is a contrast function, which identifies the target as …