Understanding target-like signals in coastal altimetry: experimentation of a tomographic imaging technique

Usage and availability of Sea Surface Height (SSH)information from satellite radar altimeters undergo knownlimitations in the coastal zone, where such data are of greatimportance and usefulness. In fact, coastal regions are a crucialzone to be investigated and monitored, due to the highimpact that sea level and circulation changes have on theenvironmental security and the related economic and societalissues. It is known that radar returns from the sea surfacesometimes present target-like echoes ("bright targets"), especiallyin correspondence of particular features of the coastalzone, thus entailing a potential interference with the measurementof SSH. Such spiky echoes generate hyperbolicpatterns in the radargram domain, which the recent literaturehas tentatively explained as resulting from flat water areas inthe proximity of the coastline, but the physical mechanismthat underlies their occurrence still remains unclear. To probefurther into this aspect, this work describes a novel applicationof a microwave tomographic reconstruction approach,applied to the Envisat RA-2 signals, tested on selected passesover the Pianosa Island (a 10 km2 island in the NW Mediterranean).The aim of this study is the analytical identificationof the signal contamination sources in terms of locationand extension of their associated electromagnetic anomaly.The obtained results confirm the idea that the origin of suchsignatures is connected with particular conditions of the seasurface, which are easier to be found in the proximity ofcoastal closed areas such as gulfs, but presumably not limitedto such circumstances.