Image Analysis for Altimetry Waveform Selection Over Heterogeneous Inland Waters

Abstract

Over inland waters the altimetry radar return is typically contaminated by both land and surrounding vegetation. Moreover, the radar returns corresponding to floodplain vegetation and exposed mud flats can have similar waveform shapes to those reflected from open water surfaces so that the derived water surface elevations are either inaccurate or difficult to extract. This letter presents a robust and automated method based on image analysis of satellite imagery for the selection of altimetry waveforms over inundated zones. The altimetry footprint is assessed as being inundated if the radiometric response of an image kernel within the footprint conforms to known remotely sensed responses for water. The method was applied in the lower middle Fly floodplain of the Fly River in the Western Province of Papua New Guinea (PNG). Altimetry waveforms were assessed for inundation extent and vegetation cover, with those that met threshold levels being flagged for further retracking and water surface elevation monitoring. The results show that the method accurately identified> 90% of inundated sites along altimeter ground tracks and correctly selected waveforms reflected from water surfaces.