Iceberg detection in open water by altimeter waveform analysis.

Small icebergs (edge lengths <1 km) are difficult to detect and track. In a recently published study, it was demonstrated that small targets (ships, islets,…) emerging from the sea can be detected by the analysis of high-rate altimeter waveforms. The analysis of Jason altimeter data revealed that small icebergs also have a detectable signature in the thermal noise part of the altimeter waveforms for open water. These signatures are very similar to that of transponders and are almost deterministic. An automated method based on the detection of parabolic shapes in the thermal part of the waveforms by analysis of the convolution product with a filter has been developed and applied to 1 year of Jason high-rate waveform data. In addition, the minimum height and backscatter of the iceberg can also be estimated by this method. More than 8000 icebergs were identified between December 2004 and November 2005 in the open water around Antarctica. The annual distribution of icebergs presents a well-defined tripole structure, with maxima near the Antarctic Peninsula, the West Ice Shelf, and the Ross Sea. This distribution is in good agreement with the main trends in Antarctic iceberg motion presented in the scientific literature. The high concentration of icebergs propagating from the Antarctic Peninsula seems to confirm the importance of this region in the discharge of Antarctic ice into the ocean. The results clearly show that altimeter data are a powerful tool in the study of the distribution of small icebergs largely inaccessible by other satellite means. The principle of detection of icebergs by altimeter is quite simple and could be easily applied to the existing archive of all the past and present altimeters (ERS, Topex/Poseidon, Jason, and Envisat) to create a database covering more than 13 years that could improve our knowledge of climate change in Antarctica.

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