Detection of iceberg using Delay Doppler and interferometric Cryosat-2 altimeter data

The Cryosat-2 Synthetic Aperture Interferometric Radar Altimeter (SIRAL) altimeter is the first altimeter that can operate in three different modes over the ocean: the classical pulse limited LRM, the Delay Doppler or SAR and the SAR Interferometric modes. It offers a unique opportunity to test, validate and compare the capabilities of the three modes for the detection and analysis of small icebergs (<3 km in length) already demonstrated for classical altimeters. Over most of the sea-ice free ocean, SIRAL operates in LRM mode and the classical iceberg detection algorithm can be applied without modification. It can also be applied to the Reduced SAR or pseudo-LRM data computed from SAR and SARin data. In SAR mode, iceberg signatures are bright spots in the waveform thermal noise part. They can be easily detected using classical image processing tools. The area of the iceberg is estimated using the size of the signature. In SARin mode, the coherence of the signals can insure the presence of scatterers above the sea surface and is used with the SAR detection algorithm to reduce the probability of false alarm and to better delineate icebergs. Interferometry allows for the first time to map the iceberg and the iceberg free-board at an unprecedented resolution opening a new way of investigation of the distributions of size, free-board and volume of the small icebergs that are responsible of large fraction of the freshwater flux into the ocean.