Satellite Altimetry in the Coastal Zone:Ppast, Present and Future
Cipollini, Paolo¹; Benveniste, Jérôme^2
1National Oceanography Centre, UNITED KINGDOM; ²ESA/ESRIN, ITALY

[This is a 'community' contribution on behalf of the international coastal altimetry community http://www.coastalt.eu/community ]

Satellite altimetry over the oceans is regarded as one of the most successful remote sensing techniques, as it has allowed an unprecedented mapping of the ocean surface dynamics at the large- and meso-scale. With the improvements in orbit models, radar processing, atmospheric and geophysical effect corrections that have emerged over the years, altimetry gives today also a very accurate estimation of the rate of sea level rise and its geographical variability. However, altimetric data in the near-land strip (0 to 50 km from the coastline) are often flagged as bad and left unused, essentially owing to 1) difficulties with the corrections; and/or 2) the modification of the radar returns due to the presence of land in the footprint, which makes the fitting of the altimetric echoes with a waveform model (the so-called 'retracking' of the waveforms) problematic. This has prevented the applications of altimetry to be extended to the very oceanic domain where the impacts of changing climate and rising sea levels are most severely felt by society: the coastal zone.

In the last few years a vibrant international community of researchers has started developing the new field of coastal altimetry: i.e. techniques to recover meaningful estimates of the altimeter-derived parameters (height, significant wave height and wind) in the coastal zone, by improving the corrections and developing specialized retracking techniques; this has opened the way to a number of new applications, that are showcased at the annual Coastal Altimetry Workshops (see http://www.coastalt.eu/community).

In this talk we will summarize the main achievements of coastal altimetry so far, for the benefit of the oceanographic community at large. We will show examples of the improvements in retracking and corrections that have been developed in the last few years. We will then describe the currently available data archives, and show some applications of the reprocessed data to coastal currents, gravity field, storm surges, lake levels. We will discuss the need for integration with models (and the related problems on how best to assimilate the reprocessed data) and other in situ observations, and the continuing efforts for calibration and validation of the coastal altimetry data. Finally, we will discuss the future of this relatively new discipline, that looks bright not only for the continuing improvements in reprocessing, but also thanks to the advent of SAR (delay-Doppler) altimetry, the technology adopted for ESA's Cryosat-2 and Sentinel-3 missions, which has inherently better coastal capabilities.