Heritage Coastal Altimetry Products from the COASTALT Project
Cipollini, Paolo1; Passaro, Marcello2; Snaith, Helen3; West, Luke1
1National Oceanography Centre, UNITED KINGDOM; 2School of Ocean and Earth Science, University of Southampton, UNITED KINGDOM; 3British Oceanographic Data Centre, UNITED KINGDOM

The ESA STSE COASTALT project (2008-2012) on the development of altimetry in the coastal zone for Envisat has pioneered the field of coastal altimetry and has achieved a number of significant results:

  • a thorough review and consolidation of the user requirements for coastal altimetry;
  • the analysis of the state of the art in atmospheric and geophysical corrections in the coastal zone, including an investigation of the benefits from a regional tidal model;
  • the design and implementation of a novel water vapour path delay ('wet tropospheric') correction, using measurements of path delay from GNSS coastal stations (GPD - GNSS-derived Path Delay, Fernandes et al., 2010);
  • a detailed specification of the coastal altimetry products and the production of the relevant documentation (including a comprehensive user handbook);
  • a study of specific waveform retracking techniques for the coastal zone, including 'peaky' waveforms due to bright targets in vicinity of the coast;
  • the design and implementation of a dedicated coastal altimetry processor for Envisat data, and its application to the production of demonstrative products for selected passes over three pilot sites;
  • some (limited) calibration and validation of the demonstrative products.

    The three COASTALT pilot sites are the Western coast of Britain, the Western coast of the Iberian Peninsula (including the Gulf of Cadiz) and the Northwestern Mediterranean (Northern Tyrrhenian and Ligurian Seas and Corsica Channel). Over these areas the project has generated demonstrative products called CGDRs (Coastal Geophysical Data Records) that have been publicly available via http://www.coastalt.eu since 2011.

    The recent improvements and extension of the COASTALT processor within the framework of the ESA DUE eSurge project for the observation, monitoring and forecasting of storm surges have created the opportunity for a complete reprocessing of the COASTALT CGDRs. In this contribution we present the results of this reprocessing of the COASTALT archive for the benefit of the whole community of altimetrists and coastal oceanographers. The specialized waveform retrackers have been re-coded based on the 'Brown plus Gaussian Peak' (BGP) model by Halimi et al (2012) and on the sub-waveform 'OceanCS' retracker by Yang et al (2012). The GPD wet tropospheric correction has also been updated to reflect its recent improvements by the University of Porto team in the ESA Sea Level Climate Change Initiative study.

    We show, with examples over the various pilot areas, that the reprocessed sea surface height anomalies and significant wave heights are significantly less noisy than the previous data in the coastal strip, and also compare favourably against data from conventional Brown retrackers, like those available in ESA's standard products.

    It is hoped that this new version (v.3) of COASTALT data will be used by many researchers worldwide to test new applications in the nearshore area, therefore consolidating the legacy of COASTALT as one of the incubators of the new discipline of coastal altimetry and a catalyst for the coastal altimetry community.