Validation of Altimeter Data for Storm Surge Research in the Adriatic Sea
Vignudelli, Stefano¹; Cipollini, Paolo²; Passaro, Marcello^3
1Consiglio Nazionale delle Ricerche (CNR-IBF), ITALY; ²National Oceanography Centre Southampton, UNITED KINGDOM; ³University of Southampton, UNITED KINGDOM

Storm surges are amongst the worst natural hazards in terms of human and infrastructural costs. The ESA DUE eSurge project has been initiated to promote the use of remote sensing data, including radar altimetry, in supporting storm surge observations, modelling and forecasting.

One of the objectives of the eSurge project is also to provide an improved coastal altimeter data set by using new and improved retrackers, and updated corrections. A parallel project called eSurge-Venice project has been set up with specific focus on the Adriatic Sea.

The Adriatic Sea and especially the city of Venice, is an area particularly affected by storm surges because of its geographical position and geometry. Storm surges are usually generated by periodic strong winds from the south-east that are directed along the main axis of the basin. These two parallel projects share processing methods and validation approaches.

In this study we illustrate the validation activities carried out for eSurge and eSurge-Venice, with an example over the Adriatic Sea. We have used Envisat and Jason-2 high-rate (20 Hz for Jason and 18 Hz for Envisat) data reprocessed by the eSurge coastal altimetry processor. The quantity used was the total water level envelope (TWLE), i.e. the sea surface height anomaly with no correction for tidal and atmospheric effects, as this is what is measured by a gauge and is a quantity of primary interest in storm surge science.

Altimeter-derived TWLE have been compared with water level records from a Tide Gauge located on the CNR Acqua Alta platform in the vicinity of the inlets of Venice Lagoon. The time series exhibit very high correlation coefficients which indicates that the altimeter captures the signal well. Moreover we compare the performance of the altimeter on approaching the coastline, especially in comparison with standard (i.e non coastally-reprocessed) data; this highlights the improvements in the quality and quantity of data in the coastal strip (particularly at <5km form the coastline) when dedicated coastal altimetry techniques are used.

Altimeter data are not routinely used in the Adriatic Sea for storm surge applications. From this study we conclude that altimeter data are of good quality for capturing the total water level envelope and that thank to reprocessing we can get more and better data than using standard products.