Coastal sea level trends and extremes from Delay-Doppler altimetry

Luciana Fenoglio (University of Bonn, Germany)

CoAuthors

Salvatore Dinardo (HeSpace,Darmstadt, Germany); Christopher Buchhaupt (University of Bonn, Germany); Bernd Uebbing (University of Bonn, Germany); Johanna Staneva (Helmholz Zentrum Geesthacht , Germany); Jürgen Kusche (University of Bonn, Germany); Jérôme Benveniste (ESA-ESRIN, Italy)

Event: 2019 Ocean Surface Topography Science Team Meeting

Session: Coastal Altimetry

Presentation type: Type Oral

A significant part of the World’s population lives in coastal areas, which are affected by coastal sea level rise and extreme events. Consequently, accurately measuring relative sea level right at the coast is of utmost importance.

It has been shown that conventional (CA) and SAR satellite altimetry provide accurate sea level measurements only up to few kilometres from the coast, the lower limits depending on the retracking procedure used.

These limits are here revised for the 50 Kilometres stripe along the North Eastern Atlantic coasts, with CryoSat-2 in SAR mode since 2010 and several tide gauge stations co-located with GPS stations.

CryoSat-2 and Sentinel-3A data are considered, with Sentinel-3A from June 2016 to Mai 2018 and CryoSat-2 from October 2010 to Mai 2018. Two SAR products are used.: the first from the Marine Copernicus distribution for Sentinel-3A, retrackered by SAMOSA2; the second from the ESA GPOD processor SARvatore distribution, for both CryoSat-2 and Sentinel-3A, retracked by the dedicated coastal retrackers SAMOSA+ and SAMOSA++. Similarly, few Reduced SAR altimetry (RDSAR) products are used : from the Marine Copernicus distribution for Sentinel-3A with standard and STAR retrackers and finally the CryoSat-2 data retracked by TALES and STAR. In addition, we compare to two model datasets: the operation BSH model and the coupled Geestacht COAstal model SysTem GCOAST. In-situ sea level and GPS data are from SONEL and BGK/BfG local organisations.

It is found that limits are 4 and 3 kilometres for CA and SAR respectively, for the best dedicated retracking procedures, which are STAR and SAMOSA++. This reduction is important for both coastal ocean dynamics and sea level change studies, and coastal sea surface height can be recovered with 4 cm accuracy, compared to 2 cm in open ocean. However, in estuaries and in coastal zones with high tidal regimes the results deteriorate. Furthermore, the improved agreement between altimetry and in-situ data near coast largely supports the use of co-located in-situ and altimeter data. A toolbox OverVirtual combines altimetry and in-situ data at coast (over-pass) and in estuaries and rivers (virtual-pass).

The impacts of improved SAR data in the coastal sea level trends and extreme sea level analysis on selected regions worldwide has been investigated. For this, we decompose the sea level variability in the coastal stripe and separate seasonal and long-term components. Sentinel-3 offers the best accuracy in seasonal components and trends for its short repeat period. Here, differences with CryoSat-2 results are related to the different repeat period and not to the accuracy of the measurements. Given the long repeat period of CryoSat-2 (369 days) methods are investigated to overcome the spatial imitations and build regional monthly long time-series from CryoSat-2 data. The coastal sea level trends are small. The sea level at extreme events is in good agreement with in-situ data
 

Oral presentation show times:

Room Start Date End Date
The Monroe Hub Wed, Oct 23 2019,11:00 Wed, Oct 23 2019,11:15
Luciana Fenoglio
University of Bonn
Germany
fenoglio@geod.uni-bonn.de