Abstract's details

Tides and bathymetry in the Severn Estuaries using FFSAR processing of Sentinel-3 data

Heidi Ranndal (DTU Space, Technical University of Denmark, Denmark)


Ole Andersen (DTU Space, Denmark); David Cotton (SatOC, UK); Amani Becker (National Oceanography Centre, UK); Jean-Christophe Poisson (vorteX.io, France); Charlie Thompson (National Oceanography Centre, UK)

Event: 2022 Ocean Surface Topography Science Team Meeting

Session: Science IV: Altimetry for Cryosphere and Hydrology

Presentation type: Type Oral

Fully focused processing of SAR altimeter data provides opportunities for exciting new applications, as it provides hitherto unachievable along-track resolution of up to 50 cm contrasting the regular 20 Hz processing resolution of 200 meters.
The results presented here, relate to the FFSAR-Coastal Project*, where the SMAP Fully Focused SAR (FFSAR) altimetry processor has been applied to Sentinel-3A and Sentinel-3B data in the Severn Estuary in order to evaluate the potential of FFSAR altimeter data to make a significant new contribution to coastal and estuarine monitoring systems.

Because of the large tidal signals in the Bristol Channel and Severn Estuary and the huge tidal flats, the Sentinel-3 satellites sometimes fly over the river during low tide, where, instead of measuring the sea surface height, it measures the seabed heights or bathymetry. These measurements could be extremely valuable for different modelling purposes, such as tidal modelling, as in-situ measurements of the Severn bathymetry are scarce due to challenges linked to the large tidal range (up to 14 m occurring twice a day) and the muddy nature of the intertidal sediment.

The FFSAR processing of the Sentinel-3 data shows a very clear bathymetry signal and the FFSAR-Coastal project aims to evaluate these measurements. As the Sentinel-3 satellites have an orbital drift reaching 1 km it rarely flies over the exact same location on the ground. Consequently, it is hard to evaluate the performance by comparing tracks at different times. Therefore, bathymetry data from other sources must be considered to account for this drift in the orbit. Several bathymetry products covering the Severn can be obtained from the National Network of Regional Coastal Monitoring Programmes of England (www.coastalmonitoring.org) and from the UKHO (https://seabed.admiralty.co.uk). These products are compared to the bathymetry derived from the Sentinel-3 FFSAR outputs to see if Sentinel-3 is in fact tracking the heights from the nadir position. Additionally, photon data from NASA’s ICESat-2 mission will be used as reference data, since these are available at a very high resolution and with very high precision and accuracy.

Combining ICESat-2 and Sentinel-3 FFSAR data would make it possible to map large parts of the Severn. The benefit of ICESat-2 is the resolution and the use of 6 beams which provides great mapping opportunities, and the contribution from Sentinel-3 is the 27-day repeat period with a slight drift. Combined, there is a very good potential for mapping the Severn bathymetry, aiding the local authorities in computing tidal and flood forecasts.

*FFSAR-Coastal is funded by ESA under the EO Science for Society Programme – Open Call.


Oral presentation show times:

Room Start Date End Date
Sala Grande Thu, Nov 03 2022,17:25 Thu, Nov 03 2022,17:35
Heidi Ranndal
DTU Space, Technical University of Denmark