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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.

Introduction The recently developed technique of “fully focused” processing of SAR altimeter data provides opportunities for exciting new applications, as it provides hitherto unachievable along-track resolution of up to (and in some cases less than) tens of metres. The objective of the FFSAR-Coastal Project is to apply the SMAP Fully Focused SAR (FFSAR) altimetry processor on Sentinel-3A and Sentinel 3B data and evaluate the potential of FFSAR altimeter data to make a significant new contribution to coastal and estuarine monitoring systems. Two different environments are being considered: • The Severn Estuary and river: A highly dynamic mixed tidal estuary environment, the confluence between a river and its estuary experiencing large tidal range and strong tidal currents. • The lower Rhone Delta and Camargue: A low lying, flat river delta and wetland environment, susceptible to inundation and rising water levels. By studying these two very different environments, the potential applicability and benefits offered by FF SAR altimeter data in other coastal, estuarine and delta locations will be demonstrated. Innovative in situ lidar water level gauges, provided by vortex.io will be used for validation. FFSAR-Coastal is funded by ESA under the EO Science for Society Programme – Open Call. Presentation The presentation will provide an overview of the FFSAR Coastal project and present early results. There are two main elements to the project. DTU Space are using the SMAP (Standalone Multi-Mission Altimetry Processor), developed by CLS, and applying it to Sentinel 3A and 3B altimeter data for two regions with very different characteristics: the Severn estuary in the UK, and the Rhône delta in France. The objective is to evaluate how well FFSAR altimeter data can resolve fine scale features in these two different environments. Initial results will be used to identify the optimum processing choices, which will then be applied to generate time series of data for selected tracks. These data will be validated against in-situ data and models, to quantify the performance against other data sources. Further analysis will then investigate the capability of FFSAR altimeter data to capture small scale physical signals (surface gradients, currents, roughness signatures) in highly tidal regions and to detect and measure tidal asymmetry/gradients across estuaries not seen with conventional altimetry For the Rhône delta the analysis will focus on the ability of FFSAR data to accurately map different low lying channels and filaments. The second element is the deployment of innovative river level “micro-gauges” (vorteX.io microstations) to provide ground truth data, and to test these as a flexible and low-cost option for satellite validation and river monitoring. Two micro-gauges will be installed in each of the selected regions, as close as possible to the Sentinel 3A and 3B ground tracks, and drone campaigns with an embedded LiDAR altimeter will be carried out to provide high resolution sea level measurements, synchronised to satellite overpasses, to provide a water level profile between the micro-gauge location and the satellite ground track. The project is also engaging with local user groups to identify key gaps in the existing monitoring systems, and to develop recommendations on how FFSAR altimeter data can best be used as part of

This is the Molecule of the Month entry for January 2018 about glycerol. It is a pdf archive version of the HTML webpage.