The aim of this programme is to model estuarine water flows and use this knowledge to better manage these coastal zones. The programme will use the intense data collection calibration and validation phase of the Surface Water and Ocean Topography mission to achieve this.
NERC and the UK Space Agency (UKSA) are working together to jointly deliver a research funding opportunity using the intense data collection calibration and validation phase of the Surface Water and Ocean Topography (SWOT) mission to model estuarine water flows and use this knowledge to manage these coastal zones.
The mission aims to make the first global survey of the Earth’s surface water, to observe the fine details of the ocean surface topography, and to measure how terrestrial surface water bodies change over time. The calibration and validation phase offers a unique opportunity to sample the Severn Estuary at fast time sampling (one day) in addition to swath altimetry providing observations of water and surface elevation, slope, inundation extent, and discharge.
The SWOT satellite mission is a $1 billion US programme funded by NASA, the National Centre for Space Studies (CNES), the Canadian Space Agency and UKSA. It will make the first global survey of Earth’s surface water, provide fine resolution detail of ocean surface topography, and measure lake and river changes over time. Current altimetry satellites, such as the Jason-3, track water heights along a line, with tracks spaced approximately 120km apart.
How the satellite takes measurements
SWOT, as a scanning instrument, will map grids of water height with around 1km resolution and will deliver over 100 times the resolution of current technologies. Instruments will measure water surface elevation to less than 10cm root mean square error when averaged over 1 square km. This will allow scientists to study small-scale features that are key components of how heat and carbon are exchanged between the ocean and atmosphere. Amongst numerous outcomes, measurements will revolutionise our understanding of the global water cycle and our knowledge of the impact of mesoscale eddies on ocean and coastal dynamics.
SWOT capabilities will enable measurement of water level spatial variability along estuaries including during low tide and low flow. It will provide a better understanding of small-scale currents and eddies important to impacts on coastal and estuarine regions such as navigation, erosion and dispersing pollutants. Estuarine tidal flux is subject to strong asymmetry and non-stationarity, making it a complex challenge for precision modelling and understanding of tidal signals. This is true of many estuaries but with the large tidal variation in the Severn, the situation is more complex than most.
Approximately three months after launch in September 2021 and following the instrument checkout, the mission will enter a three-month fast-sampling phase for calibration and validation purposes. In this phase the orbit revisit time will be one day (compared to an average of 10.5 days in the nominal orbit), and this will be achieved by only sampling a very limited number of ground tracks.
One of these tracks will pass over the UK and is the only track globally to cover an estuary during the fast sampling phase. Collecting data from this site is therefore the only opportunity to capture a rich data set from a specific coastal system. With validation on the ground, data will provide a unique insight into a complex and dynamic estuarine system.
The mission’s science team has stated this UK project will be welcomed by the mission advisory group as an equal partner and will receive timely access to the data.
Survey at ground level
A survey at ground level will be needed. It will use a range of tasks before launch, including monitoring network installation, ground and water surveys at various times. These will be used to capture, for example, tidal and discharge states, and measurement of water flow and quality (such as water height dynamics, discharge and velocity fields, temp and turbidity).
During the one day fast repeat cycle of the calibration and validation phase, intensive groundwater measurements of water surface elevation, slope, inundation extent and discharge will be captured. Together these ground and satellite measurements will provide the data required to build detailed hydrodynamics models of the estuary as well as contributing to the calibrating and validating of the satellite.