| Technology & equipment
For the first six months after launch SWOT will be operating in a “fast-sampling” phase with a one-day repeat orbit at an altitude of 857km over a limited subset of the final orbital paths. This initial period will focus on achieving calibration and validation objectives while also studying rapidly changing phenomena. The fast-sampling phase will end with an increase in the observatory’s altitude to 891km. The main operational phase will nominally last
three years, and will have a 21-day repeat orbit to balance global coverage and frequent sampling. SWOT’s 120km-wide swath will result in overlapping measurements over most of the globe with an average revisit time of 11 days. The warming of the earth’s climate may profoundly
alter the movement of freshwater resources from lakes to rivers to reservoirs, resulting in significant long-term implications for those reliant on those water resources – including the hydropower sector. To date, while fresh-water bodies in some regions are very well monitored, others are not, and no consistent measurement system exists with which to monitor change at the global scale. The SWOT satellite will provide that consistent set of measurements to help understand how the world’s fresh-water resources are being affected by both climate change and more direct human intervention. The KaRIn system’s highest resolution products are expected to be able to measure water levels in rivers as narrow as 100m and lakes as small as 250m across. The ocean is the planet’s largest reservoir of heat and carbon dioxide, which are redistributed by currents. Global ocean circulation balances earth’s climate and makes our planet habitable. Existing earth-observing satellites have revealed much about ties between climate and the ocean, including global warming and sea level rise. These sensors have also monitored currents inferred from and associated with the large-scale but low-amplitude (usually less than a metre) hills and valleys (topography – the ‘T’ in SWOT) of the sea surface, features that change dramatically in the El Niño and La Niña conditions that have been linked with extreme weather patterns around the world. SWOT’s scanning altimeter is expected to produce maps of these circulation features at a much finer scale and much closer to the coast than was previously possible. This will help improve ocean and climate models to ensure they correctly represent the heat transport associated with these currents. It will also allow subtle sea level variations caused by a wide range of other dynamic effects to be observed – information that is likely to be especially illuminating around complex coastal regions.
SWOT-UK The SWOT-UK project, focussing on the Bristol
Channel and Severn Estuary, has been funded by the UK’s Natural Environment Research Council and the UK Space Agency to contribute to the validation of the early SWOT products – activity that is expected to culminate during the fast-sampling phase in spring 2023. The SWOT-UK team will use data from a number
of pre-existing tide and water level gauges in the region that will be checked and re-aligned to the global positioning reference frame used by the SWOT
system. Similar initial comparisons with existing satellite altimeter data from CryoSat 2 are already helping to verify the quality and suitability of these datasets for the project, and similar comparisons will follow using data from the Sentinel 3 altimeter. Despite the number of tide gauges already in the
region, there are still relatively large sections of the Bristol Channel without water level measurements. The NOC will be installing several newly developed remotely measuring water level systems that use low-cost GNSS receivers to fill these gaps in measurements.
In addition, during the one-day fast sampling phase the team is planning aerial lidar flights to coincide with satellite overpasses, providing directly comparable water level data away from the coastline. Deployments of underwater Acoustic Doppler Current Meters are also planned to obtain measurements of the tidal currents in this dynamic region.
Launch The SWOT satellite is currently due for launch on 5
December 2022. The satellite arrived at Vandenberg Space Force Base in California in late October, where teams began final preparations for its launch on a SpaceX Falcon 9 rocket from Space Launch Center-4 East.
On October 16, SWOT arrived at Vandenberg from France aboard a US Air Force C-5 Galaxy aircraft and moved to the Astrotech Space Operations facility to begin launch processing. In the coming weeks, SWOT will undergo many steps in preparation for liftoff. Teams must encapsulate the satellite in a protective payload fairing, mate it to the rocket, and transport it to the launch pad before it’s ready to rocket into space. ●
Further information
Further information can be found at:
https://swot.jpl.nasa.gov/ and https://projects.
noc.ac.uk/swot-uk/
www.waterpowermagazine.com | November 2022 | 27
Below: Artist’s impression of the future SWOT satellite making sea surface height observations, even through clouds. SWOT will rely on a satellite altimeter that will use radar interferometry to make high-resolution (~1-km) measurements over two 60-km-wide swaths of water at once, with a conventional nadir altimeter in the gap in between Image courtesy of NASA/JPL
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