1. SWOT: A HIGH-RESOLUTION WIDE-SWATH ALTIMETRY MISSION
FOR OCEANOGRAPHY AND HYDROLOGY
Lee-Lueng Fu, Ernesto Rodriguez, JPL/Caltech
Douglas Alsdorf, Ohio State University
Rosemary Morrow, Nelly Mognard, CNES
2011 IGARSS
Vancouver, Canada
July 25-29, 2011

2. A Mission in Development
SWOT (Surface Water and Ocean Topography) is a satellite mission being jointly developed by NASA and CNES with contributions from CSA. Expected launch date is in 2019.
Science Goals –
(1) study hydrological processes by determining the storage and discharge rate of water on land.
(2) study the oceanic mesoscale and submesoscale processes that determine the kinetic energy of ocean circulation and its transport of water properties.
Societal Benefits – Address two key issues facing a warming planet:
(1) the variability of fresh water resources.
(2) the capacity of ocean circulation in regulating the rate of warming.
Technology Goals – Set the standard for future operational altimetry missions.

3. Water Storage in Lakes Arctic lakes are disappearing as
permafrost melts
SWOT will measure water storage change (ΔS ) to better than 10% for lakes 250m by 250m in size.
SWOT will measure ΔS in ~30 million lakes, globally; accounting for as much as 80% of the world’s changing surface water volume.

4. River Flow and Discharge Rates
Expected SWOT Sampling in North America
Floods are poorly measured whereas flow information from rivers crossing international boundaries is rarely shared.
SWOT will measure river hydraulic parameters for estimating river discharge.
SWOT will measure flood waves and estimate discharge along entire networks of rivers, globally.
Coverage by OSTM/Jason-2

5. Space time sampling of radar altimetry missions
days
1000 km
100 km
This slide shows the space and time sampling of satellite altimeters .
Before I explain how SWOT works, let me briefly go over what has been observed in the existing altimetry data and what has been missing from it
WSOA
10 km
1 km
SWOT

6. Mapping Global Ocean Eddy Variability
Cheney et al 1983
TOPEX/Poseidon & ERS Data
Ducet et al 2000 cm

7. Ocean Currents and Eddies Have Small Scales
Conventional altimeters resolve only the large mesoscale eddies (Jason-2/Envisat)
High-resolution ocean models suggest a ubiquitous presence of submesocale eddies
ECCO2
50% of the vertical exchange of heat and dissolved CO2 takes place at the submesoscales.
Deepwater Horizon oil spill

8. High resolution achieved via Synthetic Aperture Radar
Off-nadir height measurement achieved via radar interferometry
High-resolution along flight via Doppler shift in frequency
h= H –r1 cos(Ө )
δh = r1 δθ sin(θ)
= [r1 tan(θ) λ /2π B] δφ

9. Radar Interferometry was successfully demonstrated by JPL’s Shuttle Radar Topography Mission (SRTM)
X/C band (3-6 cm wavelengths)
The technique for the new observation is radar interferometry, first demonstrated by JPL’s SRTM.

10. The SWOT Mission Configuration
Ka band (0.85 cm wavelength)
Nadir interferometry signals enhanced by a nadir receiver

11. SSH wavenumber spectrumkm
Assemblage of ocean spectra
k-4
k-2
Jason noise floor
SWOT noise spectrum
SWOT resolution

12. SWOT Sampling characteristics (78 deg inclination, 22 day repeat orbit)

13. Additional Applications
Ocean Bathymetry
Sea Ice Freeboard
Ice Sheet Topography

14. Summary
SWOT will provide a revolutionary set of measurements of the elevation of land surface water and ocean topography globally.
The high-resolution swath measurements will resolve lakes of 250m x 250m area and rivers of 100 m width, and oceanic eddies of 10-km wavelength.
The unprecedented resolution and coverage of SWOT will enable breakthroughs in understanding the balance of water budget on land and energy budget of ocean circulation.
Significant improvements are expected in ocean modeling for predicting future climate and in fresh water management in response to climate change.
Other applications include ocean bathymetry, sea ice thickness, ice sheet topography, coastal processes, etc.