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
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.
A Mission in Development
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.
Water Storage in Lakes
Arctic lakes are
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 River Flow and Discharge Rates
SWOT WSOA Space time sampling of radar altimetry missions 10 100 days 1000 km 100 km 10 km 1 km
cm TOPEX/Poseidon & ERS Data Cheney et al 1983 Ducet et al 2000 Mapping Global Ocean Eddy Variability
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 50% of the vertical exchange of heat and dissolved CO2 takes place at the submesoscales. ECCO2 Deepwater Horizon oil spill
h= H –r 1 cos( Ө ) δ h = r 1 δ θ sin( θ ) = [r 1 tan( θ ) λ /2 π B] δφ Off-nadir height measurement achieved via radar interferometry High-resolution along flight via Doppler shift in frequency High resolution achieved via Synthetic Aperture Radar
Radar Interferometry was successfully demonstrated by JPL’s Shuttle Radar Topography Mission (SRTM) 60m X/C band (3-6 cm wavelengths)
The SWOT Mission Configuration Ka band (0.85 cm wavelength) Nadir interferometry signals enhanced by a nadir receiver
SWOT noise spectrum SSH wavenumber spectrum 1000 100 25 10 km SWOT resolution k -4 k -2 Assemblage of ocean spectra Jason noise floor
SWOT Sampling characteristics (78 deg inclination, 22 day repeat orbit)