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
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.
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.
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
Space time sampling of radar altimetry missions
10
100 days
1000 km
100 km
WSOA
10 km
SWOT
1 km
Mapping Global Ocean Eddy Variability
Cheney et al 1983
TOPEX/Poseidon
& ERS Data
Ducet et al 2000
cm
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
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
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
SSH wavenumber spectrum
1000
100
Assemblage of
ocean spectra
25
10 km
k-4
k-2
Jason noise floor
SWOT noise spectrum
SWOT resolution
SWOT Sampling characteristics (78 deg inclination, 22 day repeat orbit)
Additional Applications
Ocean Bathymetry
Sea Ice Freeboard
Ice Sheet Topography
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.