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 disappearing as permafrost melts

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 –r1 cos(Ө )

δh = r1 δθ sin(θ)

= [r1 tan(θ) λ /2π 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)

Additional Applications

Sea Ice FreeboardOcean Bathymetry

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.