Remote Sensing of Ocean Dynamics.

Detlef StammerInstitut für Meereskunde

Universität Hamburg.

2nd ENVISAT Summer School:Earth System Monitoring and Modelling

August 2004

Environmental Information from Envisat

Currents, bathymetry, ice

SST, topography, colour

Land cover & vegetation

Topography & Motion

Atmospheric profiles

Industrial Emissions

Stratospheric Ozone

Remote Sensing of the Ocean

– Variables:– SSH, SST, Color, Ice, Wind, Waveheight.– Systems:– Passive: VIS, IR, Mikrowave.– Aktiv: ALT,SCAT, SAR

– Ocean remote sensing is hindert through clouds and other atmospheric influence. Microwave is therefore the preferred Frequency.

Mikrowave Remote Sensing:

Background

– Ocean is part if the Earth system:Cryosphere – atmosphere – hydrosphere – biosphere – lithosphere.

– Ocean plays a big part in storing and transporting heat, freshwater, CO2, ...

– Important for transporting heat meridionally and releasing it in mid and high latitudes.

– Its external forcing arises from interactions with the atmosphere, crosphere and lithosphere.

– Remote Sensing of the ocean is necessary because of its small space and time scales, its extent and its rough conditions in some parts of the world.

Measurements:SSHSWHsigma_0/Wind speed

Satellite Altimetry

• Measures SSH rel. to reference frame.• Global coverage every 10 days (JASON)• SSH – geoid leads to dynamic topography.• High accuracy for time-varying component.• Measures also wind, waves.

Applications

• More than 1400 papers; • Fu and Cazenave book with subjects on ocean,

geodesy, bottom topography, etc.• Eddies, eddy mixing, dynamics in the ocean.• Rossby waves, interannual variability.• Tides, internal tides (HOME).• Large-scale changes; ENSO, NAO, wind forcing.• Global sea level rise.

Altimetric Correction Terms

IonosphereMass of atmosphereWater vaporEm-biasTides (ocean, land, pole)IBGeoidOrbit

Ocean signal: oder 30 cm!

Earyh Gravity Field

Temporal changes point toward changes in ground water and mass in the ocean.

Impact of Hurricanes:

Wave Height

Altimetrie

(More than 1800 pubs.)

SSH Variance, 9yrs.

Cm^2

Eddy Variability

Changes in Eddy Variability

Fractional changes in short-period SSH and Vel. Energy.

Wind

KE Variance

TOPEX SSH Drift 1993 – 2002

Global Sea Level Rise:

Secular decrease of the EarthSecular decrease of the Earth ’s flattening (J’s flattening (J22))

From Cox and Chao, From Cox and Chao, 20022002

Where to go from here:

• Preserve longest time series in oceanography.• Merging observations (data assimilation).• Regional and global sea level change.• Rebound, glacial melting.• Applications: near-realtime ocean predictions.• Operational oceanography: JASON and ARGO,

new ESA mission.• New opportunities: velocity sensing (wide-

swath).

GRACE: Gravity Change

Determine Earth’s gravity field and its geoid (equipotential surface for a hypothetical ocean at rest):

high accuracy (1 mgal and 1 cm) fine spatial resolution (~ 100 km)

Studies in:Solid Earth Physics - anomalous density structure of lithosphere and upper mantleOceanography - dynamic ocean topography and absolute ocean circulationIce Sheet Dynamics - ice sheet mass balanceGeodesy - unified height systemsSea Level change

GOCE und GRACE

Determining Geostrophic VelocitiesWide-swath altimeter on JASON-2

Wittex-Nadir

Determining Geostrophic Velocities

SSH gradients can be determined simultaneously in two directions from which the geostrophic surface flow field follows.

Sea Surface Temperature

End August 2002

Libya

Crete

End August 2003: 3 degrees warmer

Crete

Libya

AATSR

Sea Surface Temperature(October 2002)

AATSR

Cloud Coverage:

Surface Temperature from MW:

L

SS

T [°

C]

Surface Temperature from Microwave:

L ?? SSTSST(AMSR)

SST (AMSR)

12

10

8

6

4

2

0

-2

SS

T [°

C]

LS

ST

[10-

5K

/m]

5

4

3

2

1

0

Windstress Messungen:

© ESA 2003

Cloud vortexesCanary Islands

26 May 2003

MERIS

Hurricane Isidore (September 2002)

MERISASAR

Yucatan (Mexico)

Cuba

Cancun

ASAR

MERIS

MERIS Full ResolutionGreat Barrier Reef

Australia – Sept. 2003

MERIS

MERIS Full ResolutionWhere is it ?

© ESA 2003

Phytoplankton bloomBrittany (France)

15 June 2003

MERIS

Mouths of the GangaIndia - Bangladesh

Nov. 2003

MERIS

Calcutta

© ESA 2003

River discharge Yangtze mouth (China)March 2003

Shanghai

MERIS

SEA LEVEL TRENDS measured by SEA LEVEL TRENDS measured by TOPEX/POSEIDON (1993TOPEX/POSEIDON (1993--2001)2001)

Trends in mm/year

Delayed Doppler Altimeter(Includes WV Radiometer)

Swath Width:Spatial Resolution:Frequency:

Antenna Size:EDRs Met T/O:

Delayed Doppler AltimeterInstrument Type:

Mass:Peak Power:Peak Data Rate:

Technology Issues:

Configuration Issues:

Areas for further study:

35 kg50 watts20 Kbps

3km7 km along track13.28 GHz &13.575 GHz5.3 GHz1.2m

JASON II Like AltimeterWith Doppler Processing

None

None

Doppler Processing Algorithms

Satellite Altimetry

Large-scale Sea Level Changes:

Wide Swath Altimeter

Swath Width:Spatial Resolution:Frequency:

Antenna Size:

EDRs Met T/O:

Instrument Type: 200 km14km x 14km13.28 GHz &13.575 GHz5.3 GHz2-2.5mx0.5m7m apart2/1

Mass:Peak Power:Peak Data Rate:

Technology Issues:

Configuration Issues:

Areas for further study:

80 kg370 watts45 Kbps

None

7 meter boom deployment and stiffness and antennapanel deployments at both ends of the boom

Spacecraft stability requirements

Wide Swath Altimeter

Delayed Doppler Antenna