Remote Sensing of Ocean Dynamics. Detlef Stammer Institut für Meereskunde Universität Hamburg. 2nd ENVISAT Summer School: Earth System Monitoring and Modelling August 2004 Environmental Information from Envisat Stratospheric Ozone Industrial Emissions Atmospheric profiles Topography & Motion Land cover & vegetation SST, topography, colour Currents, bathymetry, ice 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: SSH SWH sigma_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 Ionosphere Mass of atmosphere Water vapor Em-bias Tides (ocean, land, pole) IB Geoid Orbit 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 Earth ’s flattening (J2) From Cox and Chao, 2002 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 Studies in: Solid Earth Physics - anomalous density GOCE und GRACE structure of lithosphere and upper mantle Oceanography - dynamic ocean topography and absolute ocean circulation Ice Sheet Dynamics - ice sheet mass balance Geodesy - unified height systems Sea Level 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) Wide-swath altimeter on JASON-2 Determining Geostrophic Velocities Wittex-Nadir Determining Geostrophic Velocities SSH gradients can be determined simultaneously in two directions from which the geostrophic surface flow field follows. AATSR Sea Surface Temperature End August 2002 End August 2003: 3 degrees warmer Crete Crete Libya Libya AATSR Sea Surface Temperature (October 2002) Cloud Coverage: Surface Temperature from MW: SST [°C] L Surface Temperature from Microwave: SST (AMSR) 12 10 8 SST [°C] 6 4 2 0 -2 L ?? SSTSST(AMSR) 5 4 K/m] 3 5 - 2 1 SST [10 0 L Windstress Messungen: MERIS Cloud vortexes Canary Islands 26 May 2003 © ESA 2003 ASAR MERIS Hurricane Isidore (September 2002) ASAR MERIS Cuba Yucatan (Mexico) Cancun MERIS MERIS Full Resolution MERISWhere Full is itResolution ? Great Barrier Reef Australia – Sept. 2003 MERIS Phytoplankton bloom Brittany (France) 15 June 2003 © ESA 2003 MERIS Mouths of the Ganga India - Bangladesh Nov. 2003 Calcutta MERIS Shanghai River discharge Yangtze mouth (China) March 2003 © ESA 2003 SEA LEVEL TRENDS measured by TOPEX/POSEIDON (1993-2001) Trends in mm/year Delayed Doppler Altimeter (Includes WV Radiometer) Instrument Type: Delayed Doppler Altimeter Swath Width: 3km 7 km along track JASON II Like Altimeter Spatial Resolution: With Doppler Processing Frequency: 13.28 GHz & 13.575 GHz 5.3 GHz Antenna Size: 1.2m EDRs Met T/O: Mass: 35 kg Peak Power: 50 watts Peak Data Rate: 20 Kbps Technology Issues: None Configuration Issues: None Areas for further study: Doppler Processing Algorithms Satellite Altimetry Large-scale Sea Level Changes: Wide Swath Altimeter Instrument Type: Wide Swath Altimeter Swath Width: 200 km Spatial Resolution: 14km x 14km Frequency: 13.28 GHz & 13.575 GHz 5.3 GHz Antenna Size: 2-2.5mx0.5m 7m apart EDRs Met T/O: 2/1 Mass: 80 kg Peak Power: 370 watts Delayed Doppler Antenna Peak Data Rate: 45 Kbps Technology Issues: None Configuration Issues: 7 meter boom deployment and stiffness and antenna panel deployments at both ends of the boom Areas for further study: Spacecraft stability requirements .