Ocean Topography from SpaceOcean Topography: Circulation and Heat Storage in the OceanSlide 3Ocean TopographyOcean Topography from Satellite AltimetryTOPEX/PoseidonTOPEX/Poseidon Measurement SystemRequired Measurement AccuracyChallenges of Ocean Topography from Satellite AltimetryLocation Map of Ocean CurrentsMean Sea Surface Topography of the OceanStandard Deviation of Sea Surface HeightTOPEX/Poseidon Performance and ResultsCalibration of Radar AltimetersSchematic Vertical Slice Along the Equatorial PacificSlide 16Sea Surface Height Anomaly during El NiñoEl Niño / La NiñaSea Surface Height, Sea Surface Temperature, and Wind AnomaliesEl Niño/La Niña Ocean Topography, Winds, and Sea Surface TemperatureArgo: A Global Array of Profiling FloatsArgo Float OperationSlide 23Slide 24OutlineTOPEX/Poseidon–Measurement approach–Data set examplesJason-1–Near-term launch plannedJason-2–Wide-swath ocean topographyArgo–A global array of profiling floatsOcean Topography from SpaceOcean Topography from SpaceModified from M. D. King’s LectureThe most effective measurement of ocean currents from space is ocean topography, the height of the sea surface above a surface of uniform gravity, the geoidOcean Topography: Circulation and Heat Storage in the OceanOcean Topography: Circulation and Heat Storage in the Oceangeoidsea surfaceocean topographyOcean topography is the height of sea surface relative to the geoid, a surface of uniform gravityOcean TopographyOcean TopographyDetermines the speed and direction of ocean surface currents–Water flows around the highs and lows of ocean topography, just as wind blows around the high and low pressure centers in the atmosphereThe ocean volume expands when heated, causing higher surface elevation, and contracts when cooled, causing lower surface elevation–Therefore, ocean topography also reveals the heat storage of the water columnOcean topography is the only observable from space that reveals the temperature and currents of the ocean at depths–This is a unique link between sea surface and deep ocean characteristics•warm watercold water•air•Water flows out of the pageWater flows into the pageOcean Topography from Satellite AltimetryOcean Topography from Satellite AltimetryA radar altimeter measures the altitude of a spacecraft above the sea surfacePrecision orbit determination measures the altitude of the spacecraft above a reference surface of the EarthThe height of sea surface relative to the same reference surface is the difference of the two altitudesOcean topography is the height of sea surface relative to the geoid, a surface of uniform gravityTOPEX/PoseidonTOPEX/PoseidonLaunched August 10, 1992TOPEX/Poseidon Measurement SystemTOPEX/Poseidon Measurement SystemRequired Measurement AccuracyRequired Measurement AccuracyOcean topography must be measured with high accuracy–A mere 1 cm error over a few km or longer gives an error in water transport of 5 megatons/sec»25 times the discharge rate of the Amazon»15% of the transport through the Florida StraitsThe amount of heat carried by 5 megatons/sec water is about 200 trillion watts–~ 20% of the northward oceanic transport of heat in the North Atlantic Ocean responsible for the relatively mild winters of northern EuropeIt is therefore critical to make ocean topography measurement within a few cm–Compared to the altitude of the spacecraft from Earth, this accuracy requirement is one in 200 millionChallenges of Ocean Topography from Satellite AltimetryChallenges of Ocean Topography from Satellite AltimetryThe largest variability of sea surface height is due to the ocean tides with a global rms amplitude of about 32 cm–The signals of tides must be removed before using the data for studying ocean circulationDue to the relatively long repeat periods of a satellite (often longer than a few days), the short period tides are often aliased to much longer time periods–A sunsyncronous orbit would alias solar tides into a period of infinity and make them become indistinguishable from the ocean topography of the mean circulation–TOPEX/Poseidon is in a 66° inclination orbit with an altitude of 1336 km to avoid aliasing tides into the ocean topography signalThe best ocean tide models are accurate derived from TOPEX/Poseidon data and are accurate with an rms error of 2-3 cm–This knowledge allows the removal of this signal from ocean altimeter measurements180°W120°W 60°W 0° 60°E 120°E 180°ELocation Map of Ocean CurrentsLocation Map of Ocean CurrentsMean Sea Surface Topography of the OceanMean Sea Surface Topography of the OceanStandard Deviation of Sea Surface HeightStandard Deviation of Sea Surface HeightTOPEX/Poseidon Performance and ResultsTOPEX/Poseidon Performance and ResultsThe TOPEX/Poseidon mission has been measuring the height of the sea surface with 4 cm accuracy, more than 10 times better than previous missionsAfter averaging over space and time scales relevant to climate, the accuracy approaches 2 cmThese remarkable achievements represent a decade-long effort involving oceanographers, geodesists, electrical and aerospace engineersCalibration of Radar AltimetersCalibration of Radar AltimetersAt the instant the satellite passes overhead, geocentric sea surface height is observed independently by the altimeter and in situ measurement systemsAssuming that the in situ systems are properly calibrated, the difference represents the ‘altimeter bias’Generally from the atmosphere to the oceansEither direction (fromthe warmer to the cooler medium).Either direction (with some chemicalsbeing transferred predominantly inone direction of the other).Non-El Niño equatorial conditionsSchematic Vertical Slice Along the Equatorial PacificSchematic Vertical Slice Along the Equatorial PacificGenerally from the atmosphere to the oceansEither direction (fromthe warmer to the cooler medium).Either direction (with some chemicalsbeing transferred predominantly inone direction of the other).El Niño conditionsSchematic Vertical Slice Along the Equatorial PacificSchematic Vertical Slice Along the Equatorial PacificSea Surface Height Anomaly during El NiñoSea Surface Height Anomaly during El NiñoEarly November 1997 was marked by a large increase in the areal extent of above-average sea level,especially off the west coast of North America (shown as red and white)–At this time, sea level “peaked” at about 35 cm