如何利用衛星觀測海洋 ? Watching the Ocean

1. 張翠玉 台灣大學 海洋研究所 資料來源: AVISO Home, www.aviso.oceanobs.com/ Radar Altimetry Tutorial, http://earth.eo.esa.int/brat/index.html JPL/NASA web, http://www.jpl.nasa.gov/videos/ostm/ostm20080520/ SeaWIFS project, http://oceancolor.gsfc.nasa.gov/SeaWiFS/ NASA web, http://www.nasa.gov/ ESA web, http://www.esa.int/esaCP/index.html NOAA web, http://www.noaa.gov/ Cipollini, P., P.G. Challenor, D. Cromwell, I.S. Robinson, G.D. Quartly, How satellites have improved our knowledge of planetary waves in the oceans, 15 years of progress in radar altimetry Symposium, Venice, Italy, 2006 Fu, L.L. and D.B. Chelton, Large-scale ocean circulation, Satellite altimetry and Earth sciences, L.L. Fu and A. Cazenave Ed., Academic Press, 2001 Fukumori, I., Data assimilation by models, Satellite altimetry and Earth sciences, L.L. Fu and A. Cazenave Ed., Academic Press, 2001 Ocean Weather Forecasting, E. Chassignet and J. Verron Ed.,Springer, 2006 如何利用衛星觀測海洋?Watching the Ocean 普通高級中學課程基礎地球科學學科中心 99年度全國地球科學教師研習實施計畫 2010.OCT.08

2. Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Outside the Earth, does there exist another “OCEAN” ? 99年度全國地球科學教師研習實施計畫 2010.OCT.08 IONTU

3. Another Ocean in the space - Jupiter’s Moon: Europa Galileo launched on October 18, 1989 Europa's surface is mostly water ice, and there is evidence that it may be covering an ocean of water or slushy ice beneath. Europa is thought to have twice as much water as does Earth. This moon intrigues astrobiologists because of its potential for having a 'habitable zone.' Life forms have been found thriving near subterranean volcanoes on Earth and in other extreme locations that may be analogues to what may exist on Europa. Europa, as seen by the Galileo spacecraft

4. The Wilkins Ice Shelf in Antarctica collapsed in 2008 –2009. The Earth • The 2008 Antarctic ozone hole • A true-color NASA satellite mosaic of Earth. • This map of the global biosphere shows plant growth (green) and phytoplankton (dark blue). • Sea-level-measuring satellites • gravity model 99年度全國地球科學教師研習實施計畫 2010.OCT.08 IONTU

5. SIGNIFICANT DATES (satellite events for studying the Earth) • 1960 — NASA launches the Television Infrared Observation Satellite (TIROS), the first weather satellite. • 1972 — The Earth Resources Technology Satellite 1 (renamed Landsat 1) is launched, the first in a series of Earth-imaging satellites that continues today. • 1987 — NASA’s Airborne Antarctic Ozone Experiment helps determine the cause of the Antarctic ozone hole. • 1992 — TOPEX/Poseidon, a U.S.–France mission, begins measuring sea-surface height. Jason 1 continues these measurements in 2001. • 1997 — TOPEX/Poseidon captures the evolution of El Niño (cold ocean water in the equatorial Pacific Ocean) and La Niña (warm ocean water in the equatorial Pacific Ocean). • 1997 — The U.S.–Japan Tropical Rainfall Measuring Mission is launched to provide 3-D maps of storm structure. • 1999 — Quick Scatterometer (QuikScat) launches in June to measure ocean surface wind velocity; in December the Active Cavity Irradiance Monitor Satellite launches to monitor the total amount of the Sun’s energy reaching Earth. • 1999–2006 — A series of satellites is launched to provide global observations of the Earth system: Terra (land, oceans, atmosphere), Aqua (water cycle), Aura (atmospheric chemistry), Gravity Recovery and Climate Experiment (gravity fields), CloudSat (clouds),and the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation mission (aerosols, clouds). • 2006 — The Antarctic ozone hole was the largest yet observed. • 2007 — Arctic sea ice reaches the all-time minimum since satellite records began. • 2008 — The third U.S.–France mission to measure sea-level height, Ocean Surface Topography Mission/Jason 2, is launched, doubling global data coverage. • 2009 — NASA and Japan release the most accurate topographic map of Earth.

6. Scientific Satellites &Space Agencies National Aeronautics and Space Administration, NASA European Space Agency, ESA Japan Aerospace Exploration Agency, JAXA Russia (RKA, RSA) China (CNSA) India(ISRO) 國家太空中心(NSPO) etc 99年度全國地球科學教師研習實施計畫 2010.OCT.08 IONTU

7. Scientific Satellites &Space Agencies National Aeronautics and Space Administration, NASA European Space Agency, ESA Japan Aerospace Exploration Agency, JAXA Russia (RKA, RSA) China (CNSA) India(ISRO) 國家太空中心(NSPO) etc • satellite = payload+ spacecraft • define its mission • Take the ex. from Formosa III… 99年度全國地球科學教師研習實施計畫 2010.OCT.08 IONTU

8. Applying Remote Sensing to Study the Earth ACTIVE Altimetry – travel time of rays Synthetic Aperture Radar (SAR) Scatterometer – backscatter PASSIVE Infrared (radiometer) SeaWIFS project photogrametry Active sensors emit energy in order to scan objects and areas where upon a sensor then detects and measures the radiation that is reflected or backscattered from the target. Passive collection, on the other hand, detects natural radiation that is emitted or reflected by the object or surrounding area being observed.

9. Applying Remote Sensing to Study the Earth ACTIVE Altimetry – travel time of rays radar, lidar, laser Electromagnetic Spectrum

10. Applying Remote Sensing to Study the Earth ACTIVE Altimetry – travel time of rays radar, lidar, laser Synthetic Aperture Radar (SAR) – phase variation in coseismic displacement, internal wave, etc

11. Applying Remote Sensing to Study the Earth ACTIVE Altimetry – travel time of rays radar, lidar, laser Synthetic Aperture Radar (SAR) – phase variation in coseismic displacement, internal wave, etc

12. Applying Remote Sensing to Study the Earth ACTIVE Altimetry – travel time of rays radar, lidar, laser Synthetic Aperture Radar (SAR) – phase variation in coseismic displacement, internal wave, etc Scatterometer – backscatter in ocean circulation, wind speed, and wind directional patterns, etc

13. Applying Remote Sensing to Study the Earth ACTIVE Altimetry – travel time of rays radar, lidar, laser Synthetic Aperture Radar (SAR) – phase variation in coseismic displacement, internal wave, etc Scatterometer – backscatter in ocean circulation, wind speed, and wind directional patterns, etc PASSIVE Infrared (radiometer) in Sea Surface Temperature (SST)

14. Applying Remote Sensing to Study the Earth ACTIVE Altimetry – travel time of rays radar, lidar, laser Synthetic Aperture Radar (SAR) – phase variation in coseismic displacement, internal wave, etc Scatterometer – backscatter in ocean circulation, wind speed, and wind directional patterns, etc PASSIVE Infrared (radiometer) in Sea Surface Temperature (SST) SeaWIFS project mainly in ocean color (biochemistry) Remote Sensingof Coral Reefs

15. ALTIMETRY Altimetry is a technique for measuring height. Satellite altimetry measures the time taken by a radar pulse to travel from the satellite antenna to the surface and back to the satellite receiver. Combined with precise satellite location data, altimetry measurements yield sea-surface heights(SSH). Improvements in measurement accuracy since the first satellite altimetry missions has enabled us to observe ocean variations at close quarters since 1992.

16. MISSIONS Precise orbit determination and location missions have transformed the way we view Earth and its oceans. Highly accurate altimetry measurements from Topex/Poseidon and made possible by the Doris system give us the ability to observe sea surface height systematically. Past missions Geosat ERS-1 Topex/Poseidon GFO Current missions Cryosat Jason-2 Envisat Jason-1 ERS-2 Spot Future missions Cryosat Sentinel-3 Saral Jason-3 HY-2 Swot

17. APPLICATIONSOF SATELLITE ALTIMETRIC OBSERVATIONS Geodesy & Geophysics Ocean Ice Climate Atmosphere Hydrology Coastal Biology A wealth of applications are possible using radar altimetry measurements, involving most geoscience fields and practiced by more than a thousand teams of users around the world. From the 'historical' applications (geodesy, general ocean circulation) to the developing ones (solid Earth and coastal applications, etc) and the ones that have become classic (ocean variability, ice topography, hydrology), altimetry has shown over and over that it is a very productive technique.

18. APPLICATIONSOF SATELLITE ALTIMETRIC OBSERVATIONS Geodesy & Geophysics Ocean Ice Climate Atmosphere Hydrology Coastal Biology The reference mean sea level since January 1993 (left) is calculated after removing the annual and semi-annual signals. A 2-month filter is applied to the blue points, while a 6-month filter is used on the red curve. By applying the postglacial rebound correction (-0.3 mm/year), the  rise in mean sea level has thus been estimated as 3.26 mm/year (mean slope of the plotted data). Analysing the uncertainty of each altimetry correction made for calculating the GMSL, as well as a comparison with tide gauges gives an error in the GMSL slope of approximately 0.6 mm/year with a 90% confidence interval. (Credits CLS/Cnes/Legos) Extreme climate…

19. Geodesy & Geophysics Geophysics is the study of the substances that make up the Earth and the physical processes occurring on, in and above it. Information derived from altimetry data can be used to study the Earth's shape and size, gravity anomalies (geodesy), seafloor relief (bathymetry), tectonic plate motion and rifts (geophysics), etc. Although often linked to plate tectonics, tsunamis are very different, transient phenomena. However, their impact on the sea surface can be seen by altimeters in some cases, thus helping the study of their propagation.

20. Geodesy & Geophysics Geophysics is the study of the substances that make up the Earth and the physical processes occurring on, in and above it. Information derived from altimetry data can be used to study the Earth's shape and size, gravity anomalies (geodesy), seafloor relief (bathymetry), tectonic plate motion and rifts (geophysics), etc. Although often linked to plate tectonics, tsunamis are very different, transient phenomena. However, their impact on the sea surface can be seen by altimeters in some cases, thus helping the study of their propagation. Global Geoid

21. Marine gravity computed from SEASAT data over region of the Indian Ocean (Rodriguez) triple junction(70oE, 26oS) of three active seafloor spreading ridges. Marine gravity computed from GEOSAT and ERS data by Sandwell and Smith [2006] for the same area.

22. Global Seafloor Relief

23. Gravity anomalies (left), computed from altimetry, and predicted topography (right) deduced from these gravity anomalies plus in situ measurements. (Credits NOAA/Scripps Institution of Oceanography)

24. Tsunami Ground track for Jason-1 (top left) and Envisat (bottom left) overlaid by the CEA wave propagation simulation at the time of the satellite's passage. The area corresponding to the tsunami's front is circled. Sea level anomalies measured by Jason-1 and Envisat compared to the CEA simulation (top and bottom right). (Credits CEA & CLS)

25. Ocean The ocean is the surface studied by the majority of altimetry applications, and some missions are even optimised for it. Ultimate applications include oceanography itself, as well as the implications of ocean movements on climate (and vice-versa, the effects of climate change on the ocean). Large-scale circulation Ocean currents and eddies Operational oceanography Tides Mean Sea Level rise and the Greenhouse effect Mean Dynamic Topography (Credits CNES) Dynamic topography=SSH - geoid

26. Large-scale ocean circulation, current Changes in the extent of the Gulf Stream and the Kuroshio, as seen by Topex/Poseidon. The currents were 'elongated' in 1993 and 1999, and contracted in 1996 and 2001. (Credits University of Washington)

27. Ocean currents and eddies: mesoscale ocean applications Ocean currents are sometimes compared to 'sea highways', because ships follow their flow to gain speed. But this picture is not wholly accurate. In fact, ocean currents are more like secondary roads branching off into narrow country roads and lanes, winding their way around hills and natural obstacles. The main flow of these currents is often disturbed by eddies that form at their edge. So the ocean is really more like a vast, slowly swirling whirlpool bath than a swimming pool divided into perfectly straight lanes.

28. tides El Niño Amplitude of the M2 tidal constituent derived from the FES99 model. (Credits Legos/CNRS) Sea level rise and the Greenhouse effect

29. ENSO: sea surface height imageshttp://topex-www.jpl.nasa.gov/elnino/index.html El Nino retreating Full El Nino condition Full La Nina conditionLa Nina fading

30. 國內相關研究領域學者: 中央研究院 地球科學所 趙丰– 衛星測高、地球系統(海水面上升)、衛星重力、地球自轉，等。 交通大學 土木工程學系 黃金維- 衛星測高、衛星資料解算、空載/船載遙測、精密重力測量，等。 台灣大學 海洋研究所 物理海洋組同仁 范光龍- 地球系統(海水面上升)、海岸變遷，等。 劉倬騰- 海洋遙測學、內波，等。 張翠玉- 衛星測高、地球物理(衛星重力、地形)、板塊形變(ALT、GPS)，等。 台灣大學 大氣科學系 (林依依 等) 台灣師範大學 地球科學系 (吳朝榮 等) 台灣海洋大學 海洋環境資訊系 (許明光、劉安國 等) 成功大學 測量及空間資訊學系 (郭重言 等) 中央大學 太空遙測中心 (以上列表若有疏漏之處，敬請見諒)

31. "All truths are easy to understand once they are discovered; the point is to discover them." Galileo Galilei (1564-1642)

32. El Nino mechanism Climate feedback between SST and winds If trade winds weaken, then Westward surface flow (SEC) weakens, allowing western Pacific warm waters to move eastward cold tongue in eastern equatorial Pac. Warms Equatorial SST gradient is thus reduced and this further reduces the tradewinds. This then becomes the El Nino condition. http://www.pmel.noaa.gov/tao/elnino/nino-home.html)

33. La Nina mechanism If trade winds strengthen, then Westward surface flow (SEC) strengthens, warm pool stays in west Upwelling in east provides cold surface water there Equatorial SST gradient is thus increased and this further increases the tradewinds. This then becomes the La Nina condition. http://www.pmel.noaa.gov/tao/elnino/nino-home.html)

34. ENSO monitoring sites http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.html http://www.ncdc.noaa.gov/oa/climate/research/enso/ http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/enso.shtml#history Etc