Satellite Oceanography

Modified from a Presentation at STAO 2003By Dr. Michael J. Passow

Ocean Satellites

• Permit observations globally, especially useful where there are no ships or buoys

• Developed later than meteorological and other environmental sensing because electromagnetic radiation penetrates ocean water only to limited depths

• Improved sensors permit inferences about ocean at greater depths

"Satellite Oceanography" • Surface topography,

El Nino, and ocean winds are some of the areas investigated from space.

http://winds.jpl.nasa.gov/

Satellite Oceanography Applications

• Sea surface temperatures • Air-sea interactions• Sea Ice patterns• Monitoring ocean waves• Determining sea level variations• Analysis of ocean currents and eddies• Biological productivity• Precipitation patterns

Two basic satellite orbits

“Polar Orbiting” (POES) • Takes about 90 minutes

to make one revolution• Covers different areas

each orbit as Earth rotates

• Provides detailed images• Can produce time

sequence

Geostationary (Geosynchronous)

(GOES)• Remains over same

portion of planet by revolving with same period as Earth’s rotation

• Can provide full disk or smaller views

• Useful for weather and communication

http://www.iitap.iastate.edu/gcp/satellite/images/image7.gif

For more detailed studies, we use “polar-orbiting” satellites

• Polar-orbiting satellites are much closer to the surface (700 – 800 km) and make about 14 passes each day. They can provide good time sequence studies.

http://www.earth.nasa.gov/history/landsat/landsat4.html

Satellites can detect what’s on Earth in two ways:

• “passive” observation of energy reflected or radiated from the surface

• “active” collection of signals beamed down from the satellite and reflected back

http://topex-www.jpl.nasa.gov/

Problem 2—How do you measure from a satellite?

Sea surface temperatures (SST) and thermal properties

• Visible satellites can monitor difference between incoming solar radiation and reflected light

• Infrared satellites can monitor IR energy emitted from surfaces

• AVHRR (Advanced Very High Resolution Radiometer) measure SSTs

• Also monitored with MODIS (Moderate Resolution Imaging Spectroradiometer)

SST Images[link through DStreme Ocean]

http://www.cdc.noaa.gov/map/images/sst/sst.gif

Sea Surface Temperature Anomalies (SSTA)

• Images constructed by measuring difference between “observed” and “expected” values – anomalies

• Better approach to recognizing “what is unusual,” not just “what is”

• Especially useful for El Nino/La Nina studies—example: http://orbit-net.nesdis.noaa.gov/orad/sub/sst_anomaly_2m.html

SSTA images

http://www.osdpd.noaa.gov/PSB/EPS/SST/climo.html

• SeaWIFS has allowed us to monitor the links between physical and chemical conditions and marine biology

• Biological response to climate changes

http://seawifs.gsfc.nasa.gov/SEAWIFS.html

Sea Surface Topography

• Variations in sea surface heights caused by gravity variations (sea floor topography and geology)

• Also seasonal changes in atmospheric and ocean circulation patterns

• Radar altimeters aboard TOPEX/Poseidon and Jason satellites

• AMS “Measuring Sea Level from Space”

TOPEX-Poseidon is…

• a partnership between the U.S. and France to monitor global ocean circulation, discover the tie between the oceans and atmosphere, and improve global climate predictions. Every 10 days, the TOPEX/Poseidon satellite measures global sea level with unparalleled accuracy.

http://topex-www.jpl.nasa.gov/mission/mission.html

TOPEX has been especially useful in understanding…

• Variations in sea surface temperatures. This has been the most important instrument for observing El Nino/ La Nina changes in the Pacific Ocean, and all the effects on climate

http://topex-www.jpl.nasa.gov/elnino/elnino.html

Jason 1 is a follow-on mission to TOPEX-Poseidon• Monitors global ocean circulation, studies

ties between the oceans and atmosphere, improves global climate forecasts and predictions, and monitors events such as El Niño conditions and ocean eddies.

http://www.jpl.nasa.gov/missions/current/jason1.html

Sea Ice Extent

• Areal extent, amount, and thickness important for oceanographers and operationally

• Visible images not feasible during winter• POES microwave sensors provide

operational ice analyses• The next slide shows an example of sea

ice cover in the Northern Hemisphere

http://polar.wwb.noaa.gov/seaice/Analyses.html

Canadian Sea Ice Imagery

Ice conditions monitored by satellite and ships are available at http://ice-glaces.ec.gc.ca/App/WsvPageDsp.cfm?ID=1&Lang=eng