Earth Remote Sensing*Definition: The use of electromagnetic radiation
(EMR) to acquire information about the ocean, land and atmosphere without being in physical contact with the object, surface, or phenomenon under investigation (Martin, 2004).
Unlike in situ measurements, the geophysical quantity of interest derived from remote sensing is inferred from the properties (intensity, polarization, spectral signatures) of the reflected or emitted radiation.
* The term ”Remote Sensing” was coined by Dr. Evelyn Pruitt, ONR, in the 1940s
History / Impact EM Radiation Ocean Features Orbits / Satellites / Sensors Trends
Reflected
Reflected
Emitted
Passive
Active
Sea surface temperatureSurface wind speedsIce concentrationNight time lights
Sea sfc heightSurface windsWave heightsIce conc., ageOil slicksShip wakes
Satellite-borne sensors record emitted and/or reflected radiation, and ocean features are inferred from the radiation measurements
Transmitted
Active sensors are bothsource and receiver of the radiation
Ocean colorIce concentrationShip wakesOil slicksCoral reefs
History / Impact EM Radiation Ocean Features Orbits / Satellites / Sensors Trends
Ocean Remote Sensing
Chlorophyll, Sea IceOil Slicks, Shoals
Surface Temperature
Ice Concentration
Surface Winds
Sea Level
Wave Heights
What are we sensing?Electromagnetic Radiation (EMR)
What phenomena do we inferfrom the radiation measurements?
We use the visible, infrared, and microwaveportions of the electromagnetic spectrum
History / Impact EM Radiation Ocean Features Orbits / Satellites / Sensors Trends
visible
infrared
microwave
http://physics.uoregon.edu/~jimbrau/BrauImNew/Chap03/FG03_09.jpg
Microwaves are usuallydenoted by frequency (gigahertz)
Visible and IR are usually denoted by wavelength (microns or nanometers)
Visible solar radiationreflects from Earth’s surfaceand from particles and organisms in the ocean.
Most active sensors transmit microwave radiation and receive some of the energy which reflects back from Earth’s surface.
The Earth (land, ocean, and atmosphere) emits infrared and microwave radiation.
Passive
Active
Satellite-borne sensors record emitted and/or reflected radiation, and ocean features are inferred from the radiation measurements
There are two new satellites (ICESat and CALIPSO) which use lidar (visible and infrared lasers) for Earth remote sensing.
History / Impact EM Radiation Ocean Features Orbits / Satellites / Sensors Trends
Oceanographic Applications and Primary Satellites / Sensors
History / Impact EM Radiation Ocean Features Orbits / Satellites / Sensors Trends
Application Sensor Type Satellite / Sensor
Sea Surface Temperature
Infrared Radiometer
(passive)
POES / AVHRR
Aqua / MODIS
Ocean Color Multispectral Radiometer
(passive)
SeaWiFs
Aqua / MODIS
Sea Surface Height Altimeter
(active)
JASON-1
ENVISAT / RA-2
GFO
Ocean Surface Winds Scatterometer (active), Polarimetric Radiometer
(passive)
QuikScat
Coriolis / Windsat
Sea Ice Microwave Radiometer
(passive)
Synthetic Aperture Radar
DMSP / SSM/I
POES / AMSU-B
Radarsat-1
Ocean Color Observations
http://seawifs.gsfc.nasa.gov/SEAWIFS/IMAGES/IMAGES.html
History / Impact EM Radiation Ocean Features Orbits / Satellites / Sensors Trends
Coastal UpwellingOregon & California
6 October 2002NASA / Terra MODIS
• Visible light emitted from the sun reflects off suspended particles
• Based on the nature and quantity of this reflected light, we can make estimates of chlorophyll concentration (primary productivity) and water clarity
Diatoms
• Most abundant plankton• Nutrient rich, high latitudes• 2-1000 m• autotrophic• chlorophyll in chloroplasts – absorb red
and blue• Appear yellow-brown (“Golden Algae”)
From www.dnr.state.md.us
Diatom Bloom off mid-Atlantic coast(from http://seawifs.gsfc.nasa.gov/)
History / Impact EM Radiation Ocean Features Orbits / Satellites / Sensors Trends
Dinoflagellates• Unicellular• Autotrophic,
heterotrophic or mixotrophic
• Rapid reproduction can lead to red tides
• Some produce neurotoxins
50 m
Ceratium
Red Tide
History / Impact EM Radiation Ocean Features Orbits / Satellites / Sensors Trends
Coccolithophorids
• Shells composed of calcium coccoliths – milky white appearance
• Able to thrive in nutrient-poor conidtions
Photo by Kurt Buck, 1995http://www.mbari.org/~reiko/work/phyto.htm
http://oceancolor.gsfc.nasa.gov/cgi/image_archive.cgi
History / Impact EM Radiation Ocean Features Orbits / Satellites / Sensors Trends
50 km
TERRA MODIS, 21 JUN 04:Coccolithophore blooms off of Icelandhttp://visibleearth.nasa.gov
Ocean Color Applications• Ocean Color features are caused by scattering and
absorption of visible wavelengths by:– Plankton (also emit certain wavelengths)
• Represent 25% of global vegetation• Provide food for zooplankton and fish• Convert CO2 into carbon; important in global carbon cycle• Harmful Algal Blooms
– Colored Dissolved Organic Matter (CDOM) or “Gelbstoff” – organic runoff, detritus, decaying matter
– Sediments, Pollutants
• Ocean optical properties (scattering and absorption) affect swimmer visibility, submarine vulnerability, and performance of electro-optical systems (underwater video, laser)
• Features indicate positions of fronts, eddies, and direction of currents
History / Impact EM Radiation Ocean Features Orbits / Satellites / Sensors Trends
Oceanographic Remote Sensing• Satellite remote sensing has revolutionized
oceanography, opening our eyes to energetic small scale (50-200 km) processes
• A wide variety of observations are available• Some observations, such as sea ice
concentration, are now available for relatively long periods of time (~30 years)
• Applications support scientific, commercial and military interests
History / Impact EM Radiation Ocean Features Orbits / Satellites / Sensors Trends
Walter Munk: “1 + 1 = 3” (When satellite data is combined with in situ ocean observations, the resulting info is worth more than the sum of two separate measurements).
Links• Imagery from NASA
– Visible Earth: http://visibleearth.nasa.gov/ – Earth Observatory (including “Image of the Day”):
http://earthobservatory.nasa.gov/
• Imagery from NOAA– Geostationary Satellite Server: http://www.goes.noaa.gov/
– CoastWatch: http://coastwatch.noaa.gov/cw_index.html
• NOAA NESDIS Education and Outreach– http://www.nesdis.noaa.gov/outreach_edu.html
• NASA Remote Sensing Tutorial– http://rst.gsfc.nasa.gov/
• Visualization of Satellites on Orbit– http://science.nasa.gov/Realtime/jtrack/3d/JTrack3D.html
Links• Ocean Color
– Brief Overview: http://disc.gsfc.nasa.gov/oceancolor/index.shtml – Data and Imagery Gallery: http://oceancolor.gsfc.nasa.gov/ – http://nasascience.nasa.gov/earth-science/oceanography/living-ocean/remote-sensing
• Sea Surface Temperature, Topography, Winds– NASA JPL: http://podaac-www.jpl.nasa.gov/
• Overview of POES and GOES (NOAA)– http://www.nesdis.noaa.gov/satellites.html
• DMSP Program– Historical Overview:
http://www.aero.org/publications/crosslink/winter2005/02.html– Data Archive, Research, Products:
http://www.ngdc.noaa.gov/dmsp/index.html • NPOESS Program
– http://www.npoess.noaa.gov/ • CORONA Program
– http://www.nro.gov/corona/facts.html