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