1 Lecture 17 Ocean Remote Sensing 9 December 2008

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Lecture 17

Ocean Remote Sensing

9 December 2008

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Final Exam

• Friday – December 19• 1:30-3:30

2/3 from lectures 12-17, 1/3 from previous lectures (focusing on topic areas covered in the first 2 exams)

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Office Hours

• Not available this afternoon –• Office hours on Thurs, Dec 11• Can meet Thurs/Fri, Dec 11/12 by

appointment• Not available Mon-Thurs, Dec 15-

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4Ocean Chlorophyll/Production

SAR Ocean Observations

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Lecture Topics

1. Geographic perspectives on importance of oceanic processes

2. SAR Ocean Observations3. Global SST data products4. Sea surface topography5. Monitoring El Nino with satellite

data6. Monitoring ocean productivity

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Geographic perspectives on importance of oceanic processes

• Influences of oceans on continental climates

• Large-scale oceanic circulation

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http://orbit-net.nesdis.noaa.gov/arad/gpcp/colormaps.html

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Geographic perspectives on importance of oceanic processes

• Influences of oceans on continental climates

• Large-scale oceanic circulation

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1. Ocean current drivers2. Ocean current modifiers

– Continents– Coriolis effect

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Thermocline

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Currents are also influenced by the rotation of the earth

This rotation causes a natural deflection of currents

Clockwise in the Northern Hemisphere

Counter clockwise in the Southern Hemisphere

This is called the coriolis effect

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Lecture Topics


2. SAR Ocean Applications3. Global SST data products4. Sea surface topography5. Monitoring El Nino with satellite


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Microwave backscatter from water surfaces results from Bragg Scattering from small surface waves – Many processes alter the Bragg wavelength, and thus cause changes in EM energy detected by SARs

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SAR Ocean Applications

• Detection of oil slicks• Monitoring surface gravity waves• Monitoring internal waves• Detection of bottom features

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Airborne SAR Imagery of Oil Spills

Oil on water surface dampens formation of short wavelength Bragg Waves

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Seasat SAR (L-band) image of an oil spill

U.S. Coast Guard deploys airborne SAR systems for detection of oil spills in coastal

waters

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Tilt and hydrodynamic modulation by gravity waves

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Airborne SAR imagery of gravity waves

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Monochromatic light

Monochromatic light is diffracted as it passes through a narrow slit

Degree of diffraction ~ 1 / slot width

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SAR Image of gravity waves

digital

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SAR Image of gravity waves

In a fourier transform, the distance between the peaks of energy is proportional to the wavelength of the imaged gravity waves, and a line connecting the peaks represents the direction of the waves

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Seasat SAR image of gravity waves

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Internal Wave Formation

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Internal Wave Formation

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Surface Hydrodynamic Modulation by Internal Waves

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Internal Waves

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Airborne SAR Images of Internal Waves

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ERS C-VV SAR image collected off of west African Coast

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ERS C-VV SAR image collected off of Galopagos Islands showing internal waves

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Seasat SAR Image of Natucket Shoals

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Hydrodynamic Modulation by Bottom Feature/Current

Interactions

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Hydrodynamic Modulation

Current slows down Current speeds up

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Current Direction

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Lecture Topics




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Figure 4 in Njoku and Brown, Sea Surface Temperature, pages 237-249

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Global Sea Surface Temperature Products

• Data are compiled over a weekly or monthly period

• Algorithms to remove cloud-contaminated pixels are applied to data

• Average SST for the remaining pixels are calculated

• Data are resampled to a coarse resolution (e.g, 36 km)

• Data are interpolated to fill in missing pixels

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

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AVHRR Sea Surface Temperature Map

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MODIS Sea Surface Temperature Map

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SST Map

SST AnomalyMap

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Lecture Topics


2. SAR Ocean Applications3. Estimating Sea Surface

Temperature (SST) with AVHRR4. Global SST data products5. Sea surface topography6. Monitoring El Nino with satellite


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AltimetersAltimeters measure round-trip travel time

of microwave radar pulse to determine distance to sea surface!

From this (and additional info) we can determine the dynamic sea surface topography

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Spaceborne Scatterometer

Resolution = 50 km

Obtains measurements looking upwind, cross-wind, and downwind

Empirical Algorithms used to estimate wind speed and direction

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Lecture Topics




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Thermocline

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Thermocline

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Movies of SST and Elevation Anomalies

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Lecture Topics


2. SAR Ocean Applications3. Estimating Sea Surface

Temperature (SST) with AVHRR4. Global SST data products5. Sea surface topography6. Monitoring El Nino with satellite


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SeaWiFs

Launched 1997

2800 km swath

1.1 x 1.1 km pixel

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Example SeaWifs Chlorophyll Algorithms

Chl = 10 (a + bR)

Algorithm 1 - R = log (R443/R550)

Algorithm 2 – R = log [(R520 + R565)/R490]

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Data obtained from ORBIMAGE at:

http://seawifs.gsfc.nasa.gov/cgibrs/seawifs_browse.pl?dy=11627&tp=MO&lev=2&hp=

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Monthly Composite

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1 Lecture 17 Ocean Remote Sensing 9 December 2008