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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

1. Geographic perspectives on importance of oceanic processes

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

data6. Monitoring ocean productivity

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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

1. Geographic perspectives on importance of oceanic processes

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

data6. Monitoring ocean productivity

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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

1. Geographic perspectives on importance of oceanic processes

2. SAR Ocean Applications3. Estimating Sea Surface

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

data7. Monitoring ocean productivity

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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

1. Geographic perspectives on importance of oceanic processes

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

data6. Monitoring ocean productivity

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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

1. Geographic perspectives on importance of oceanic processes

2. SAR Ocean Applications3. Estimating Sea Surface

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

data7. Monitoring ocean productivity

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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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