Summary

1
Summary

• Data Acquisition
• Satellite Orbits
• Receiving Satellite Data
• GMU Setup
• Data Processing
• EM Spectrum and Atmospheric Transparency
• Low Level
• Sensor Calibration
• Georectification
• High Level
• Use of Remote Sensing Data in a Business
  Environment
• Vegetation (NDVI - LAI - Hyperspectral)
• Sea Surface Temperature, Sea Height, Sea Surface
  Winds
• Data Distribution

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About the Projects

• Progress?
• Difficulties?
• Questions?

3
Vegetation

• Any questions?

4
Hydrological Cycle

• Oceans and large freshwater bodies cover more
  than 70 of the Earth's surface.

5
Sea Surface Temperature

• Sea surface temperature (SST) is an important
  geophysical parameter, providing the boundary
  condition used in the estimation of heat flux at
  the air-sea interface.
• On the global scale this is important for climate
  modeling, study of the earth's heat balance, and
  insight into atmospheric and oceanic circulation
  patterns and anomalies (such as El Niño).
• On a more local scale, SST can be used
  operationally to assess eddies, fronts and
  upwellings for marine navigation and to track
  biological productivity.

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Sea Surface Temperature

• Presumably sailors have always been concerned
  with ocean currents as they affect their ships
  courses and changes in ocean temperature or
  surface condition. 
• Many of the earlier navigators, such as Cook and
  Vancouver, made valuable scientific observations
  during their voyages in the late 1700s, but it is
  generally considered that Mathew Fontaine Maury
  (1855) started the systematic large-scale
  collection of ocean current data, using ships
  navigation logs as his source of information. 
• The first major expedition designed expressly to
  study all the scientific aspects of the oceans
  was that of the British  H.M.S. Challenger which
  circumnavigated the globe from 1872 to 1876.
• The first large-scale expedition organized
  primarily to gather physical oceanographic data
  was the German FS Meteor expedition to study the
  Atlantic Ocean from 1925 to 1927. 
• Some of the earliest theoretical studies of the
  sea were of the surface tides by Newton (1687)
  and Laplace (1775), and of waves by Gerstner
  (1847) and Stokes (1874). 

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SST and Global Warming
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Buoys and Ships Observations
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Satellites Observations
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Main Methods To Estimate SST

• Thermal Infrared
• Passive Microwave

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Thermal Infrared

• Long Temporal Coverage (20 years)
• They are derived from radiometric observations at
  wavelengths of 3.7 µm and/or near 10 µm
• Though the 3.7 µm channel is more sensitive to
  SST, it is primarily used only for night-time
  measurements
• Both bands are sensitive to the presence of
  clouds and scattering by aerosols and atmospheric
  water vapor
• Thermal infrared measurements of SST first
  require atmospheric correction of the retrieved
  signal and can only be made for cloud-free
  pixels.
• Maps of SST from thermal infrared measurements
  are often weekly or monthly composites

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Thermal Infrared

• Thermal infrared instruments that have been used
  for deriving SST include
• Advanced Very High Resolution Radiometer (AVHRR)
  on NOAA Polar-orbiting Operational Environmental
  Satellites (POES),
• Along-Track Scanning Radiometer (ATSR) aboard the
  European Remote Sensing Satellite (ERS-2),
• Geostationary Operational Environmental Satellite
  (GOES) Imager
• Moderate Resolution Imaging Spectroradiometer
  (MODIS) aboard NASA Earth Observing System (EOS)
  Terra and Aqua satellites.

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Thermal Infrared Pros Cons

• Strengths
• Good resolution and accuracy
• Long time series ( 20 years)
• Weaknesses
• Obscured by clouds
• Atmospheric corrections required

14
Passive Microwave

• Due to lower signal strength of the Earth's
  Planck radiation curve in the microwave region,
  accuracy and resolution is poorer for SST derived
  from passive microwave measurements compared to
  SST derived from thermal infrared measurements

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Passive Microwave Vs. Thermal Infrared
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Passive Microwave Vs. Thermal Infrared
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Passive Microwave

• Passive microwave instruments that have been used
  for deriving SST include the
• Scanning Multichannel Microwave Radiometer (SMMR)
  carried on Nimbus-7 and Seasat satellites
• Tropical Rainfall Measuring Mission (TRMM)
  Microwave Imager (TMI),
• Advanced Microwave Scanning Radiometer (AMSR)
  instrument on the NASA EOS Aqua satellite
• Japanese Advanced Earth Observing Satellite
  (ADEOS II).

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Passive Microwave Pros Cons

• Strengths
• Clouds are mostly transparent
• Relatively insensitive to atmospheric effects
• Weaknesses
• Poorer accuracy and resolution
• Sensitive to surface roughness and precipitation

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How is SST Derived

• Sea surface temperature is routinely estimated
  from satellites using infrared sensors sensitive
  to emitted radiation at wavelengths of 10-12m m,
  at or near the peak of the Planck thermal
  emission spectrum for bodies at a temperature of
  about 300K
• These emissions can be blocked by cloud, and are
  therefore not always visible from space
• A small but measurable amount of this 300K energy
  is emitted in the microwave frequency range of
  10-100GHz
• This radiation is not as affected by cloud and is
  almost always visible.

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How is SST Derived

• Radiation emitted by a surface is the Planck
  emission times the surface emissivity
• Since the Planck function is dependent on
  temperature and is well known, sea surface
  temperature can be estimated if the surface
  emissivity can be sufficiently estimated
• Subsequent to atmospheric corrections, then,
  coefficients are applied to the retrieved
  brightness temperature signals in the derivation
  of SST which factor in estimations of the surface
  emissivity

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Different depths of SST an important
consideration

• The depth at which measurements are made will
  significantly impact the SST.
• Measurements made at only a depth of one or two
  molecules below the ocean's surface are
  considered the "interface SST" and cannot be
  realistically measured
• Just below this, however, at a depth of roughly
  10 µm is what is known as the "skin SST
• The attenuation length of thermal infrared
  radiation corresponds to this depth
• The "sub-skin SST" is at a depth of 1 mm and
  corresponds to the attenuation length of
  microwave radiation
• Beyond this depth is what is commonly referred to
  as the "bulk SST", "near-surface SST", or
  "SSTdepth"

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SST Gradients
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Problems?

• Diurnal heating and evaporative cooling make
  comparison of SSTs at different depths difficult
• Special care must be taken to correct for their
  effects

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Blending TIR and Microwave

• Given the desire to combine the high accuracy and
  resolution of the thermal infrared SST
  measurements with the better temporal and spatial
  coverage of passive microwave SST measurements
  (due to cloud transparency), efforts are being
  made to create a blended product which combines
  these strengths
• http//www.ghrsst-pp.org/

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SST Overview

• http//podaac-www.jpl.nasa.gov/sst/

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SST Case Study

• SST has been extensively studied to either prove
  or disprove Global Warming
• Most study use only first order statistics
• How does second order statistics look like?

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Higher Order Statistics of SST
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Variance and Wavelets
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Sea Winds

• Temperature variations are major factors in the
  development, strength, and directional behavior
  of winds
• Their prevailing motions change over time, but
  tend to follow certain preferred paths in various
  parts of the world
• We determine wind directions indirectly, by
  relating them to the patterns of waves they
  produce, especially in the open seas

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Sea Winds
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How To Compute Sea Winds
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Topex Poseidon
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Topex Poseidon

• Satellite position is known relative to the
  center of the Earth and so we measure sea height
  relative to the Earth's center
• T/P has 2 altimeters that measure the distance
  from the satellite to the ocean
• These altimeters send radar signals straight down
  to "bounce off" the ocean surface where they are
  bounced back to the satellite
• The time it takes for the radar signal to return
  to the satellite tells us how far the satellite
  is from the ocean's surface
• To improve the altimeter measurement, we measure
  the water content of the atmosphere. This is
  because water in the atmosphere changes the speed
  at which the altimeter signal travels
• T/P makes very precise measurements of sea
  surface height (4.3cm)

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Wind Speed and Wave Height
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Tides

• TOPEX-Poseidon also has shed new light on the
  oceans tides
• There has been an ongoing mystery as to balancing
  the energy provided by the Moon's gravitational
  attraction, which produces the tides, and the
  dissipation of that energy
• What was known is that much of the energy goes
  into setting up surficial ocean currents that
  carry water from higher areas to lower
• Ocean heights measurements by T-P have now better
  fixed the areas of the seas that are higher and
  lower than mean sea level

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Tides
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Jason

• A follow-up to TOPEX-Poseidon, named JASON-1, is
  a component of the EOS program
• Operated jointly by NASA JPL/CNES, this
  spacecrafts sensors include C and Ku band radar
  altimeters, a microwave radiometer, and a Doppler
  radar
• Again, sea surface heights (SSH) are the main
  oceanographic phenomenon being measured for
  Jason, differences in SSH as small as 4.1 cm can
  be determined.

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QuickScat

• On July 19, 1999 NASA JPL launched QuickScat, a
  satellite whose prime sensor (SeaWinds) is a
  radar with 25 meter resolution.
• Its primary mission is to provide near-realtime
  measurements of surface roughness that translate
  into wind velocities.

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Data Portals

• http//daac.gsfc.nasa.gov/data/datapool/
• http//edcimswww.cr.usgs.gov/pub/imswelcome/
• http//oceancolor.gsfc.nasa.gov/cgi/level3.pl?
• http//ingrid.ldeo.columbia.edu/
• http//precip.gsfc.nasa.gov/
• http//www.ssmi.com

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References

• http//rst.gsfc.nasa.gov/ (Chapter 14)
• http//podaac-www.jpl.nasa.gov/sst/
• http//ccar.colorado.edu/asen5215/chapter_1_wje_fi
  gs_10.6.doc
• http//cires.colorado.edu/maurerj/class/SST_prese
  ntation.htm
• http//www.rmc.ca/academic/gradrech/environment17_
  e.html