Remote Sensing Basics

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Remote Sensing Basics
Dr. Ana I. Prados University of Maryland
Baltimore County /JCET, Baltimore, MD NASA
Goddard Space Flight Center, Greenbelt, MD World
Bank September 25th, 2009
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What is Remote Sensing?
Remote sensing is a method of obtaining
information about the properties of an object
without coming into physical contact with it.
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How Do Satellites Make Measurements?

• Satellites do not make direct measurements of
  the Earths geophysical parameters.
• Most passive satellite sensors measure the
  radiance reflected or emitted by the
  earth-atmosphere system
• This radiance is converted to geophysical
  parameter of interest, e.g. Aerosol Optical Depth
  (AOD), ozone, nitrogen dioxide, etc.

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Why use Remote Sensing to Study the Earth?

• Consistent, routine, global measurements
• Overview of information at the local, regional,
  hemispheric, or global scale the big picture
• Complement ground-monitoring network or provide
  information where there are no ground-based
  measurements
• Advance warning of impending environmental events
  and disasters
• Visual appeal a picture is worth a thousand
  words

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Global View
Satellite data are used for assessing global
weather, climate, environment and for
understanding the earth-atmosphere system
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Air Pollution A local, regional and global
problem
Long range transport of pollution local
emissions lead to regional and global impacts
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Long Range Transport of Air Pollutants
smoke
fires
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World Wide Ground Based Measurements of Fine
Particles

• Fine Particles or PM2.5 and the Air
  Quality/Health Index are traditionally assessed
  from ground monitors.
• Ground monitors are almost non existent in many
  countries.

Large gaps in ground monitors
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A Picture is Worth a Thousand Words!
Satellites provide consistent, routine, global
coverage of environmental events
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Two Types of Satellite Orbits
Polar Orbiting Global coverage Limited
frequency over any location
Geostationary Frequent measurements Limited
coverage
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Examples of Geostationary Satellites
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Polar-Orbiting Satellites

• In low altitude orbit (700-800 km)
• Orbit around North and South Poles
• Earth rotates under satellite as it orbits, so
  each time satellite makes a pass over Earth, it
  observes a new area
• Polar-orbiting satellites observe the same area
  on Earth once per day (or less)
• Low temporal resolution
• Global coverage!
• Used for a variety of applications, including air
  quality, land cover, water quality, and
  vegetation studies

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NASA Observing Spacecraft for Earth System Science
June 20, 2008
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Temporal resolution of Polar Orbiting Satellites

• Satellite observations are available only at the
  time of the satellite overpass which means that
  there is no information (imagery) for other times
  of the day

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Satellite observation footprints vary
OCO 1x1.5 km
Washington DC USGS Map
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High spatial resolution imagery (10m,
250m) Detailed features such as buildings,
roads, trees are visible!
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Air Pollution and High Resolution Imagery

• Certain pollution features require higher
  resolution
• imagery

Individual Smoke Plumes from forest fires in
Brazil
Source NASA MODIS imagery (fire smoke in Brazil)
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Low Resolution Imagery

• Air pollution is often regional in nature, so it
  CAN be detected with Low spatial
  resolution imagery

Smoke in Central Africa
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Principles of Remote Sensing
Passive - Reflected and Emitted Radiation
Passive Satellite Remote Sensing Can be broadly
classified into Solar Reflected and Thermal
Emissive components
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Principles of Remote Sensing
Different spectral bands measure Clouds Aerosols
Land features Ocean color, iogeochemistry Land
and atmospheric temperature Precipitation
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Satellites Measure the total amount of pollution
for the entire atmospheric column from the
surface of the Earth to the Satellite
The satellite observed pollution may not reflect
conditions at the surface, the pollution may be
higher in the atmosphere
Ozone Layer
Health/human impacts
Source www.ucar.edu
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NASA Satellites for Air Quality Applications

• Terra
• 2000-Present
• 1030 AM local overpass
• Aqua
• 2002 -Present
• 130 PM local overpass
• Aura
• 2004 -Present
• 130 PM local overpass

• Calipso
• 2006 - Present
• Narrow swath with detailed Vertical information

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NASA Satellite Instruments for Air Quality
Applications

• MODIS (MODerate Resolution Imaging
  Spectroradiometer ) Terra and Aqua Satellites
• OMI (Ozone Monitoring Instrument) - Aura
  Satellite
• Calipso

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Land Remote Sensing
Satellite data useful for studying land- cover
changes
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MODIS Normalized Difference Vegetation Index
(NDVI)

• NDVI measures plant growth, vegetation cover, and
  biomass production
• Green colors indicate high amounts of vegetation
  (trees, grasses, plants)
• NDVI values near zero indicate non-vegetative
  features (rocks, soil, water, snow, urban areas)