Satellite Imagery

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Satellite Imagery
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Geostationary Satellites

• Geostationary satellites orbit high
  (approximately 36,000 km) above the equator and
  orbit around the Earth at the same rate as the
  Earth rotates on its axis.
• Thus, geostationary satellites appear to remain
  above the same location on the Earth at all
  times.

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Geostationary Satellites (Cont.)

• Advantage always located above the same region
  of the Earth, providing continuous images of that
  region.
• Disadvantage The great distance from the
  surface of the Earth limits the resolution of the
  images (i.e. it is harder to see smaller weather
  features).

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Polar Orbiting Satellites

• Polar orbiting satellites orbit at a lower
  distance (around 850 km) above the Earths
  surface and the orbit takes the satellite near
  the north and south poles.
• These satellites are generally in a
  sun-synchronous orbit in which they cross the
  equator at the same time on each orbital pass.

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Polar Orbiting Satellites (Cont.)

• Advantage the low orbit allows for the
  generation of higher resolution imagery.
• Disadvantage polar orbit results in gaps in
  coverage and many places are often observed twice
  a day or less.

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Active versus Passive Sensors

• A passive sensor is an instrument that measures
  the incoming amount of energy in the form of
  electromagnetic radiation in a band of
  wavelengths.
• An active sensor is an instrument that transmits
  electromagnetic radiation in a given wavelength
  and measures the amount of energy
  reflected/backscattered to the sensor.

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Active vs. Passive Sensors (Cont.)

• A passive sensor weighs less but it is dependent
  on the energy naturally occurring in the
  environment.
• An active sensor is heavier, but it is able to
  transmit energy at a specific wavelength. This
  enables the sensor to be designed for specific
  purposes (e.g. to sense surface characteristics
  through clouds and rain.).

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Operational Geostationary Satellites

• GOES-E (GOES-12) longitude 75W
• GOES-W (GOES-10) longitude 135W
• Meteosat-9 longitude 0
• Meteosat-7 longitude 57E
• MTSAT-IR longitude 140E

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Operational Geostationary Satellites (Cont.)

• GOES-E and GOES-W are operated by NOAA
• Meteosat-7 and Meteosat-9 are operated by
  EUMETSAT
• MTSAT-IR is operated by the Japanese
  Meteorological Agency

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Geostationary Operational Environmental Satellite
(GOES)

• GOES contain two main instrument systems.
• The GOES imager.
• 2. The GOES sounder.

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The GOES Imager

• The GOES imager is a multichannel instrument that
  senses radiant energy emitted in the terrestrial
  (longwave) and reflected in the solar (shortwave)
  wavelengths.

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The GOES Sounder

• The GOES sounder measures emitted radiation in
  18 infrared bands and reflected solar radiation
  in one visible band. The energy in the bands is
  affected by the temperature, moisture and ozone
  content of the air.

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The GOES Sounder (Cont.)

• The measurements are used to determine the
  vertical profiles of temperature and moisture,
  the surface and cloud top temperatures, and the
  ozone distribution.

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GOES Imager Bands

• Visible (0.52-0.72 µm) is useful for cloud and
  severe storm identification.
• Shortwave infrared (3.78-4.03 µm) is useful for
  discriminating between snow and low clouds.

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GOES Imager Bands (Cont.)

• Upper level water vapor (6.47-7.02 µm) is useful
  for estimating the water vaport content of the
  upper troposphere.
• Longwave infrared 1 (10.2-11.2 µm) is useful for
  identification of clouds and severe storms.

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GOES Imager Bands (Cont.)

• Longwave infrared 2 (11.5-12.5 µm) is useful for
  determination of sea surface temperatures.

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Types of GOES Images

• Visible images
• Infrared images
• Water vapor images

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Visible Satellite Imagery

• Visible satellite imagery is constructed from the
  solar radiation reflected by an object to the
  sensor on the satellite. Objects that reflects a
  lot of visible light (i.e. have a high albedo)
  appear bright. These objects include fresh snow
  on the ground and thick clouds like cumuli and
  cumulonimbi.

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Cumuliform Cloud High Albedo
Snow
High Albedo
Bare soil (low albedo)
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Infrared Satellite Imagery

• Infrared satellite imagery is constructed from
  the terrestrial radiation in the longwave band 1.
  Cold objects, such as the tops of cumulonimbi or
  cirrus clouds, emit less radiation. Generally,
  cold objects, are depicted as bright regions on
  infrared images. Warm objects, such as the
  Earths surface or low clouds, emit more
  radiation and are generally depicted as darker
  areas on infrared satellite images.

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Stefan-Boltzmann Law

• E s T4
• where
• E is the energy emitted by the object
• s is the Stefan-Boltzmann constant
• T is the temperature of the object in Kelvins

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Cirrus T -50C
Cloud top T -45C
Cumulo- nimbus
Surface T 20C
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Water Vapor Imagery

• Water vapor imagery is constructed from emitted
  radiation in the upper level water vapor band.
  Regions of the upper troposphere with higher
  concentrations of water vapor emit more infrared
  (longwave) radiation in this band.

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Water Vapor Imagery (Cont.)

• Generally, more humid areas in the upper
  troposphere appear as bright regions on water
  vapor images and drier areas appear as darker
  regions.
• Looping of water vapor images provides an
  indication of the flow of air in the upper levels
  of the troposphere.

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GOES Special Rapid Scan Imaging

• Rapid Scan Operations (RSO) imagery is
  collected over a reduced area at 7.5 minute
  intervals.
• Super Rapid Scan Operations (SRSO) imagery is
  collected over a greatly reduced sector at 1
  minute or 30 second intervals. The 1 minute
  interval produces 22 images in an hour in 2
  segments of 11.

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GOES Imaging

• Normal operation (times are past the hour)
• 0-15 minutes full disk scan
• 16-30 minutes full disk scan
• 31-45 minutes full disk scan
• 46-60 minutes full disk scan
• Total of 4 full disk scans per hour.

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GOES Imaging (Cont.)

• Rapid Scan Operations (times are past the top of
  the hour).
• 0-15 minutes normal full disk scan
• 15-22.5 minutes Rapid Scan
• 22.5-30 minutes Rapid Scan
• 31-45 minutes normal full disk scan
• 45-52.5 minutes Rapid Scan
• 52.5-60 minutes Rapid Scan

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GOES Imaging (Cont.)

• Super Rapid Scan Operations (times are minutes
  past the top of the hour).
• 0-15 minutes normal full disk scan
• 17-18 minutes 1 Super Rapid Scan
• 18-28 minutes 10 Super Rapid Scans
• 30-45 minutes normal full disk scan
• 47-48 minutes 1 Super Rapid Scan
• 48-58 minutes 10 Super Rapid Scans

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GOES Sounder Channels

• Ch. 1 14.7 µm Ch. 2 14.4 µm
• Ch. 3 14.1 µm Ch. 4 13.6 µm
• Ch. 5 13.3 µm Ch. 6 12.7 µm
• Ch. 7 12.0 µm Ch. 8 11.0 µm
• Ch. 9 9.7 µm Ch. 10 7.4 µm
• Ch. 11 - 7.0 µm Ch. 12 - 6.5 µm
• Ch. 13 - 4.57 µm Ch. 14 - 4.53 µm

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GOES Sounder Channels (Cont.)

• Ch. 15 4.45 µm Ch. 16 4.13 µm
• Ch. 17 3.98 µm Ch. 18 3.76 µm
• Vis 0.68 µm

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GOES Sounder Products

• Total Precipitable Water (PW)
• Lifted Index
• Showalter index
• Cloud Top Pressure

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Polar-orbiting Operational Environmental
Satellites (POES)

• POES are currently operated by NOAA and the
  Defense Meteorological Satellite Program (DMSP).
  These two programs are merged into the National
  Polar-orbiting Operational Environmental
  Satellite System (NPOESS).

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Polar-orbiting Research Meteorological Satellites

• Agencies such as NASA launch research satellites
  to demonstrate technology, but operational
  meteorologists will use some of the products of
  these satellites.
• Examples of this include the TRMM (Tropical
  Rainfall Monitoring Mission) and the SeaWinds or
  QuikSCAT satellite.

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Operating POES

• METOP-A
• NOAA-15
• NOAA-16
• NOAA-17
• NOAA-18

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Some Sources of Real Time Satellite Imagery

• http//www.goes.noaa.gov
• http//www.ssd.noaa.gov
• http//cimss.ssec.wisc.edu
• http//www.nhc.noaa.gov/satellite/shtml
• http//www.nrlmry.navy.mil/tc_pages/tc_home.html

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Some Other Satellite Links

• http//www.oso.noaa.gov
• http//www.cira.colostate.edu/ramm/visit/satellite
  _links.html

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Supplemental Readings

• Kidder, S.Q. and T.H. Vonder Haar, 1995
  Satellite Meteorology An Introduction. Academic
  Press, San Diego, 466 pp.
• Menzel, W.P. and J.F.W. Purdom, 1994 Introducing
  GOES-I The First of a New Generation of
  Geostationary Environmental Satellites. Bulletin
  of the American Meteorological Society, 75,
  757-781

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Supplemental Readings (Cont.)

• Legeckis, R. and T. Zhu, 1997 Sea Surface
  Temperatures from the GOES-8 Geostationary
  Satellite. Bulletin of the American
  Meteorological Society, 78, 1971-1987.