Remote Sensing Imagery

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Remote Sensing Imagery

• Clouds

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Today

• Discussion
• Imagery Presentation
• Class activity
• Cloud spotting
• Clouds

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Converting data

• We know all about the sensor from pre-flight
  calibration
• So instead of actually finding the energy and
  then converting we do a straight conversion from
  the byte value to albedo
• This will be something like

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Real albedo

• Have to take account of illumination as albedo is
  the proportion reflected
• If incoming solar changes, then reflected energy
  changes
• We should know incoming solar, based on time of
  year, day and latitude

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Presentation of data

• The numerical values of albedo, temperature or
  other measurements are converted into a colour
  scale for presentation as an image
• The standard scales are as follows

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Visible grey scale
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The scale

• Brighter pixels mean higher albedo Brighter
  surface
• Sea is dark, land is medium, clouds are bright
• Different land types have different brightness
• Different clouds have different brightness

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Monday Morning
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Monday Morning
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IR Grey scale

• Brighter means colder Lower temperatures
• Clouds appear white (as we like them)
• Dark areas are warm

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Check this out

• http//www.comet.ucar.edu/dstreme/sat/composite_ir
  .html

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IR colour scale
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IR colour Scale

• Warmer colours are warmer
• Colder colours are colder
• Clouds appear blue
• Colder clouds appear deeper blue or violet or
  indigo

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Water Vapour Grey scale
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WV grey scale

• Brighter areas show more water vapour
• WV is an integrated quantity all the water
  vapour in the column is shown. Determining low or
  upper level moisture is another matter. (More
  details later)
• White areas show cloud areas of liquid water
  (atmosphere must be saturated, so lots of water
  vapour)

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WV Grey/colour scale scale
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Enhanced WV grey scale

• Cold coloration used to depict clouds.
• Warm colours show very dry areas.
• Actual scale is temperature (6.7µm channel
  detects temperature of WV), therefore detection
  is of mean WV level in the atmosphere.

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So called true color

• Using red-green-blue (rgb) colouring using
  different channels to create an image with
  colours we might expect
• Sea appears blue
• Land appears yellow/brown or green depending on
  the measure of vegetation (NDVI see later)

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True colour Mexico