Comparison of Insitu and Satellite derived soundings

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Comparison of In-situ and Satellite derived
soundings

• LT Michael Vancas

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Advanced Microwave Sounding Unit (AMSU)

• Polar orbiting satellites (NOAA-15)
• 15 channels for temperature
• channels 12 for near surface
• 5 channels for humidity soundings
• amsu.cira.colostate.edu/
• Microwave spectrum
• Passive (outgoing Terrestrial emission)

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Microwave Spectrum
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Weighting functions are used to correct the
brightness temperature for each AMSU channel.
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Weighting functions for channels sensing nearest
the surface must account for the different
emissivity of the surface
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AMSU-B channels sense tropospheric moisture
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Satellite derived soundings

• Advantages
• Remote locations
• Requires little infrastructure
• Easily ingested into model fields
• Generate many products
• Rain Rates
• Snow Cover

• Disadvantages
• Require heavy computing
• Complicated code
• Limb corrections
• Boundary conditions
• Atmospheric effects
• CLW
• Precip
• Dust

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Example Products
Snow is bad

• Rain Rate product
• Derived from AMSU
• Global product
• Several passes
• No good over snow covered land
• equatorial gaps
• Calculated using changes in Tb caused by rainfall
  (AMSU-A)

Gaps in coverage at EQ
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Another Example

• Total Precipitable Water
• Shows water vapor available to form precipitation
• Again, subject to limits over land, snow cover
  and near the equator
• Time averaged

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Data Collected

• Insitu Measurements conducted on the Cruise
• Balloon launches
• Processed and figures generated by Mary Jordan
• AMSU-A data collected by NRL
• Preprocessing by Joe Turk and Clay Blankenship at
  NRL

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Limitations

• PCRTM trials and tribulations
• Program promises to be very useful, several
  professors have expressed an interest
• Very complicated code
• Only partial success thus far
• Able to generate AMSU-A Brightness temperatures
• Unable to fully integrate with Rawinsonde data
• TB's generated for 15 channels only, unable to
  generate Lat/Lon information
• Forward Radiative Transfer Model requires
  Rawinsonde field as boundary conditions

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Rawinsonde vs TB
jump likely caused by cloud cover
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Previous slide discussion

• The TB plot generated shows the Brightness
  temperature at the center of the channel
• TB temperatures are "lower" than would be found
  in the actual atmosphere due to nature of MW
  radiation emissions
• Decreases with height
• Rawinsonde data is (near) continuous vice
  extremely discretized

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Goes satellite derived sounding vs Rawinsonde
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Conclusions

• AMSU derived satellite products very promising
• Limited by several factors
• Revisit time (several hours)
• partial fix is increased number of satellites
• computing resources
• Radiative xfr models

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Questions?