Sounders

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Sounders

• METR280 Satellite Meteorology/Climatology

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Partially based on the following...
Short Course on Satellite Meteorology
AMS 78th Annual Meeting
Phoenix, Arizona
Applications and Interpretation Part 3 -
Sounder Products and Applications
Donald G. Gray NOAA/NESDIS Office of Research and
Applications Washington, DC
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Outline

• Brief review of sounder fundamentals, including
  absorption spectra and weighting functions
• Characteristics of GOES soundings (spatial
  coverage, production methodology, derived
  parameters) and validation
• Applications of GOES sounding products to weather
  analysis and forecasting

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Atmospheric Soundings

• How can we retrieve vertical profiles of
  temperature and moisture information from
  satellite data?

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What is a sounder?

• A sensor for collecting vertical profiles of
  temperature and moisture using sensors with
  multiple, narrow bands

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How do sounders work?

• Weak absorption channels effective emission level
  is near surface
• Strong absorption channels upper atmosphere
• Moderate absorption channels vary in altitude

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Sounding theory

• Assume free of scattering (no clouds)
• We must account for
• Earths emission (absorption spectra)
• Transmission between layers
• Weighting function

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Fundamentals of Soundings

• Absorption spectra
• Transmittances, weighting functions
• Examples of GOES sounder channels
• Longwave CO2
• H2O
• Shortwave CO2
• Visible

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Absorption Spectra - IR

• Carbon dioxide (CO2)
• Longwave 11 - 18 mm (Surface/ Atmospheric
  Temperature)
• Shortwave 4 - 6 mm (Surface/Lower Atmospheric
  Temperature)
• Water Vapor (H2O)
• Midwave 6 - 10 mm (Atmospheric Moisture)
• Ozone (O3)
• 9.6 mm (Total Column Atmospheric Ozone)

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Fundamentals of Soundings

• Absorption spectra
• Transmittances, weighting functions
• Examples of GOES sounder channels
• Longwave CO2
• H2O
• Shortwave CO2
• Visible

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Transmittances and weighting functions

• Transmittance Percent of radiation of
  particular wavelength transmitted through
  atmosphere
• Transmittance 1 - Emissivity
• Weighting Function Derivative of transmittance
  with respect to height (lnP). Larger values
  correspond to atmospheric layers with the
  greatest contribution to radiance values.

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Example GOES-8 Transmittances
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Weighting Functions for GOES
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Weighting Functions for GOES
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Weighting Functions for GOES
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Fundamentals of Soundings

• Absorption spectra
• Transmittances, weighting functions
• Examples of GOES sounder channels
• Longwave CO2
• H2O
• Shortwave CO2
• Visible

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GOES-8/9 Sounder - Channel 8
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GOES-8/9 Sounder - Channel 7
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GOES-8/9 Sounder - Channel 6
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GOES-8/9 Sounder - Channel 5
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GOES-8/9 Sounder - Channel 4
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GOES-8/9 Sounder - Channel 3
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GOES-8/9 Sounder - Channel 2
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GOES-8/9 Sounder - Channel 1
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GOES-8/9 Sounder - Channel 11Water Vapor
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GOES-8/9 Sounder - Channel 12Water Vapor
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The retrieval problem

• What temperatures (gas concentrations) could have
  produced the observed set of radiances?
• An infinite number of solutions exist
• (_at_!)

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Retrieval methods

• Physical
• Based on knowledge of radiative transfer
• Statistical
• Based on comparison to archive of radiosonde
  observations
• Hybrid
• Combination of physical and statistical

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Characteristics of GOES soundings

• Spatial coverage and frequency
• Production methodology
• Resolution, effect of clouds
• Use of NWP model forecasts
• Quality assessment
• Radiosonde comparison statistics
• ETA forecast model impact study

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Spatial coverage and frequency

• Scan cycle is one hour
• Two scans each, GOES 8 and 10
• GOES-8
• 35 Minutes - Eastern CONUS
• 20 Minutes - Selectable Atlantic Sector
• GOES-10
• 20 Minutes - Western CONUS
• 35 Minutes - Pacific Sector
• No Southern Hemisphere coverage

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GOES 8/10 hourly sounder coverage
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8
8B
10
8A
8C
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Characteristics of GOES soundings

• Spatial coverage and frequency
• Production methodology
• Resolution, effect of clouds
• Use of NWP model forecasts
• Quality assessment
• Radiosonde comparison statistics
• ETA forecast model impact study

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Resolution and effect of clouds

• GOES Sounder Field of View (FOV) - 10 km at nadir
• Sounder Radiances Processed Using Arrays
• 5x5 FOVs - Operational
• 3x3 FOVs - Experimental
• Clouds Act as a Radiating Surface, Contaminate IR
  Measurements

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Resolution and effect of clouds

• Individual FOVs Screened for Clouds
• Cloud-Free Sounder FOVs Used to Generate
  Sounding
• 9 - 25 Clear FOVs Required - Operational
• 1 - 9 Clear FOVs Required - Experimental

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GOES-9 TPW (mm)8 JAN 1998 1500 GMT
Tan 0 - 9 mm Yellow 10 - 19 mm
Green 20 - 29 mm
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GOES-9 TPW (mm) Phoenix, AZ
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Characteristics of GOES soundings

• Spatial coverage and frequency
• Production methodology
• Resolution, effect of clouds
• Use of NWP model forecasts
• Quality assessment
• Radiosonde comparison statistics
• ETA forecast model impact study

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ETA Forecast Used as Initial Conditions

• Forecast Temperature and Moisture Profiles
  Interpolated to GOES Sounding Location and Time

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NAM Forecast Used as Initial Conditions

• Sounder Radiances Computed from NAM Forecast
• Observed Radiances Corrected for Bias Relative to
  Forecast
• Differences Between Computed and Observed
  Radiances Used to Modify Initial NAM Profile
• Adjustments Made Primarily to Moisture Profile

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Little Change to ETA T/Td ForecastGOES-9
Sounding - Phoenix, AZ 6 JAN 98 15 GMT
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Big Change to ETA T/Td ForecastGOES-9 Sounding -
Gainesville, FL 6 JAN 98 15 GMT
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GOES Observed BTs - ETA Computed BTs

• Larger differences are observed in Gainesville
  sounding, particularly in channels sensitive to
  atmospheric moisture

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Characteristics of GOES soundings

• Spatial coverage and frequency
• Production methodology
• Resolution, effect of clouds
• Use of NWP model forecasts
• Quality assessment
• Radiosonde comparison statistics
• ETA forecast model impact study

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Colocation Statistics - TPW (mm)Radiosondes vs.
ETA Forecast and GOES Soundings
Root Mean Square Error
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Characteristics of GOES soundings

• Spatial coverage and frequency
• Production methodology
• Resolution, effect of clouds
• Use of NWP model forecasts
• Quality assessment
• Radiosonde comparison statistics
• ETA forecast model impact study

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ETA Model Impact Study (NCEP) August
1997Equitable Threat Score - Precipitation
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Applications/Examples

• Nowcasting/Forecasting of severe weather
• Individual soundings and associated parameters
  (e.g. stability indices)
• Horizontal fields of derived products
• Gradient winds
• Derived product images
• Sounder water vapor winds
• Cloud amount and cloud top pressure

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Eastern Kansas, July 13-14, 1997

• GOES visible
• Severe weather reports
• ETA precipitation forecast
• Precipitable water and lifted index fields
• ETA forecast
• GOES soundings
• Time tendency analyses

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GOES-8 Visible Imagery 1915Z 7/13/97 - 0115Z
7/14/97
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Severe Weather Reports 23Z 7/13/97 - 05Z 7/14/97
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ETA 00-12 Hour Precip Forecast (mm) Valid 00Z
7/14/97
GOES-8 Visible Image 00Z 7/14/97
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ETA Forecast TPW 18Z-00Z 7/13/97 (2 Hour
Intervals)
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GOES TPW 18Z-00Z 7/13/97 (2 Hour Intervals)
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ETA Forecast LI 18Z - 00Z 7/13/97 (2 Hour
Intervals)
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GOES LI 18Z - 00Z, 7/13/97 (2 Hour Intervals)
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ETA/GOES 4 Hour Time Tendency (LI) 18Z-22Z
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ETA/GOES 4 Hour Time Tendency (TPW) 18Z - 22Z
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Applications/Examples

• Nowcasting/Forecasting of severe weather
• Individual soundings and associated parameters
  (e.g. stability indices)
• Horizontal fields of derived products
• Gradient winds
• Derived product images
• Sounder water vapor winds
• Cloud amount and cloud top pressure

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Phoenix, Arizona 6 Jan 98 20 GMT - 7 Jan 98
19GMT
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Applications/Examples

• Nowcasting/Forecasting of severe weather
• Individual soundings and associated parameters
  (e.g. stability indices)
• Horizontal fields of derived products
• Gradient winds
• Derived product images
• Sounder water vapor winds
• Cloud amount and cloud top pressure

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Applications/Examples

• Nowcasting/Forecasting of severe weather
• Individual soundings and associated parameters
  (e.g. stability indices)
• Horizontal fields of derived products
• Gradient winds
• Derived product images
• Sounder water vapor winds
• Cloud amount and cloud top pressure

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GOES-8 500mb Gradient Winds - Montserrat
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Applications/Examples

• Nowcasting/Forecasting of severe weather
• Individual soundings and associated parameters
  (e.g. stability indices)
• Horizontal fields of derived products
• Gradient winds
• Derived product images
• Sounder water vapor winds
• Cloud amount and cloud top pressure

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Derived Product Image - TPW 6 Jan 98 21 GMT
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Summary

• GOES Soundings Provide 24 Hour High Resolution
  Coverage for CONUS and Adjacent Ocean Areas
• Horizontal Resolution of 50KM (30KM Currently
  in Experimental Mode)
• Provide Information on Mesoscale Features of
  Moisture and Stability in Pre-Convective
  Environments
• Case Studies Indicate Strong Correlation Between
  GOES Soundings Fields and Convective Development

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Summary

• Positive impact demonstrated using GOES TPW in
  ETA Forecast Model
• Other Applications Depiction of Moisture
  Eastern Pacific, Gulf of Mexico Return Flow,
  Southwest Monsoons, East Coast Winter Storms

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Summary

• Limitations
• Coarse vertical resolution (3 - 4 km)
• Soundings Precluded in Cloudy Areas
• Geographic Coverage Limited by Slow Scan Rate
• Retrieval of Boundary Layer T/Td Not Possible

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Acknowledgements - Don Gray
Bill Smith, Kit Hayden and Paul Menzel
Tim Schmit, Tony Schreiner, CIMSS, University of
Wisconsin
Jaime Daniels (NOAA), Gary Gray (Raytheon/Hughes)
Web Addresses (NOAA/NESDIS/ORA)
http//orbit7i.nesdis.noaa.gov8080/temp.html
GOES Sounder Products
http//orbit7i.nesdis.noaa.gov8080/goes.html
Other GOES Quantitative Products
http//orbit7i.nesdis.noaa.gov8080/index.html
POES/GOES Satellite Products