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Sounders

Sounders. METR280 Satellite Meteorology/Climatology. 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

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Sounders

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  1. Sounders METR280 Satellite Meteorology/Climatology

  2. 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

  3. 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

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

  5. What is a “sounder”? • A sensor for collecting vertical profiles of temperature and moisture using sensors with multiple, narrow bands

  6. How do sounders work? • Weak absorption channels effective emission level is near surface • Strong absorption channels: upper atmosphere • Moderate absorption channels: vary in altitude

  7. Sounding theory • Assume free of scattering (no clouds) • We must account for: • Earth’s emission (“absorption spectra”) • Transmission between layers • Weighting function

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

  9. 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)

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

  11. 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.

  12. Example: GOES-8 Transmittances

  13. Weighting Functions for GOES

  14. Weighting Functions for GOES

  15. Weighting Functions for GOES

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

  17. GOES-8/9 Sounder - Channel 8

  18. GOES-8/9 Sounder - Channel 7

  19. GOES-8/9 Sounder - Channel 6

  20. GOES-8/9 Sounder - Channel 5

  21. GOES-8/9 Sounder - Channel 4

  22. GOES-8/9 Sounder - Channel 3

  23. GOES-8/9 Sounder - Channel 2

  24. GOES-8/9 Sounder - Channel 1

  25. GOES-8/9 Sounder - Channel 11Water Vapor

  26. GOES-8/9 Sounder - Channel 12Water Vapor

  27. The “retrieval problem” • What temperatures (gas concentrations) could have produced the observed set of radiances? • An infinite number of solutions exist • (#$%@!)

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

  29. 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

  30. 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

  31. GOES 8/10 hourly sounder coverage 10 8 8B 10 8A 8C

  32. 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

  33. Resolution and effect of clouds • GOES Sounder Field of View (FOV) - 10 km at nadir • Sounder Radiances Processed Using Arrays • 5x5 FOV’s - Operational • 3x3 FOV’s - Experimental • Clouds Act as a Radiating Surface, Contaminate IR Measurements

  34. Resolution and effect of clouds • Individual FOV’s Screened for Clouds • Cloud-Free Sounder FOV’s Used to Generate Sounding • 9 - 25 Clear FOV’s Required - Operational • 1 - 9 Clear FOV’s Required - Experimental

  35. GOES-9 TPW (mm)8 JAN 1998 1500 GMT Tan: 0 - 9 mmYellow: 10 - 19 mmGreen: 20 - 29 mm

  36. GOES-9 TPW (mm) – Phoenix, AZ

  37. 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

  38. 00Z 06Z 12Z 18Z 00Z 12Z ETA 12,18hr Fcst 00Z ETA 06,12hr Fcst 00Z ETA 12,18hr Fcst 12Z ETA 06,12hr Fcst ETA Forecast Used as Initial Conditions • Forecast Temperature and Moisture Profiles Interpolated to GOES Sounding Location and Time

  39. 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

  40. Little Change to ETA T/Td ForecastGOES-9 Sounding - Phoenix, AZ 6 JAN 98 15 GMT

  41. Big Change to ETA T/Td ForecastGOES-9 Sounding - Gainesville, FL 6 JAN 98 15 GMT

  42. GOES Observed BT’s - ETA Computed BT’s • Larger differences are observed in Gainesville sounding, particularly in channels sensitive to atmospheric moisture

  43. 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

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

  45. 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

  46. ETA Model Impact Study (NCEP) August 1997Equitable Threat Score - Precipitation

  47. 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

  48. 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

  49. GOES-8 Visible Imagery 1915Z 7/13/97 - 0115Z 7/14/97

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