1. METR280 Satellite Meteorology/Climatology
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?
Purposes
– Augment information from rawinsonde data, typically for use in numerical models
– Also used to determine concentrations of gases that are absorbers (such as ozone)
Advantages
– Complete temporal coverage (rawinsondes only 2X/day)
– Much better spatial coverage... oceans
Disadvantages
– Much more difficult to interpret than radiosondes
– Clouds (MW better than IR here)
– Limited vertical resolution

5. What is a “sounder”?
A sensor for collecting vertical profiles of temperature and moisture using sensors with multiple, narrow bands
Narrow bands
– Sensitive to a small electromagnetic region.
Multiple bands?
– Need 1 band for each level you wish to resolve

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
Absorption channel
– Ranges of wavelengths (regions of the EM spectrum) that absorb (and therefore emit) radiation. This is due to “radiatively active” gasses such as CO2, H2O, O3.
– Therefore, sensor operating in atmospheric channel can detect temperature of that gas or moisture content (if in a H2O abs.chan.)
Effective emission level
– Altitude from which radiation reaching the sensor is being emitted.
– Weak absorption channel: surface energy absorbed close to surface, then relatively unaffected until it gets to satellite
– Strong absorption channels: energy keeps getting emitted by each layer then absorbed by the next higher layer.
Satellite sees “top” layer
– Moderate absorption channel: These are the key to sounders

7. Sounding theory Assume free of scattering (no clouds)
We must account for:
Earth’s emission (“absorption spectra”)
Transmission between layers
Weighting function
Weighting function
– Tell us how important each channel is for determining the moisture (gas concentration) at a particular height
– At each channel, the satellite “sees” to a different depth within the atmosphere... weaighting function tells us where each channel is looking
– Where each channel “sees” overlaps (each channel may see an 8km thick layer), but they “see best” at a particular layer

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: mm (Surface/ Atmospheric Temperature)
Shortwave: mm (Surface/Lower Atmospheric Temperature)
Water Vapor (H2O)
Midwave: mm (Atmospheric Moisture)
Ozone (O3)
9.6 mm: (Total Column Atmospheric Ozone)

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

12. 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.

13. Example: GOES-8 Transmittances

14. Weighting Functions for GOES

15. Weighting Functions for GOES

16. Weighting Functions for GOES

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

18. GOES-8/9 Sounder - Channel 8

19. GOES-8/9 Sounder - Channel 7

20. GOES-8/9 Sounder - Channel 6

21. GOES-8/9 Sounder - Channel 5

22. GOES-8/9 Sounder - Channel 4

23. GOES-8/9 Sounder - Channel 3

24. GOES-8/9 Sounder - Channel 2

25. GOES-8/9 Sounder - Channel 1

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

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

28. The “retrieval problem”
What temperatures (gas concentrations) could have produced the observed set of radiances?
An infinite number of solutions exist

29. Retrieval methods Physical Statistical Hybrid
Based on knowledge of radiative transfer
Statistical
Based on comparison to archive of radiosonde observations
Hybrid
Combination of physical and statistical
Physical
– Must start with some kind of “first guess” in order to find the right solution
Climatology from radiosondes
Recent, nearby radiosonde observations
Statistical
– Usually using regression analysis
– A different set of regression coefficients for different latitudes (5 latitude bands for TOVS) and are frequenctly updated (weekly for TOVS)

30. 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

31. 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

32. GOES 8/10 hourly sounder coverage8B 10 8A 8C

33. 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

34. 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

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

36. GOES-9 TPW (mm) 8 JAN GMT
Tan: mm Yellow: mm Green: mm

37. GOES-9 TPW (mm) – Phoenix, AZ

38. 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

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

40. 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

41. Little Change to ETA T/Td Forecast GOES-9 Sounding - Phoenix, AZ 6 JAN 98 15 GMT

42. Big Change to ETA T/Td Forecast GOES-9 Sounding - Gainesville, FL 6 JAN 98 15 GMT

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

44. 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

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

46. 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

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

48. 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

49. 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

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

51. Severe Weather Reports: 23Z 7/13/97 - 05Z 7/14/97

52. ETA 00-12 Hour Precip Forecast (mm) Valid 00Z 7/14/97
GOES-8 Visible Image 00Z 7/14/97

53. ETA Forecast TPW 18Z-00Z 7/13/97 (2 Hour Intervals)

54. GOES TPW 18Z-00Z 7/13/97 (2 Hour Intervals)

55. ETA Forecast LI 18Z - 00Z 7/13/97 (2 Hour Intervals)

56. GOES LI 18Z - 00Z, 7/13/97 (2 Hour Intervals)

57. ETA/GOES 4 Hour Time Tendency (LI) 18Z-22Z

58. ETA/GOES 4 Hour Time Tendency (TPW) 18Z - 22Z

59. 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

61. Phoenix, Arizona 6 Jan 98 20 GMT - 7 Jan 98 19GMT

62. 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

64. 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

65. GOES-8 500mb Gradient Winds - Montserrat

66. 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

67. Derived Product Image - TPW 6 Jan 98 21 GMT

68. 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

69. 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

70. 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

71. 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)
GOES Sounder Products
Other GOES Quantitative Products
POES/GOES Satellite Products