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Students as Ground Observers for Satellite Cloud Retrieval Validation

This study explores the use of student data in validating satellite cloud retrievals, focusing on the S'COOL (Students' Cloud Observations On-Line) project. It discusses data sources, comparisons, proof of concept, new comparisons, and the impact of bright surfaces on cloud retrievals.

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Students as Ground Observers for Satellite Cloud Retrieval Validation

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  1. Students as Ground Observers for Satellite Cloud Retrieval Validation Lin H. Chambers, P. Kay Costulis, David F. Young NASA Langley Research Center, Hampton, VA Tina M. Rogerson Science Applications International Corporation, Hampton, VA 13th Conference on Satellite Meteorology & Oceanography Norfolk, VA Sept. 2004

  2. OUTLINE • Sources of student data • What is the S’COOL Project? • Comparisons • Proof of Concept • New Comparisons • Bright Surfaces • Conclusions

  3. Sources of Student Data • The CERES S’COOL Project • More than 35,000 complete observations • 9,172 now have corresponding CERES data • http://scool.larc.nasa.gov • The GLOBE Program • More than 2.5 M cloud data points • http://www.globe.gov

  4. What is S’COOL? • Began Jan. 1997 • Students’ Cloud Observations On-Line • K-12 Education and outreach portion of CERES: Clouds and the Earth's Radiant Energy System • 1700+ participants in 65 countries • Focused on obtaining ground-based cloud observations for validation of the CERES data

  5. The S’COOL Concept • Students provide ground observations for CERES overpass • Determine satellite overpass time • Observe cloud properties • Transmit results to NASA • Compare to satellite-retrieved properties • Data of value to CERES scientists • Real-world learning for students

  6. Data Collected Cloud type Contrails Cloud cover Visual opacity Surface Cover Surface Measurements Comments

  7. Comparing to Satellite • S’COOL Site Matched to 1 degree Satellite Region • Observation Times Within 15 Minutes

  8. FIRST S’COOL ComparisonCloud Observations Over Gloucester, VAJanuary 13 & 17, 1997

  9. Initial Comparisons:Proof of Concept • Measurements in 1998 • CERES on TRMM only (~50 correspondences) • Augmented with AVHRR and geostationary data (~50): Analyzed by hand

  10. Cloud Amount Comparison 62% in complete agreement 0% in complete disagreement Stats: Chi-Squared value of 82; significant to 5e-12

  11. Cloud Layer Comparison

  12. Interim Conclusions • Clearly some useful information • Insight into cloud layering • Insight into sparse, thin cirrus • Educationally a big success

  13. New Comparisons - 2004 • New CERES angular models • (see talk by Loeb this afternoon) • CERES on TRMM, Terra, Aqua • Feb. 1998 to April 2004 • Production data products

  14. Data Available Max: 479 (High School in Pennsylvania) Min: 1 (70 schools)

  15. Cloud Amount Comparison 54.5% in complete agreement 2% in complete disagreement Stats: Chi-Squared value of 5636; significant!!!

  16. Students Overcast vs. Satellite Clear (48 cases) • Spatial Mismatch?: >1/3 are schools located less than 0.1 degree from the edge of a lat/long grid box. • Universal Time?: 3 cases with incorrect UT • Student/Satellite error?: remaining cases have no clear explanation. Study needed. • Snow: 10 cases, yet the satellite still reports clear sky.

  17. Students Clear vs.Satellite Overcast (143 cases) • Spatial mismatch?: About 22% • Universal Time?: ~10 • Snow?: 18 cases students report snow. • Only one satellite retrieval is suspect: low cloud temperature 2.5K below the surface temperature. • Satellite/Student error?: stratus = clear?

  18. Cloud Amount Comparison 191 3-class errors (2%) - ~1/3 easily explainable 711 2-class errors (8%) - need more study 3271 1-class errors (36%) - may be near-matches

  19. First look at 1-class errors Students say 0-5% cloud Satellite says 5-50% cloud 20% of CERES has 10 < fc < 15 24% of CERES has 5 < fc < 10

  20. Subvisual Cirrus? • MODIS vs GLOBE cloud type comparison indicated some subvisual cirrus (Stephens and Rogers, 2004). • This CERES/S’COOL dataset: • 19 cases where ttot< 3 • None high cloud only • 5 cases where ttot < 1 • None high clouds • No evidence of subvisual cirrus in this dataset • May be due to location of the S’COOL student data, over land with few data points in the Tropics.

  21. Cloud Layer Comparison

  22. Effect of Bright Surfaces • 1057 reports (~11%) with snow or ice in ground report • Data from 1/4 of respondents Max - 86 (4th grade in NH) Min - 1 (31 schools)

  23. Snow Effect on Cloud Amount Chi-squared = 671

  24. Snow Effect on Cloud Amount

  25. Snow Effect on Cloud Layers

  26. Snow Effect on Cloud Layers

  27. Conclusions First major analysis of student ground observer data to validate cloud retrievals from a satellite instrument. A few pitfalls are evident. Useful information can be derived.

  28. Future Plans Inviting S’COOL participants to do detailed analysis of their correspondences More analysis to be done (2-class and 1-class errors, cloud levels, opacity….) Data available via the Internet for analysis: http://asd-www.larc.nasa.gov/SCOOL/usedata.html

  29. Acknowledgments Science and Education support from NASA’s Earth Science Enterprise. This work would not be possible without the participation of our extended network of educators and their students, and we thank them most sincerely for their efforts.

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