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

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

Sources of Student Data  The CERES S’COOL Project –More than 35,000 complete observations –9,172 now have corresponding CERES data – The GLOBE Program –More than 2.5 M cloud data points –

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

The S’COOL Concept Students provide ground observations for CERES overpass 1. Determine satellite overpass time 2. Observe cloud properties 3. Transmit results to NASA 4. Compare to satellite-retrieved properties Data of value to CERES scientists Real-world learning for students

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

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

FIRST S’COOL Comparison Cloud Observations Over Gloucester, VA January 13 & 17, 1997

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

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

Cloud Layer Comparison

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

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

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

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

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.

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?

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

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

Subvisual Cirrus? MODIS vs GLOBE cloud type comparison indicated some subvisual cirrus (Stephens and Rogers, 2004). This CERES/S’COOL dataset: 19 cases where  tot < 3 None high cloud only 5 cases where  tot < 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.

Cloud Layer Comparison

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)

Snow Effect on Cloud Amount All Ground Observers ClrPCMCOV SATSAT Clr PC MC OV Snow/Ice Ground Observers ClrPCMCOV SATSAT Clr PC MC OV Chi-squared = 671

Snow Effect on Cloud Amount All - scaled Ground Observers ClrPCMCOV SATSAT Clr PC MC OV Snow/Ice Ground Observers ClrPCMCOV SATSAT Clr PC MC OV

Snow Effect on Cloud Layers All Ground Observers No Cloud 1-layerMulti- layer SATSAT No Cld layer Multi Snow/Ice Ground Observers No Cloud 1-layerMulti- layer SATSAT No Cld layer Multi

Snow Effect on Cloud Layers All - scaled Ground Observers No Cloud 1-layerMulti- layer SATSAT No Cld layer Multi Snow/Ice Ground Observers No Cloud 1-layerMulti- layer SATSAT No Cld layer Multi

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.

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:

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.