November 16, 2011
Students Help NASA Validate Satellites With Cloud Observations
In between recess, geography class and eating the lunch their moms packed, NASA scientists have found the time to help validate Earth-observing satellites.
These scientists are the younger variety -- students in NASA's S'COOL project (Students' Cloud Observations On-Line), a worldwide effort to collect cloud observations from the ground.
The students make observations like a NASA scientist and submit reports for their area to NASA. In return, the students receive a corresponding cloud observation from a NASA satellite to help them compare and learn.
This week, the S'COOL program received its 100,000th cloud observation, prompting a look into what NASA has been doing with all of these cloud observations.
"We often hear about how NASA satellite data helps students, but there are also quite a few things the students do for us," says Lin Chambers, the lead for the S'COOL program, which is based out of NASA's Langley Research Center in Hampton, Va.
According to Chambers, the most common way S'COOL ground observations help scientists is by confirming the presence of clouds in areas and under conditions that are challenging for satellite instruments.
For example, in a number of instances, students submitted cloud observations that reported a single layer of clouds in their area while the corresponding satellite was reporting a clear sky.
When the S'COOL team looked further into this discrepancy, they found that students were reporting small amounts of thin cirrus clouds, which are not detectable by the Clouds and Earth's Radiant Energy System (CERES)/Imager algorithm for the Tropical Rainforest Measuring Mission (TRMM) spacecraft or the CERES/Imager algorithms for the Terra and Aqua satellites. With these student observations, scientists can now quantify how often satellites overlook cirrus clouds.
"The data are most useful to help confirm the cloud scenes that we know are difficult to detect with passive remote sensing," says David Young, a NASA climate scientist who served as the first S'COOL science advisor. "You can't see through layers, so you often miss low clouds that are under high clouds. It has been useful to get these data to see how often that occurs."
Other tricky circumstances for satellites are observing clouds in areas with bright surfaces, such as snow, and complex surfaces, such as mountains.
Strong agreement between satellite data and student observations from snowy or icy areas helped NASA scientists confirm that the CERES instrument can in fact make cloud observations when surfaces are bright. To analyze satellite capabilities in areas with complex backgrounds, scientists looked instead toward student observations that reported clear skies.
"Seeing a completely clear sky from the satellite can be a challenge in certain circumstances, given the variable background of the Earth's surface," explained Chambers. "Once again, S'COOL observers helped scientists make sure that their satellites were making accurate observations."
Student observations have also provided a more accurate approach for comparing cloud cover between the ground and the satellite. This improvement came as a result of another inconsistency found between satellite and S'COOL observations -- students were reporting clear skies while satellites were reporting overcast skies.
"The S'COOL team found this difference often occurred when observers were located on the edge of a longitude and latitude line, and in many cases, student observations were being compared to satellite data that covered a different grid region than their actual location," explains Chambers.
Additional studies are currently underway comparing S'COOL student reports to new data on cloud layers from the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) and CloudSat satellites in NASA's A-Train satellite constellation. A fifth edition of CERES will also be launching October 2011 on the NPOESS Preparatory Project (NPP) satellite, providing another opportunity for S'COOL observers to coordinate cloud observations.
While science goals were never the primary goal of the S'COOL program, Young explains that he and other scientists are proud that these results have been published, especially since these science outcomes are not very common with student outreach projects.
"People often ask why we don't just use the data from trained cloud observers at the weather stations and airports," says Young. "The answer is that we do. However, the S'COOL measurements are valuable because they are timed to coincide with the CERES measurements, and they provide observations from a wide variety of locations all over the world."
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