Students to the Rescue

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Aerosol-observing instruments measure the density of aerosol particles in a given parcel of air. On days when there is an abundance of aerosols overhead, less sunlight reaches the Earth’s surface because the particles scatter and reflect the Sun’s incoming rays. Today, thanks to Brooks and his partner Forrest Mims, GLOBE students all over the world are using handheld Sun photometers to determine how much sunlight is prevented from reaching the surface by aerosols. With these devices students derive a unitless measure, ranging from 0 to 5, called aerosol optical depth. An optical depth of less than 0.1 indicates a crystal-clear sky with maximum visibility, whereas a value of 4 indicates the presence of aerosols so dense you would have difficulty seeing the mid-day Sun!

Students who collect aerosol data following GLOBE protocols can help scientists understand local haze events, and can help to validate satellite-based observations. Moreover, GLOBE offers the advantage of being geographically distributed and can provide scientists with needed data from remote locations. “Especially when they are taken at the time of an EOS-Aura overflight of an observation site, the GLOBE Sun photometer measurements provide data of great scientific interest,” says Brooks. Brent Holben, manager of the international Aerosol Robotic Network (AERONET) at NASA Goddard Space Flight Center, agrees. “If we can get 100 dedicated kids around the world to do this, it will be the world’s largest haze network.”

  Group Portrait of Czech Students Involved in GLOBE

To demonstrate to herself and the scientific community that students’ GLOBE measurements could be used to validate satellite data, Levelt and her colleagues first decided to conduct a pilot study to determine whether or not GLOBE Sun photometers could measure aerosol optical thickness accurately. From September 2002 until July 2003, Levelt, Boersma, and Joris de Vroom, a Master’s degree student, made 138 measurements using GLOBE Sun photometers. The team compared the GLOBE Sun photometer data they collected with coincident measurements they made using a professional Sun photometer. They found the precision (exactness) and accuracy (freedom from mistakes) of the GLOBE Sun photometer data were comparable to the same measures made by the professional device.

After making sure the handheld Sun photometers were capable of making accurate measurements in the hands of professionals, De Vroom and Boersma conducted another experiment to find out whether or not students could make the measurements accurately. When scientists use professional instruments and observation techniques, a level of uncertainty in their aerosol measurements of less than 0.01 is quite good. Could students come close to that level of accuracy and precision?

A group of high school students at De Populier school in The Hague made 58 measurements of aerosol optical thickness using the handheld Sun photometers. Levelt and her colleagues compared the student measurements with the same measurements made by NASA scientists as part of AERONET. The student measurements and the professional AERONET measurements measured on average the same Aerosol Optical Thickness within 0.03. On average, the student measurements and the professional AERONET measurements differed from each other only by a value of about 0.03.


The GLOBE Program enables a network of scientists and students to make scientifically valid measurements for research on air and water quality, climate change, land cover analysis, and many other Earth system investigations. This class of students at Esko-anglicke school in the Czech Republic makes ozone measurements in collaboration with atmospheric scientist Jack Fishman and colleagues at NASA Langley Research Center. (Photograph courtesy Renata Kollarzykova)

Graph comparing GLOBE to AERONET aerosol optical depth measurements

“Students can do it,” concludes Levelt. “Measurements made by students are basically not different from measurements by anyone professional. If the person understands how to prepare for the measurements, and if they are careful, the measurements will be good.”

Levelt acknowledges that work remains to be done on teaching students to more precisely collect their Sun photometer data, but she is very optimistic about the students’ ability to contribute meaningful data to satellite-based aerosol research. Seventeen schools are now involved in her student project, and six of the schools routinely collect data for her. To learn more about the project, visit the GLOBE Aerosol Monitoring Project.


Folkert Boersma and Joris De Vroom, at the Royal Netherlands Meteorological Institute (KNMI), conducted a pilot project to determine whether students using GLOBE Sun photometers could accurately measure aerosol optical thickness. Dots on the graphs combine the values of aerosol optical thickness measured by students with professional AERONET measurements collected at the same place, date, and time. The distance of the point along the horizontal axis shows the student values; the distance along the vertical axis shows the professional observations. The student measurements were generally in agreement with AERONET measurements at both 508 nm (left) and 625 nm (right) wavelengths. (Graphs courtesy Joris de Vroom, KNMI)

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