06 August 2004

Measuring haze for GLOBE

If we define an amateur scientist as a person who practices science without formal academic credentials, then student scientists form by far the largest group of amateur scientists.

Since 1990 I have been trying to tap this resource to do environmental measurements on a scale not possible by professional scientists.

Dr. David R. Brooks of Drexel University shares this goal. For more than five years he and I have worked with the GLOBE program to transform a new kind of Sun photometer I developed in 1989 into an instrument that can be easily be used by students and professionals alike. The result is the GLOBE Sun photometer shown in the nearby photograph.

The GLOBE Sun photometer is properly aligned when sunlight passing through an angle bracket on the upper side of the instrument forms a bright circle of light over an alignment target on an angle bracket on the lower side of the instrument. Click image to enlarge.

The GLOBE Sun photometer measures the aerosol optical thickness (AOT) in a column through the atmosphere. In other words, the instrument is a very good haze meter. It works well enough to validate AOT measurements by NASA's Terra and Aqua satellites, which was the subject of my talk at the recent 2004 GLOBE conference in Boulder, Colorado.

GLOBE Sun photometers are calibrated against standard instruments that have been carefully calibrated using the Langley method at Mauna Loa Observatory, Hawaii. Airfare for the calibration trips to Hawaii has been provided by the University of the Nations at Kailua-Kona, Hawaii, where I teach an annual course on experimental science. The first student Sun photometers, the VHS-1, were built and tested by students at the University of the Nations.

For information about the GLOBE aerosols protocol, visit the GLOBE protocols page. To see a 14-year time series of AOT measured by the first LED Sun photometer, click here.

Forrest M. Mims III