Forces of Change

Pat Neale

SR-18 UV Monitor


The SR-18 UV monitor was invented at the Smithsonian Environmental Research Center (SERC). A disk with 18 different filters rotates 15 times every minute. The filters select different UV wavelengths, which are passed to a sensor and recording computer. The sensor is kept dry and at a constant temperature to get a stable response. Smithsonian Institution scientists pioneered atmospheric monitoring in the late 1800s.

SR-18 in the woods
In the woods, an SR-18 records that even leafless trees block about half the usual UV radiation.
Photo Chip Clark © Smithsonian Institution
Pat Neale uses the SR-18 UV monitor
Pat Neale uses the SR-18 UV monitor to measure ultraviolet light reaching Earth’s surface.
Photo Chip Clark © Smithsonian Institution
SR-18 perched on a tower
The SR-18 is one of several meteorological instruments perched on a tower at SERC to get a clear view of the sky. Cables feed data from the instruments to computers in the small shed at the base.
Photo Chip Clark © Smithsonian Institution