Rotating shadowband photometer measurement of atmospheric turbidity: a tool for estimating visibility

Abstract

The rotating shadowband photometer (RSP) is a simple, low-cost instrument that automatically measures the total, diffuse and direct solar illuminance. On clear days, the direct component yields a measure of the total column extinction. This extinction calculation compares favorably with an independent and more conventional determination of extinction. The column extinction measurements can be corrected for the effect of stratospheric aerosols, thereby yielding the lower atmosphere extinction coefficient. This extinction coefficient should be useful in assessing small changes in atmospheric visibility over the long term.