Finite bandwidth and scattered light effects on the radiometric determination of atmospheric turbidity and the solar constant.

ABSTRACT

Multispectral solar radiometric measurements are routinely performed at a large number of sites, using equipment of varying degrees of sophistication. From the standard Langley plot technique, one may extract the total optical thickness of the atmosphere (and hence the aerosol component) plus the extraterrestrial solar flux. With increasing concern about possible climatic effects of increased turbidity, or changes in the solar constant, it is becoming more important to know the expected accuracy of these results. In this paper, we analytically examine the effects of finite filter bandwidth (in the absence of spectral lines) and find them to be less than one part in a thousand. This is compared with our earlier results on the effects of scattered light, which turns out to be typically an order of magnitude larger.