All-weather calibration of broadband (Robertson-Berger type) meters for ozone dependency.

Broadband solid-state detectors, which are robust, relatively inexpensive and uncomplicated to operate, are particularly suitable for routine measurements of biologically damaging solar ultraviolet-B (UV-B: 280-320 nm) radiation, especially in developing countries with limited financial resources and human technical capacity. Specific tables of conversion factors provided by manufacturers of these instruments correct for their dependence on solar zenith angle (SZA) but not on total column ozone; this dependence is due to slight wavelength mismatches between the instruments' spectral responses and biological action spectra. An entirely instrument-based calibration procedure has been described but is applicable only at sites with clear skies and abnormally Iow atmospheric pollution. We have investigated the practicality of calibrating such equipment customarily operating under all weather conditions with typical atmospheric pollution by comparing satellite observation of total column ozone with simultaneous broadband pyranometer and spectroradiometer measurements of erythemal-weighted solar UV-B irradiance over a 42-month monitoring period. The numerous (2657) measurements taken were inadequate to quantify, within statistically acceptable limits, the divergence of ozone-related observations by pyranometer and spectroradiometer of UV-B irradiance at different solar zenith angles. However, a general linear regression that quantified differences in UV-B irradiance measured by broadband instruments as a function of total column ozone inclusive of all SZA values conformed to statistically acceptable criteria. Application of the regression slope and intercept coefficients in a remedial equation reduced the total number of broadband instrument errors in measurement of UV-B irradiance by 40% but by small margins only; these averaged 2.40 ± 0.44%. The considerable time and expenditure entailed for such small corrections are not readily justified. [ABSTRACT FROM AUTHOR]