Total ozone is derived from direct spectral irradiance (DSI) with a method similar to that employed by the Dobson and Brewer instruments; for details of the method please see [Mayer and Seckmeyer, 1998] or [Mayer et al., 1997]. The graph shows the time series of daily averaged total ozone, measured at Garmisch-Partenkirchen. The yellow area shows the longterm (1968-1993) monthly averages measured at the nearby station Hohenpeissenberg ± 2 standard deviations.

The calibrated measurement of direct spectral irradiance allows the calculation of aerosol optical depth following Lambert-Beer's law. For details see e.g. [Mayer and Seckmeyer, 1998]. The graph shows the daily averaged aerosol optical depth at 320 nm. The pronounced annual variability is probably due to the larger humidity during summer, resulting in the growth of the aerosol particles leading to an increase in the scattering optical depth.

Comparison of the ozone data, derived from direct spectral irradiance (DSI), with Brewer data measured at the nearby station Hohenpeissenberg. Each data point shows a single DSI ozone measurement. For the comparison, the Brewer data were interpolated to the DSI measurement times. The right plot shows the ratio between DSI and Brewer data as a function of solar zenith angle. The average ratio is 1.01 and the standard deviation is 0.016.

[Stamnes et al., 1991] proposed a method to derive total ozone from measurements of global irradiance at two wavelengths. The figure shows the results of a slightly modified Stamnes algorithm in comparison with the direct spectral irradiance (DSI) results. The average ratio is 1.00, the standard deviation is 0.014. For details of the method please refer to [Mayer and Seckmeyer, 1998].

References

1

Stamnes, K., J. Slusser, and M. Bowen.
Derivation of total ozone abundance and cloud effects from spectral irradiance measurements. Applied Optics, 30, 4418-4426, 1991.