Use of the Dobson spectrophotometer in a variable wavelength mode as an alternative to the Umkehr measurement for observing trends in the vertical distribution of ozone
Vertical ozone distribution information contained in the Umkehr measurement is derived from the scanning effect of the effective scattering layer (a layer in the atmosphere from which most of the scattered radiation arises) moving up through the atmosphere as the solar zenith angle increases. The altitude at which the effective scattering layers exists depends upon the strengths of molecular scattering and ozone absorption (i.e., wavelength) and the solar zenith angle. For fixed wavelengths, the change in sun-angle produces the scanning effect. Alternatively, a scanning effect can be produced by varying the wavelength at some fixed solar zenith angle such as the multiple-wavelength technique, a principle used in the Nimbus-4 backscattering ultraviolet satellite experiment. Greater flexibility for special applications can be had if both sun angle and wavelength are allowed to vary. It is shown that the ozone distribution information contained in the variable solar zenith angle (Umkehr) method is indifferent to the technique, within certain bounds dictated by the opacity of the atmosphere combined with limitations in instrumental sensitivity.
In WMO Geophys. Aspects and Consequences of Changes in the Composition of the Stratosphere
- Pub Date:
- Umkehr Effect;
- Vertical Distribution;
- Balloon-Borne Instruments;
- Radiative Transfer;