A new actinic flux 4p-spectroradiometer: instrument design and application to clear sky and broken cloud conditions

[摘要] A new 4p-spectroradiometer was developed for measuring actinic flux especially under cloudy conditions based on afixed grating imaging spectrograph and a CCD-detector leading to a simultaneous measurement of the spectrum. The newinstrument incorporates a novel optical head with a 4p-field of view independent of angle of incidence. Comparisonswith the actinic flux spectroradiometer of the Institute of Atmospheric Chemistry of ForschungszentrumJülich showed a very good agreement within the limit of the uncertainties of the two instruments. Our spectroradiometer was applied toinvestigate the effects of broken clouds on the actinic flux and photolysis frequencies on the ground during theBERLIOZ campaign. Reductions as well as enhancements compared to the clear sky case were seen, both effects are largerin the UV-A than the UV-B spectral region. Furthermore the new instrument was used for simultaneous measurements in different altitudes ona tower to studythe transmission and attenuation of actinic flux in low clouds. A correlation of attenuation with the simultaneouslymeasured liquid water content of the cloud was found.

[学科分类] 大气科学