An Ultralight Aircraft as Platform for Research in the Lower Troposphere: System Performance and First Results from Radiation Transfer Studies in Stratiform Aerosol Layers and Broken Cloud Conditions

Abstract

The ultraviolet actinic radiation flux governing the photochemical reactions in the atmosphere is dependent on the optical properties of atmospheric aerosols and reflective surfaces of ground and clouds. Theoretical models exist for horizontal stratified atmospheres without clouds and currently becoming available are the first three-dimensional models that include broken cloud conditions. The experimental database for model verification is scarce for both ground and vertical distribution. To close this experimental gap an airborne system was developed and is described in this paper. An ultralight aircraft was used as an instrument platform to provide detailed measurements of radiation transfer in the ultraviolet and complimentary parameters that can be used for comparison with model calculations. The measurement system consists of standard, but in size and power consumption strongly modified, instruments. It produces a dataset covering upwelling and downwelling radiation as well as absorbing gaseous compounds and aerosol optical properties, their size, number, and scattering coefficients. The system is designed to be used on a variety of aircraft, from medium size to microlight. Measurements in an altitude range of up to 4500 m above sea level are presented using the ultralight aircraft under conditions with clouds, haze, and dust layers of natural and anthropogenic origin within a visibility range of 120 to about 1 km. Selected vertical distributions are presented, measured in remote and polluted environments. The results presented clearly demonstrate the capability of the ultralight aircraft as an instrument platform for lower-tropospheric research missions.