Development and Application of a Versatile Balloon-Borne DOAS Spectrometer for Skylight Radiance and Atmospheric Trace Gas Profile Measurements
In the framework of this thesis, a novel balloon-borne DOAS instrument was developed, characterized in the laboratory and employed during 5 stratospheric balloon flights. Its light weight and small size allows versatile applications on different platforms and under several observation geometries (scanning and fixed limb, nadir, and direct sunlight). Skylight radiances in the UV/visible range between 330 and 550 nm are measured, and the recorded spectra are analyzed for column densities of ozone, NO2, BrO, H2O, and O4 along the line of sight by applying the Differential Optical Absorption Spectroscopy (DOAS) method. Radiative Transfer (RT) calculations are used to (a) simulate the measured quantities and (b) infer vertical profiles of O3, NO2, and BrO concentrations. Since the measurements were performed under a variety of viewing geometries, they provide a stringent validation of the applied Monte Carlo RT model. The new method of atmospheric trace gas profiling by balloon-borne UV/vis limb scatter measurements is tested against simultaneous measurements of the same parameters available from in-situ, or UV/vis/near IR solar occultation observations performed on the same payload. Reasonable agreement is found between (a) measured and RT calculated limb radiances and (b) inferred limb O3, NO2, and BrO and correlative profile measurements when properly accounting for all relevant atmospheric parameters (temperature, pressure, aerosol extinction, and major absorbing trace gases). Additionally, scanning limb observations provide time-resolved profile information of radicals during sunset.
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