Development of a novel balloon-borne optical sonde for the measurement of ozone and other stratospheric trace gases

Abstract

In the frame of this work, a new small-size balloon-borne sonde was developed. A miniature grating spectrometer in the sonde measures simultaneously the solar spectral irradiance at a wide wavelength range from 200 to 850. As a first application, ozone profiles have been determined by measuring the changes in the spectral irradiance, caused by ozone absorption in the Huggins band. The wide spectral coverage of the spectrometer offers the possibility for measurements of other trace gases which absorb within the wavelength range, e.g. NO2 and BrO. The low weight of the new sonde (1.7 kg), the moderate price, and the autonomous portable telemetry system makes it a very versatile tool for satellite validation and for case studies, which requires a high number of launches.The newly developed sonde works well without temperature stabilisation, even so the spectrometer experiences rather large temperature changes (15 - 20 K) during the ascent through the atmosphere. Laboratory measurements were performed in order to quantify the temperature induced wavelength shift, the absolute irradiance changes, and the dark current behaviour. Based on the laboratory characterisation, inflight corrections could be applied, which compensate the effects of temperature changes. The system was tested in twelve flights and continuously improved. A technical status could be achieved, which guarantees for reliable measurements.For the retrieval of ozone profiles of the irradiance measurements, the analysis algorithm of the ground-based Dobson spectrometer was adapted. The determined ozone profiles were compared to ozone profiles measured by electrochemical sondes and LIDAR. The comparsion shows good agreement within 10% to 20% for altitudes above 15 km. For low solar zenith angles, reliable agreement with comparison measurements even at lower altitudes (8 and 15 km) were achieved. A quality criterion was developed, which allows the evaluation of the calculated ozone profile, independent from the comparison to other measurements.Absorption structures due to NO2 could be identified in the irradiance spectra measured at different altitudes (15 and 35 km). This demonstrated the feasibility of the new instrument to measure other trace gases beside ozone.