The development of a miniature optical sensor for balloon-borne measurements of ozone profiles

A new autonomous balloon-borne sounding system for the measurement of stratospheric trace gas profiles was designed and constructed. Major components of the sonde are a miniature grating spectrometer, which covers a wavelength range from the ultraviolet (200 nm) to the visible (850 nm), and a commercial radiosonde. The low-weight sonde (approximately 1.7 kg) measures the spectral solar irradiance and meteorological parameters during the ascent through the atmosphere. Because of the decreasing ambient temperature during an ascent, the temperature of the spectrometer decreases by about 15 K. Active temperature stabilization is not included, and the irradiance measurements show a strong temperature dependence. The temperature-induced wavelength shift, the absolute irradiance, and the dark signal behavior were characterized as a function of the spectrometer's temperature. Based on this laboratory characterization, an inflight correction for changes in the dark current and for the wavelength drift was applied. In the test program described herein, ozone profiles were determined from changes in the measured solar spectral irradiance caused by ozone absorption in the Hartley and Huggins bands. Comparisons were performed with results of simultaneous electrochemical ozonesonde and lidar measurements. The ozone number density profile retrieved using the new sonde agrees with the independently measured ozone profiles within 20% for altitudes above 18 km. In the lower stratosphere, the discrepancies increase to 50%.