Moisture contamination at altitude by balloon and associated equipment

Spectra of the 6.3-μ water band were recorded by a balloon-borne spectrometer at 23.5-km altitude and over a wide range of sun elevations. Reduced in terms of transmittance they show an unexpected increase in humidity with increasing solar elevation angle. This feature is interpreted as a contamination by moisture carried at altitude by the package, the balloon, and associated train. An analysis based on this interpretation gives 1.05×10−5 as the corrected stratospheric mixing ratio above 23.5 km.