Hygrometer for long duration stratospheric measurements (≥ 1 month)

Photodissociation of minor species, with the aid of ultraviolet sources is used here to improve a hygrometer for stratospheric in situ measurements between 18 and 31 km. The water vapor mixed with the air is measured by detecting the spontaneous luminescence from the OH radical at a 3100 Armstrong wavelength. The radical loses this energy when the water vapor is photo dissociated with a Lyman-alpha-photon beam inside the photolysis chamber. As the instrument has been designed for long duration balloon flights, we have used space materials and space technical methods for its construction. This combination has greatly diminished its volume and weight, allowing it at the same time to resist high temperature and pressure gradients. This new generation of hygrometers will give precise temporal and latitudinal measurements of the atmospheric water content, resulting in a better understanding of the atmospheric dynamics and the transport phenomena of this element. (Author)