In situ measurements of methane in the troposphere and the stratosphere by the Ultra Light SpEctrometer Amulse

Methane plays an important role in the radiative balance of the Earth climate: about 20% of the manmade global warming is related to methane emissions. To contribute to the study of CH₄ trends, we have developed a compact lightweight spectrometer (2.5 kg) by combining an antimonide laser diode at 3.24 µm with an 8 m optical multipass path cell open to the atmosphere. This laser sensor is to be operated from weather balloons to provide with regular in situ methane soundings from ground level up to ~ 25 km. In this paper, the laser sensor is described as well as the processing of the absorption spectra and the calibration of the instrument. The concentration data obtained from recent stratospheric balloon flights are reported and discussed.