An innovative rotational Raman lidar to measure the temperature profile from the surface to 30 km altitude
Résumé
The temperature is a fundamental parameter for meteorology and climatology. It is measured firstly twice a day using radiosondes with good vertical resolution but in a limited number of stations in the world and secondly from space but often with a vertical resolution limited by the weighting function of the instrument. Lidars provide a good vertical resolution and continuity of measurements. Currently the temperature is measured by lidar Rayeigh from NDACC ground stations but only above 30 km due to the presence of aerosols below this altitude. There is currently no space lidar in flight or in project measuring the temperature. The rotational Raman lidar technology allows access to the evolution of the temperature profile in the troposphere and lower stratosphere. It requires developing an efficient optical system with separation between the Rayleigh and the rotational Raman signal, the first being 2 to 3 orders of magnitude stronger than the second. It requires acquiring the full rotational Raman spectrum of molecular nitrogen, the temperature being deduced from the evolution of the relationship between the spectral lines.
We are developing at LATMOS a prototype rotational Raman lidar with daylight measurement capability that will be implemented in the NDACC station at Haute-Provence Observatory to benefit from the facilities available on site (laser source, telescopes, ...). The Rayleigh-Mie line is attenuated using a Fabry-Pérot etalon with a line spacing exactly equal to the line spacing of the N2 rotational Raman spectrum Such a system will perform a continuous survey of the temperature profile from the surface to the middle stratosphere and could serve as a reference to define a future space lidar for measuring the temperature in the troposphere and lower stratosphere.