A novel spectroscopic filter used in rotational Raman lidar for the temperature profiling

Abstract

We perform the rotational Raman temperature measurements in the troposphere and lower stratosphere with high performance. Depending on the aerosol content and presence of clouds in the lower troposphere, the rotational Raman lidar (RRL) is the lidar technique of choice for temperature measurements. However, the Raman filter design is a technical difficulty in RRL systems. Considering the higher spectral resolution and compactness, we select several photonic crystals to construct a novel spectroscopic filter for extracting the required rotational Raman spectrum (RRS) signals of atmospheric molecules. We describe in detail the principle to design the photonic-crystal filter. To verify the feasibility of the novel spectroscopic filter, we carry out some numerical calculations, and our results show that the novel spectroscopic filter has the capability to fine draw the required RRS signal and suppress sufficiently elastic signals. For the RRL system which uses the novel spectroscopic filter, we obtain that a statistical temperature error is less than 1 K up to a height of 3.2 and 5.6 km for daytime and nighttime measurements, respectively. Our simulation conditions are as follows: 532 nm laser with 500 mJ energy, and 10 Hz pulse repeating rate, a 300 mm diameter Cassegrain reflecting telescope with 1000 mm focus length, 0.2 mm diameter multimode optical fiber which sets the field of view (FOV) of receiving system to 0.2 mrad, 45 m range resolution, 9 min observation time, overall optical-system efficiency of 0.6, and a special atmospheric model which integrates the US standard model of 1976 with an actual Mie scattering profile obtained from practical observations.