Raman Lidar Techniques for Atmospheric Profiling

Raman lidar has emerged as a cornerstone in remote sensing of the atmosphere, exploiting inelastic scattering of laser light by gas molecules to retrieve detailed vertical profiles of temperature, water vapour and aerosol properties. Unlike elastic backscatter lidar, which relies on photons scattered without change in wavelength, Raman lidar isolates the weaker wavelength‐shifted signals arising from rotational and vibrational transitions in molecules such as nitrogen and water vapour. By analysing the intensity ratios of these Raman returns, it is possible to infer atmospheric thermodynamic parameters with high vertical resolution (tens of metres) and in both daytime and nighttime conditions. Recent advances in laser engineering have yielded compact, high‐repetition micro‐pulse UV lasers with elevated average power and low divergence, coupled to increasingly large‐aperture telescopes and multichannel detectors. These improvements have driven gains in signal‐to‐noise ratio, enabling routine retrievals of water‐vapour mixing ratios from the surface to the tropopause and temperature profiles throughout the troposphere and lower stratosphere. Concurrently, developments in retrieval algorithms—ranging from Monte Carlo–based calibration‐function optimisation to optimal estimation methods that rigorously account for statistical and systematic uncertainties—have bolstered the accuracy and stability of Raman lidar measurements. Collectively, these technological and methodological enhancements have broadened the global applicability of Raman lidar from research campaigns to continuous monitoring networks, yielding critical insights into atmospheric dynamics, climate variability and air‐quality processes.

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Raman Lidar Techniques for Atmospheric Profiling publication trend

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Technical terms

Raman scattering: Inelastic scattering process in which incident photons exchange energy with molecular rotational or vibrational modes, resulting in wavelength‐shifted backscatter used for species‐specific detection.

Elastic backscatter: Scattering of laser photons by particles or molecules without change in wavelength, commonly used for aerosol and cloud profiling but lacking thermodynamic information.

Pure rotational Raman (PRR): Raman scattering involving rotational energy transitions, exploited for temperature retrieval by comparing intensity ratios of rotational lines.

Calibration function: Mathematical relationship that links observed Raman signal ratios to atmospheric temperature, whose choice critically affects retrieval accuracy.

Optimal estimation method (OEM): Statistical retrieval framework that incorporates measurement uncertainties and a priori constraints to improve parameter estimation from lidar signals.

Micro‐pulse laser: High‐repetition, low‐pulse‐energy ultraviolet laser source enabling compact Raman lidar designs with enhanced average power and reduced divergence.

References

1. Atmospheric Thermodynamic Profiling through the Use of a Micro-Pulse Raman Lidar System: Introducing the Compact Raman Lidar MARCO. Sensors (2023).
2. Comparative Analysis and Optimal Selection of Calibration Functions in Pure Rotational Raman Lidar Technique. Remote Sensing (2024).
3. Single-line-extracted pure rotational Raman lidar to measure atmospheric temperature and aerosol profiles.. Optics Express (2018).
4. Retrieval of temperature from a multiple channel pure rotational Raman backscatter lidar using an optimal estimation method. Atmospheric Measurement Techniques (2019).