A versatile instrument with an optical parametric oscillator transmitter tunable from 1.5 to 3.1 μm for aerosol lidar and DIAL

Lidar is a valuable tool for atmospheric monitoring, allowing range-resolved profile measurements of a variety of quantities including aerosols, wind, pollutants and greenhouse gases. We report here the development of a versatile fielddeployable instrument for monitoring the lower troposphere. This region includes the effects of surface–atmosphere interactions and is an area where the resolution of satellite data is generally poor. Our instrument has been designed with the goal of making range-resolved measurements of greenhouse gases such as carbon dioxide, as well as probing the structure of the boundary layer. The key component is a tunable laser source based on an optical parametric oscillator covering the wavelength range 1.5–3.1 μm. This relatively eye-safe spectral region includes absorption lines of carbon dioxide and other greenhouse gases enabling the application of the differential absorption lidar (DIAL) technique, whilst also being suitable for aerosol lidar. We also report the use of an avalanche photodiode detector with high sensitivity and low noise. Field tests of the instrument were performed, recording continuous lidar signals over extended periods. The data were digitized at up to 8 signals per second. Scattering from aerosols and molecules was detected to a maximum range of 2 km, whilst scattering from cloud was recorded at up to 6 km. The data are plotted as time-versus-range images to show the dynamic state of the atmosphere evolving over time. These results demonstrate that the lidar achieves key requirements for both aerosol scatter and DIAL: tunability of the transmitter wavelength, sensitivity to molecular and aerosol scattering and robustness for field use.