CIEMAT-Madrid Lidar station, with new fluorescence line and set of filters to prevent interferences.

Figure 1: CIEMAT-Madrid Lidar station, with new fluorescence line and set of filters to prevent interferences

 

The lidar station is located at Madrid (40,45ºN, 3,73ºW, 669 m asl) inside the CIEMAT facilities. This station is part of the European Aerosol Research Lidar NETwork (EARLINET), now ACTRIS (Figure 1).

The multi-wavelength (3+2+1) Raman lidar system is based on:

A pulsed Nd:YAG, Spectra Physics model Quanta-Ray Lab 130-70, operating at a repetition rate of 30 Hz and emitting 214 mJ at 1064 nm, 145 mJ at 532 nm and 138 mJ at 355 nm.

Dall-Kirkham telescope (Raymetrics) with a 300 mm diameter primary reflective mirror and a 1500 mm focal length.

Detection line optics consist on 6 channels separated by dichroic mirrors and interferential filters implemented for elastic channels (1064, 532 and 355 nm) and Raman channels (387, 407 and 607 nm).

A new detection line, to detect fluorescence produced by bioaerosols, was implemented with an Alluxa pass-band filter (466/44 nm) and Notch filters to avoid interference by elastic signals.

 

Measurement case: Fluorescence shown inside PBL, coincident with strongest aerosol peak.

Figure 2: Measurement case: Fluorescence shown inside PBL, coincident with strongest aerosol peak

 

Figure 2 shows the quicklooks (time-height plots) on the left panels for range-corrected lidar signal at 1064 nm (top), ratio of fluorescence vs 387 Raman signals (centre) and volume linear depolarization ratio at 532 nm (bottom). The right panels show the processed signals for the time window highlighted in red for the backscattering coefficient at 1064 nm (left), the ratio 466/387 nm (centre) and the volume linear depolarization (right) on the 9 February 2023. As one can observe, fluorescence signal can only be detected up to 2 km height, approximately, due to weak return of both the fluorescence and Raman signals. The aerosols present in that layer arise from the ground at 20:30, as it can be observed in the RCS@1064nm quicklook and produced a low depolarization ratio of about 0.02, indicating nearly spherical particles. The fluorescence ratio reached 0.021. A sharp boundary is observed at 1.8 km, producing a strong peak with high depolarization, and above that height, several aerosol-rich layers are detected, reaching up to 4 km, with depolarization ratios between 0.02 and 0.04.