Daytime measurements of bioaerosol simulants using a hyperspectral laser-induced fluorescence LIDAR for biosphere research

Abstract

A new compact home-built hyper-spectral laser-induced fluorescence (LIF) light detection and ranging (LIDAR) system is presented that can detect and identify bioaerosol clouds in an open atmosphere in daylight up to a distance of 3−4 km. The system is based on a 266 nm laser source and a dual-stage micro-channel plate intensified charge-coupled device sensor, which provides a high-resolution fluorescence spectrum with the sensitivity of a single photon counting imaging detection at a 10 Hz repetition rate. Controlled remote sensing experiments on biological simulants in the aerosol-phase within an enclosed chamber (ΔR=1.2 m) were conducted from a short distance of ∼170 m. A meticulous comparison between the remote fluorescence signal detected by the system and the instantaneous concentration and particle size distribution of the bioaerosol inside the chamber detected by an aerodynamic particle sizer yielded a threshold of ∼20 and 137 μgr s m-3 for the spectral identification of tryptophan and ovalbumin, respectively. This showed that the LIDAR can measure environmental airborne biological aerosol remotely in the daytime and can be utilized as a real-time biosphere research tool. Next, the system was tested in open atmospheric field campaigns in the Israeli desert during the day. It successfully detected bioaerosol clouds at up to 2.5 km in strong wind and sunny conditions. These empirical detection and identification results provide robust estimates that a biological cloud can be sensed at a distance of ∼ 4 km.