Eye-safe polarization lidar for biosurveillance and aerosol hotspot localization

Kurzfassung

Bioaerosols, including bacterial spores, viruses, bacteria, and pollen, elicit adverse health effects ranging from irritation to severe respiratory issues. The potential release of highly hazardous bioaerosols necessitates the remote detection of aerosol hotspots. While UV Raman lidars provide effective remote sensing, their lack of eye safety prevents continuous monitoring in populated areas. Consequently, eye-safe pre-classification systems are imperative to localize anomalies and guide secondary biological identification tools to the target. We present a compact, eye-safe polarization lidar operating in the near-infrared range at 1550 nm for the remote sensing and pre-classification of aerosol hotspots. The bistatic system utilizes a linearly polarized fiber laser (1 W, 8 ns) and two-channel polarization-resolved detection to differentiate between spherical liquid and non-spherical solid aerosols. Classified as Class 1M eye-safe (IEC 60825-1:2014), the system features optimized parallel optical axes, ensuring complete overlap between 50 m and 100 m, which was verified using a hard target at 6.3 km. Backscattered light is captured by two InGaAs avalanche photodiodes, with data acquisition handled at 125 MS/s via a custom FPGA. Integrated GNSS and inertial measurement units provide precise spatial localization to coordinate subsequent in-situ investigations. Field experiments involving the controlled release of synthetic aerosols (Arizona test dust, water fog, dipropylene glycol methyl ether, kaolin, and ethanol) demonstrated the system's ability to map spatially resolved drift behavior and velocity fields at distances up to 500 meters. Crucially, the system successfully discriminated between particle types: solid aerosols such as kaolin exhibited a measurable volume depolarization ratio of 29 %, allowing clear discrimination from liquid droplets, which showed a ratio of 3 %. This validates the system's efficacy as a robust early-warning trigger for aerosol hazard mitigation.