Indoor aerosols are known to have a significant influence on atmospheric environment and human health. Therefore, it is meaningful to study the physical processes and movement patterns of them, such as transport, diffusion, and deposition. Although numerical simulations can provide strong support for the analysis of indoor aerosol flow field, it remains challenging to quantify the random factors in real environments. Thus, further research is needed through experimental measurements. Conventional measurement methods, such as high-speed photography and pulsed lidar, are difficult to meet the range and resolution requirements for indoor aerosol research due to their inherent limitations. The Scheimpflug lidar, a type of lidar technology based on the Scheimpflug principle, has the potential to provide high-resolution detection at short range. However, the dead zone of a single field-of-view (FOV) Scheimpflug lidar still occupies a large proportion, hindering accurate studies of indoor aerosol distribution and diffusion patterns. Therefore, we propose a dual-FOV Scheimpflug lidar.

The proposed dual-FOV Scheimpflug lidar emits a continuous laser beam that interacts with the aerosol particles and produces elastic scattering. The backscattering signals from different ranges are collected respectively by two FOVs and then simultaneously captured by the corresponding image sensors (Fig. 1). In our study, a dual-FOV Scheimpflug lidar is developed with a 520 nm laser diode as the laser source. The lens for the primary FOV has a focal length of 100 mm and is designed to receive aerosol scattering signals from the far range, while the secondary FOV lens with a focal length of 45 mm is adopted to receive near-range signals. Two identical CMOS cameras serve as detectors for each FOV. In an indoor environment, we experiment to test the performance of the dual-FOV Scheimpflug lidar system (Fig. 3), with the artificially released aerosol source placed at 4.5 m. As the aerosol concentration along the path changes during the experiment, the signal intensity at the hard target at 7.1 m varies accordingly. By calibrating the system constants, interpolating the range resolution in the overlapping area, and splicing signals of the two FOVs, a full path signal profile with a very small dead zone can be obtained (Fig. 5). The signal intensity variation observed at the hard target is considered to be indicative of the changes in aerosol optical depth, which provides a constraint for the iterative determination of the boundary value. Subsequently, by utilizing the Klett method, the aerosol extinction coefficient profile is retrieved by employing the determined boundary value.

The dual-FOV Scheimpflug lidar has a detection range of 0.36–7.1 m, which reduces the dead zone from 1.26 m to 0.36 m compared with a single FOV structure. The system's range resolution is 0.1 mm at the nearest distance and 15 mm at the farthest, enabling high-resolution detection at short distances. The accuracy of the pixel-distance relations for both FOVs is verified by comparing signals in the overlap area. The high correlation coefficient of 0.872 indicates a good correlation and consistency between the signals of the two FOVs. Through the signal calibration and fusion of the two FOVs, the obtained signal profiles exhibit sound spatiotemporal continuity over the entire coverage range (Fig. 6). The inversion results at typical moments demonstrate that the dual-FOV Scheimpflug lidar effectively and accurately describes the aerosol variation trends in different aerosol concentration conditions (Fig. 7). The time-space map of the extinction coefficient shows good spatiotemporal continuity throughout the detection process (Fig. 8), enabling high-precision quantitative inversion of the short-range aerosol distribution. The correlation between signal intensity and extinction coefficient at the near end of 0.36 m is analyzed (Fig. 9), with a correlation coefficient of 0.991. This confirms the feasibility of adopting the signal of a hard target as a boundary value constraint and verifies the reliability and accuracy of the dual-FOV Scheimpflug lidar data.

We propose a dual-FOV Scheimpflug lidar for indoor aerosol detection, which features a small dead zone and extremely high resolution. The system comprises two FOVs, one designed for receiving near-range aerosol backscattering signals and the other for far-range signals. The dual-FOV Scheimpflug lidar system is employed to detect artificially released aerosols, and the full path signal profile is obtained by combining the signals from two separate FOVs. The system achieves dynamic self-calibration with the boundary value provided by a hard target, enabling the retrieval of the aerosol extinction coefficient profile without boundary value assumptions. The experimental results demonstrate that the secondary FOV supplements the aerosol information in the near range, and the inversion results show good spatiotemporal continuity. These results suggest that the dual-FOV Scheimpflug lidar can realize fine detection of indoor aerosols and provide a new technical means for detecting small-scale aerosol flow fields.