A dynamic grayscale-triggered hydrometeor particle observation system with automatic detection and tracking

A novel high-speed area-array imaging instrument, the Dynamic Grayscale-Triggered Hydrometeor Particle Observation System (DGHOS), is presented for comprehensive observation of hydrometeor particles. DGHOS is capable of directly imaging the descent trajectories of hydrometeor particles while simultaneously capturing both their kinematic and morphological characteristics. To minimize sensitivity to variations in particle distance from the lens, the system employs a high-resolution area-array camera integrated with a bi-telecentric optical system. A frame rate of up to 400 fps is achieved by reducing the ROI (region of interest). The use of a high-intensity monochromatic LED area light source effectively avoids chromatic dispersion. Through a grayscale-change-triggered acquisition mode, the volume of stored data is reduced by approximately 98.5% in the presented rainfall case compared with continuous recording at the same frame rate. Multiple parameters, including position, velocity, equivalent diameter, and axis ratio, are extracted using Canny edge detection and centroid-matching algorithms. System performance was evaluated through calibration experiments and natural hydrometeor particle observations, yielding a spatial resolution of 11.3 lp mm −1 and a scale factor of approximately 39 μm px −1 . Under natural conditions, extensive populations of raindrops and snowflakes were successfully captured by DGHOS. Representative images of both types are presented, accompanied by a detailed quantitative analysis focused on their dynamics.