HSI: High Speed Imaging Flight Probe
Aircraft-based droplet and ice crystal measurements
Theory of Operation
The HSI optics consists of a transmitter and a receiver optics. Multiple, pulsed, laser beams cross at the same point to form a measurement volume where a particle is probed when its presence is detected. Each beam is produced by its own laser source in the transmitter and is therefore optically incoherent with respect to other beams. The intersection of multiple laser beams provides an intense uniform illumination in the sample volume. Since each laser beam takes a different path from the transmitter optics to the sample volume, particles that may momentarily block parts of any one beam will not, at the same time, block any of the other beams. As a result, unlike conventional imaging systems that use only a single beam path to illuminate the particle field, the illumination profile at the sample volume of the HSI system does not lose uniformity at any time. The transmitted laser beams are re-focused onto a fast frame rate imaging sensor where a shadow of the particle is cast. The images are processed in real-time by the AIMS software to extract various size and shape parameters.
Particle imaging with multi-laser beam illumination