An inverse problems approach to micro-PIV for measuring flow around freely flying tiny insects

Brightfield micro-particle image velocimetry (micro-PIV) has traditionally been limited to aqueous media and by a poor signal to noise ratio. Here, we introduce a brightfield micro-PIV system suitable for measuring the 2D flows generated by freely flying sub-millimeter insects while simultaneously measuring the 3D wing and body kinematics. Our methodology couples a novel aerosolization system and an inverse problems approach to image preprocessing to alleviate these limitations. Using optimization, the inverse problems approach obtains each particle's position relative to the focal plane and generates a synthetic image comprising the in-focus and nearly in-focus particles and excluding noise from out-of-focus particles. We find that a 0.85 mm tobacco whitefly (Bemisia tabaci) utilizes a deep U-shaped wingtip trajectory to generate a 0.5 m s-1 downward jet as the wings clap together. Our technique can validate numerical simulations of tiny insect flight and measure the aerodynamics of various insect species exhibiting high morphological diversity.