Digital Particle Image Velocimetry (DPIV) data on a hovering hawkmoth to determine the strength of the vortex loop

This 2 dimensional flow field data is acquired on a hovering hawkmoth(1.47 g, wing span length of 4.2 cm) using Digital Particle Image Velocimetry method. This velocity field data is acquired to determine the strength of the vortex loop captured on hovering hawkmoths. 

Methods
To quantify the strength of vortex loop, resolved in the high-speed schlieren photography study on hovering hawkmoth during the down-stroke, The Digital Particle Image Velocimetry (DPIV) was implemented on a hawkmoth (1.47 g, wing span length of 4.2 cm) that was hovering and feeding on nectar . The starting vortex flow on the hovering hawkmoth was measured in a 0.77 × 0.32 × 0.32 m glass tank that is seeded by 1~5 micron fog particles in the beginning of the measurement. The fog particles were illuminated by a 1 mm thick laser sheet created by a 2W diode continues wave 532 nm solid state laser. The laser sheet was projected at 75 % wing span section, parallel to the sagittal plane, where the starting vortical flow is recorded by a high speed camera (Photron Mini UX 100) at a frame rate of 2000 fps. The obtained DPIV images were first enhanced and preprocessed through background subtraction. Then the images were imported into the PIVLAB, an open source MATLAB program, for calculating velocity vectors. A 128 × 128 pixel interrogation window with a 75% window overlapping was applied in the program, resulting in a spatial resolution of 2.6 mm/ velocity vector. Finally, the velocity data were filtered with outliers manually rejected in the program.