Large Scale Volumetric Flow Measurements using Air-Filled Soap Bubbles*

Coarse-grained volumetric flow measurements at large scales are relevant to

numerous biological and industrial applications, but pose a scaling challenge for conventional techniques suited to controlled experimental settings. Here we present a three-dimensional particle tracking velocimetry (PTV) system suitable for volumes on the order of 10² meters cubed using

air-filled soap bubbles and high-resolution DSLR cameras. Air-filled soap bubbles are attractive

tracer particles due to high light scattering efficiency, near neutral buoyancy, and ease of production.

The low-cost instrumentation, detailed measurement protocols, and open-source processing software are

discussed along with limitations for increasing accessibility to non-specialist users. Preliminary analyses of

measurements of insect-relevant flows made in the rural regions of Salt Lake City are also presented.