  A three-dimensional (3D) scanning velocimetry system is developed to quantify
the 3D configurations of particles and their surrounding volumetric,
three-component velocity fields. The approach uses a translating laser sheet to
rapidly scan through a volume of interest and sequentially illuminate slices of
the flow containing both tracers seeded in the fluid and particles comprising
the aggregation of interest. These image slices are captured by a single
high-speed camera, encoding information about the third spatial dimension
within the image time-series. Where previous implementations of scanning
systems have been developed for either volumetric flow quantification or 3D
object reconstruction, we evaluate the feasibility of accomplishing these tasks
concurrently with a single-camera, which can streamline data collection and
analysis. The capability of the system was characterized using a study of
induced vertical migrations of millimeter-scale brine shrimp (Artemia salina).
Identification and reconstruction of individual swimmer bodies and 3D
trajectories within the migrating aggregation were achieved up to the maximum
number density studied presently, $8 \, \times\,10^5$ animals per
$\textrm{m}^3$. This number density is comparable to the densities of previous
depth-averaged 2D measurements of similar migrations. Corresponding velocity
measurements of the flow indicate that the technique is capable of resolving
the 3D velocity field in and around the swimming aggregation. At these animal
number densities, instances of coherent flow induced by the migrations were
observed. The accuracy of these flow measurements was confirmed in separate
studies of a free jet at $Re_D = 50$.
