Data relating to fluid dynamics is obtained using a flow field sensor that measures acceleration and angular velocity of the sensor on three axes. Ballast control allows the sensor to obtain neutral buoyancy within the fluid. The sensor is effective in opaque fluids and closed containers as data is stored in a removable memory. Froth flotation systems are among the applications for the sensor. The small size, the geometry, and the center of mass of the sensor allow it to follow the flow field in a vessel without material disruption of the flow field or weight-induced angular displacement.