FIG. 6.
Kinetic energy spectra and vertical velocity profiles during vertical migration. (a) Vertical component of the velocity spectrum tensor for the three time delays corresponding to different stages in the migration at which data were acquired. The vertical lines indicate the wavenumbers corresponding to the domain size (i.e., field of view), organism size, and the Nyquist limit (i.e., twice the PIV vector spacing). The yellow shaded region indicates increasing kinetic energy at length scales greater than the individual animal size (i.e., wavenumbers smaller than that corresponding to the individual animal size). (b) Mean vertical velocity along a horizontal transect across the center of the field of view for each stage of the migration. The left edge of the field of view approximately matches the central region of the green laser sheet (see Figure 2).