Direction of the vertical velocity

A data file may start before an instrument is even in the water. Vertical profilers are often held near the surface before they are released. During such a time, the vertical velocity may fluctuate significantly around a mean of zero, but the data cannot be used for dissipation rate estimation. A data file may also contain many profiles that are interrupted by useless data, such as the retrieval of a tethered profiler back to the surface. The direction of profiling can be used to eliminate such segments.

A data file may start before an instrument is even in the water. Vertical profilers are often held near the surface before they are released. During such a time, the vertical velocity may fluctuate significantly around a mean of zero, but the data cannot be used for dissipation rate estimation. A data file may also contain many profiles that are interrupted by useless data, such as the retrieval of a tethered profiler back to the surface. The direction of profiling can be used to eliminate such segments.

The criteria listed above are mainly for vertical profilers and for gliders. For AUVs and for moored instruments, the minimum speed of profiling – the speed of the AUV or the speed of the current past the mooring – will be the most relevant criterion for selecting a profile.

The minimum magnitude of the vertical velocity is a criterion that can be applied to both vertical profilers and to gliders. However, the minimum vertical speed is about two times smaller for a glider compared to a vertical profiler because the glider path angle is about 30°.

The direction of the vertical velocity of the profiler is important – some profilers are designed to collected data while they are ascending. Gliders can produce meaningful data while descending and ascending.