Minimum speed: Difference between revisions
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Many profiles start with the instrument accelerating from zero to its typical speed of profiling. A substantial portion of the acceleration phase should be excluded from data processing. Typical values for a minimum speed is ~70% of the typical speed of profiling for a glider and a vertical profiler. | Many profiles start with the instrument accelerating from zero to its typical speed of profiling. A substantial portion of the acceleration phase should be excluded from data processing. Typical values for a minimum speed is ~70% of the typical speed of profiling for a glider and a vertical profiler. | ||
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°. | |||
Revision as of 09:55, 7 May 2021
Many profiles start with the instrument accelerating from zero to its typical speed of profiling. A substantial portion of the acceleration phase should be excluded from data processing. Typical values for a minimum speed is ~70% of the typical speed of profiling for a glider and a vertical profiler.
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°.
