Direction of the vertical velocity: Difference between revisions

From Atomix
← Older edit
VisualWikitext
KikiSchulz (talk | contribs)
107 edits
No edit summary
Aleboyer (talk | contribs)
256 edits
mNo edit summary
 
(5 intermediate revisions by 4 users not shown)
Line 1: Line 1:
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 direction of the vertical velocity of the profiler is important.
Most vertical profilers collect data while they are '''descending''', and the data collected while '''ascending''' is useless because the probes are in the wake of the instrument and there is no oncoming flow over the shear probes.  
However, some profilers are designed to collect data while they are ascending and the data collected during it descent is not useable.
'''Gliders can produce meaningful data while descending and ascending'''.
So, it is important to know what type of instrument was used to collect your shear-probe data, so that you select data from when it was travelling in the appropriate direction.  


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.
-----------------------------
return to [[Flow chart for shear probes]]
 
 
[[Category:Shear probes]]

Latest revision as of 16:07, 6 June 2024

The direction of the vertical velocity of the profiler is important. Most vertical profilers collect data while they are descending, and the data collected while ascending is useless because the probes are in the wake of the instrument and there is no oncoming flow over the shear probes. However, some profilers are designed to collect data while they are ascending and the data collected during it descent is not useable. Gliders can produce meaningful data while descending and ascending. So, it is important to know what type of instrument was used to collect your shear-probe data, so that you select data from when it was travelling in the appropriate direction.



return to Flow chart for shear probes

Retrieved from "http://atomix.app.uib.no/index.php?title=Direction_of_the_vertical_velocity&oldid=4629"