Sea-Bird Electronics SBE 38 Manual de usuario descargar pdf (Pagina 75)

Manual revision 006 Section 4: Deploying and Operating SBE 19plus V2 SBE 19plus V2

When very heavy seas cause severe ship motion, the 19plus V2 descent can

actually stop or reverse direction if the ship heaves upward faster than the

package can descend. These occurrences can often be seen as loops in the real-

time temperature trace. If the winch payout rate is too high, a loop of wire can

form under water when the package descent is slowed or reversed by ship

heave and the winch is still paying out wire. Inevitably, the loop formation

gets out of phase with the heave and the loop closes on itself when the ship

heaves, causing a kink. If the package includes a Carousel Water Sampler as

well as the CTD, the package creates much more drag than with only the CTD,

further increasing the possibility that a loop will form in the cable. After

1000 to 2000 meters of cable are paid out, it can be difficult or impossible to

detect a loop in the cable. Adding 100 to 200 kg (maybe more by

experimentation) of lead weights to the Carousel frame will help overcome the

effect of drag, and allow the package to descend faster and stay more in line

directly below the overboarding sheave.

Spiking is sometimes seen in the derived values for salinity, density, or sound

velocity. Spiking results largely from a response time mismatch of the

conductivity and temperature sensors, especially when the profiling descent

rate is non-uniform. The greatest reduction in spiking is found by using

premium CTD equipment such as the SBE 9plus, which uses very fast sensors

(0.07 second) and high speed (24 Hz) parallel signal acquisition. The 19plus

V2 static accuracy is the same as that of the 9plus, but its dynamic responses

are not as ideal, as a result of its simpler, less costly, and more compact

design. Much of the spiking can be removed from the data set by aligning the

data in time. This alignment can be performed when post-processing the data

in SBE Data Processing.

The amount of spiking depends on the temperature gradient, and is much

worse when coupled surface motion causes the instrument to stop - or even

reverse - its descent. In the event of heavy ship motion, it may be worth letting

the instrument free-fall. When very heavy seas cause severe ship motion and

result in periodic reversals of the instrument descent, the data set can be

greatly improved by removing scans taken when the pressure is not increasing,

using SBE Data Processing.

Note:

See the SBE Data Processing

manual for information on data

processing modules that can correct

data for the influences of ship motion

and minimize salinity spiking.

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Sea-Bird Electronics SBE 38 Manual de usuario Pagina 75