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USER MANUAL / MANUEL UTILISATEUR
(5) Descent to Profile Depth
The user may select a starting depth for the ascent profile that is deeper than the drift depth. If this is
the case, PROVBIO-B must first descend to the profile depth before beginning the ascent profile.
PROVBIO-B can detect a possible grounding during this descent and take corrective action (as
described on section
(6) Wait for Ascent Time
The user can program several floats to conduct profiles simultaneously. This makes it possible to use
several PROVBIO-B floats in a network of synoptic measurements, even though the instruments are
not all deployed at the same time. If this is the case, it may be necessary for PROVBIO-B to standby
at the profile starting depth while awaiting the scheduled ascent time.
(7) Ascent
Ascent lasts a few hours, during which time PROVBIO-B ascends to the sea surface at an average
speed of 10 cm/sec. PROVBIO-B can collect CTD and optical measurements during ascent.
Start of ascent time will be calculated to end the ascent to the surface at 12:00 PM ± 2 h (UTC) so as
to perform the irradiance measurements when the sun is at is zenith.
3.2. Descent
While the float is still at the sea surface PROVBIO-B measures and records its pressure sensor offset. This
offset is used to correct all pressure measurements. The offset is transmitted in a technical message (see
section
6. page 20
for a description of the technical message format).
Descent takes the float from the sea surface to the drift depth. Initially - in order to avoid possible collision
with shipping - PROVBIO-B's objective is to lose buoyancy in the shortest possible time. It does this by
opening the solenoid valve for a time period that is initially long, but decreases as the float approaches its
target depth. This behaviour can be seen in the sample descent data shown in
If the user chooses, PROVBIO-B will collect CTD measurements during descent and / or ascent. The
interval between measurements is user-programmable.
3.3. Grounding
PROVBIO-B monitors itself for possible grounding on the seabed. During descent to drift depth, if the
pressure remains unchanged for too long, PROVBIO-B enters a correction mode. The user selects one of
two available modes during Mission programming before launch:
•
Grounding Mode = 0: The pre-programmed drift depth is disregarded. The pressure at the time of
grounding minus an offset (5 bar) is taken as the new value for the drift pressure. The float adjusts its
buoyancy to reach this new drift depth. The drift depth reverts to its programmed value for subsequent
cycles.
If the grounded pressure is lower than a programmed threshold (20 bars), the float remains on the
seabed until the next programmed ascent time.
•
Grounding Mode = 1: the float remains where it is until the next scheduled ascent time. The pressure
measured at grounding becomes the profile start pressure for the cycle in progress. The profile start
pressure reverts to its programmed value for subsequent cycles.
3.4. Submerged Drift
While PROVBIO-B is drifting at drift depth, it checks the external pressure every 30 minutes to determine
whether there is need either for depth adjustment or for an emergency ascent.
If the measured pressure differs from the drift depth pressure by more than a specified tolerance - and this
difference is maintained - PROVBIO-B adjusts its buoyancy to return to the drift depth.
If the pressure increases by an amount that exceeds a factory-set danger threshold, PROVBIO-B
immediately ascends to the sea surface.
If the user chooses, PROVBIO-B will collect CTD measurements at user-selected intervals during
submerged drift.
3.5. Ascent
If the chosen ascent profile starting pressure is higher than the drift pressure, the float must first descend
to reach the profile starting pressure.
If grounding is detected while PROVBIO-B is descending to the profile starting pressure, the present
pressure is substituted for the profile starting pressure. This substitution is only for the cycle in progress; the
PROVBIO-B
3.3. page
7).
PAGE : 7 / 72
DATE : 26/03/2008
INDEX : A
REF. : DOC08018
Figure 7: page
30.
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