Submerged Drift; Ascent; Transmission / Reception - Kannad PROV-CARBON Manuel Utilisateur

USER MANUAL / MANUEL UTILISATEUR
pressure remains unchanged for too long, PROV-CARBON 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 PROV-CARBON 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 - PROV-CARBON adjusts its buoyancy to return to the drift depth.
If the pressure increases by an amount that exceeds a factory-set danger threshold, PROV-CARBON
immediately ascends to the sea surface.
If the user chooses, PROV-CARBON will collect CTD, DO and transmittance 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 PROV-CARBON 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
profile starting pressure reverts to its pre-programmed value for subsequent cycles.
Once the profile starting pressure has been reached, the float waits for the programmed time to begin the
ascent. If this time is reached before the float has arrived at the profile starting pressure, the ascent starts
immediately.
PROV-CARBON ascends by repeated use of the pump. When the pressure change between two
successive measurements is less than 1 bar, the pump is activated for a pre-set time period. In this way,
the pump performs minimum work at high pressure, which ensures minimum electrical energy consumption.
The average speed of ascent is approximately 10 cm/sec. For a 2,000 m profile, the ascent would, therefore,
last 6 hours. Please refer to
ascent.
When the pressure drops below 1 bar (signifying completion of ascent), PROV-CARBON waits 10 minutes
and then activates the pump. It does this to empty the reservoir and obtain maximum buoyancy.
If the user chooses, PROV-CARBON will collect CTD, DO and transmittance measurements during ascent.
CTD, DO and transmittance measurements begin at the profile start time and stop 10 minutes after the float
rises above the 1 bar isobar in its approach to the sea surface. The interval between measurements is user-
programmable.

3.6. Transmission / Reception

IRIDIUM system being bi-directional, only one transmission is necessary. Set-up commands can also be
received during the mission.
Descriptions of the transmitted message formats is detailed section
Description of sending commands via downlink is detailed section
PROV-CARBON
Figure 6: page 27 for a chart of PROV-CARBON's speed during a typical
PAGE : 7 / 70
DATE : 20/12/2007
INDEX : A
REF. : DOC07220
6. page 20.
6.8. page 25.