Descent; Grounding - Kannad PROV-CARBON Manuel Utilisateur

USER MANUAL / MANUEL UTILISATEUR
(1) Delay Before Mission
To prevent PROV-CARBON from trying to sink before it is in the water, the float waits for this time
before starting its descent. This happens only before the first cycle; it is not repeated at each cycle.
(2) Transmission / Reception / GPS location
Before each cycle, the PROV-CARBON float stays at sea surface and transmits the data collected
during the previous descent - drift - ascent cycle.
The IRIDIUM satellites system receives these data. Thanks to a GPS receiver, an accurate position of
the float can be obtained and the clock of the float be updated at UTC/GMT time. If commands are sent
by mail to the IRIDIUM system, they are dowloaded and processed at this time.
Before the first cycle, only the technical message including the GPS position of launching is transmitted
by the float. This enables to check if the float is operational before starting the mission.

(3) Descent

The float descends at an average speed of 5 cm/sec. During descent, which typically lasts a few hours,
PROV-CARBON can detect possible grounding on a high portion of the seabed and can move away
from such places (see section
CTD and DO measurements during descent.
Transmittance measurements acquisition are not performed during descent.
In order to respect the requirement of the ARGO program, the first cycle of the mission collect CTD and
DO measurements during the descent at the sampling period of 10 seconds.
(4) Drifting at Depth
During the drift period, PROV-CARBON drifts underwater at a user-selected drift depth, typically 1,000
m to 1,500 m below the sea surface. The drift period is user-selectable and can last from a few days to
several weeks, but is typically 10 days. The float automatically adjusts its buoyancy if it drifts from the
selected depth by more than 5 bars over a 60-minute period. PROV-CARBON can collect CTD, DO
and transmittance measurements at user-selected intervals during this drift period if the user selects
this option.
(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, PROV-CARBON must first descend to the profile depth before beginning the ascent profile.
PROV-CARBON 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 PROV-CARBON 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 PROV-CARBON to
standby at the profile starting depth while awaiting the scheduled ascent time.
(7) Ascent
Ascent lasts a few hours, during which time PROV-CARBON ascends to the sea surface at an average
speed of 10 cm/sec. PROV-CARBON can collect CTD, DO and transmittance 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 PROV-CARBON 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
Descent takes the float from the sea surface to the drift depth. Initially - in order to avoid possible collision
with shipping - PROV-CARBON'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, PROV-CARBON will collect CTD and DO measurements during descent. The interval
between measurements is user-programmable.

3.3. Grounding

PROV-CARBON monitors itself for possible grounding on the seabed. During descent to drift depth, if the
PROV-CARBON
3.3. page 6 for more on grounding). PROV-CARBON can collect only
3.3. page 6).
for a description of the technical message format).
PAGE : 6 / 70
DATE : 20/12/2007
INDEX : A
REF. : DOC07220
Figure 7: page 28.