SENSOR AND ACQUISITION SYSTEM
In this section, brief descriptions
of the buoy sensors and of the acquisition system that
manage these sensors are provided.
More details here
|Sensors and data collection scenario
Instruments on the buoy*, simultaneously
collecting data in a continuous way, include the following:
- Radiometers of the Satlantic 200 series, measuring Es (at
4.5 meters above the water surface), and Ed, Eu,
and Lu (nadir) at 2 depths (4 and
- Two-axis tilt and compass at 9 m.
- A Sea-Bird Electronics CTD at 9 m for temperature,
conductivity and pressure.
- Fluorometers at 4 and 9 m for a proxy to the chlorophyll a concentration.
- Transmissometers, at 4 and 9 m for a proxy to the
- Backscattering meter at 9m measuring a proxy to bb at
two wavelengths (442 and 560nm).
These data are collected every 15min during
daylight, and every hour at night. Each data acquisition
sequence lasts one minute.
* Instrument names are sometimes
cited here, as well as the corresponding manufacturers,
because they have been identified as suitable for our
particular application. This identification does not
mean, however, that we recommend the use of any of these
instruments; this does not mean as well that we imply
that these instruments are the best suited for our application
or for other similar projects. In addition, we keep the
possibility to use any other instrument than those cited
here without notice.
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|The integrated acquisition system
The central component of the buoy system is the Data
Aquisition and Control Network (DACNet) unit which houses
the primary system computer (a PC104 Cool RoadRunner
II 200MHz 6x86 with 32MB of RAM) and the serial data
acquisition equipment (saving to a 1GB IBM Microdrive).
These components are used in the collection, storage,
and offloading of the data obtained from the instrumentation
suite. For the majority of the time, when the instrument
system is not active, the DACNet system remains unpowered.
A small internal micro-controller is responsible for
the power supervision and control, and for a precision
The power management is an important feature when considering
the limited power supply available from the solar-power
recharged 12 VDC 105 Ah underwater battery. Its functions
can be summarized as follows:
- Accurate wall clock.
- An alarm clock for powering up the system for the
- A watchdog timer that protects against draining the
battery in the event of a computer lock-up.
- Powerfail shutdown or prevent computer startup if
battery power becomes too low.
The operating system of the DACNet runs on Red Hat Linux
6.2 Kernel 2.2.19 which accommodates Satlantic's custom-made
Java software; Satlantic Telemetry Acquisition Manager
(STAM) and Node Manager. These programs fulfill the operational,
configuration and interface requirements of the buoy
to run autonomously and then to enable communication
of data and files with the user.
The third piece of Satlantic software, Base Manager,
runs on Windows NT or Windows 98 on a PC and provides
the operator with administrative tools each with a graphical
user interface (GUI). These tools enable the user to
configure the Node Manager, transfer data and files,
update the Acquisition Node's internal clock, to view
data from specified instruments in real time and completely
shutdown the acquisition node for maintenance. More details
of this software can be found in Satlantic's manual DACNet
Software Overview--Villefranche Remote Optical Mooring.
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The complete data stream can be downloaded through
a wireless high-rate ethernet link, established between
the buoy and the ship (same equipment aboard the buoy
and aboard the ship). This link is functioning with the
ship positioned a few hundred meters from the buoy. The
connection is driven by the buoy itself, with a wakeup
sequence each hour of the day; this solution was adopted,
rather than establishing the communication from the ship,
in order to minimize the time during which the buoy communication
hardware is awake and consuming energy.
This data retrieval is performed from the DACNet via
a Cisco Aironet 340 series wireless bridge, manufactured
by Cisco Systems and is stored directly on a PC. The
data is retrieved in a binary format and consists of
one daily log file for each of the following seven groups:
the instruments connected to the DATA-100 at 4m (Ocean
Color Profiling (OCP) systems and fluorometer), those
connected to the 9m DATA-100 (OCPs, fluorometer, transmissometer),
CTD, HOBI Labs Hydroscat, strain gauge, MVD and tilt.
However, the daily file is closed when communication
through the Cisco system occurs. In this case a new file
is created starting from the next measurement taken by
the DACNet system until midnight or until a subsequent
link up via the Cisco system is performed. Storage space
on the hard disk of the DACNet has the capacity to store
up to approximately three months of data.
Part of the data stream is transmitted via the ARGOS
system and is used for surveying the functioning of the
system; the sample data include the tilt and depth of
the buoy, the strain of the mooring cable, the battery
voltage, the disk space, the spectrum of the above-water
irradiance, and instrument health parameters, which are
indicating whether or not instruments and the acquisition
system are functioning nominally.
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