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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 9 m).
  • 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 particle load.
  • 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 clock.

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:

  1. Accurate wall clock.
  2. An alarm clock for powering up the system for the programmed schedule.
  3. A watchdog timer that protects against draining the battery in the event of a computer lock-up.
  4. 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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Data communications

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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