2. Technology

2.1 J-CAD system Overview

2.2 J-CAD sensors

2.3 J-CAD Platform

2.4 J-CAD System Electronics



2.1 J-CAD system Overview
  The main features of J-CAD technology include:
  1. To reduce size and cost, the scope of observation has been limited to ocean physics (water temperature, salinity, and ocean current) and weather.
  2. J-CAD is the world's first drifting buoy, which adopts the ORBCOMM system for satellite data communication.
  3. Accurately measuring the speed of ice- drifting is essential for calculating the absolute speed of the upper ocean currents. J-CAD is equipped with global positioning system (GPS) so that its position and drift can be precisely determined.
  4. J-CAD uses a non-contract inductive modem (IM) system, which is an underwater data telemetry system with an electromagnetic inductive modem developed by Sea-Bird Electronics Inc. IM is used to transmit data from ocean sensors to the system electronics on the J-CAD platform to minimize problems such as water leakage and faulty contacts at junction points.
  5. The total weight of the J-CAD system was designed to weight 255 kg or less, so that it can be deployed using a small, light crane system. The maximum external diameter of the J-CAD underwater sensors is 28 cm, so that each of these sensors can be lowered through a 30-cm hole in the ice. A hole this size can be made by a 30-cm twist drill without the necessity of using a large warm-water drill.
  The J-CAD system has three types of sensors: meteorological, oceanographic, and buoy status sensors. The four meteorological parameters measured are air temperature, barometric pressure, wind speed and direction. For oceanographic observations, the J-CAD can be equipped with four CT sensors (SBE37IM), two CT sensors with a pressure sensor (SBE37IM), and two ADCPs (WH-ADCP 300 kHz). The buoy monitor sensors comprise a compass with a tile sensor, GPS, and thermistor to measure the temperature of water surrounding the J-CAD hull.
  The depth of the underwater sensors can be easily adjusted according to the sea area under observation. The data from each underwater sensor are acquired and processed at each sensor and then transmitted to the J-CAD electronics via the IM system. The 192 bytes of hourly observation data generated by the J-CAD are formatted and sent to an exclusive J-CAD data receiving and processing unit in JAMSTEC via the ORBCOMM and ARGOS satellite systems.

2.2 J-CAD sensors
2.2.1 Oceanographic sensors

SBE37IM
  Ocean temperature and conductivity data are obtained from the Sea-Bird SBE37IM CT sensors. Depth data are obtained from two pressure sensors that are integral parts of the CT sensors. Four CT sensors and Two CTD sensors can be mounted on the J-CAD. Normally, the CT sensors are attached at 25 m, 50m, 80 m, 180 m, and two CTD sensors are at 120m and 250m below the surface. But the depth of the underwater sensors can be easily adjusted according to the sea area under observation. Data from these six sensors are transmitted to the system electronics on the J-CAD platform through the IM system.

WH-ADCP (upward)
  Under-ice ocean current data are measured by two WorkHorse 300 kHz ADCPs from RD Instruments (San Diego, California) attached to the underwater cable at about 12 meters, facing downward, and at 260 meters, facing upward/downward. The ADCPs are set to measure 16 layers every ten meters.

WH-ADCP (downward)
with watson compass
The ADCPs also report heading, pitch, and roll data using an onboard fluxgate compass equipped with two-axis tilt sensors. Furthermore, a thermistor provides a time-series of water temperature at the instrumental depth. These ADCP data are also transmitted to the system electronics on the J-CAD platform via Sea-Bird Inductive modem (SBE44).
  An external Heading Reference Module can be co-located with the ADCP to give an independent determination of ADCP heading, pitch and roll. The J-CAD-4, deployed in April 2002, is equipped with the Watson Industries, Inc Strapdown Heading Reference System (SHR-360) secured inside the ADCP cage. The SHR-360 is a 3-axis fluxgate magnetometer with patented precision tilt indicators and it measures heading, pitch, roll, and 3-axis magnetometers. Heading sensor calibration can compensate for any magnetic influences from the overall assembly into which the sensor is installed. The above SHR-360 data are also transmitted to the J-CAD platform via Sea-Bird Inductive modem (SBE44).


cutaway of J-CAD body
2.2.2 Meteorological sensors
  The air temperature sensor is a model_44032 high-precision thermistor produced@by YSI Inc. (Yellow Springs, Ohio). The thermistor is placed inside a naturally aspirated Gill-plated radiation shield at the top of the sensor mast.
  The barometer is the model 216B manufactured by Paroscientific Inc. (Redmond, Washington). It is installed on the electronics support channel located inside the J-CAD platform, and is linked to outside environment by a small, narrow, plastic hose and a barometer port. This port is located inside the top of the Argos antenna mast and includes a water trap and a Gore-Tex membrane in the air path to protect the barometer from water ingression.
  The wind sensor is an anemometer model 5106-MA manufactured by RM Young Co. (Treverse City, Michigan). The wind sensor, which provides measurements of wind speed and direction at about 2 meters above the ice surface, is vertically mounted on a stand-off bracket attached to the top of a tripod tower on the J-CAD platform. The tower is designed to withstand winds of 120 knots.

2.2.3 Buoy status sensors
  The J-CAD platform orientation is measured using a model TCM2, a three-axis magnetometer from Precision Navigation Inc. (Santa Rosa, California) mounted on the electronics support channel inside the hull. This magnetometer provides estimates of platform direction and vertical tilt. The absolute direction of the wind can be determined by noting the relative direction of the anemometer in relationship to the J-CAD platform direction. The compass reading also indicates the rotation of the ice base on which the J-CAD platform is installed. The vertical orientation of the J-CAD platform is the same as that for each of the meteorological sensors. The wind sensors must be perpendicular to the ice surface in order to obtain accurate wind speed and direction data. The oceanographic sensor system is normally suspended on a 260-meter cable beneath the platform, and functions as a weight to keep the platform on a vertical plane. However, if the cable is accidentally cut, resulting in the loss of this weight and expected normal platform tilt, this vital sensor will monitor the change. The tile value of the J-CAD platform is indicated not only XY axis, but also by an absolute angle of incline from the vertical position.
  The J-CAD is equipped with two GPS receivers: the Jupiter model TU30-D140-231, a 12-channel receiver manufactured by Conexant Systems Inc. (Newport Beach, California) and interfaced with the MetOcean Digital Controller (MDC). The second receiver is integral to the ORBCOMM communication device. The reported J-CAD GPS position is that of the Jupiter GPS receiver. The GPS position information obtained from the Panasonic KX-G7101 ORBCOMM Subscriber Communicator (SC) is not transmitted since it is only used complement the ORBCOMM satellite system.
  The sensor to measure the temperature of water surrounding the J-CAD hull is the same as an air temperature sensor, the YSI model_44032 high-precision thermistor. The thermistor is housed inside the platform so that it is in constant contact with the inside wall of the platform hull through a spring-loaded mechanism. Due to the excellent thermal conductivity characteristics of the J-CAD aluminum hull, the temperature reading on the inside hull surface is an accurate representation of the external sea ice or seawater temperature.

2.3 J-CAD Platform
  The flotation collar consists of the aluminum enclosure and buoyancy material that is made of foam resin. The aluminum enclosure houses the J-CAD electronics consisting of the following components: an Onset Computer Inc. (Pocasset, Massachusetts) Tattletale model 8 (TT8) data logger/controller engine with a 48 MB flash card memory; a GPS receiver; two satellite communication systems for data transmission; the MDC; and two 245 Ahr lithium battery packs for the power supply. Attached to the top of the aluminum enclosure is an Argos antenna mast that includes the air temperature sensor, the barometer port, two GPS antennas, and one Argos antenna. A PC can be interfaced to the Tattletale controller via a watertight RS-232 port mounted on the external wall of the aluminum enclosure. This RS-232 port can be accessed without dismantling the J-CAD platform. This port enables the users to download data from the flash card memory, configure the data logger and to set various sensor operating parameters.
  The foam resin buoyancy material is Surlyn Ionomer resin manufactured by the Du Pont Co., and processed and modeled by The Gilman Co. (Gilman, Connecticut). This material was also used in the IOEB, and unlike buoyancy devices made from hollow steel, it is highly flexible and will not lose buoyancy even if buffeted and damaged by ice in marginal ice zones.
  The antenna for the ORBCOMM telemetry system is a very robust 1/4-wave style Sinclabs model SRL-201 antenna manufactured by Sinclair Technologies Inc. (Auora, Ontario, Canada). It is attached to the top of the tripod tower and is approximately three meters above the ice surface. The wind sensor, one of the meteorological sensors, is also attached to the top of this tower. The J-CAD is powered by two 245 Ahr lithium battery packs housed inside the platform. One battery pack powers the ORBCOMM communication system, and the other battery pack powers all other systems in the platform, including the Argos communication system. The reason the power supply is spilt between two batteries is to ensure that the J-CAD can continue to transmit data through the Argos system, even if the ORBCOMM system battery becomes depleted. The battery voltage for each battery pack is monitored by the buoy monitoring sensors, and the information is send to the laboratory as well as other observational data.

2.4 J-CAD System Electronics [image-video : mpeg 16,051KB]

system block diagram
  The J-CAD platform electronics system is designed in a modular form to provide a fail-safe method of protecting the data collection and storage. Each major underwater sensor and the MDC, which collects the meteorological sensors data and platform location, has the ability to operate without the platform master controller, guaranteeing underwater data collection and storage and the ability to locate the buoy via satellite.
  The electronics system in the platform provides six major functions: ORBCOMM data telemetry via satellite, ARGOS satellite telemetry as a backup, meteorological data collection, inductive coupling for underwater sensor data delivery, data logging of all platform sensors, and Global Positioning System (GPS) location of the platform.
  The TT8 master controller provides control functions that include central system timing, central data logging of sensors, inductive modem data delivery from underwater sensors, and control of ORBCOMM telemetry. The external test port is also routed to the master controller. The data logger memory is a 48Mbyte solid-state PCMCIA card mounted in the controller, in which all sensor data will be stored for the operating lifetime of the platform.
  The ORBCOMM Subscriber Communicator (SC) is a Panasonic KX-G7101 unit with GPS location capability. The GPS location is only used by the SC and is not used by the platform.
  The MetOcean Platform Transmitter Terminal (PTT) is an Argos transmitter data acquisition system configured to gather all the meteorological sensor data and acquire GPS location. This self-contained unit passes the meteorological sensor data to the master controller for storage in the data logger. This data can be passed to the PTT for transmission via the Argos. The Argos transmitter is a backup communications method that will only be fully activated to transmit data if the ORBCOMM system or master controller fails. At any other time, transmissions are made only once per week for six hours to provide confidence that the Argos transmitter is operating.
  The Sea-Bird IM system uses a single conductor oceanographic cable for transmitting data from the oceanographic sensors to the J-CAD CPU. The underwater cable is 6 mm in diameter, torque-balanced and coated with synthetic resin. The oceanographic sensors, which include Sea-Bird Inductive modem connected with the ADCP or the Watson Compass, are attached to this cable by clamps at predetermined depths. The underwater sensors all communicate on a single conductor support cable via a Seabird inductive modem in the platform. This method of data delivery requires each sensor to house its own power supply. This requirement also allows each sensor to contain its own data logger in which all data samples will be stored while the sensor battery is available. This design ensures identical data is stored in two loggers (platform and sensor) guaranteeing completely saved data even if the master controller fails.
  The data acquisition and processing system on the J-CAD platform consists of the MDC and the TT8 data controller. The MDC and TT8 operate on cycles within the J-CAD processing system. At first, the MDC begins its cycle of collecting reading from the meteorological sensors and buoy status sensors. After collecting these data, the MDC sends a signal to the TT8 that it is ready to transmit data. Then, the TT8 is ready to collect data from the oceanographic sensors. When data storage function is completed, the formatted messaged data is made and passed to the ORBCOMM SC for data transmission. Then, the ORBCOMM SC transmits data to the satellite. If, for some reason, the ORBCOMM transmission fails and 11 hours' worth of data is stored in the TT8 without being transmitted, the Argos transmitter that is controlled by the MDC will begin to transmit Argos data messages. The data messages received in the satellite are then transmitted back to earth receiving station. The data are then automatically sent to a computer in JAMSTEC.