Observatory Description

The long term vision is to develop internet-based teleoperated observatories at both near shore and Shelf locations near Palmer Station. A regional observatory system should provide end-to-end capability (Oceans US, 2002), including: a (1) monitoring subsystem (platforms, sensors, measurement techniques) to measure key variables on the space and time scales appropriate to the region and issues of concern, (2) a data communications and management subsystem to collect, quality assess/control, archive/store and disseminate data, and model products and (3) a data analysis and data assimilation modeling subsystem to nowcast and forecast variables of principal concern to the regional/local user community.

This kind of observatory system will be built at Palmer Station in 2 phases: Phase I (this project) will establish a cabled, primary node within 3 km of Palmer Station, probably near Station F or E of the LTER near shore permanent sites at a depth of 100-150 m. Selection of the final location will be made following our bathymetyry survey in April-May 2005 and in collaboration with Principal Investigators in the Palmer LTER and SO GLOBEC programs, and operation managers with Raytheon Polar Services. Phase II will establish a secondary node on the Shelf about 20 km offshore at a depth of about 500 m and more of the data analysis and assimilation components required in a comprehensive observation system. Observatory nodes will be connected to shore via a fiber optic cable providing both continuous power and communications between the instruments and shore. All communications will follow standard Ethernet/TCPIP and will allow scientists, engineers, and students to access and control instrumentation, and observe data in real time from literally anywhere in the world.

Observatory Subsystems

Subsystem components consist of the following: 1) Buoyant profiling vehicle (BPV) and associated sensor suite, 2) Bottom mounted platform including the winch and main controller, 3) Shore station, and 4) G profiler round cable. Each of these will be described in detail below.

Buoyant Profiling Vehicle (BPV, left)

The buoyant profiling vehicle (BPV) will be based on the successful and mature design we have deployed elsewhere and will benefit from the lessons learned in those experiments. Its low drag, both vertically and horizontally, substantial payload for sensors, access to undisturbed water for sampling by the Video Plankton Recorder (VPR), and protection of sensors from contact with the under ice surface make it ideal for this application. This configuration allows for a variety of biological, physical and bio-optical sensors to sample an undisturbed volume while the vehicle is both ascending and descending. Other sensors such as the fluorometers, oxygen sensor, and CTD receive a pumped supply allowing the intake to be positioned remote to the sensors. With 300 m of tether paid out, the PRIMO profiling vehicle will have 100 lbs of excess buoyancy provided by syntactic foam in the pontoons. The vehicle will be balanced to remain level and the rear vertical fin forces the vehicle to always point into flow while a low-friction slip ring provides for free rotation of the vehicle relative to the tether.

Table 1. (below) provides information on the basic sensor suite to be integrated into the BPV. With the exception of the hydrophone and nitrate sensor, all of these sensors have been tested on the autonomous Vertically Profiling Plankton Observatory (AVPPO) while deployed at the Martha’s Vineyard Observatory.

http://4dgeo.whoi.edu/vpr

Sensor	Properties Measured	Sample Frequency	Power Requirements	Communi-cations
SeaBird SBE-49	Conductivity, Temperature, Pressure	16 Hz	3.5 W @ 12 VDC	RS232
Nobska, Inc. MAVS-3	Vector averaging 3 axis acoustic current meter	10 Hz	1 W @ 12 VDC	RS232
Satlantic Nitrate sensor	NO₃	0.5 Hz	12 W @ 12 VDC	RS232
AXIS 2130 PTZ Pan and tilt video camera and LED ring illuminator	Operator controlled to observe large organisms (adult krill, fish, penguins, seals, particles) and under ice surface	30 Hz	1 W @ 12 VDC	10 BT Ethernet
Seascan Video Plankton Recorder	Plankton and particulates (100 um to 2 cm)	30 Hz x 2 ml = 60 ml/s	20 W @ 24 VDC	10 BT Ethernet
Aanderaa 3830 dissolved oxygen optode	O₂	1 Hz	0.5 W @ 12 VDC	RS232
WetLabs CDOM fluorometer	Colored dissolved organic material	3 Hz	0.9 W @ 12 VDC	RS232
WetLabs Chorlophyll fluorometer	Chlorophyll a	3 Hz	0.9 W @ 12 VDC	RS232
WetLabs transmissometer	absorption/attenuation of water	1 Hz	2 W @ 12 VDC	RS232
Satlantic OCR-507 irradiance	Upwelling irradiance at 7 discrete spectral bands	6 Hz	0.5 W @ 12VDC	RS232
Satlantic OCR-507 irradiance	Downwelling irradiance at 7 discrete spectral bands	6 Hz	0.5 W @ 12VDC	RS232
Imagenix 881a sector scanning sonar	Acoustic scattering from targets 1 cm to 10 m in 360 degrees out to 100 m	360 degree scan in 10 s	2 W @ 12 VDC	RS232
Datasonics PSA-900 Sonar altimeter	Wave height, under ice topology, obstacle avoidance, distance to surface/ice	10 Hz	1.2 W @ 12 VDC	RS232
Hydrophone with digital interface	Underwater sound 20 Hz to 20 kHz	continuous	2 W @ 12 VDC	100 BT Ethernet
Digi 16 port RS232 to 100 BT Ethernet	Converts serial devices to Ethernet		1W @12 VDC	100 BT Ethernet
Netgear fast Ethernet switch	6 port Ethernet switch		2 W @ 12 VDC	100 BT Ethernet
TOTAL POWER REQUIREMENT			56 W @ 12 VDC

Power budget

Table 2 Power Budget	W	VDC	A
1. BPV sensor package	60	12	4.4
2. BPV telemetry modules	2	12	0.16
3. winch under full power	500	24	7.5
4. node telemetry	3	12	0.25
5. node package	3	12	0.25
6. camera illumination	200	24	8.3
Total	768		20.8

Power will be supplied from Palmer Station at 208 VAC to charge a set of batteries acting to isolate power and as a UPS. Battery supply will be inverted and stepped up by transformer to 1500VAC for transmission to the bottom platform. There it will be rectified to 24 and 12VDC in an underwater housing called the BPV telemetry bottle, which contains a series of newly designed WHOI guest port boards. These boards also contain ground fault detectors and provide Ethernet-based control for the power distribution system to all sensors. The initial requirement of 448 w will likely expand quickly as new sensors are added. Therefore we have designed the power transmission system to provide 4 kw at 1500 VAC.

Bottom Mounted Platform

The bottom mounted platform consists of an aluminum frame surrounding the underwater winch, junction box, controller housing, and remotely controlled camera with pan and tilt and remote zoom control capable of observing winch operation and scanning the benthic habitat. The AXIS 2130 PTZ network camera has a built in web server allowing multiple viewers without slowing down the network. Pan, tilt and zoom controls are through a web site GUI. A user would log into cameras’ website using an IP address and password and view and control the camera from anywhere in the world. A ring of white LEDs provide illumination for observation to a distance of about 5 m.

Underwater Winch

Without question, the mechanical aspects of an underwater winch are the most difficult to solve in an autonomous system. We have spent five years building and working with various designs of autonomous underwater winches and have found two working solutions: In shallow, but highly energetic conditions less than 100 m in depth, a single wrap linear drum with a powered lead screw level wind works well. However, in deep water a narrow but deep-cheeked drum with powered slack tensioner allows cable lengths of 100s of m. With either design, the cable that leaves the drum before turning on an overboarding sheave must be under tension if backlashes and bird-nesting are to be avoided. With more than 10,000 cycles in four years, the linear drum concept has worked very well for the AVPPO. Deep Sea Systems, Inc., Cataumet, MA, a designer and supplier of high end ROVs, tether management winches, and other electromechanical devices, has built a series of underwater winches for the Navy using the narrow drum concept. Based on their experiences and ours we have teamed with Deep Sea Systems to produce a narrow drum underwater winch the will survive for year-long deployments operating at depths of 100 to 500 m, be easily serviceable with modular components, and be cost effective such that multiple units could be manufactured for a variety of observatory needs.

Figure 5. Underwater platform with winch, main controller and BPV.

Figure 6. Deep Sea Systems autonomous underwater winch capable of holding 600 m of fiber optic tether.

The WHOI/Deep Sea Systems winch is simple in design and uses the best combination of materials to resist corrosion and maintain strength under extreme conditions. The 40 inch diameter 6 inch wide storage drum is made of fiberglass and epoxy composite with titanium hardware and bearings. Drum capacity is 600 m of 0.40 inch HDPD jacketed 3 fiber, 3 conductor double steel armored tether. An oil filled 3 fiber 4 conductor rotary joint is accommodated on the main shaft. The drive mechanism is a 1.3 hp brushless DC motor with feedback resolver coupled to a 200:1 high precision planetary gear head. The tether is directed over an 18 inch idler wheel and onto a 18 inch powered sheave. The sheave has a groove specially designed with knurled surface to grab the outer jacket of the tether. A series of spaced rollers ride over the outside of the tether pressing it into the knurled groove. The sheave is designed to apply about 50 lbs continuous back tension on the tether between the drum and the point where the tether exits the sheave. The sheave is driven by a similar, but slightly smaller, 1.0 hp brushless motor and a 100:1 gear head. Motor control is through brushless DC electronic amplifiers, which are housed in the controller pressure housing, in a closed loop servo with the resolver as the feedback device. A control board sets up the lag and lead constant tension locally between the powered sheave and the main drum regardless of external commands to payout or haulback. Simple operational commands transmitted to the controller board consist of payout at a given speed (10 cm/s typical), stop, and haul back at a given speed. A wire out counter wheel provides positive feedback to the main controller. A set of triple redundant magnetic switches detect when the termination on the BPV has successfully docked which results in the controller sending the stop command to the servos. As a secondary docking detection system, the controller monitors motor torque and sends a stop command if it exceeds a predetermined threshold. When stopped, a power-off brake is applied to the main motor shaft keeping the tether from drifting.

Controller housing

Figure 7. Winch base Electrical Architecture: power and communications

The controller housing consists of the main controller, a communications LAN and a new WHOI guest port board for power distribution. The winch controller is a PC104 computer with 100 BT Ethernet interface. The controller monitors data coming form the BPV and provides an interface to the winch servos. High level commands from shore such as “pay out at 10 cm/s” are interpreted by the controller which then sends the appropriate signals to the winch servos. Thus closed loop control of the brushless DC motors is local to the controller and BPV with no need for intervention from shore. For example, the controller monitors data from the servo resolvers, the wire out counter, and the pressure sensor on the BPV. A command from shore might include: “pay out at 10 cm/s and stop at 20 m from the surface”. The controller’s primary response to stop would be the pressure sensor reading 20 m, but if the pressure sensor was damaged for some reason, secondary responses would be necessary based on wire out and servo counts (i.e. all the cable would not be allowed to spool of the drum). A hierarchy of commands and responses is necessary for a fail-safe control system (see section on mission control).

The controller is also responsible for the power distribution system. 240 VAC enters the controller housing from the junction box and is distributed directly to the BPV and to a WHOI guest port board to achieve 12 and 24 VDC each at 100 W. A separate converter from 240 to 120 VAC is used to provide power to the winch motors. Power to the controller’s PC104 is applied when the main power from shore is supplied at 1500 VAC. If the need arises, the PC104 may be re-booted by cycling shore power, while power to the winch telemetry and BPV may be cycled independently by commands from shore. The purpose of the guest port board is to provide independent power switching and ground fault protection for each component thereby minimizing the possibility of a single point failure causing catastrophic loss of data or control.

Seafloor Cable

The seafloor cable is based on earlier successes at the Martha’s Vineyard and Leo15 observatories: 0.84 inch double armor, 6 Awg No.13 conductors, 6 Awg No.20 conductors, and up to 10 single-mode fiber optic loose-tube strands manufactured by South Bay Cable. A minimum 30 year life is expected. Two fibers will be used for the 100 BT Ethernet communications, and one for the raw VPR images, and another for the two web cams leaving five spare fibers available for expansion. Four copper conductors are used for transmission of the 1500 VAC power to PRIMO. Remaining copper conductors will be available for expansion.

Communications

Figure 8. Buoyant Profiling Vehicle Architecture: power and communications

The intent of the communications system is to standardize all devices making plug and play a reality. All sensors communicate via RS232 or Ethernet. Each RS232 to Ethernet converter has a unique IP address while each RS232 device has a unique channel which is configured for the communications protocol required for a particular device. All sensors with RS232 communications will interface through a 16 port Digi RS232 to 100 BT Ethernet converter. The single Ethernet output is then networked through a 100 BT switch which collects inputs from other Ethernet based devices and provides a single output for conversion to fiber optic. Some room for expansion will be available since only 13 out of 16 available RS232 ports are being used. Although all sensors are initialized in immediate mode, meaning that they start sending data upon power up, two way communications allow for changes in configurations as necessary. For example, the SBE49 CTD starts sending data upon power-up, but new calibration constants could be downloaded as necessary by breaking in to the data stream with appropriate commands from shore.

The interconnection diagram illustrates the LAN provided by the devices in the BPV and in the controller. Since Ethernet must be converted to fiber optic (FO) signals for telemetry through the tether, a dual fiber (transmit and receive) communications protocol may be required as we have used under similar conditions. Alternatively, it may be possible to use wave division multiplexing (WDM) at wavelengths of 1550 and 1300 nm over a single fiber. This decision will be made at the time of final implementation.

Shore station

Physical Structure and Data processing

Figure 9 Shore Station Architecture: power and communications

The shore station will be housed in either the new biology building or one of the small huts at Palmer Station. The ground cable will run from shore directly into the hut, which contains redundant power supplies each with a battery backup. A 100 BT LAN is established between the BPV, controller, and two shore computers to handle data logging and processing. One shore computer running Linux contains a FO to Ethernet card and acts as a system data logger acquiring and time stamping all sensor data from Ethernet ports assigned to each sensor. This computer also acts as the system controller and web server for the main control and data display GUI. All sensor data files are backed up each day onto a hard drive server. A second computer acts as the image processor for the video data coming in from the VPR.

Newly constructed IMS building