Feature ArticleWire-Following Profiler for The Ocean Observatories Initiative
By Michael Mathewson • Cleo Zani
Solid model of the profiler and sensor suite for the Global (left) and Coastal (right) WFP.
The contract included proposed improvements to the existing McLane Moored Profiler (MMP), production of first-article profilers and options for additional profilers to populate the OOI’s Coastal Pioneer, Global and Endurance Arrays.
To meet OOI specification 3310-00003 for wire following profilers, McLane proposed four improvements to the commercially produced MMP: integration of a faster inductive modem, an electronics upgrade, creation of a mission planner and the addition of a motion sensor.
The faster inductive modem was proposed for the Coastal profiler only, but the remaining three features would be included in both Coastal and Global WFP.
Manufactured by McLane under the Woods Hole Oceanographic Institution (WHOI) license, the neutrally buoyant MMP autonomously profiles the water column in a time series along a fixed mooring and is driven by a magnetically coupled drive motor.
Profiling depth, time intervals and pressure stops are user-defined, and profiling patterns can span specific seasons or time frames.
Integrated sensors include CTD, acoustic current meters, chlorophyll a, turbidity, photosynthetically active radiation (PAR) and dissolved oxygen. An underwater inductive modem provides real-time communication between the profiler and a surface buoy or seabed node. Over the past decade, more than 150 profilers have been delivered and deployed around the world.
In order to shorten this data transfer time without decimating the data, the profiler required a faster inductive modem. The existing MMP uses the Sea-Bird Electronics Inc. (Bellevue, Washington) Inductive Modem Module (IMM) for inductive data transfer to a surface or seafloor controller with an effective transfer speed of 1,000 to 1,200 baud.
Since the transfer of engineering, CTD and current-meter data files occurs at the end of a profile, the inductive transfer speed is directly related to the minimum time between profiles. The proposed MLM-1000 inductive modem, manufactured by RBR Ltd. (Kanata, Canada), was integrated into the profiler and field tested. Since the head end modem card was similar in size to the existing profiler interface board, the mechanical fit and connections in the electronics chassis were straightforward.
In addition, the transparent link architecture allowed McLane to port the existing inductive modem protocol and retain the data transfer command syntax used in previous profilers.
After completing the integration and bench testing in air, McLane and RBR cooperated to execute a field test in Buzzards Bay, Massachusetts, and confirm the system throughput of the profiler and inductive modem communication system.
In January 2012, they deployed a seafloor node with profiler electronics (a simulated profiler) and preloaded data files ready to transfer. The surface controller was on the vessel, which was connected to the seafloor node by 1,500 meters of 3/16-inch 3 x 19 jacketed wire rope. The effective length of the seawater distance between the two inductive modems was 1,425 meters (measured by GPS). A series of automated data transfers confirmed a modem-to-modem transfer rate of 4,800 baud and system throughput of 3,200 to 3,500 baud.
The additional sensors and data density specified on the OOI profiler required an upgrade to the controller electronics. McLane chose Persistor Instruments’ (Marstons Mills, Massachusetts) CF2 because of its 1-megabyte internal RAM, 1-megabyte flash memory and compact flash data storage of up to 16 gigabytes. In order to provide an upgrade path for existing profilers, McLane and RBR also developed a secondary interface board to map the I/O and power from the CF2 to existing profiler sensors, motor, inductive modem and watchdog circuit.
Mapping the electrical connections and porting the firmware to control the profiler was a significant task. However, the effort resulted in an updated controller with all the previous profiler functionality and a path to future expansion.
For the planned OOI arrays, a mission planner was needed to manage the database of profilers, data and schedules, some of which may be updated during the deployment based on science requirements. The Mission Planner is an integrated tool with a functional user interface, basic data processing and battery-endurance estimator that meets the OOI specification. To continue this article please click here.
Michael Mathewson is the general manager at McLane Research Laboratories Inc. He received a degree in mechanical engineering from Cornell University and a master’s degree from the University of Washington.
Cleo Zani is the lead software engineer at McLane Research Laboratories Inc. and is responsible for development of embedded underwater data acquisition, control and instrumentation systems.