Overview of the Moored Profiling Apparatus 

Observations once obtained from a network of ocean weather ships provided a tantalizing glimpse of ocean variability on seasonal to decadal time scales.  Although these stations were positioned to optimize meteorological sampling and to aid aircraft navigation, a few were sited in oceanographically interesting regions.  For example, Station Bravo located in the middle of the Labrador Sea  (an important formation region for intermediate water) resolved the seasonal cycle of deep winter convection and summer-time restratification  over a 10+ year period beginning in the mid-1960's.  These observations document notable interannual variation in the winter convection that have been related to basin-scale variations in water properties and characteristics of the overlying atmosphere (in particular, winter-season weather patterns over North America and Europe).  As interest in global climate change grows, so does our need for long records of ocean variability.  Data over long times are valuable for constraining and/or testing ocean-atmosphere models, and revealing new modes of air-sea interaction and behavior.  However, the cost of maintaining manned vessels on station 12 months of the year is prohibitive.  The Moored Profiler (and companion autonomous instruments now under development within the oceanographic community) were conceived to address the long-term ocean-sampling problem in a far more cost effective manner.  These instruments fall into three categories: bottom-anchored systems (like the Moored Profiler) that sample at fixed geographic positions, free-drifting instruments like the ARGO float (see the ARGO web site ), and self-maneuvering instruments including gliders and AUV's.  A mix of these instruments is envisioned within a global ocean observing system.

The Moored Profiler utilizes a small, battery-powered traction motor to climb up and down a standard subsurface mooring  carrying sensors that document the water properties and currents versus depth.  Depending on the design of the mooring, the Profiler is able to sample from just below the surface to just above the bottom with a total endurance of approximately  one million meters per deployment.  Complex sampling schedules are possible under control of the onboard microprocessor including burst sampling wherein several profiles are collected in a day followed by a rest period of several days, with the whole pattern repeated through the deployment (a scheme to minimize so-called alias errors when unresolved high-frequency motions contaminate long-period signals).  Moored Profiler data are presently stored on board for the duration of each deployment and downloaded once the instrument is recovered. The technology to return data in real-time via satellite and possibly modify the sampling program within a deployment is envisioned.

Development of the Moored Profiler was initiated with grants from the U. S. National Science Foundation and the WHOI Director's Discretionary Fund.  Follow-on support was obtained from the Office of Naval Research and the National Oceanic and Atmospheric Administration.  The culmination of this engineering effort was an operational prototype WHOI Moored Profiler.

                                     Schematic drawing and close-up photograph of the WHOI Moored Profiler
 

Click on figures to see more detailed images


 

The WHOI Moored Profiler is oblate-spheroidal in shape with a 2x1 aspect ratio: 80 cm tall and 40 cm wide.  The front face of the cowling is cut off to allow the guide and drive wheels to flush freely.  The sensors for the Conductivity-Temperature-Depth instrument (CTD) and the acoustic phase-shift current meter (ACM) extend out from the front face into undisturbed flow.  The instrument's mass is approximately 50 kg and is ballasted to be neutrally buoyant within its profiling interval.
 

To date, the WHOI Moored Profiler has been fitted with a CTD for sampling the ocean's temperature and salinity versus depth and an Acoustic Current Meter to measure the ocean currents.  Both of these sensors are manufactured by  Falmouth Scientific, Inc.  of Falmouth MA.  We are presently converting WHOI Profilers to use the FSI Excel MicroCTD that operates at very low power.  The current meter used is the FSI 3-D ACM fitted with a customized transducer mount that is deployed remote from the ACM pressure case using a multi-conductor oil-filled cable.  Operationally, these sensors are turned on at the start of each profile and they log internally at 1.5-2 Hz while the vehicle travels along the mooring wire.  At the completion of each profile, the main instrument controller downloads the CTD and ACM data and archives the information to a hard disk.  During post processing, these raw data are normally bin-averaged to a 2-dbar grid for scientific analysis.

In 1998, the Moored Profiler technology was licensed to  McLane Research Laboratories, Inc.  of Falmouth MA. who are now marketing a more capable version of the Moored Profiler (called the McLane Moored Profiler, MMP).  The main difference in instrument designs is the pressure vessel for the main electronics and battery.  The WHOI prototypes placed these systems inside glass spheres; the MMP uses sealed glass spheres for buoyancy and a titanium pressure case for the electronics and battery.  This change was motivated by the comparative ease in servicing metal pressure cases as compared to glass.   To accommodate the added pressure case, a new mechanical layout was developed, resulting in a streamlined-cylinder instrument shape.

                                                        Schematic drawing and photograph of the McLane Moored Profiler

Click on figures to see more detailed images

The MMP is 24 cm tall x 34 cm wide x 51 cm fore-aft and has a mass of approximately 70 kg.  It has been interfaced to the FSI Excel MicroCTD and the FSI 2D- ACM with customized transducer sting.
 

                    Please access other areas of this web site to see examples of data recently acquired by Moored Profilers.
 

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