What do you know about the Nortek Continental Profiler?

Overview

The Continental Profiler is Nortek's answer for longer range profiling.  Typically used for profiling projects on the continental shelf or at the top of open ocean mooring lines, the Continental Profiler has a  nominal profile range of about 200-250 m (190 kHz) and 100-125 m (470 kHz).

Comparisons

The Continental Profiler is a good replacement for older Workhorse products.  The 470 kHz Continental has a similar profiling range as a 300 kHz ADCP, yet it costs nearly $8,000 less.  The 190 kHz Continental has a similar profiling range as a 150 kHz ADCP and it costs nearly $10,000 less.  These instruments use very little power and provide exceptional observations of current velocity during very long term deployments.

The Nortek Technical Note (TN-024) compares the profile range of the Nortek Continental Profiler with a 300 kHz ADCP.

Long Range Capability

In a recent project offshore Venezuela, a 190 kHz Continetal profiler was deployed at 310 m and was able to profile all the way to the surface. Because of the surface sidelobe contamination (standard for all current profilers), some information close to the surface is lost.  Still, our analyses shows that the data in this case was valid all the way to 290 m.  In the attached plot, the north-south component of velocity is seen to be quite strong in a 100-m deep surface layer.  This episodic event lasted for almost 10 days and the peak velocity 20 m below the surface was about 1.5 m/s. 

Contour plot from 190 kHz Continental Profiler showing 300 m profile range.

Seasonal Sampling

Do you need to deploy your profilers for one or more years?  Are there some seasons (spring bloom, summer melt, fall storms, etc) that are more important to your studies?  Do you want to sample these seasons in higher temporal resolution, and then save power and memory during the less important times? 

You are not alone.  These were the requirements for researchers at Université Laval (Quebec, Canada) working in the Arctic as part of the ArcticNet program.  To meet these important requirements, Nortek developed the Seasonal Sampling mode that is now implemented as an option in all Continental Profilers.  The Seasonal Sampling mode allows the user to set a high-temporal resolution profile interval for one part of the year, and a separate (lower temporal resolution) profile interval for the remainder of the year.  This mode allows the user to save some power and memory for very long deployments without sacrificing high temporal resolution during the most important seasons of the year.  Université Laval owns over one dozen Continental Profilers and they have been deployed in various Arctic locations since 2007.

Side-Looking Profiler

The large transducers on the Continental Profiler greatly reduce the acoustic side-lobes and thus make the Continental ideally suited to side-looking profile applications.  Researchers at University of Delaware mounted two 470 kHz Continental Profilers to opposite piers of a bridge to measure across-stream and down-stream currents, eddies and suspended material in support of a bridge scour project.

Bathymetry of channel showing two Continental Profilers mounted on bridge piers. 
The black lines show the acoustic beam paths.  Data in plot below is from one of the (primarily) across-channel acoustic beam angles.

The current velocity and acoustic backscatter (amplitude) data from the Continental's deployed on the bridge pier are very interesting.  Data were collected in BEAM coordinates and logged at 1 Hz in order to get the most raw format of data for observations of eddies and other coherent structures.  The top plate in the figure below shows the along-beam velocity from one of the Continental Profilers over 100 m range (beam angle is nominally across-channel).  The highest velocities are located in the middle of the channel (distance 10-65 m).  The lower velocity at the edges of the plot (distance 0-10 m) is found in the lee of the bridge pier.  The current reversal (dark blue) found at distance 75-90 m is presumably back-eddies in the lee of the opposite bridge pier.  The alternating current velocity (red/blue) in the middle of the profile (distance 40-50 m) is likely large scale eddies propagating downstream.

Current velocity (top) and signal strength (bottom) from Continental Profiler
looking across a river near a coastal inlet. (click for high resolution image)

The lower plot shows the signal strength from the 100 m range across the channel.  Overall, the signal strength is expected to reduce as a function of distance away from the transducer.  This is apparent as the signal strength is highest at range 0-10 m and decreases to the right.  However, increased signal strength at distance 70-80 m is observed.  This region of increased signal strength is likely due to an increase in suspended sediments (scour?) caused in the lee of the opposite bridge pier.  This is coincident with high velocity shear observed in the current velocity profile.