Call me a nerd (I’m doing that all the time) but there is something beautiful about the coming together of superb engineering and design to create a gadget that does what it is meant to do, simply, efficiently and fool-proof.
I met Iain White of Nortek Group at the Marine Measurement Forum in November 2022, where I represented the charity Seas Your Future with a talk about what STEM education and sail training aboard a tall ship can achieve for the outlook of young people from disadvantaged backgrounds.
My appeal for scientific instrumentation fell on fertile ground and in September 2023, I got to play with the Nortek ECO, an acoustic Doppler current profiler (ADCP) on two of our STEM/ocean science education voyages aboard the sail training tall ship Pelican of London. I’ve already written about our first deployment in Ireland in a previous blog post, but here I’d like to go into a little more detail about some technical aspects – because it’s worth highlighting what goes on behind the scenes before we hold a well-designed product in our hands!
The Nortek ECO was developed to fill a large and empty niche in the market of hydrographic instruments that can be described as low cost, portable and fool-proof. As a concept brief, this must have been an interesting challenge for designers and engineers and the reason I think that comes from my experience as scientist on research ships, when I got used to scientific instruments that work beautifully for a purpose but also have some shortcomings. This includes that instruments are often large and heavy, or small and light so that they need to be secured to a heavy frame to remain stable in the water column, either way limiting their portability and requiring heavy-duty infrastructure on ships for deployment. Waterproof connectors on submersible instruments for data transfer and power cables introduce vulnerabilities regarding water ingress and corrosion, managing even short cables by hand can be frustrating and longer ones require winches and a platform from which to operate them. In addition, scientific instrument software is rarely intuitive to the first-time user.
All of these issues have been beautifully resolved by Nortek for the ECO and as a result, its design and engineering phase was the most elaborate for any of the company’s instruments so far. To get a first impression of what was achieved, watch this video by Nortek showing the deployment of ECO from a paddleboard!
The most constraining element of the design concept must have been the size: it was to be comparable to a standard (330 mL) soda can, so that it would be deployable with ease in shallow waters [1]. This required reviewing and stripping down the elements of traditional ADCPs, developing a new electronics platform around eliminating external ports, reducing power consumption and minimising circuitry size. The resulting system is a short range (0.5 -20 m) upward-looking, three-beam, 1 MHz carrier frequency APDC packed into a cylinder of 130 mm height, 85 mm diameter and 1 kg weight with an internal battery that is charged exclusively by induction [1].
The next challenge was the design of a simple user interface that provides non-experts and first-time users with sufficient control over essential parameters during autonomous deployments. ECO was to be a fully functioning entry-level system. As a result, the ECO self-configures with minimum user input (when to start measurements, how often to sample, approximate water salinity) and just gets on with it. ECO uses an internal pressure sensor to determine deployment depth and calculates the resolution of measurements necessary to achieve a horizontal velocity precision of 1 cm/s or better [1]. I used the software with ease from the start, as the app paced me through everything I needed to do to set, deploy and recover the instrument, as well as the data upload, visualisation and processing! It couldn’t be more user friendly.
Wireless Near Field Communication and Bluetooth Low Energy technology deals nicely with avoiding connectors, which helps saving space and also reduces points of failure (see above). Rather sweetly, you can give the ECO a little wake up shake to tell it that you want to communicate with it :).
As an (not even quite yet) amateur hydrographer (the Nortek ECO was my first brush with current measurements ever) I have no scientific background that helps me with understanding the technicalities of 3D current measurements, beam characteristics, frequencies and Nortek’s Multi Correlation Pulse Coherent method, but I’m sure all of these design features were excellent choices, along with the implementation of the wideband processing technique used in Nortek’s AD2CP platform (it’s patented in the US). At some point, I’ll sit down and get my head around this, but for now, I’ll refer you to the papers [1], [2] and [3] for more detailed information in case you are more expert than me (which is not difficult) and want to know more.
Quality control is something of keen interest to me as a scientist. ECO undertakes a lot of quality assurance automatically using algorithms. For example it detects and eliminates signals coming from fish and other improbable movement of ‘particles’, compensates for the tilt of the instrument, applies a range of filters to the data that account for elements, such as low correlation, high acceleration or being out of water and also transforms data [1]. Again, ADCP experts will understand better than me what the advantages and disadvantages are in having all of that is done by the internal firmware before data is stored in the memory and before it is accessible to the hydrographer. However, as a first-timer, I was pretty happy that I didn’t need to worry myself with it, although in my own field of science, I prefer to have access to both, raw data and the data to which algorithms had been applied by instrumentation.
Nortek ECO can be deployed in depths up to 50 m and there are two modes of doing so:
1) The instrument is mounted on a tripod and ‘walked’ to a location where the tripod can be placed on the sediment at shallow depths.
2) As shown in the video embedded above, the ADPC is mounted into a flotation buoy, which is attached to a 60 m line. The line is flaked into a second, smaller buoy and secured with a shackle at a short distance from the instrument buoy. Both buoys are weighed down with an anchor (or similar) and dropped into the sea at the desired deployment point. At a pre-set time (also programmed by the APP), a motor in the smaller buoy releases the shackle and long line to enable the instrument buoy to float to the surface, where it can be recovered.
So, what did I get out of the ECO?
Screenshots from the webapp of the Nortek ECO showing processed data at four deployment locations from Pelican of London in August/September 2023. (c) Nortek Group – reproduced with permission.
The data shown above are the result of four deployments of ECO from the Pelican of London for durations of at least one half of a tidal cycle with measurement intervals of 2 minutes. For ECO, these were ‘quick dips’, as it is capable of continuous deployments for over 40 days. Data show how the water velocity and direction changes with the tides and highlight how each coastal location has its own current profile: a circular motion in Dun Laoghaire Bay, stronger northwards than southwards currents along the coast off Aberystwyth, almost symmetrical ebb and flood tides at Blackpool Sands in Devon and the more complex pattern in Falmouth Harbour that is influenced by river flow in addition to the tidal movement.
The web app produces a wide range of graphs and I found the radar charts particularly useful to visualise the current velocity and direction (in meters per second), as well as displaying the extrapolated water flow and direction (in meters cubed per meters squared per day).
The data can be exported from the web app as csv file and imported into statistics and spreadsheet software packages. The example above shows box and whisker plots and correlation calculations for current velocity and direction at three depths, as I wanted to know whether there are changes with depth. The one thing I stumbled across here was the inability to tell the web app that I wanted the data from just below the surface, no matter what the tidally influenced height above the sensor was. That could not be achieved easily, and would require quite painstaking processing to approximate. I am sure professional hydrographers find a lot more sensible things to do with the data and at some point I’ll seek their guidance.
Application notes: it works perfectly the first time and then again and again! The only snag in the operation is the rather thin material the 60 m line is made from. We made sure to wear rigger’s gloves the second time we pulled the system and anchor from the seabed. If I use ECO again, I’ll devise a system that makes recovery of the 28 kg weight easier. The tripod and its 3×3 kg weights were shipped to me in a transport case, weighing around 18 kg in total. The ECO, induction charger, buoys and release mechanism in their transport case weighed around 23 kg in total. We used the anchor of our RIB and a range of massive shackles and bronze chain links as weights during deployment. A couple of kettlebells would have been easier to handle. The tripod deployment seems simple enough, but I did not get the chance of trying it out.
Conclusion: I am a convert (!) and the ECO has enabled me to dabble with current measurements pretty much from a zero start. As explained in my first blog on the ECO, I deployed the instrument within hours of first laying hands on it – it is really that simple. On the Pelican of London, I used it primarily as an STEM educational tool, showcasing engineering, ocean science and the physics of the measurement principle to young people on the ship for sail training. It worked perfectly for these purposes.
References:
[1] Velasco DW, Jorgensen M, Nesheim A, Nyund S (2020) Development of a low cost, self-configuring ADCP and integrated deployment and recovery system. Conference Paper at Oceans 2020. DOI: 10.1109/IEEECONF38699.2020.9389146
[2] Hay AE, Zedel S, Nylund R, Culina C, Culina J (2015) The Vectron – a pulse coherent acoustic Doppler system for remote turbulence resolving velocity measurements. Conference Paper IEEE/OES Eleventh Current, Waves and Turbulence Measurement. DOI: 10.1109/CWTM.2015.7098130
[3] Shcherbina AY, D’Asaro EA, Nylund S (2018) Observing finescale oceanic velocity structure with an autonomous Nortek acoustic Doppler current profiler. Journal of Atmospheric and Oceanic Technology 35(2) 411-427. DOI: https://doi.org/10.1175/JTECH-D-17-0108.1
