Community Oceanography with low-cost, open-source CTDs

On September 14, 2022, I gave a talk on community oceanography and the OpenCTD for the AtlantOS Ocean Hour “Democratizing ocean observations through low-cost technologies” workshop. Below is the transcript from that talk.

Good morning and thank you for inviting me.

Access to the tools of science is not equitable, and nowhere is this inequality of access more pronounced than in the ocean sciences, where all but a few entities have the capital to mount major oceanographic research campaigns. I come from the world of deep-sea ecology, where budgets can quickly climb into the tens of millions of dollars. But even small-scale coastal research can be stymied by the need for vessels, equipment, and instruments, access to which is often controlled by research institutions.

As the need to understand the dramatic changes happening both at the surface and beneath the waves accelerates, barriers to access that precludes the participation of the full breadth of ocean stakeholders erodes our potential to understand, anticipate, and mitigate those changes.

One of the missions of my post-Academic career has been to make the tools of ocean science more accessible to more people. I believe that the ocean belongs to everyone and that the tools to study the ocean should be available to anyone with the curiosity and motivation to pursue that inquiry.

Chief among those tools is the workhorse of oceanography, the CTD.

Just in case anyone is unfamiliar, a CTD is a device that measures salinity, temperature, and depth. It can be used to profile a water column, affixed to other instruments to correlate observations to water conditions, or deployed as a fixed mooring for long term monitoring. Almost all marine scientific research includes a CTD cast.

But commercial CTDs are expensive. This creates a barrier to access for many of the people most imminently affected by our changing oceans.

The OpenCTD is a low-cost, open-source alternative to commercial CTDs designed intentionally for budget-restricted scientists, educators, and practitioners working in nearshore coastal ecosystems, where entire research projects can be conducted for less than the cost of a commercial CTD. The sensor quality is acceptable for the vast majority of ecology and conservation studies – though you probably won’t want to use one for chemical or physical oceanography – and it operates to a depth of 140 meters.

An OpenCTD can be built for about $350 in parts and another $200 in tools and consumables.

I began developing the OpenCTD during my journey through the post-docalypse, looking for inexpensive ways to continue to conduct my own marine research while bouncing between short-term academic appointments. Because I am not an engineer, the early years of OpenCTD development was a steep learning curve as I partnered with members of the nascent maker community to create increasingly more sophisticated devices. In the eight years since the project began, the OpenCTD family has grown from a core team of marine ecologists to a distributed community of scientists, engineers, makers, and conservation practitioners around the world.

Throughout this entire development cycle, the core mission has always been to produce an instrument which could be built and understood by any user. We didn’t want to create another data black box, we wanted to create something that would be just as at home in a high school classroom as a top tier research institution.

The brain of the OpenCTD is an Arduino microcontroller, a commonly available baby computer that can control a suite of sensors using a relatively approachable coding language. Arduinos are used in classrooms around the world as an introduction to coding and hardware development. The Arduino talks to a real-time clock, which timestamps all the data, as well as an SD card reader where all the data is logged. All these components, when combined with a commercial chip to interpret salinity and a 3.7-volt lithium polymer battery form the control unit.

The control unit then interfaces with a sensor package that includes a battery of three temperature sensors, an absolute pressure sensor which provides depth, and a graphite probe which measures conductivity, which is then translated to salinity. Everything is housed within a very boring PVC pipe. The sensors are fully potted in epoxy and the open end is capped with an off-the-shelf pressure cap that plumbers use to test pipework but that we’ve found to hold air down to 140 meters for a fraction the cost of an engineered solution.

With a custom circuit board that we designed and released under an open-source license, someone with no prior experience in electronics, soldering, coding, or fabricating can build, calibrate, and deploy an OpenCTD over a long weekend.

And that design process really highlights the core principles of the OpenCTD program. We want our device to be as inexpensive as possible while still producing high quality data. We want everything we possibly can to be released under an open-source license, so that anyone can take the base OpenCTD and expand, iterate, and adapt it to their needs. And we want the materials we use to be as accessible as possible, so that people who want to built a CTD can find the parts they need in their local hardware stores, and from major online retailers.

We’ve also adopted a values-agnostic approach to implementation. By values agnostic I mean that I don’t believe that technology is, in itself, a panacea, but rather that carefully designed conservation technology programs can help fill the gap between the discovery of emerging problems and the will to solve them at a policy level. I focus on conservation technology that promotes ownership of both data and the tools to collect data within communities in a stakeholder-up implementation model. This means that rather than taking a top-down approach to delivering technological fixes to the problems facing our oceans, I prefer to work with communities to develop solutions that reflect and respect their specific needs and values. This often means my goals are misaligned with the dominant paradigm of Imported Magic, where technology developers want to deliver one-size-fits-all solutions to local and regional problems.

Imported Magic, incidentally, is the technological sibling of Parachute Science.

So, anyone can build their own CTD, but the major way that we’ve kept this program funded is through hosting training workshops to teach students at many levels how to build their own instruments. Over the last few years, I’ve hosted CTD building workshops local to me in Maryland, with marine educators at Stellwagen Bank National Marine Sanctuary and, remotely, with middle and high school students in Homer, Alaska.

For students, the process of building an OpenCTD offers an introduction to coding, 3D-printing, hardware prototyping, electronics and can provide a practical foundation for courses in earth science and marine or environmental science.

I do want to introduce you to one other project, which is currently ongoing. This year we sent OpenCTDs to naturalist working aboard commercial whale watching boats throughout New England to log and upload opportunistic pilot data while looking for whales. You can track their progress and check out their data at community oceanography dot com.

There are far too many people to thank in this short time. The OpenCTD is and always will be a community effort, but I do want to acknowledge our key funders whose support kept the project alive long enough for us to reach this point. And if you do want to check out the entire OpenCTD project, I recommend you start with our GitHub Repository, where we house all the documentation and source files. From there you can find the full OpenCTD construction and operation manual, which lays out the process of building an OpenCTD in detail.

And thank you. 


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