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Build your own research-quality oceanographic instrument for a fraction of the cost of commercial alternatives.

Let's explore the ocean, together.

Updated 5/21/2023

Development Notes:

Please be advised that the rubber o-rings in the yellow Cherne brand endcaps is much stiffer than the rubber used in other endcap brands and has been found to fail consistently in cold water. We do not recommend using Cherne endcaps in you CTD build.

A new version of the control board is in production. If you have a Rev 6 control board, we have released Power Management Upgrade for OpenCTD rev 6, a guide to fixing the annoying "must be on to charge" feature of the OpenCTD rev 6 control board. Some batteries ordered from Amazon have the positive and negative termninal reversed. Please check battery polarity before attempting to power your CTD.

OpenCTD: Oceanography for Everyone

The OpenCTD Construction and Operation manual provides a comprehensive, step-by-step guide to building your own OpenCTD, with a standard construction pathway as well as numerous alternatives depending on parts availability and technical skills.

The OpenCTD core software is designed to be used with an M0-style Arduino microcontroller, for which we recommend the Adafruit Adalogger Feather M0.


There is something radical about making and using your own scientific instruments. The structure of scientific inquiry has coalesced around a model that is, in general, both expensive and exclusive. This centralizes knowledge production within a small circle of individuals, organizations, and institutions who have access to substantial financial resources. This circle rarely reflects the breadth of identities, experiences, and ways of knowing that are most directly connected to the places being explored.

By building your own instruments to study and understand the natural world, you are expanding the circle of knowledge production. A scientist who can make their own instruments is not beholden to the cycles of funding and access that constrain formal, institutional inquiry. A researcher who can build and repair their own equipment is not dependent on the whims of academic sentiment to decide what is and is not worthy of study. A community leader who has the tools to create their own data does not have to wait for institutions to take notice of an emerging crisis before taking action.

The OpenCTD

You don’t need to ask for permission to understand your world.

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. Even localized coastal research can be thwarted by lack of access to vessels, equipment, and instruments. As the need to understand the dramatic changes at the surface and beneath the waves accelerates, baring the participation of ocean stakeholders erodes our power to understand, anticipate, and mitigate those changes.

The ocean belongs to everyone. The tools to study the ocean should be accessible to anyone with the curiosity and motivation to pursue that inquiry. Chief among these tools is the workhorse of oceanography, the CTD, an instrument that measures salinity, temperature, and depth. By these characteristics, scientists can begin to unlock ocean patterns hidden beneath the sea's surface.

CTDs come in a variety of shapes, sizes, and applications. Most oceanographic research vessels have a CTD connected to a rosette platform, which houses other instruments and collects water samples in parallel with real-time data. CTDs are also commonly attached to fixed moorings, autonomous underwater vehicles (AUVs), remote-operated vehicles (ROVs), and even to marine animals.

Unfortunately, commercial CTDs are expensive. The most affordable models cost several thousand dollars. For near-shore oceanographic research on the relatively shallow continental shelf, this cost can be prohibitive. This effectively excludes formal researchers from low and middle income countries, and small island states. Even in high-income countries, formal researchers at teaching institutions or at early career stages may also find themselves priced out of ocean research. Informal researchers such as citizen oceanographers, educators, conservation and management practitioners and students of all levels face severe challenges accessing expensive scientific instruments.

Build Your Own CTD

The OpenCTD is a low-cost, open-source CTD designed for budget-restricted scientists, educators, and researchers working in nearshore coastal ecosystems. In these waterways, entire research projects can be conducted for less than the cost of a commercial CTD. OpenCTD was developed by a core team of marine ecologists in collaboration with a community of scientists, engineers, makers, and conservation practitioners from around the world. It is assembled from components commonly available at large hardware stores or through major online retailers. An Arduino-based microcontroller controls an array of sensors sealed within a PVC pipe. Power is provided by a standard 3.7V lithium polymer battery and data are stored in a tab-delimited text file accessed via SD card. All OpenCTD software is released open source with no restrictions on use.

The OpenCTD is designed to be built by the end-user, providing both access to the tools of oceanography as well as the skills to maintain, repair, and replace OpenCTDs. For scientists working in remote settings, the repairability of the OpenCTD is intended to prevent equipment failures from spiraling into project failures. For educators seeking novel, in-depth, hands-on STEM experience for advanced students, the process of building an OpenCTD offers an introduction to coding, 3D-printing, hardware prototyping, and electronics. Construction of an OpenCTD can provide a practical foundation for courses in oceanography and marine or environmental science.

Core Resources

The OpenCTD Construction and Operation manual provides a comprehensive, step-by-step guide to building your own OpenCTD, with a standard construction pathway as well as numerous alternatives depending on parts availability and technical skills. A shorter manual covering just the calibration process is also available.

The OpenCTD core software is designed to be used with an M0-style Arduino microcontroller, for which we recommend the Adafruit Adalogger Feather M0.

You can find all the Arduino libraries as described in the manual, as well as software for calibrating the conductivity sensors in Support.

Hardware file for both 3D printable components and the control unit PBC can be found in Hardware

Updated 5/21/2024

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The OpenCTD is a low-cost, open-source CTD for researchers and citizen scientists.

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