Developing low-cost, open-source oceanographic hardware for researchers, educators, and knowledge seekers around the world.

Build your own CTD. 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. A CTD measures salinity, temperature, and depth. By measuring these variables, scientists unlock ocean patterns hidden beneath the sea’s surface.

Unfortunately, commercial CTDs are expensive. 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 find themselves priced out of ocean research. Informal researchers such as community oceanographers, educators, conservation and management practitioners, and students of all levels face severe challenges accessing expensive scientific instruments.

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 and electronics stores and major online retailers. All OpenCTD software is released open source with no restrictions on use.

The OpenCTD is 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 prevents 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.

Getting Started with the OpenCTD

If you want to build your own OpenCTD, we have provided a full manual, Construction and Operation of the OpenCTD (pdf), which covers all of the skills and materials you need to build, calibrate, deploy, and maintain an OpenCTD. The manual is periodically updated and the most up-to-date edition is the 4th Edition, published in December 2023. The manual contains to alternate build pathways, depending on the availability of parts, as well as several options for upgrades and customization. If you have an OpenCTD and need to calibrate it, we provide the OpenCTD Calibration and Data Management (pdf) guide as a stand-alone document.

All of the source code, 3D printer shapefiles, support firmware, data management programs, and instructions are available in the OpenCTD GitHub Repository.

The paper “The OpenCTD: a low-cost, open-source CTD for collecting baseline oceanographic data in coastal waters.” has been accepted for publication in Oceanography and will be made available as soon as possible.

DIY Oceanography

The OpenCTD is designed to be built by you! We focus on accessibility of parts, tools, consumables, and skills.

Connection to the Sea

Providing access to the tools to study and understand the ocean fosters stronger connections to the sea around us.

Three open CTDs. Photo by Andrew Thaler.
Data Ownership

Knowledge seekers collect their data with their instruments, driven by curiosity rather than the priorities of funders.


Creating a community of researchers, makers, advocates, and knowledge seekers to build a resilient future.

“We believe that ocean exploration shouldn’t require a research grant, it should require curiosity.”

Eric Stackpole, Sofar Oceans

Meet the OpenCTD Team

Andrew Thaler

Andrew is a deep-sea ecologist and conservation geneticist investigating the impacts of human activity at hydrothermal vent ecosystems around the world. He wants to make oceanographic tools available to anyone interested in exploring and understanding the sea, from the highest alpine lakes to the deepest trenches.

Kersey Sturdivant

Kersey is a marine ecologist who studies the effects of human disturbance on the seafloor, and develops marine technology to enhance human understanding of the ocean. His goal is to increase the capacity of ocean research through innovative technology, and by making ocean observation tools more cost accessible.

Russell Neches

Russell is a microbiologist who studies large-scale migration patterns of microbes, particularly in the built environment. He is using cichlid fish as a model system for investigating how host-microbe associations have evolved over deep time. He is an advocate of Free Software, Open Hardware, Open Access scientific publishing and reproducible research.

How to Contribute

The OpenCTD is a completely open-source project and you are invited to contribute to it at any level—from helping develop and refine code, to building and testing instruments, to taking these tools out in the field and collecting data. If you just want to build a CTD for your personal use, that’s great too!


We use GitHub to host our various projects. GitHub can seem a bit daunting to people who aren’t familiar with it. At its core, GitHub is a tool to organize files, coordinate files, and maintain version control (multiple people can edit the same file, while keeping everything in sync). GitHub has compiled a set of useful guides to help you get started.

Getting started.

Projects are organized into repositories (‘repos’) that contain the source code, supporting documents, data files, and other materials needed for each project. When you visit a repo, check the, this will describe the project (including the current status), contain necessary guides, and let you know how to help.


If you see a problem or have an idea for how something can be improved, raise an issue. The “issue” tab can be found at the far right corner of each repo, under the “code” tab. An issue can be as small as a typo or as big as an entirely new project. Here is an example of the issue we raised when we realized that the site would benefit from this guide.


When you are ready to make contributions to the projects, send a pull request. A pull requests creates a new copy of the project files that you can edit. When you’re happy with the changes you’ve made “commit” them to the repo. Don’t worry about breaking anything, commits have to be reviewed before they are added to the master file.