Dissolved Oxygen
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A dissolved oxygen sensor measures how much oxygen gas (O₂) is mixed into the water.
Oxygen is essential for fish, crabs, and almost all underwater life to survive.
The most well known and widely used oxygen sensor is the `Aanderaa optodes <https://www.aanderaa.com/oxygen-sensors>`_. These usually work by measuring `fluorescence quenching <https://en.wikipedia.org/wiki/Quenching_(fluorescence)>`_. 

.. image:: /images/optode.jpg

`These <https://atlas-scientific.com/probes>`_ guys have low cost oxygen sensors which can be used in our project.