# A perfect CTD profile

I love the $\tanh$ function. A lot. It’s such a perfect model for a density interface in the ocean, that it is commonly used in theoretical and numerical models and I regularly used it for both research and demonstration/example purposes. Behold, a $\tanh$ interface:

But whenever I use it, especially for teaching, I’m always saying how it’s idealized and really doesn’t represent what an ocean interface actually looks like. UNTIL NOW.

Yes, this is real data.

Just how close to a $\tanh$ is it?1

1. My PhD advisor, who also taught me introductory physical oceanography, once said to a class of students while using tanh to describe an idealized interface: “tanh – it’s like ‘lunch’, only better!”