Predicting correlation between two signals

Hello,

I have potential measurements, as well as resistance measurements of a plant during it's growth phase. I was wondering if there is certain MATLAB algorithm I could use to highlight where do the two signals correlate (increase together, decrease together,...).

Also is there an algorithm that could calculate the SNR (Signal to Noise Ratio) in a specific period of time (1 day long data, 1 week long data, 1 hour long data), and calculate potential drifts in the signals?

Thanks