I am currently looking at a time-series of CO2 data, logged at 30-minute intervals over the course of the entire year. The are a total of 17521 points in this dataset spread over 365 days.
I need to find the exact day in which the uptake of CO2 (which is represented by negative graph values), crosses below the red line I have drawn (which is at a value of -4.352), and when it crosses back up again. I have included where these 2 points are in the example spreadsheet to help.
The other alternative is if there is a way of capturing the lower or upper envelopes of this very noisy dataset with a curve? In which case I could subsequently use that curve for analysis.
I am currently taking a pretty visual approach to the problem - zooming in 400% and trying as best as I can to identify when this date is but that is highly unscientific.. I would greatly appreciate any help and advice.
Thank you! =)