WIP: ENH: add quality prediction to Carbon Flux

[stsievert]

This adds a prediction from all global sites. This is still a work in progress: I need to make this a better predictor.

[stsievert]

I need a baseline to start of with. To do this, I used a linear regressor on every site to predict the last year at the same site. I used the same model as a baseline with the global prediction, but predicted a different (unseen) site, not the latest year.

Apparently, the correlation coefficient is the metric cared about. I run these simulations 179 times (once for each station). Here are the distribution of correlation coefficients from these trials:

We can see that the linear model at one site significantly outperforms the global linear model.

The summary statistics are

Statistic	One site predicting last year at same site	All sites predicting one held out site
Median	0.573	0.441
Mean	0.497	0.398

[jbednar]

Sounds promising. Still WIP?

[stsievert]

Still a WIP. Mostly, I know the baseline performance (what's considered "good"), and have a metric to improve upon.