You might have seen previous studies (including several from me) showing that lighting on the country and continental scale is increasing. Globally, the rate of increase is about 2% per year.

Those studies looked at (very) large areas, and used monthly or annual composite images. The new study analyzes change at the spatial scale of individual pixels (~0.5 square km) and at the temporal scale of individual nights.

That's like... A whole lot of work. A mindbogglingly large amount of work.

There were 1.16 million daily (NASA Black Marble) *images*. Now think about how many pixels make up each image... 🤯

For each pixel, the lead author Tian Li from the University of Connecticut fits a trend line (solid line left) and generates a prediction (dotted line left).

When something changes, the observations stop agreeing with the prediction (middle). If the change persists for at least 14 consecutive observations, then a break point in the trend is assigned. From that point on, a new model predicts future changes. And so on and so forth (right) for the following years.

This is where looking at the daily data (rather than monthly composites) becomes a REALLY BIG DEAL.

Nighttime lights data are really noisy. Part of the noise comes about because the satellite can view a scene from different directions. When that happens, it's viewing LITERALLY DIFFERENT LIGHTS, as in the aerial photos here.