They have been testing a laser system for measuring lunar dust and soil kicked up by rocket exhausts, and while using precipitation as a substitute to calibrate the laser, they found they could measure the average size of raindrops passing through it.

ENGADGET: NASA accidentally improves weather forecasting with lunar dust-measuring lasers

The raindrops blown a couple of miles west of our ranch would land in creeks that percolated through the Columbia River system into the Pacific, whereas the water in Feely Creek, our creek, was blessed with the task of traveling a thousand miles more, all the way down to the bayous of Louisiana before spilling through the loamy delta into the Gulf of Mexico.

NPR: Excerpt: 'The Selected Works of T.S. Spivet'