Back in 2011, soon after the 3/11 disaster, Safecast was born. Today, the global volunteer-centered citizen science organization is home to the world's largest open data set of radiation measurements.
Safecast was a response to the lack of publicly available, accurate and trustworthy radiation information. The group initially set out to collect radiation measurements from many sources and put them on a single website. What the volunteers quickly realized was that there was simply not enough official data available.
Soon after the disaster, members attached a homemade Geiger counter to the side of their car and drove around Fukushima taking measurements. They quickly noticed that radiation levels were radically different even between streets, and that the government-issued city averages were far from sufficient as data that could be used by citizens to determine the safety of their areas.