Tepco, the Japanese power company responsible for Fukushima Daiichi has published a series of radiation survey maps of the nuclear plant and the surrounding area. According to asahi.com these are being used to monitor exposure of workers and prepare work plans.
The maps consist of technical drawings over-layed with radiation readings dating back to March 20 – nine days after the tsunami hit Japan – and updated every few days afterwards. Radiation levels are measured in microSieverts per hour. Areas containing debris from the explosions have the highest readings – up to 300 mSv/h. To put that in context the dose limit applied to workers involved in containment and clean-up is 250 mSv per year.
Has to be said, they aren’t the most comprehensible diagrams – readings are colour coded according to the date they were collected, and that coding sometimes changes between images. A couple pointers to help navigate – the four reactors are represented by blue squares, and up points east towards the sea.