Two years after the March 11th tsunami in Japan that triggered the Nuclear disaster at the Fukushima power plant, there are still just over 300 thousand people who have not been able to return to their homes due to high radiation levels. The government has decided that radiation levels must be below 1 micro sieverts/hour (=5mSv/year, see here for what this means) before children can return to school in the area (adults may return to their home at 1.9micro-sieverts/hour, 10mSv/year) and there is a building-by-building clean-up effort that is going on to try and get the radiation levels down to the required levels.
The radiation levels are being measured from manned helicopters flying at approximately 300m but the issue is that the ground level where people actually live can only be estimated roughly from the air. To get the more accurate "human level" readings the government is relying on mobile surveying trucks or individuals wearing protective clothing but there has also been some limited use of UAVs.
In particular the very top image was taken at the Yamakiya elementary school (40km from the plant) using the Chiba University's MiniSurveyor hexacopter outfitted with a geiger counter. The readings were performed twice, once back in August 2012 and then again in December.
What you can see is that over the 4 months that significant portions of the school ground has returned to near natural levels and the part of the ground that was high radiation (2 ~ 3 micro-sieverts/hour) has mostly fallen to 1~2 micro-sieverts/hour. This area, by the way, is where the top few cm of earth from the school playground was removed and placed in the middle of the ground and covered by a plastic sheet.
During this test an EBA Japan Hyper-spectral camera was also used (although, in fact it was mounted on a manned helicopter mostly because it weighs 2kg and the mini-surveyor was perhaps unable to lift that weight for an extended period). These sorts of cameras can produce an image broken down into hundreds of bands of bands of light which can be used to determine what surface the radiation has fallen on. This is important because the level of radiation remaining at a site is greatly determined by the surface. For example it has been found that different types of trees retain radiation differently. A cedar will retain 50% of the radiation within it's leaves while an oak will only retain 20% (the rest falls to the ground).
The Mini-surveyor was developed under the guidance of Professor Nonami (who wrote this book). It costs about about $15k each including a fancy simulator for learning how to use it. It apparently uses a "physical model" instead of PID controllers for attitude control. You can see a video of it flying here.