Radiation dose rate maps of Japan after the March 2011 Fukushima Dai-ichi Nuclear Power Plant accident.

Here's a compilation of available radiation dose rate maps collected from the Web. Click on the thumbnail and you will be redirected to the original Web site or high-resolution jpeg image. For comments and questions please feel free to contact the author of this page Dr. A. Ennyu at
1. Dose rate measurements by local authorities compiled by @nnistar
This is an iconic piece generated by @nnistar and his collaborators. He started to collect 'official' radiation dose rate measurement data available on the Web as early as April 2011, and plotted the data on his original Google Map by assigning geographic coordinate for each data point. As of November 27, 2011, the total number of data points on the map exceeds 96k. This is a heckuva dataset! All the measurements were made by thousands of local governmental officials who do not have prior experience in using dosimeters and survey meters. Therefore, calibration issues remain and the dataset may accompany uncertainty for some extent. However, the entire data plotted on the map well present the general trend of the degree of the radiological contamination. The huge effort in measurements by local officials nationwide and compilation by anonymous contributors is remarkable and should be remembered. This is the first time in the history of the Internet that thousands of inflexible local officials and anonymous gridding nerds to collaborate towards a common objective to figure out the extent of the unprecedented radiation contamination in such a short period of time. Hats off to those involved in generating this map.

2. Radiation dose rate contour map by @r_isotope

Click on the thumnails and you can download high-resolution jpeg files. These files are heavy (approx. 10MB each) and thus make sure that you have a high-speed Internet access. The left panel was plotted using about 63k data points taken from @nnistar's map above. The entire dose rate dataset with geographic coordinate formatted in csv by @h_okumura was downloaded on October 3, 2011 and processed using natural neighbour interpolation algorithm, a weighted average interpolation method based on Voronoi tessellation. Calculation was performed such that the interpolated data were resampled every 0.005° coordinate (i.e., approx. 550 m meridional interval). Although this map could be regarded as a subjective evaluation of the contamination, some of the original data provided by local authorities who are not scientists may lack common scientific data collecting methodology - any local government does not want to admit that their municipal territory is contaminated and hence tends to underestimate the radiation dose rate values reported. A good example of such potential objectivity in data gathering is presented by the prefecture of Tokyo - dose rates decrease dramatically towards Tokyo territory across the Tokyo/Chiba border. This is refuted by various 'unofficial' independent measurements (see an example below by @r_isotope). In other words, the dose rate data set published on the Web by the prefecture of Tokyo is not reproducible. That said, the map above is currently the only available radiation dose rate contour map encompassing the entire eastern Japan based on surface reconnaissance effort and is still a premier representation of the impact of the Fukushima nuclear disaster. Any places that look even slightly greenish in the left hand side panel are more or less contaminated by radioactive cesium. The center panel was plotted using the same method as the left panel but the coloring of the plot stresses the dose rate alert levels. The green area represent dose rate higher than 0.2μSv/h. This encompasses the majority of Fukushima prefecture and some distant locations such as the E and NE Metropolitan Tokyo area. The yellow area in Fukushima represent dose rate higher than 1μSv/h. The city of Fukushima, the second most populated municipality in Fukushima prefecture, is situated within this severely contaminated area. The right panel shows the locations of the 63k measurement points.
高解像度のファイルは10MBくらいになるのでダウンロードするときは要注意。左の地図は@nnistarさんがまとめた自治体測定地図のデータを2011年10月3日に@h_okumuraさんのウェブサイトからダウンロードし、約6万3千点をnatural neighbour interpolationという空間補間法を用いて機械的に等値線を描いた。この地図は元データを表現する意味では客観性が保たれているものと考えられる。しかし、自治体によっては低い値を公表したいという心理により、報告値が主観的になる可能性があり、これによる影響は排除されない。東京都がこの例に該当する。この地図で少しでも緑色に見える所は少なからず放射性セシウムにより汚染されている。二つ目の地図は、作図法は左の地図と同じであるが、0.2μSv/hや1μSv/hの等値線を強調するように色付けした。右のパネルは、地図をプロットする際に使用したデータの位置を示す。
3. Dose rate contour map presented by @hayakawayukio The latest 5th Edition (9 December 2011)
This is probably the most comprehensive contour map based on a compilation of available radiation dose rate data from various sources. The author of this map @hayakawayukio subjectively drew conceptual contours on the basis of various datasets as well as his own measurements. Some critics, for unexplained reasons, or emotionally, argue that the map is not scientific. However, the contouring method adopted here is the common procedure practiced by geologists for geological mapping, resources exploration, and scientific research in general. Now that this piece is regarded as the most widely perceived radiation dose rate contour map and has been referenced by committees of the national assembly and published in various media sources. The reason for such public perception is the simplicity of the representation of what we are most interested in. The impact of this map is enormous.

4. Airborne monitoring survey map by MEXT

↑ MEXT's radiation dose rate data projected on the?Geospatial Information Authority's interactive map.Click on the bottom left button (Agree) to view the map.
← Link to the MEXT's original PDF file (16 Dec. 2011).
The Ministry of Education, Culture, Sports, Science and Technology (MEXT) has been flying over the eastern Japan with the Aerial Measuring System borrowed from the U.S. DOE to depict the magnitude and extent of radiological contamination on the ground. The left panel shows the latest radiation dose rate estimates based on the AMS survey. The general trend in dose rate contouring is consistent with the map based on ground measurement data plotted by @r_isotope above. Sporadic occurrence of light blue regions in the central Honshu may be due to natural radiation - this must be assessed by field reconnaissance survey and soil collection and laboratory analysis. Right panel is an interactive map (but the data update is a bit late).

5. Radiation dose rate measurements by @r_isotope

↑ Data from the left panel plotted on a Google Map hosted in @nnistar's server.
← Field radiation dose rate measurements made by @r_isotope.
This is a legacy map generated by @r_isotope. His effort was featured in a Science article in June 2011. He measured radiation dose rates mainly in the Tokyo Metropolitan area from the late April 2011 (when the most of iodine-131 decayed) to late July. During the 3-month period, he extended his survey to the West in Kobe and Osaka to collect data from the presumably non-contaminated areas. The two major findings: (1) the urban radiological contamination is obvious in the Central Tokyo; (2) severely contaminated areas exist in the eastern Tokyo through Saitama, Chiba, and Ibaraki prefectures. Along with the conceptual contour map by @hayakawayukio, the early reconnaissance effort by @r_isotope alerted citizens in the area and prompted them to urge their local municipal offices and assembly members to take measures against the immediate but insensible threat they were facing. No change in dose rate across the Tokyo/Chiba border was recognized.
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