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Radiation dose rate maps of Japan after the March 2011 Fukushima Dai-ichi Nuclear Power Plant accident
平成23年3月に発生した福島第一原子力発電所事故後の放射線量率マップたち


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 admin@radioisotope.jp
ウェブ上にアップされている放射線量マップを取りまとめました。各サムネイルをクリックすると、当該ページにジャンプするか、高解像度の図が表示されます。
1. Dose rate measurements by local authorities compiled by @nnistar
@nnistarさんが作成した地方自治体が測定した線量率データのまとめ地図
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.
原発事故後の早い段階から@nnistarさんが自治体測定データを取りまとめてグーグルマップに落とした線量マップ。元データは各自治体がホームページにアップしたものを、@nnistarさんとその協力者がデータベース化して緯度経度を割り出しまとめた。測定器の校正の問題やデータに不確実性があるものの、汚染状況の傾向をよく表している。何千人もの地方公務員による測定と匿名の協力者によるデータ取りまとめによりマッピングがなされたことは、特筆すべきである。

2. Radiation dose rate contour map by @r_isotope
@r_isotopeさんが作成した放射線量率等値線地図

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)
@hayakawayukioさんが各種データを用いて独自に放射線量率の等値線を描いた地図
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.
原発事故後の早い段階から線量の可視化を目指し等値線マップを作成してきた@hayakawayukioさんの作品。入手可能な様々なデータを用い、地質学の分野では一般的なマッピング手法を適用し作成した。この地図は様々なメディアに紹介され、東日本の放射能汚染マップとしては、テレビや雑誌記事を通して、最も広く一般に伝えられた。

4. Airborne monitoring survey map by MEXT
文科省による航空機モニタリング調査の測定結果地図


↑ 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.
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).
文科省が県ごとに進める航空機モニタリング調査地図。所々に自然放射能による影響があると思われるが、これは地表調査と土壌分析による確認が必要。右の図は電子国土版。

5. Radiation dose rate measurements by @r_isotope
@r_isotopeさんが作成した放射線量率測定地図


↑ 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.
福島第一原発事故後の平成23年4月末〜7月末の約4ヶ月間にわたり@r_isotopeさんが首都圏を中心に大阪・神戸まで足をのばし放射線量を測定。同一人物が同一測定器を用いて広範囲にわたり測定したので、機器間や機種間の校正の問題は無く、相対的な値の違いは信頼性が高い。測定値の信頼性も高い。@r_isotopeさんの測定活動は米科学誌サイエンスに紹介された
© 2011 RADIOISOTOPE.JP Last updated 9 December 2011