Airborne Monitoring in the Distribution Survey of Radioactive Substances
FY 2011 - FY 2013   The Ministry of Education, Culture, Sports, Science and Technology, the U.S. Department of Energy, and the Secretariat of the Nuclear Regulation Authority

This series of data was created based on the radioactive cesium deposition density measurement results of the airborne monitoring survey by The Ministry of Education, Culture, Sports, Science and T...
This series of data was created based on the radioactive cesium deposition density measurement results of the airborne monitoring survey by The Ministry of Education, Culture, Sports, Science and Technology, the U.S. Department of Energy, and the Secretariat of the Nuclear Regulation Authority.

Results of Deposition of Radioactive Cesium of the Airborne Monitoring Survey in the Areas to which Evacuation Orders Have Been Issued ( Decay correction: March 11, 2013 )
  1. This data was created based on the measurement results from the airborne monitoring survey conducted by MEXT in the restricted areas and areas to which evacuation orders have been issued.
  2. This published data was prepared based on the results obtained from March 4 to March 11, 2013 by one helicopter, in a total 13 flights.
  3. Their flight altitudes were from about 300 m above ground, and the air dose rate at the ground surface is the averaged value of air dose rates in a roughly about 600 m diameter circle (varies by flight altitude) below the aircraft.
  4. The width of the track is around 1.85 km.
  5. The deposition densities of radioactive cesium were prepared by first assessing the characteristics of the energy spectra of gamma rays measured in the air by type of helicopter and measuring equipment used, and then sorting out areas where the energy spectra of radioactive cesium (Cs-134 and Cs-137) were detected in significant amounts and those where they were not.
    • ① Areas where the energy spectra of radioactive cesium were detected in significant amounts; In order to calculate the amount of radioactive cesium in detail, we used the method for conducting detailed assessment of the influence of natural radionuclides based on the energy spectra of gamma rays measured in the sky that were applied in western Japan and Hokkaido. Refer to Attachment 9 of “Results of Airborne Monitoring Survey by MEXT in the Kyushu Region and Okinawa Prefecture” [Announced on May 11, 2012]. Based on this method, deposition densities of radioactive cesium were calculated by deducting the contribution by natural radionuclides from the measurement results of air dose rates at the respective measuring points, and also based on the correlation between air dose rates and the results of the in-situ measurement using germanium semiconductor detectors*1, which was conducted by the Japan Chemical Analysis Center in the course of the project by the 2011 Strategic Funds for the Promotion of Science and Technology, entitled “Establishment of the Base for Taking Measures for Environmental Impact of Radioactive Substances - Study on Distribution of Radioactive Substances” (June-August, 2011).
    • ② Areas where the energy spectra of radioactive cesium were not detected in significant amounts; As with before, these were indicated as areas showing the minimum range of radioactive cesium "<1.0E+04" (Bq/m2) for the sake of simplicity.
  6. The values have been decay-compensated to the value for March 11, 2013, which is the final day in which the airborne monitoring survey was conducted in the restricted areas and areas to which evacuation orders have been issued. Regarding deposition densities of Cs-134 and Cs-137, physical attenuation from the measurement time up to a certain point in time (March 11, 2013) was taken into account.
  7. There was snow coverage in some part of the targeted areas of this monitoring. It has been expected that the air dose rate measurements are apt to be lower due to the effect of snow coverage. Therefore, in order to distinguish areas covered by snow, such areas are indicated as data. When identifying areas covered by snow, we used data obtained by NASA's earth observation satellites, Terra and Aqua*3, which are available on JASMES*2 released by the Japan Aerospace Exploration Agency.
  8. The data consists of radioactive cesium deposition densities at the median points of the Quarter Grid Squares (approximately 250 m x 250 m) defined by JIS X 0410. See the Ministry of Internal Affairs and Communications Statistics Bureau website for "Grid Square Statistics".
    9. *1: In-situ measurement using germanium semiconductor detectors: A means to analyze the concentration of radionuclides accumulated in soil by setting up transportable germanium semiconductor detectors in the environment and detecting gamma rays that are emitted from radiation sources distributed in soil.
    *2: JAXA Satellite Monitoring for Environmental Studies
    *3: We used the data of snow coverage around Japan, which were observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) installed on NASA’s earth observation satellites, Terra and Aqua, and were analyzed by the Japan Aerospace Exploration Agency (JAXA) using its original processing algorithm. JAXA has been planning the Global Change Observation Mission (GCOM) to observe the Earth’s environment as a whole, including the atmosphere, ocean, land, snow and ice, from space on a long-term basis (10 to 15 years), thereby monitoring hydrologic circulation and climate change and figuring out the mechanisms thereof. Said data have been collected and processed for the purpose of assessing the analytical algorithm for optical sensors used in the Global Change Observation Satellite (GCOM-C). As they are 500 m-grid data, snow coverage over 5 cm with an even surface can be indicated correctly, but it is sometimes difficult to accurately identify snow coverage of a shallower depth or with an uneven surface.
Results of Deposition of Radioactive Cesium of the Sixth Airborne Monitoring Survey and Airborne Monitoring Survey Outside 80 km from the Fukushima Dai-ichi NPP ( Decay correction: December 28, 2012 )
  1. This data was created based on the measurement results of the sixth airborne monitoring survey and the airborne monitoring survey outside the 80 km range from the Fukushima Dai-ichi NPP by MEXT (second time in FY2012).
  2. This published data was prepared based on the results obtained from October 31 to November 16, 2012 by a helicopter, in a total 37 flights for the sixth airborne monitoring and from October 31 to December 28, 2012 by two helicopters, in a total 87 flights for the airborne monitoring outside the 80 km range from the Fukushima Dai-ichi NPP (second time in FY2012).
  3. Their flight altitudes were from about 300 m above ground, and the air dose rate at the ground surface is the averaged value of air dose rates in a roughly about 600 m diameter circle (varies by flight altitude) below the aircraft.
  4. The width of the flight path of the aircraft is around 1.85 km in the sixth airborne monitoring, and around 3 km for the airborne monitoring outside 80 km from the Fukushima Dai-ichi NPP (second time in FY2012).
  5. The deposition densities of radioactive cesium were prepared by first assessing the characteristics of the energy spectra of gamma rays measured in the air by type of helicopter and measuring equipment used, and then sorting out areas where the energy spectra of radioactive cesium (Cs-134 and Cs-137) were detected in significant amounts and those where they were not.
    • ① Areas where the energy spectra of radioactive cesium were detected in significant amounts; In order to calculate the amount of radioactive cesium in detail, we used the method for conducting detailed assessment of the influence of natural radionuclides based on the energy spectra of gamma rays measured in the sky that were applied in western Japan and Hokkaido. Refer to Attachment 9 of “Results of Airborne Monitoring Survey by MEXT in the Kyushu Region and Okinawa Prefecture” [Announced on May 11, 2012]. Based on this method, deposition densities of radioactive cesium were calculated by deducting the contribution by natural radionuclides from the measurement results of air dose rates at the respective measuring points, and also based on the correlation between air dose rates and the results of the in-situ measurement using germanium semiconductor detectors*1, which was conducted by the Japan Chemical Analysis Center in the course of the project by the 2011 Strategic Funds for the Promotion of Science and Technology, entitled “Establishment of the Base for Taking Measures for Environmental Impact of Radioactive Substances - Study on Distribution of Radioactive Substances” (June-August, 2011).
    • ② Areas where the energy spectra of radioactive cesium were not detected in significant amounts; As with before, these were indicated as areas showing the minimum range of radioactive cesium "<1.0E+04" (Bq/m2) for the sake of simplicity.
  6. The values have been decay-compensated to the value for December 28, 2012, which is the final day in which the airborne monitoring survey outside the 80 km range from the Fukushima Dai-ichi NPP by MEXT (second time in FY2012) was conducted. Regarding deposition densities of Cs-134 and Cs-137, physical attenuation from the measurement time up to a certain point in time (December 28, 2012) was taken into account.
  7. Snowfall was confirmed in certain regions (western Fukushima Prefecture, Gunma Prefecture, eastern Yamagata Prefecture, etc.) within the range where the monitoring outside 80 km from the Fukushima Dai-ichi NPP (second time in FY2012) was conducted. With regard to these regions, it has been expected that the air dose rate measurements are apt to be lower due to the effect of snow coverage. Therefore, in order to distinguish areas covered by snow, such areas are indicated as data. When identifying areas covered by snow, we used data obtained by NASA’s earth observation satellites, Terra and Aqua*3, which are available on JASMES*2 released by the Japan Aerospace Exploration Agency.
  8. The data consists of radioactive cesium deposition densities at the median points of the Quarter Grid Squares (approximately 250 m x 250 m) defined by JIS X 0410. See the Ministry of Internal Affairs and Communications Statistics Bureau website for "Grid Square Statistics".
    9. *1: In-situ measurement using germanium semiconductor detectors: A means to analyze the concentration of radionuclides accumulated in soil by setting up transportable germanium semiconductor detectors in the environment and detecting gamma rays that are emitted from radiation sources distributed in soil.
    *2: JAXA Satellite Monitoring for Environmental Studies
    *3: We used the data of snow coverage around Japan, which were observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) installed on NASA’s earth observation satellites, Terra and Aqua, and were analyzed by the Japan Aerospace Exploration Agency (JAXA) using its original processing algorithm. JAXA has been planning the Global Change Observation Mission (GCOM) to observe the Earth’s environment as a whole, including the atmosphere, ocean, land, snow and ice, from space on a long-term basis (10 to 15 years), thereby monitoring hydrologic circulation and climate change and figuring out the mechanisms thereof. Said data have been collected and processed for the purpose of assessing the analytical algorithm for optical sensors used in the Global Change Observation Satellite (GCOM-C). As they are 500 m-grid data, snow coverage over 5 cm with an even surface can be indicated correctly, but it is sometimes difficult to accurately identify snow coverage of a shallower depth or with an uneven surface.
Results of Deposition of Radioactive Cesium of the Fifth Airborne Monitoring Survey and Airborne Monitoring Survey Outside 80 km from the Fukushima Dai-ichi NPP ( Decay correction: June 28, 2012 )
  1. This data was created based on the measurement results of the fifth airborne monitoring survey and the airborne monitoring survey outside the 80 km range from the Fukushima Dai-ichi NPP by MEXT.
  2. This published data was prepared based on the results obtained from June 22 to June 28, 2012 by two helicopters, in a total 20 flights for the fifth airborne monitoring and from April 2 to May 7, 2012 by two helicopters, in a total 59 flights for the airborne monitoring outside the 80 km range from the Fukushima Dai-ichi NPP.
  3. Their flight altitudes were from about 300 m above ground, and the air dose rate at the ground surface is the averaged value of air dose rates in a roughly about 600 m diameter circle (varies by flight altitude) below the aircraft.
  4. The width of the flight path of the aircraft is around 1.85 km in the fifth airborne monitoring, and around 3 km for the airborne monitoring outside 80 km from the Fukushima Dai-ichi NPP.
  5. The deposition densities of radioactive cesium were prepared by first assessing the characteristics of the energy spectra of gamma rays measured in the air by type of helicopter and measuring equipment used, and then sorting out areas where the energy spectra of radioactive cesium (Cs-134 and Cs-137) were detected in significant amounts and those where they were not.
    • ① Areas where the energy spectra of radioactive cesium were detected in significant amounts; In order to calculate the amount of radioactive cesium in detail, we used the method for conducting detailed assessment of the influence of natural radionuclides based on the energy spectra of gamma rays measured in the sky that were applied in western Japan and Hokkaido. Refer to Attachment 9 of “Results of Airborne Monitoring Survey by MEXT in the Kyushu Region and Okinawa Prefecture” [Announced on May 11, 2012]. Based on this method, deposition densities of radioactive cesium were calculated by deducting the contribution by natural radionuclides from the measurement results of air dose rates at the respective measuring points, and also based on the correlation between air dose rates and the results of the in-situ measurement using germanium semiconductor detectors*1, which was conducted by the Japan Chemical Analysis Center in the course of the project by the 2011 Strategic Funds for the Promotion of Science and Technology, entitled “Establishment of the Base for Taking Measures for Environmental Impact of Radioactive Substances - Study on Distribution of Radioactive Substances” (June-August, 2011).
    • ② Areas where the energy spectra of radioactive cesium were not detected in significant amounts; As with before, these were indicated as areas showing the minimum range of radioactive cesium "<1.0E+04" (Bq/m2) for the sake of simplicity.
  6. The values have been decay-compensated to the value for June 28, 2012, which is the final day in which the fifth airborne monitoring survey was conducted. Regarding deposition densities of Cs-134 and Cs-137, physical attenuation from the measurement time up to a certain point in time (June 28, 2012) was taken into account.
  7. Snowfall was confirmed in certain regions (western Fukushima Prefecture, Gunma Prefecture, eastern Yamagata Prefecture, etc.) within the range where the monitoring outside 80 km from the Fukushima Dai-ichi NPP was conducted. With regard to these regions, it has been expected that the air dose rate measurements are apt to be lower due to the effect of snow coverage. Therefore, in order to distinguish areas covered by snow, such areas are indicated as data. When identifying areas covered by snow, we used data obtained by NASA’s earth observation satellites, Terra and Aqua*3, which are available on JASMES*2 released by the Japan Aerospace Exploration Agency.
  8. The data consists of radioactive cesium deposition densities at the median points of the Quarter Grid Squares (approximately 250 m x 250 m) defined by JIS X 0410. See the Ministry of Internal Affairs and Communications Statistics Bureau website for "Grid Square Statistics".
    9. *1: In-situ measurement using germanium semiconductor detectors: A means to analyze the concentration of radionuclides accumulated in soil by setting up transportable germanium semiconductor detectors in the environment and detecting gamma rays that are emitted from radiation sources distributed in soil.
    *2: JAXA Satellite Monitoring for Environmental Studies
    *3: We used the data of snow coverage around Japan, which were observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) installed on NASA’s earth observation satellites, Terra and Aqua, and were analyzed by the Japan Aerospace Exploration Agency (JAXA) using its original processing algorithm. JAXA has been planning the Global Change Observation Mission (GCOM) to observe the Earth’s environment as a whole, including the atmosphere, ocean, land, snow and ice, from space on a long-term basis (10 to 15 years), thereby monitoring hydrologic circulation and climate change and figuring out the mechanisms thereof. Said data have been collected and processed for the purpose of assessing the analytical algorithm for optical sensors used in the Global Change Observation Satellite (GCOM-C). As they are 500 m-grid data, snow coverage over 5 cm with an even surface can be indicated correctly, but it is sometimes difficult to accurately identify snow coverage of a shallower depth or with an uneven surface.
Results of Deposition of Radioactive Cesium of the Airborne Monitoring Survey by Prefecture ( Decay correction: May 31, 2012 )
  1. This data was created based on the measurement results of the airborne monitoring surveys for 47 Prefectures by MEXT.
  2. This published data was prepared based on the results obtained in the measurement periods shown in the table below.
  3. As flights are difficult in mountainous areas over 2,000 m in height, there were no data available for such areas.
  4. Their flight altitudes were from 150 to 300 m above ground (varies by Prefecture). The air dose rate at the ground surface is the averaged value of air dose rates in a roughly 300 m to 600 m diameter circle (varies by flight altitude) below the aircraft.
  5. The width of the flight paths of the aircraft are around 1.85 km within the 80 km area, 5 km within the 80-100 km (120 km south side) area, 3 km for eastern Japan, 5 km for western Japan and Hokkaido.
  6. The deposition densities of radioactive cesium were prepared by first assessing the characteristics of the energy spectra of gamma rays measured in the air by type of helicopter and measuring equipment used, and then sorting out areas where the energy spectra of radioactive cesium (Cs-134 and Cs-137) were detected in significant amounts and those where they were not.
    • ① The deposition densities of cesium 134 and cesium 137 on the areas where the energy spectra of radioactive cesium were detected in significant amounts were calculated by deducting the contribution by natural radionuclides from the measurement results of air dose rates at the respective measuring points (see method below), and also based on the correlation between air dose rates and the results of the in-situ measurement using germanium semiconductor detectors,*1 which was conducted by the Japan Chemical Analysis Center in the course of the project by the 2011 Strategic Funds for the Promotion of Science and Technology, entitled “Establishment of the Base for Taking Measures for Environmental Impact of Radioactive Substances - Study on Distribution of Radioactive Substances” (June-August, 2011).
      • (1) Regarding Western Japan and Hokkaido, air dose rates were obtained by subtracting the average air dose rates due to natural radionuclides from the measured values using "Method to Assess Influences of Natural Radionuclides in Airborne Monitoring over the Western Part of Japan" (For the detail of method, see Attachment 9, Results of Airborne Monitoring Survey by MEXT in the Kyushu Region and Okinawa Prefecture, May 11, 2012)
      • (2) With regard to the areas in the eastern part of Japan where the monitoring surveys were conducted using the same combination of helicopter and measuring equipment used in the airborne monitoring survey in the western part of Japan (the areas targeted in the Second Airborne Monitoring (within an 80 to 100 km-range (or 120 km-range on the southern part) from Fukushima Dai-ichi NPP), and part of the areas targeted in the Fourth Airborne Monitoring (within a 40 to 80 km-range from Fukushima Dai-ichi NPP), as well as Aichi, Aomori, Akita, Ishikawa, Iwate, Kanagawa, Gifu, Saitama, Shizuoka, Chiba, Tokyo, Toyama, Nagano, Niigata, Fukui and Yamanashi Prefectures, and the western part of Fukushima Prefecture), the method (1) is applicable. Therefore, using this method, the measurement results of the monitoring for the aforementioned area were revised by subtracting the air dose rates due to natural radionuclides.
      • (3) With regard to areas in the eastern part of Japan where the airborne monitoring surveys were conducted using disaster-prevention helicopters owned by respective Prefectures, (within a 40 km-range of the Fourth Airborne Monitoring, in the northern part of Miyagi Prefecture out of a 100 km range of Fukushima Dai-ichi NPP, in the southern part of Tochigi Prefecture out of a 120 km range of Fukushima Dai-ichi NPP, outside of an 120 km range of the Fukushima Dai-ichi NPP in Ibaraki Prefecture, and outside of an around 100 km range of the Fukushima Dai-ichi NPP in Yamagata Prefecture and Gunma Prefecture), the combination of helicopters and measuring equipment used was not the same as that used in the airborne monitoring survey in the western part of Japan. Since the method (1) is not applicable, the measurement results of the monitoring for the aforementioned area were revised by subtracting the air dose rates due to natural radionuclides using the average value for eastern Japan before the Fukushima dai-ichi NPP accident (0.0687 µSv/h).
    • ② Areas where the energy spectra of radioactive cesium were not detected in significant amounts; As with before, these were indicated as areas showing the minimum range of radioactive cesium "<1.0E+04" (Bq/m2) for the sake of simplicity.
  7. Regarding air borne monitoring throughout Japan, results have been announced by Prefecture or blocks. Due to the development of analysis methods including radioactive cesium deposition considering the influence of natural radionuclides, the past announced results have been subjected to be revised. In such circumstances, this database stores data throughout Japan using the latest analysis methods and decay-compensation as of May 31, 2012 which is the final day of the air borne monitoring of Hokkaido where the latest monitoring area throughout Japan.Deposition densities of cesium 134 and cesium 137 were obtained considering physical attenuation of cesium 134 and cesium 137 from the measurement time up to a certain point in time (May 31, 2012).
  8. The data consists of radioactive cesium deposition densities at the median points of the Quarter Grid Squares (approximately 250 m x 250 m) defined by JIS X 0410. See the Ministry of Internal Affairs and Communications Statistics Bureau website for "Grid Square Statistics".
  9. *1: In-situ measurement using germanium semiconductor detectors: Means to analyze the concentration of radionuclides accumulated in soil by setting up transportable germanium semiconductor detectors in the environment and detecting gamma rays that are emitted from radiation sources distributed in soil.

    10. ∙Measurement Period of Each Prefecture
Results of Deposition of Radioactive Cesium of the Airborne Monitoring Survey in the Restricted Areas and Planned Evacuation Zones ( Decay correction: February 10, 2012 )
  1. This data was created based on the measurement results through the airborne monitoring survey conducted in the restricted areas and deliberate evacuation areas by MEXT.
  2. This published data was prepared based on the results obtained from February 6 to February 10, 2012 by one helicopter, in a total 7 flights.
  3. Their flight altitudes were from about 300 m above ground, and the air dose rate at the ground surface is the averaged value of air dose rates in a roughly about 600 m diameter circle (varies by flight altitude) below the aircraft.
  4. The width of the track is around 1.8 km.
  5. Regarding air dose rates, we established one test line within the target area of this monitoring survey, and first ascertaining trends at each altitude in counting rates (cps) measured in the air on the test line (150 to 900 m) (altitude correction function), and then based on the counting rate at a certain altitude above the test line and air dose rates (µSv/h) at a height of 1 m above the ground measured around the test line using NaI scintillators, obtaining the conversion factor between counting rates and air dose rates at a height of 1 m above the ground (cps/(µSv/h)). Air dose rates 1 m above the ground were calculated by converting counting rates measured in the air above each monitoring point, using said altitude correction function and the conversion factor.
  6. Deposition of radioactive cesium were calculated by subtracting the average air dose rates due to natural radionuclides throughout all of East Japan from the values measured at respective airborne monitoring points, and were based on the correlation between air dose rates and the results of the in-situ measurement using germanium semiconductor detectors *1, which was conducted by the Japan Chemical Analysis Center in the course of the project, the 2011 Strategic Funds for the Promotion of Science and Technology, entitled “Establishment of the Base for Taking Measures for Environmental Impact of Radioactive Substances - Study on Distribution of Radioactive Substances.”
  7. The decay-compensated values as of the final day of the monitoring (February 10, 2012) were used. Regarding deposition densities of Cs-134 and Cs-137, physical attenuation from the measurement time up to a certain point in time (February 10, 2012) was taken into account.
  8. There was snow coverage in some part of the targeted areas of this monitoring. Past monitoring results by MEXT have shown that air dose rates are apt to be lower at points covered by snow, with gamma rays being shielded, and the same tendency is expected to be observed. Therefore, in order to distinguish areas covered by snow (where the measurement results of air dose rates are supposed to show a lower deposition of radioactive cesium), such areas are indicated in data. When identifying areas covered by snow, we used data obtained by NASA’s earth observation satellites, Terra and Aqua,*3 which are available on the JASMES *2 released by the Japan Aerospace Exploration Agency.
  9. The data consists of radioactive cesium deposition densities at the median points of the Quarter Grid Squares (approximately 250 m x 250 m) defined by JIS X 0410. See the Ministry of Internal Affairs and Communications Statistics Bureau website for "Grid Square Statistics".

    10. *1: In-situ measurement using germanium semiconductor detectors: Means to analyze the concentration of radionuclides accumulated in soil by setting up transportable germanium semiconductor detectors in the environment and detecting gamma rays that are emitted from radiation sources distributed in soil.
    *2: JAXA Satellite Monitoring for Environmental Studies
    *3: We used the data of snow coverage around Japan, which were observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) installed on NASA’s earth observation satellites, Terra and Aqua, and were analyzed by the Japan Aerospace Exploration Agency (JAXA) using its original processing algorithm. JAXA has been planning the Global Change Observation Mission (GCOM) to observe the Earth’s environment as a whole, including the atmosphere, ocean, land, snow and ice, from space on a long-term basis (10 to 15 years), thereby monitoring hydrologic circulation and climate change and figuring out the mechanisms thereof. Said data have been collected and processed for the purpose of assessing the analytical algorithm for optical sensors used in the Global Change Observation Satellite (GCOM-C). As they are 500 m-grid data, snow coverage over 5 cm with an even surface can be indicated correctly, but it is sometimes difficult to accurately identify snow coverage of a shallower depth or with an uneven surface.
Results of Deposition of Radioactive Cesium of the Fourth Airborne Monitoring Survey ( Decay correction: November 5, 2011 )
  1. This data was created based on the measurement results of the fourth airborne monitoring survey by MEXT.
  2. This published data was prepared based on results obtained from October 22 to November 5, 2011 by two helicopters, in a total 27 flights.
  3. Their flight altitudes were from 150 to 300 m above ground. The air dose rate at the ground surface is the averaged value of air dose rates in a roughly 300 m to 600 m diameter circle (varies by flight altitude) below the aircraft.
  4. The width of the track of airborne is around 1.8 km. However, comparing the ratios of measurement results of the third airborne monitoring and the first airborne monitoring, it was confirmed that there were some monitoring points where air dose rates were larger through interpolation due to differences in the flight method. Therefore, as in the first airborne monitoring, we additionally conducted monitoring at 300 m intervals in each of the coastal areas at the southern and northern parts of the Fukushima Dai-ichi NPP.
  5. The new method adopted for compiling the results of airborne monitoring in Iwate Prefecture, etc. (already publicized on November 11, 2011) was again used, that is, to assess the characteristics of energy spectra of gamma-rays measured in the air with respect to each type of helicopter and measuring instruments used, to sort out areas according to whether energy spectra of radioactive cesium (Cs-134 and Cs-137) were detected in significant amounts or not, and then to calculate the deposition of radioactive cesium. The details are as follows
    • ①Deposition of radioactive cesium were calculated by subtracting the average air dose rates due to natural radionuclides throughout all of East Japan from the values measured at respective airborne monitoring points, followed by using the correlation between air dose rates and the results of the in-situ measurement using germanium semiconductor detectors, which was conducted by the Japan Chemical Analysis Center in the course of the project, the 2011 Strategic Funds for the Promotion of Science and Technology, entitled “Establishment of the Base for Taking Measures for Environmental Impact of Radioactive Substances - Study on Distribution of Radioactive Substances.”
    • ②Areas where the energy spectra of radioactive cesium were not detected in significant amounts; As with before, these were indicated as areas showing the minimum range of radioactive cesium "<1.0E+04" (Bq/m2) for the sake of simplicity.
  6. The values have been decay-compensated to the value for November 5, 2011, which is the final day in which the fourth airborne monitoring survey was conducted. Regarding deposition densities of Cs-134 and Cs-137, physical attenuation from the measurement time up to a certain point in time was taken into account.
  7. The data consists of radioactive cesium deposition densities at the median points of the Quarter Grid Squares (approximately 250 m x 250 m) defined by JIS X 0410. See the Ministry of Internal Affairs and Communications Statistics Bureau website for "Grid Square Statistics".
Results of Deposition of Radioactive Cesium of the Third Airborne Monitoring Survey ( Decay correction: July 2, 2011 )
  1. This data was created based on the measurement results of the third airborne monitoring survey by MEXT.
  2. This published data was prepared based on results obtained from May 31 to July 2, 2011 by two helicopters, in a total 29 flights.
  3. Their flight altitudes were from 150 to 300 m above ground. The air dose rate at the ground surface is the averaged value of air dose rates in a roughly 300 m to 600 m diameter circle (varies by flight altitude) below the aircraft.
  4. The width of the flight path of the aircraft is around 2 km.
  5. The deposition of cesium 134 at the ground surface was calculated based on the results of airborne monitoring and of in-situ measurements which the NUSTEC took on the ground using germanium semiconductor detectors. The deposition of cesium 137 at the ground surface was calculated based on the results of the in-situ measurements of cesium 134 on the ground by the NUSTEC using a germanium semiconductor detectors, and analysis values of cesium 137.
  6. The values have been decay-compensated to the value for July 2, 2011, which is the final day in which the third airborne monitoring survey was conducted. Regarding deposition densities of Cs-134 and Cs-137, physical attenuation from the measurement time up to a certain point in time was taken into account.
  7. The data consists of radioactive cesium deposition densities at the median points of the Quarter Grid Squares (approximately 250 m x 250 m) defined by JIS X 0410. See the Ministry of Internal Affairs and Communications Statistics Bureau website for "Grid Square Statistics".
Results of Deposition of Radioactive Cesium of the Second Airborne Monitoring Survey ( Decay correction: May 26, 2011 )
  1. This data was created based on the measurement results of the second airborne monitoring survey by MEXT.
  2. This published data was prepared based on results obtained from May 18 to 26, 2011 by a helicopter, in a total 13 flights.
  3. Their flight altitudes were from 150 to 300 m above ground. The air dose rate at the ground surface is the averaged value of air dose rates in a roughly 300 m to 600 m diameter circle (varies by flight altitude) below the aircraft.
  4. The width of the track is around 3-5 km.
  5. The deposition of cesium 134 at the ground surface was calculated based on the results of airborne monitoring and of in-situ measurements which the US. DOE took on the ground using germanium semiconductor detectors. The deposition of cesium 137 at the ground surface was calculated based on the results of the in-situ measurements of cesium 134 on the ground by the US. DOE using a germanium semiconductor detectors, and analysis values of cesium 137.
  6. The values have been decay-compensated to the value for May 26, 2011, which is the final day in which the second airborne monitoring survey was conducted. Regarding deposition densities of Cs-134 and Cs-137, physical attenuation from the measurement time up to a certain point in time was taken into account.
  7. The decay-compensated values as of May 26 were used for the data within 80 km from the Fukushima Dai-ichi NPP.
  8. The data consists of radioactive cesium deposition densities at the median points of the Quarter Grid Squares (approximately 250 m x 250 m) defined by JIS X 0410. See the Ministry of Internal Affairs and Communications Statistics Bureau website for "Grid Square Statistics".
Results of Deposition of Radioactive Cesium of the First Airborne Monitoring Survey ( Decay correction: April 29, 2011 )
  1. This data was created based on the measurement results of the first airborne monitoring survey by MEXT.
  2. This published data was prepared based on results obtained from April 6 to 29, 2011 by a small airplane and two helicopters, in a total 42 flights.
  3. Their flight altitudes were from 150 to 700 m above ground. The air dose rate at the ground surface is the averaged value of air dose rates in a roughly 300 m to 1,500 m diameter circle (varies by flight altitude) below the aircraft.
  4. The eastern part of Inawashiro Town is a mountainous area, making low altitude flights difficult, so there are no measurement results there.
  5. Airborne monitoring just above the Fukushima Dai-ichi NPP has to be consist of the measurement of the air dose rate directly from the power plant, so such monitoring has not been done.
  6. The deposition of cesium 134 at the ground surface was calculated based on the results of airborne monitoring and of in-situ measurements which the US. DOE took on the ground using germanium semiconductor detectors. The deposition of cesium 137 at the ground surface was calculated based on the results of the in-situ measurements of cesium 134 on the ground by the US. DOE using a germanium semiconductor detectors, and analysis values of cesium 137.
  7. For the air dose rate and deposition of radioactive substances in the ground surface, decay of radioactive substances was considered and actual readings were converted into values as of April 29, when this monitoring was last done. Deposition densities of cesium 134 and cesium 137 were obtained considering physical attenuation of cesium 134 and cesium 137 from the measurement time up to a certain point in time.
  8. The data consists of radioactive cesium deposition densities at the median points of the Quarter Grid Squares (approximately 250 m x 250 m) defined by JIS X 0410. See the Ministry of Internal Affairs and Communications Statistics Bureau website for "Grid Square Statistics".
Publicly available data collected from the website of the relevant organizations and converted into CSV, XML, and KML formats that were easy to use.

Results of Deposition of Radioactive Cesium of the Airborne Monitoring Survey in the Areas to which Evacuation Orders Have Been Issued ( Decay correction: March 11, 2013 )
Results of Deposition of Radioactive Cesium of the Sixth Airborne Monitoring Survey and Airborne Monitoring Survey Outside 80 km from the Fukushima Dai-ichi NPP ( Decay correction: December 28, 2012 )
Results of Deposition of Radioactive Cesium of the Fifth Airborne Monitoring Survey and Airborne Monitoring Survey Outside 80 km from the Fukushima Dai-ichi NPP ( Decay correction: June 28, 2012 )
Results of Deposition of Radioactive Cesium of the Airborne Monitoring Survey by Prefecture ( Decay correction: May 31, 2012 )
Results of Deposition of Radioactive Cesium of the Airborne Monitoring Survey in the Restricted Areas and Planned Evacuation Zones ( Decay correction: February 10, 2012 )
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