Based on "Comprehensive Radiation Monitoring Plan", Japan Coast Guard has long been conducting radiation monitoring in sea areas. Samples of sea water and marine soil in Tokyo bay and sea water offshore of Fukushima Prefecture and Ibaraki Prefecture were collected. The data here was created based on the analyses of sea water samples collected on July 17, 2012 in Tokyo bay and on August 3, 2012 offshore of Fukushima Prefecture and Ibaraki Prefecture (announced on November 6, 2012). In addition, data of August 2011 was shown as reference.
Publicly available data collected from the website of the relevant organizations and converted into CSV, XML, and KML formats that were easy to use.