In the early period after the accident, most of the fixed monitoring posts near FDNPP lost their function a a result of the earthquake. Therefore, the Ministry of Education, Culture, Sports, Science and Technology (MEXT) started air dose rate monitoring using monitoring cars . In parallel with such monitoring, a radiation survey on the environment and measurement of the concentration of radionuclides in some environmental media (such as airborne dust, food, drinking water, weeds, groundwater, and soil) was initiated by the Japanese and prefectural governments [1, 2]. Radioiodine, radiocesium, and some other radionuclides were detected in these environmental samples. These monitoring data were utilized for planning measures to protect the public.
Comprehensive environmental monitoring was conducted by MEXT with the cooperation of various universities and research institutes, and distribution maps of radiation dose and soil deposition density were prepared . For example, distribution maps of ambient dose rates based on continuous measurement results through a vehicle-borne survey are shown in Fig. 1.2. This vehicle-borne survey was mainly carried out by the KURAMA system ; the details of this system are presented in this book in Chap. 7. The vehicle-borne survey was carried out repeatedly, and distribution maps of ambient dose rates prepared by the survey are used to predict the reduction of dose rates in future . Various kinds of environmental monitoring continue to be conducted by the Japanese and prefectural governments.
Some research organizations or individuals in Japan also carried out environmental monitoring from an early stage after the accident. The “Proceedings of International Symposium on Environmental Monitoring and Dose Estimation of Residents after Accident of TEPCO's Fukushima Daiichi Nuclear Power Stations”  include 12 papers on a radiation survey on the environment and 18 papers on environmental radioactivity related to the accident. For example, Iimoto et al. surveyed the environmental status in and around Tokyo immediately after the accident (see Chap. 5 in this book). Zheng et al. investigated the distribution of plutonium isotopes in marine sediments off the coast of Japan before and after the accident (see Chap. 10 in this book). These monitoring data are important and valuable to supplement the large-scale monitoring data and to accurately estimate the radiation dose for the public.
Fig. 1.2 Distribution map of ambient dose rates based on continuous measurement results from vehicle-borne survey 
Environmental monitoring data and analyses conducted using mathematical models are both necessary to accurately evaluate the levels of radiation exposure resulting from the accident. Therefore, it is important to collect a wide range of these data for an estimation of the radiation dose. In addition, these monitoring data should be preserved as a record of the earthquake and the accident.
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