During the decades after the Fukushima Daiichi Nuclear Power Station (FDNPS) accident, ambient dose rates have markedly decreased when compared to those at the early state of the accident. Government projects have been continuously conducted by surveying the ambient dose rate and radiocesium distributions. Airborne surveys using crewed helicopters and unmanned aerial vehicles (UAVs) are the best methods for obtaining an overall picture of the distribution. However, ground-based surveys are required for accurate measurements near the population. The differences between these methods include the knowledge of the post depositional behavior of radionuclides in land use. The survey results form the basis for policy decisions such as lifting evacuation zones, decontamination, and other countermeasures. These surveys contain crucial findings regarding post-accident responses. This paper reviews the survey methods of government projects and current situation around the FDNPS. The visualization methods and databases of ambient dose rates are also reviewed to provide information to the population.

1. Introduction
2. Environmental Radiological SurveyMethods and Results
    2.1 Large-Scale Radiation Survey Project
    2.2 Airborne Radiation Survey
    2.3 Ground-based Survey
    2.4 Intercomparison of Methodology
3. Discussion
    3.1 Temporal Change of Ambient Dose Rate
    3.2 Integration of Different Survey Results
    3.3 Publication of Databases
4. Summary
Acknowledgements
REFERENCES

• Yukihisa Sanada(Sector of Fukushima Research and Development) Corresponding author
• Miyuki Sasaki(Sector of Fukushima Research and Development)
• Hiroshi Kurikami(Sector of Fukushima Research and Development)
• Fumiya Nagao(Sector of Fukushima Research and Development)
• Satoshi Mikami(Sector of Nuclear Safety Research and Emergency Preparedness)