  In 2016, UNSCEAR published an attachment to its Fukushima 2015 White Paper,
entitled "Development of isodose maps representing annual external exposure in
Japan as a function of time," in which the committee presented annual
additional 1 mSv effective dose ab extra isodose lines for 1, 3, 5, 10, 30, 50
years after the accident, based on the soil deposition data of radionuclides
within 100 km from FDNPP. Meanwhile, the median of the ratio, c, between the
external effective dose rates and the ambient dose equivalent rates at 1 m
above the ground obtained by the airborne monitoring has been established to be
c~0.15. We here compare the UNSCEAR predictions with respect to estimates based
on the airborne monitoring. Although both methods and data used in the two
approaches are di erent, the resultant contours show relatively good agreement.
However, to improve the accuracy of long-term annual effective isodose lines,
feedback from continuous measurements such as airborne monitoring is important.
