Edogawa-ku is one of the 23 Special Wards (ku) of Tokyo, situated in the eastern-most Tokyo right next to Chiba. The eastern Wards of Tokyo, including Edogawa, Katsushika, Adachi have elevated radiation levels compared to the western Tokyo.
Professor Hayakawa walked from the southern tip of Edogawa (Kasai Seaside Park) to Shinkoiwa JR Station. Along the way, he measured "black dust" (dark sediment) at two locations, and one of them (in Kasai Seaside Park) measured 1.385 microsievert/hour on his survey meter.
He also used a stick-type cheap survey meter called "Air Counter" (aka "Ea-bo" エア棒）, which seems to measure pretty well if the radiation level is above 0.1 microsievert/hour.
EveryTrail - Find hiking trails in California and beyond
Right now, Professor Hayakawa is walking somewhere in Koriyama City, Fukushima Prefecture with his survey meter. Soon it will be on the Everytrail map he will create.