The Gunma University professor took a walk in part of Abiko City and Kashiwa City, in the so-called "Tokatsu area" in the northwest corner of Chiba Prefecture with elevated radiation levels.
He says there is a statistically significant difference between the radiation levels on the ground levels and the levels at 1 meter off the ground, with the levels at 1 meter off the ground 20 to 30% less than at the ground levels.
The radiation levels of "black dust" he found along the way (in microsievert/hour):
Professor Hayakawa's walk from Abiko City to Kashiwa-no-ha in Kashiwa City on April 16, 2012:
EveryTrail - Find hiking trails in California and beyond