Hi. From time to time, I talked with law profs and other legal experts on the copyright status of works of US federal government agencies. Their views tend to be that the public domain status is not global.
Under Japanese copyright law, the U.S. copyright law’s clause for not protecting the federal government works is not respected. (How much risk of being sued for infringement exists is a different matter). Some of the online explanations seem to allow an interpretation that the government agencies mean to offer those resources under public domain globally.
Some relevant links:
USGS Information policy page (section on “Copyrights and Credits”: https://www2.usgs.gov/laws/info_policies.html
DOI Copyright Restrictions and Permissions page: https://www.doi.gov/copyright