CC 4.0 Attribution International will work just fine. I think the size is ok to include in the repo, which is a bit nicer since the test will run against every PR. What we'd want is for the file to live under:

cdm/radial/src/test/data/sigmet

and along side of it, create a README file that references the file name and provides the attribution details following the the requirements laid out by the license. I believe this is the license, but you'd want to confirm that. If that is the license, this is what is required:

Attribution — You must give appropriate credit , provide a link to the license, and indicate if changes were made . You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.

Your test code can live under cdm/radial/src/test/java/ucar/nc2/iosp/sigmet, and you can access the test file using the path TestDir.localTestDataDir + "sigmet/<test-file-name>";. Note that the existing test in that directory requires access to our large test datasets, so it is annotated with @Category(NeedsCdmUnitTest.class) - your test will not use that annotation since the test file will live in the repository :-)

Thank you again!