TY  - RPRT
TI  - Secular, annual, and semiannual changes in the baseline level of the earth's magnetic field at North American locations
AU  - W.H. Campbell
PY  - 2012
DO  - 10.1029/jb085ib11p06557
UR  - https://pubs.usgs.gov/publication/70012332
ID  - 70012332
ER  -