Resolution No.13 (1981): DGRF1965-75, PGRF1975, and IGRF1980
IAGA, recognising the continuing need for an International Geomagnetic Reference Field, recommends that:
- IGRF 1980 be used for the interval 1980 to 1985
- DGRF 1965, DGRF 1970, and DGRF 1975 be used, with linear interpolation, for applications requiring definitive values for the interval 1965 to 1975
- PGRF 1975 (i.e. DGRF 1975 and IGRF 1980 interpolated linearly) be used for the interval 1975 to 1980 until DGRF 1980 is produced.
- This pattern be maintained in future updates.
(In the above text, DGRF denotes a Definitive International Geomagnetic Reference Field, and PGRF a Provisional International Geomagnetic Reference Field. The values of spherical harmonic coefficients for DGRF 1965, DGRF 1970, DGRF 1975, and IGRF 1980 with secular variation terms for 1980-1985 are shown in this publication on page 101.)