A Predicted Geomagnetic Field Model for Epoch 1990.0

An epoch 1990.0 geomagnetic field model will be produced by the Naval Oceanographic Office (NAVOCEANO) using magnetic field measurements from the recently launched (April 1990) Polar Orbiting Geomagnetic Survey satellite for part of the input data. To aid in the production and evaluation of this model, NAVOCEANO requested that the Naval Oceanographic and Atmospheric Research Laboratory (NOARL) develop a predicted field model for 1990.0. A predicted model of the geomagnetic field for epoch 1990.0 has been developed. The model is based on the Definitive Geomagnetic Reference Field (DGRF) model for 1980.0 updated to 1990.0 by use of a secular variation model for 1980.0 developed at NOARL. The NOARL secular variation model is based upon annual means of vector geomagnetic field components from 73 magnetic observatories for years 1976.5 through 1983.5. The predicted model is of spherical harmonic degree and order 10. The rms error of the predicted model is estimated to be 200 nT relative to an accurate degree 10 field model for epoch 1990.0. Peak errors relative to an accurate model are estimated to be 500 nT for vector field error magnitude and +/-350, +250, and +/ -500 nT for north, east, and vertical field components errors, respectively. If the DGRF model for 1980.0 were used without updating to represent the degree 10 field for 1990.0, estimated errors would be about four times as large.... Geomagnetism, Magnetic navigation.