ADJUSTMENT OF UARS, POGS, AND DE-1 SATELLITE MAGNETIC-FIELD DATA FOR MODELING OF EARTHS MAIN FIELD

In the absence of Magsat quality satellite magnetic field measurements , the use of data of lesser quality is sought. The DE-1 and UARS satel lite magnetic field experiments were not designed for the purpose of m odeling Earth's main field. The FOGS satellite acquired data for model ing of Earth's main field, but at a lower accuracy than Magsat. All of these data were acquired with fluxgate magnetometers, which are subje ct to calibration drifts. On Magsat the fluxgate magnetometer was cali brated in-flight by comparison with a Cesium-Vapor scalar magnetometer . Such calibration is not possible on the satellites considered here, leaving uncertainty as to the accuracy of the resulting data. A formal ism is developed to compare the data from these satellites with a fiel d model derived from all other available data. This model included dat a from Magsat, so it is highly accurate at 1980. Its accuracy at the e pochs of the satellites considered then depends upon the accuracy with which the field at 1980 can be extrapolated to future epochs. Adjustm ent of DE-I data requires estimation of only two parameters for data s panning about 10 years. The resulting adjusted data are in good agreem ent with the model for those 10 years and exhibit residuals generally interpretable in terms of sources in the ionosphere and magnetosphere. Adjustment parameters of the FOGS data vary substantially over the th ree years of available data. The resulting residuals indicate that the adjusted data set is suitable for main field modeling up to about deg ree 10, as used for the International Geomagnetic Reference Field. How ever, the resulting residuals are considered to be due mainly to error in measurement and not to geophysical sources. Adjustment of the UARS data is more difficult. The data used are not sufficient to resolve a ll of the adjustment-model parameters. If a priori information regardi ng the magnetic field from attitude torquer rods is included, the ambi guity is mostly resolved. Residuals after adjustment are of comparable magnitude and quality to those from POGS.