Adjustment of UARS, POGS, and DE-1 Satellite Magnetic Field Data for Modeling of Earth's Main Field

Abstract

In the absence of Magsat quality satellite magnetic field measurements, the use of data of lesser quality is sought. The DE-1 and UARS satellite magnetic field experiments were not designed for the purpose of modeling Earth's main field. The POGS satellite acquired data for modeling of Earth's main field, but at a lower accuracy than Magsat. All of these data were acquired with fluxgate magnetometers, which are subject to calibration drifts. On Magsat the fluxgate magnetometer was calibrated 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 formalism is developed to compare the data from these satellites with a field model derived from all other available data. This model included data from Magsat, so it is highly accurate at 1980. Its accuracy at the epochs of the satellites considered then depends upon the accuracy with which the field at 1980 can be extrapolated to future epochs. Adjustment of DE-1 data requires estimation of only two parameters for data spanning about 10 years. The resulting adjusted data are in good agreement 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 POGS data vary substantially over the three years of available data. The resulting residuals indicate that the adjusted data set is suitable for main field modeling up to about degree 10, as used for the International Geomagnetic Reference Field. However, 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 all of the adjustment-model parameters. If a priori information regarding the magnetic field from attitude torquer rods is included, the ambiguity is mostly resolved. Residuals after adjustment are of comparable magnitude and quality to those from POGS.

The Geomagnetic Field 1900-1995, Including the Large-Scale Field from Magnetospheric Sources, and the NASA Candidate Models for the 1995 Revision of the IGRF

“…from POGO for comparable altitudes, local times, and magnetic activity was unable to find any residual patterns that were similar to those from POGS. Langel et al (1997) found that the POGS residuals could be significantly reduced by a rudimentary recalibration. However, no single, consistent recalibration was found applicable to large segments of the POGS data.…”

“…In their evaluation of the POGS data, Langel et al (1997) concluded that the corrections attributed by Quinn et al (1995) to ionospheric and magnetospheric sources are more likely due to measurement error. A large volume of absolute accuracy scalar data were collected by the OGO-2, OGO-4, and OGO-6 spacecraft, also known as POGO.…”

“…Also, an independent evaluation of the POGS data was conducted by Langel et al (1997). Because of additional uncertainty regarding the timing of the 1991 data, only data from 1992 and 1993 were utilized.…”

“…The GSFC(S95-xx) models were derived before the study of POGS data by Langel et al (1997) was complete. Various levels of weighting were investigated, as described in a later section.…”

Numerical model for computation of effective and ambient dose equivalent at flight altitudes

“…Several models, tools, algorithms to calculate geomagnetic cut-off rigidity, particle trajectories and the asymptotic viewing cones were proposed during the years (McCracken et al 1962(McCracken et al , 1968Shea et al 1965;Smart et al 2000). As the internal field we consider the IGRF geomagnetic model, which is a Gauss spherical harmonic model of the geomagnetic field, based on magnetic field measurements from geomagnetic stations, magnetometers and satellites (Langel 1987). As the external field model we use a semi-empirical Tsyganenko (1989) model which is based on a large number of satellite observations (Tsyganenko 1989).…”