Abstract
We present an attempt to improve the quality of the geomagnetic field measurements from the Polar Orbiting Geophysical Observatory (POGO) satellite missions in the late 1960s. Inaccurate satellite positions are believed to be a major source of errors for using the magnetic observations for field modelling. To improve the data, we use an iterative approach consisting of two main parts: one is a main field modelling process to obtain the radial field gradient to perturb the orbits and the other is the state-of-the-art GPS orbit modelling software BERNESE to calculate new physical orbits. We report results based on a single-day approach showing a clear increase of the data quality. That single-day approach leads, however, to undesirable orbital jumps at midnight. Furthermore, we report results obtained for a much larger data set comprising almost all of the data from the three missions. With this approach, we eliminate the orbit discontinuities at midnight but only tiny quality improvements could be achieved for geomagnetically quiet data. We believe that improvements to the data are probably still possible, but it would require the original tracking observations to be found.
Highlights
Measurements of the magnetic field during the previous century are of importance for characterising the secular variation
We report on data collected by the series of Orbiting Geophysical Observatory (OGO) satellites from the 1960s
Data compilation OGO-2 acquired data from October 14, 1965 until October 2, 1967, but because of an early failure in the attitude control system, the measurements were limited to twilight local times
Summary
Measurements of the magnetic field during the previous century are of importance for characterising the secular variation. Starting with Cosmos-49 in 1964, satellite data has played an increasingly important role in defining the magnetic field, culminating in the present-day Swarm mission beginning in 2013 (Olsen and The Scarf team 2013). We report on data collected by the series of Orbiting Geophysical Observatory (OGO) satellites from the 1960s. These data quite likely suffer from imprecision in their geographical positions as a result of poor tracking abilities and rudimentary gravitational models. The original tracking data were lost, so our efforts represent a compromise at what could be done if the original data were to be found
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