AMPERE Data Limitations

The Iridium low-time resolution data available at present have a number of limitations that users need to understand.

First, the time resolution is coarse, about 200 seconds between samples on a given space vehicle (SV), which leads to quite sparse data sampling when attempting to reconstruct a view of the global Birkeland currents. It also can lead to a spatial gap in the sampling which must be considered when assessing the reliability of a Birkeland current inversion.

Second, at present only the cross-track magnetic perturbation can be reliably derived which leads to considerable spurious currents near the orbit crossing point. Variations within the noise level near the crossing point can lead to spurious and intense filamentary currents located between tracks.

Third, significant offsets that are not real occasionally survive the automated noise rejection steps in our processing. Since it is impossible to manually review all these data and sift for apparently bad data points, users need to be on the look-out for outliers.