Optimal noise filtering for the ionospheric correction of GPS radio occultation signals

The ionosphere-corrected variables derived from radio occultation signals--such as the phase, Doppler, and bending angle--are affected by small-scale ionospheric effects that are not completely eliminated by the ionospheric correction. They are also affected by noise from mainly the L2 signal.

This paper introduces a simple method for optimal filtering of the L4 = L1 - L2 signal used to correct the L1 signal, which minimizes the combined effects of both the small-scale ionospheric residual effects and L2 noise on the ionosphere-corrected variables. Statistical comparisons to high-resolution numerical weather models from the European Centre for Medium-Range Weather Forecasts (ECMWF) validate that this increases the accuracy of radio occultation inversions in the stratosphere.