A bi-local estimation approach for residual ionospheric correction of radio occultation bending angles
Presenter:
Stig Syndergaard
Danish Meteorological Institute, Copenhagen, Denmark
Wegener Center for Climate and Global Change (WEGC) and Institute for Geophysics, Astrophysics, and Meteorology/Institute of Physics, University of Graz, Graz, Austria
Poster
We have developed the theory for a bi-local estimation of residual ionospheric errors in bending angle profiles retrieved from radio occultation (RO) measurements. Bi-local in this context refers to the situation where the electron density is different, though still spherically stratified, on the transmitter-inbound and receiver-outbound sides of the RO tangent points. As opposed to local spherical symmetry, we call this bi-local spherical symmetry. So far, theoretical estimates of ionospheric residual errors have been based on the assumption of local spherical symmetry. We here extend such estimates to the case of bi-local spherical symmetry. The theory also takes into account the contribution from the geomagnetic field in the ionospheric refractive index, and as well allows for a non-zero local electron density at the receiver in orbit. As part of the derivations, we found a small term not previously noted, which can become appreciable for elliptical satellite orbits. The results were verified by ray tracing through simple models of the ionospheric electron density and geomagnetic field. The accuracy of a residual error correction based on these results would be limited by the uncertainty in knowledge of the ionospheric electron density and by horizontal electron density gradients along the ray paths. Finally we point to results from follow-on work that applied the theory to test-day ensembles of real RO data from Metop, GRACE, and CHAMP.
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