A refractive index mapping operator for assimilation of occultation data

Mapped refractivity profiles are compared with retrieved refractivity profiles obtained via accurate 3D ray tracing simulations of GPS radio occultation events with ray path tangent points near the weather front. The simulations indicate that the mapping is a good representation of occultation measurements, including the influence large horizontal gradients have on retrieved refractivity profiles. To further the results, a simple ad hoc modification is introduced to approximately account for the ray path bending near the tangent points.

The forward-inverse mapping allows for the near cancellation of otherwise crude approximations-for example, straight-line propagation-and the general concept could perhaps be adapted for the development of fast and accurate observation operators for the assimilation of other types of remote sensing data.