Error Estimate of Bending Angles in the Presence of Strong Horizontal Gradients

Abstract

The CT/FSI (Canonical Transform/Full-Spectrum Inversion) technique permits achieving a high accuracy and vertical resolution in the retrieval of bending angle from radio occultation data. This technique can be universally applied for the (hypothetical) spherically-symmetric atmosphere and any multipath situation can be unfolded. The reason is that the CT/FSI technique uses a Fourier Integral Operator that maps the measured wave field into the impact parameter representation, and for a spherically-symmetric medium each ray has a unique impact parameter. For the real atmosphere with horizontal gradients the situation is different. Horizontal gradients result in the variation of the impact parameter along a ray. In the presence of strong horizontal gradients, a bending angle profile can become a multi-valued function. In this case, the CT/FSI technique in its standard variant will fail to correctly retrieve the bending angle profile. It is, however, possible to estimate bending angle errors. For this purpose we apply the sliding spectral analysis of the CT-transformed wave field. The spectral width is used as a measure of the bending angle errors. We perform numerical simulations with global fields from re-analyses of the European Centre for Medium-Range Weather Forecasts and show that this radio holographic technique can be effectively used for error estimation in the areas of multi-valued bending angle profiles.