A nonlinear optimal, estimation inverse method for radio occultation measurements of temperature, humidity, and surface pressure

An optimal estimation inverse method is presented which can be used to retr ieve simultaneously vertical profiles of temperature and specific humidity, in addition to surface pressure, from satellite to-satellite radio occulta tion observations of the Earth's atmosphere. The method is a nonlinear, max imum a posteriori technique which can accommodate most aspects of the real radio occultation problem and is found to be stable and to converge rapidly in most cases. The optimal estimation inverse method has two distinct adva ntages over the analytic inverse method in that it accounts for some of the effects of horizontal gradients and is able to retrieve optimally temperat ure and humidity simultaneously from the observations. It is also able to a ccount for observation noise and other sources of error. Combined, these ad vantages ensure a realistic retrieval of atmospheric quantities. A complete error analysis emerges naturally from the optimal estimation theory, allow ing a full characterization of the solution. Using this analysis, a quality control scheme is implemented which allows anomalous retrieval conditions to be recognized and removed, thus preventing gross retrieval errors. The i nverse method presented in this paper has been implemented for bending angl e measurements derived from GPS/MET radio occultation observations of the E arth. Preliminary results from simulated data suggest that these observatio ns have the potential to improve numerical weather prediction model analyse s significantly throughout their vertical range.