Inversion of COSMIC atmospheric open-loop radio occultation data

The GPS open-loop receiver has been used in COSMIC GPS radio occultation to improve the data quality of the troposphere occultation and the ability of tracking the rising occultation events. The open-loop data are affected by the navigation data modulations. This effect must be removed in the post-data processing to get the high quality scientific inversion results. Two methods for removing the effect, one using the external navigation data modulation bit information and the other method using the internal relationship of the atmospheric excess phase data between adjacent epochs, were investigated. For a case study, the above methods were applied in the data processing of one COSMIC radio occultation event's atmospheric excess phase data to remove the navigation data modulation effect and to output the corrected atmospheric excess phase data. By using the corrected atmospheric excess phase data, the ray bending angles were estimated with the geometric optics approximation method and the full spectrum inversion method. The estimated bending angles with the full spectrum inversion method and the corresponding retrieved temperatures agree excellently with those provided by the COSMIC data center. The agreement suggests that our algorithms for open-loop data processing work efficiently.