Derivation of the water vapor content from the GNSS radio occultation observations

The present work investigates the possibility of retrieving humidity profiles using the bending angle data obtained from GNSS Radio Occultations (Global Navigation Satellite System RO) without data constraint. In particular with the proposed approach. the dry pressure profiles are obtained by fitting the bending angles of the outer troposphere layers (from h=h(250K) tip to the stratopause) using the Hopfield dry atmosphere model. In this model the ground pressure and temperature are the parameters to be estimated. The humidity profiles are extracted by subtracting the contribution due to the dry atmosphere from the measured bending angles. In the first part we discuss the mathematical approach adopted for the derivation of refractivity profiles without using the Abel inversion and water vapor directly from the bending angle. In the second part the results are shown from applying the method oil CHAMP data. In particular, we have used refractivity profiles front CHAMP which were derived using a heuristic retrieval algorithm based on the canonical transform.