Improvements in Geodetic Surveying Using GNSS Radio Occultation Observations

Abstract

The coordinates of a static Global Navigation Satellite System (GNSS) station placed on the ground are estimated together with the delay suffered by the incoming satellite signals through the atmosphere. The tropospheric delay (TD) is shaped as the product of the zenith total delay (ZTD) times a slant factor or mapping function (MF) depending on the sine of elevation angles. In processing chain ZTD is just estimated together with the coordinates; while the MF is modeled apart, in an independent way, by using atmospheric profiles retrieved with balloon observations (RAOB) as done for the Niell (1996) or provided by climate or Numerical Weather Prediction (NWP) models as in the Vienna MFs. The several space missions devoted to GNSS-RO (e.g. COSMIC-FORMOSAT, METOP, CHAMP, GRACE end others) are providing a huge amount of data which makes worthwhile to be attempted the reconstruction of a new mapping function (MTMF) based on such kind of data. First results have been achieved merging GNSS-RO data with model. The merging is made necessary because often the GNSS-RO profiles don’t reach the ground. The validation activity however has pointed out not meaningful improvements. Thus we have changed algorithms just to minimize the impact of external data provided by the model. We have performed of course comparisons and validation activities as already done, working with data of GNSS stations spread in the Mediterranean area. In particular formal errors and repeatability of ZTD, coordinates and baselines estimated with the MTMF will be compared with those achieved applying the Niell mapping function. In validation activities we have implemented new MTMFs in bernese software.