Using GPS Radio Occultation in Producing of the Atmospheric Profiles

One of the most recent and promising atmospheric remote sensing technique is the GPS Radio Occultation(GPS RO). Its importance has been increasing the last decade, since the first related mission (the GPS/MET) highlighted its possibilities. The GPS RO technique is based on the inversion of excess-phase measurements related to the signal transmitted by a GPS satellite and detected by a GPS receiver placed on low earth orbit(LEO). In this study, based on the occultation theory, produced the refractivity, pressure and temperature profiles from the earth surface to above 50 Km. The results showed a good agreement between produced parameters and corresponding in radiosonde and global models such as the ECMWF and NCEP. The low accuracy of retrieved temperature profiles in the lower troposphere is one of the weaknesses of this technique. We proposed a new method to improve the accuracy of temperature profiles in these regions. Surface temperature (from the Europian Center for Medium range Weather Forecasting (ECMWF)) with the temperature generated above lower troposphere are combined in a linear model and the solution is obtained through a least squares method in this range of altitudes. Also 81 temperature profiles that produced in different latitudes and seasons were compared with Radiosondes, Constellation Observing System for Meteorology, Ionosphere and Climate(COSMIC) RO profiles, ECMWF and National Centers for Environmental Prediction(NCEP) global models. Obtained results show the accuracy of modified temperature profiles is 1 Kelvin below 7 Km altitude which is much better than that of COSMIC RO profiles. While the temperatures generated by the COSMIC mission in these areas are erroneous up to 6 K. Additionally, the accuracy of the obtained profiles is the same as that of COSMIC profiles above 7 Km. Both of them are precise to 0.5 K in 7-17 Km and at altitudes above 17 Km approaches 0.7 K.