Investigation into the atmospheric parameters retrieved from ROPP and CDAAC using GPS radio occultation measurements over the Australian area

GPS Radio Occultation (RO) is a space-based technique for sounding the Earth's atmosphere. This technique has demonstrated great potential for improving numerical weather prediction and climate monitoring. This investigation utilises FORMOSAT-3/COSMIC RO data to identify the differences between the results obtained using two different data processing packages - the Radio Occultation Processing Package (ROPP) and the COSMIC Data Analysis and Archive Center (CDAAC) software package. The introduced RO measurements for two software packages are all obtained from CDAAC dataset. This study analyses 20,210 events located in the Australian region in the year 2010. The results of this study show a negative bias between the two software packages in the bending angle at heights below approximately 5 km. The refractivity also shows a negative bias, which is consistent with previous results from the Global Navigation Satellite System Receiver for Atmospheric Sounding Satellite Application Facilities (GRAS SAF) report. A negative bias between the two processing software packages also appears for the pressure parameter at all heights and for dry temperatures from 5 to 16 km in height. The height intervals showing differences less than 1% in the bending angle, refractivity, pressure and dry temperatures are 0-25 km, 0-16 km, 0-16 km and 6-23 km, respectively. In general, the differences between the ROPP and CDAAC processing methods in the bending angle, refractivity, and pressure increase with altitude but are always less than 3%. The difference in dry temperature is also less than 3% at heights greater than 5 km, but it is larger at heights below 5 km.