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Abstract
In this paper, the study of noise level and point- to - point stability of Global Positioning System radio occultation (RO) neutral atmospheric bending angle data at the UCAR COSMIC Data Analysis and Archive Center (CDAAC). The Global Positioning System (GPS) radio occultation (GPS-RO) technique is an active limb sounding observation of the Earth's atmosphere using a GPS receiver onboard a low Earth orbit (LEO) satellite. Since the observation data taken by such technique have high accuracy and excellent height resolution, they are very useful for analyzing atmospheric structures including small-scale vertical fluctuations in the troposphere and stratosphere. Vertical resolution of (GO )method in stratosphere is 1.7 km due to Fresnel radius limitations, but full spectrum inversion (FSI) can provide superior resolutions. The archived GPS-RO data have been calculated applying FSI to COSMIC GPS-RO profiles in an altitude from ground level up to 30 km. The height resolution of archived data is 0.1 km and we averaged the original RISHANA data (refractivity, pressure, temperature, and tangential point of latitude and longitude) in a bin of 0.05 km for nominal height.Atmospheric radio occultation relies on the detection of a change in a radio signal as it passes through a planet's atmosphere, i.e. as it is occulted by the atmosphere. When electromagnetic radiation crosses through the atmosphere, it is refracted . The magnitude of the refraction depends on the gradient of reflectivity normal to the path, which in turn depends on the density gradient. The effect is most marked when the radiation traverses a long atmospheric limb path. At radio frequencies the amount of bending cannot be measured directly; instead the bending can be calculated using the Doppler shift of the signal given the geometry of the emitter and receiver. The amount of curve can be related to the refractive index by using an Abel transform on the formula relating bending angle to refractivity. when the atmosphere is neutral (below the ionosphere) information on the atmosphere's temperature, pressure and water vapour content can be derived giving radio occultation data applications in meteorology. GNSS or GPS radio occultation (GNSS-RO, GPS-RO, GPSRO) is a type of radio occultation that relies on radio transmissions from GPS (Global Positioning System), or more generally from GNSS (Global Navigation Satellite System), satellites. This is a relatively new technique for performing atmospheric measurements. GNSS or GPS radio occultation as a weather forecasting tool, and could also be harnessed in monitoring climate change. The method involves a low-Earth orbit satellite receiving a signal from a GPS satellite. The signal has to pass through the atmosphere which has gases,dust and gets refracted along the way. The magnitude of the refraction depends on the temperature and water vapor concentration in the atmosphere when it observed.