Chuan-Sheng Wang

ANALYTICAL MODEL OF ELECTROMAGNETIC WAVES PROPAGATION AND LOCATION OF INCLINED PLASMA LAYERS USING OCCULTATION DATA

An analytical model for the description of the electromag- netic waves propagation in a layered medium consisting of sectors hav- ing the locally spherical symmetric distributions of refractivity is in- troduced. Model presents analytical expressions for the phase path and refractive attenuation of electromagnetic waves. In∞uence of the inclined ionospheric layers is a cause of the ionospheric interference in the trans-ionospheric communication satellite-to-satellite or satellite- to-Earth links. It follows from the analytical model that the identiflca- tion of the inclined ionospheric layers contributions and measurements of their location and parameters may be fulfllled by use of compara- tive analysis of the amplitude variations and the eikonal acceleration

Precipitable Water Vapor Estimates in the Australian Region from Ground-Based GPS Observations

We present a comparison of atmospheric precipitable water vapor (PWV) derived from ground-based global positioning system (GPS) receiver with traditional radiosonde measurement and very long baseline interferometry (VLBI) technique for a five-year period (2008–2012) using Australian GPS stations. These stations were selectively chosen to provide a representative regional distribution of sites while ensuring conventional meteorological observations were available. Good agreement of PWV estimates was found between GPS and VLBI comparison with a mean difference of less than 1 mm and standard deviation of 3.5 mm and a mean difference and standard deviation of 0.1 mm and 4.0 mm, respectively, between GPS and radiosonde measurements. Systematic errors have also been discovered during the course of this study, which highlights the benefit of using GPS as a supplementary atmospheric PWV sensor and calibration system. The selected eight GPS sites sample different climates across Australia covering an area of approximately 30° NS/EW. It has also shown that the magnitude and variation of PWV estimates depend on the amount of moisture in the atmosphere, which is a function of season, topography, and other regional climate conditions.

A study on the relationship between ionospheric correction and data control for GPS radio occultation in Australia

GPS radio occultation, (RO) is an emerging and robust space-based earth observation system, with the potential for atmospheric profiling and meteorological applications. GPS RO requires GPS receivers onboard Low Earth Orbit (LEO) satellites to measure the radio signals from GPS satellites so that the atmospheric profiles of parameters such as temperature, pressure and water vapour can be obtained via a complicated atmospheric retrieval process. This research focuses on the ionospheric correction using the Radio Occultation Processing Package (ROPP) to investigate the effect from ionosphere for GPS radio occultation in the Australia region. The MSISE-90 model with the statistical optimization method produced the best results for altitudes greater than 40 km. The influence from the ionosphere can be removed using the generic Lc method which produced the best results for altitudes less than 40 km.

Comparing GPS Radio Occultation Observations with Radiosonde Measurements in the Australian Region

GPS Radio Occultation (RO) is a robust space-based Earth observation technique, with the demonstrated potential for atmospheric profiling and meteorological applications. The GPS RO technique uses GPS receivers onboard Low Earth Orbit (LEO) satellites to measure the received radio signals from GPS satellites to obtain atmospheric profiles such as temperature, pressure, water vapour and electron concentration in the ionosphere using complicated atmospheric retrieval processes. The Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) was launched in April 2006. GPS RO data from this constellation of six LEO micro-satellites provides an observational data type for operational meteorology, providing significant information on the thermodynamic state of the atmosphere with the potential to improve atmospheric analyses and prognoses. Thus it is important to know and understand how COSMIC RO measurements compare to conventional atmospheric and meteorological sounding devices. In this study the COSMIC GPS RO temperature and pressure profiles are compared to those measured from radiosondes (Vaisala RS-92) in the Australian region.

Simulating GPS Radio Occultation Using 3-D Ray Tracing

Numerical 3-D ray tracing techniques are commonly used for calculating the path of an electromagnetic signal in a medium specified by a refractive index that depends upon position. Numerical ray tracing is an important tool for applications of L-band frequency propagation such as GPS Radio Occultation (RO), where accurate and near real-time results are required. In this study, 3-D numerical ray tracing techniques are used to simulate GPS signals received by the Low Earth Orbit (LEO) satellites and to investigate their variability as a function of time and position due to the refractivity gradients in the ionosphere and the lower atmosphere. The GPS signal paths from the GPS to LEO satellites are simulated with an emphasis on the signal paths propagating through regions of the ionosphere where the refractive gradients are greatest. The effects of the Earth’s magnetic field on the L-band RO propagation paths are also investigated.