Inversing The Sea Surface Atmospheric Refractivity Profiles From GPS Signals

Atmospheric duct is an abnormal refraction mechanism in offshore atmospheric environment, which can capture VHF and microwave and influence its propagation, the blind area for radar and the over-horizontal propagation will happen. Thus, it is of great significance to predict the real-time environment refractivity parameters in the region the radar is operated. It has more advantages and more dazzle to inversing the atmospheric refraction index profile using the GPS's duct propagation, comparing with the traditional method of monitoring the atmospheric factors.In this paper, the formation, classification and the forest method of atmospheric duct are introduced firstly. The propagation characteristics of low-elevation Global Positioning System (GPS) signals under different troposphere environment are calculated using the parabolic equation method, and the impact of the height of evaporation duct on the propagation of low-elevation GPS signals. The results show that the propagation of GPS signals in atmospheric duct conditions is obviously different with that of standard atmosphere condition, and the propagation power is more. The propagation characteristics of GPS signals in condition of horizontal-inhomogeneous- evaporation-duct are studied, it is concluded that the propagation of GPS signals will be more complex due to the horizontal inhomogeneity of the evaporation duct. At last, the Particle swarm optimization is illustrated, according to the numeric inversion of evaporation duct profile and surface duct profile using GPS signals, it shows that the Particle swarm optimization is practical and the results converge more rapidly.