Comparison between mountain-based GPS occultation observations and results from automatic weather station

Mountain-based GPS occultation technique can measure the profile of the lower atmospheric refractivity exactly,its observation theory is to install the GPS receiver at the top of high mountain and receive the radio signals of GPS satellites with very low elevations and negative elevations,and we can obtain the profile of the bending angle due to atmospheric refraction through the change of carrier wave's phase,then the refractivity profile below the altitude in which the receiver is located can be retrieved by using some inversion method.An mountain-based GPS occultation observation experiment of one month was performed at Mt.WuLing(40.60°N,117.48°E,2118m) in HeBei province during August 1～29,2005.The JAVAD receiver we used has worked for about 576 hour,and the JAVAD receiver is installed towards south.Totally 1136 occultation events were recorded.Out of the total occultation events,621 events are rising occultation events and 515 events are setting occultation events.During the experiment,the automatic weather station at the top of Mt.WuLing can observe the local temperature,humidity and pressure all day,from which we can calculate the atmospheric refractivity.In this paper,we retrieved the atmospheric refractivity successfully using the observation data of mountain-based GPS occultation observation experiment at Mt.WuLing,and then compared the refractivity of the altitude in which the receiver is located with the result of automatic weather station.The result illustrates a good agreement in mountain-based GPS occultation and automatic weather station.Mountain-based occultation observations provide a lot of refractivity data for monitoring lower atmospheric environment.This novel technique has potential applications.