Atmospheric Inversion Methods of GPS Radio Occultation
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Abstract:
GPS radio occultation is a new technique to explore the global atmosphere. Both the inversion methods of geometric optics and full spectrum inversion are described in detail. The geometric optics method is a classic inversion method used before. The full spectrum inversion can deal with the multi-path propagation problem frequently occurring in the lower atmosphere where the classic method usually becomes inefficient. A new inversion scheme that combines the geometric optics method and the full spectrum inversion method is proposed for atmospheric radio occultation inversion. It is applied to data processing with one GPS/MET radio occultation event data and one CHAMP event data, and successfully obtains atmospheric parameter profiles, which suggest the combined method is an efficient inversion scheme.Keywords:
Radio occultation
Occultation
Inverse transform sampling
Atmospheric refraction
Atmospheric models
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Radio occultation
Occultation
Atmospheric wave
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Abstract The Mars Express Radio Science (MaRS) experiment on board Mars Express has been providing radio‐occultation data since early 2004. The analysis method currently used to retrieve neutral atmosphere and ionosphere profiles is based on the resolution of a complex inverse problem. The solution to such a problem is obtained under strong assumptions on the atmosphere and the ionosphere and with some limitations. Here we developed a novel method for radio‐occultation data analysis based on a direct approach which overcomes some of the difficulties related to the standard inversion. This new method is based on a numerical model of the atmosphere and the ionosphere of Mars computing the propagation of the radio waves from the spacecraft to the receiver on Earth. The main interest of such an approach lies in the intrinsic and coherent coupling between the neutral part and the ionized part of the planetary environment, which gives physical constrains on the retrieved profiles. We have applied this new method to radio occultation experiments performed by MaRS, and we present the results obtained in two different occultation configurations. We discuss the differences which emerge from the standard analysis and the gain that such a method can give to the analysis of planetary environments.
Radio occultation
Occultation
Radio Science
Planetary science
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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.
Occultation
Radio occultation
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Radio occultation
Occultation
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Radio occultation
Occultation
Atmospheric Infrared Sounder
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The small/micro satellites equipped with spaceborne GPS receivers have been proved suitable platform for GPS radio occultation observation, as they can form a cheap network for global atmosphere observation. The quality of GPS radio occultation observation varies with the orbit chosen for the LEO satellite. As a result, the impact of the orbit on the observation quality should be studied. For this purpose, this paper develops an occultation events simulation system, in which positions of small/micro observation satellite and GPS satellites at different time are calculated by SGP4 model and SDP4 model, and then a Matlab program deals with these positions, judges the occurrence of occultation events, taking the field of view of the GPS antenna into account, calculates the longitude and latitude of the spot and also the duration of the occultation events, based on which distribution pictures can be drawn. With the system, two topics have been discussed: simulation for satellites with different orbit parameters, and the impact of each parameter on the number and distribution of occultation events. With these rules, the optimized orbits for global GPS radio occultation observation or observation of a certain region can be designed.
Occultation
Radio occultation
Orbit (dynamics)
Longitude
Orbit Determination
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Abstract Mountain‐based GPS radio occultation observations were conducted at Yaogu mountain top and Jiugong mountain top in Hubei province respectively. Occultation events data were successfully obtained. Analysis and statistics of the occultation events have been completed. Principle and methods estimating bending angles of the radio rays and atmospheric refractivity profiles with the mountain‐based radio occultation data are given. The simulation data of mountain‐based occultation events are used for testing the inversion method. Testing results show the inversion method is efficient. The atmospheric refractivity profiles below the height of the GPS receiver are obtained with this inversion technique, as well as the bending angle of rays. Results suggest that the mountain‐based radio occultation technique is a potential new technique monitoring the lower atmospheric environments.
Radio occultation
Occultation
Inverse transform sampling
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Radio occultation
Occultation
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Mountain-based GPS radio occultation observations were conducted at the Yaogu mountain and Jiugong mountain in Hubei province, respectively. Occultation event data were successfully obtained. Analysis and statistics of the occultation events have been completed. The principle and methods estimating bending angles of the radio rays and atmospheric refractivity profiles with the mountain-based radio occultation data are given. The simulation data of mountain-based occultation events are used for testing the inversion method. Testing results show that the inversion method is efficient. The atmospheric refractivity profiles below the height of the GPS receiver are obtained with this inversion technique, as well as the bending angle of rays. The results suggest that the mountain-based occultation technique is a potential new method for monitoring lower atmospheric environments.
Radio occultation
Occultation
Inverse transform sampling
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In this paper, the mountain-based radio occultation is simulated using the 3D ray tracing technique. The starting time, the azimuth angle and the duration of the occultation events are obtained. The height and the excess phase variations of the occultation caused by water vapor and the temperature variety in the atmosphere boundary layer are studied in details. The influence of the geography on the height of the occultation is analyzed using data observed by CHAMP occultation, and it is very obvious. These results may be significant for explaining occulted processing, signal block and the height variation when the occulted signals' tangent height enters the atmospheric boundary layer.
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