Lin Leke

Tropospheric refractivity profiling based on single ground-based GPS

Based upon the zenith delay and slant-path delay of single ground-based GPS receivers, the retrieving methods are developed to obtain atmospheric refractivity profiles, which include the statistical method based on zenith wet delay, the method based on refractivity profile model, and the neural network method based on slant-path delay. Using historical radiosonde data by these methods, the atmospheric refractivity profiles are retrieved by simulating, which show that the methods in this paper can obtain better results than the general meteorological models.

A prediction model of rain attenuation along Earth-space path

Rain attenuation is the dominant propagation impairment for satellite communication systems operating at frequencies above about 10 GHz. Based on ITU-R model and experimental cumulative distribution functions of in the database of ITU-R study group 3, a modified method to predict the long-term statistics of the slant-path rain attenuation is proposed where the new rain height model, path adjustment factor and formula for estimating attenuation of other percentages of an average year are developed. Compared with ITU-R model, this model improves the accuracy of rain attenuation prediction.

Prediction models for rain effects on Earth-space links

Based on the experimental data of Eearth-space paths in the ITU-R and OPEX database and rain rate statistics data measured in China, the new models for rain and its effects on Earth-space links developed in CRIRP are introduced in this paper, including models to predict the long-term statistics of the slant-path rain attenuation and rain-induced XPD, and the conversion models for annual statistics to worst-month statistics of rainfall rates and for 1-minute rainfall rate statistics from 5 and 10-minute integration time data. Comparisons of the new models for rain attenuation and rain-induced XPD with current ITU-R models show that new models have better accuracies. In the meantime, the new models for rain rate statistics can be used in different rain zones with good accuracies. The new models presented in this paper can improve the prediction of propagation effects, which is essential for Earth-space system design.

A novel prediction model of rain attenuation along Earth-space path

Rain attenuation is the dominant propagation impairment for satellite communication systems operating at frequencies above about 10 GHz. In order to guarantee the service quality and reliability for the communication systems, a novel model is proposed to predict the rain attenuation statistics for an average year on Earth-space path. The model has been developed based on the EXCELL rain cell model and the experimental data in the rain attenuation database of ITU-R and ESA. A new rainfall rate adjustment factor is developed and the full rainfall rate probability distribution has been utilized, which is different from the conventional models. Compared with the ITU-R model, new model can provide a better fit to the experimental data and improves the accuracy of rain attenuation prediction.

Rain fade slope on 12.5GHz earth-space link at Qingdao

A statistical analysis is made from the measured distribution of fade slope of rain attenuation. The experiment has been performed in Qingdao, while the signal of the beacon is from the ChinaStar-1 satellite at the frequency of 12.5GHz. The distribution of conditional probability density of fade slope shows that the positive and negative slopes are distributed symmetrically. Based on the experimental data and the ITU-R model, an improved mode of the fade slope prediction is proposed The comparison with the ITU-R model shows that the improved model obtains better performance.

The difference in variation characteristics of the F2-peak height hmF2 at the low and middle latitudes

There is a continuing requirement for simple, but representative methods for determining the height of maximum electron concentration of the F2-layer (symbol hmF2), both for communication and navigation. The techniques for estimating the F2-peak height hmF2 from M(3000)F2 are reviewed with particular stress put upon those in which the effects of underlying ionization are accounted for by a correction to M(3000)F2, formulated in terms of the ratio f0F2 and f0E. Changes in the neutral atmosphere and in the hmF2 model have minor effects at low latitudes, where the fluxes are larger, but can appreciably alter the results at middle latitudes. At 21° latitude, neutral winds have a major effect on the distribution of ionization from the equatorial fountain. Thus, at the solstices the day-time flow is about 4 times larger in winter than summer. This paper reports on a comparison of the difference in variation characteristics of the observed monthly mean ionospheric F2-peak height hmF2 at Lanzhou (36.06°N latitude) and Haikou (20°N latitude) for both solar minimum (2005–2007) and solar maximum (2010–2011). The diurnal, seasonal, and solar variation of the hmF2 at the two sites compared with results of detailed calculations. Also, the contemporary practical implementations will be compared and contrasted in the light of this investigation and the scope for further refinements will be discussed.

Application perspective of Qujing incoherent scatter radar acting as a high power source at 500MHz

The Incoherent Scatter Radar is the most powerful tool to measure the ionosphere on the ground. Its high power output provides us a unique opportunity in some research fields more than the ionosphere sounding. The potential application perspective of the QJISR (25.6°N, 103.8°E), the first one in China, acting as the high power source is described including the bi- or multi-static receiving of signal scattered from the troposphere, ionosphere, space debris, meteoroid etc.

Retrieving the troposphere duct by using ground-based radiometric profiler in South Coast in China

Coastal areas worldwide are known to be especially ‘rich’ in super refractive layers and waveguides that affect microwave propagation. Radiosonde data of Xiamen and Haikou in south coast in China were chosen to analysis the rule and characteristics of the troposphere duct in this paper. Based on the historical data, improved learning vector quantization neural network method (LVQ) and improved Radial Basis Function neural network method (RBF) is used to retrieving the troposphere duct. The two algorithms are presented by using the brightness temperature detected by the ground-based multi-channel microwave radiometer both in zenith and gradient angles. Feasibility of this method is demonstrated with the results by the measure data. Ground-based multi-channel microwave radiometer has been proven to be a powerful tool to sensing troposphere duct, which can perform continuous troposphere duct profiles and provide information of electromagnetism environment for the application of radar, communication and navigation systems.

Diagnose the marine atmospheric duct using satellite remote sensing technique

Atmospheric duct can exert an important influence on radio wave propagation in the lower atmosphere, especially over oceanic or coastal locations. The refractivity profiles in duct are the requirement for input to the radio wave propagation model and predict the effects of radars. Considering the satellite sensing technique development, we pose a method to fuse the Satellite Electromagnetic Electro-Optical (SEMO) technique and evaporation model for the atmospheric duct diagnose and refractivity profiles determination.

THz atmospheric propagation measurement system of CRIRP

The trend of higher frequency band than microwave and millimeter wave used in various regions, ultrafast broadband communication and high accuracy imaging application, etc., calls for the development of the Terahertz (THz) technology. Unlike the hot concentration on the study of the THz sources and detectors, the study of the propagation characteristics of THz wave in the atmosphere is relatively rare. The measurements of atmospheric absorption are the most important research works in advance. CRIRP (China Research Institute of Radiowave Propagation) build an atmospheric propagation measurement system in the frequency band of 0.26–0.34THz. The system comprises of a transceiver front, a Quasi-Optical Circulator system and software for the signal receiving and data recording. The system will be operated in a long-term schedule for the analysis of the THz atmospheric propagation effects which can be concluded into two categories: the atmospheric effect including the absorption attenuation and scintillation caused by the atmospheric molecules and atmospheric turbulence along the path, and the effect caused by the small particles (rain, fog, aerosol, etc.) in atmosphere. The system has been set up between two buildings in CRIRP, Qingdao, China, and the signal will experience a 150m round trip which makes the path length become 300m. This is a THz system aims not only at the rain attenuation effects but also the general effect of the atmosphere and the particles in it. The investigation based on the system is the foundation of various future applications of THz wave in troposphere.