Inversion for atmosphere duct parameters using real radar sea clutter

This paper addresses the problem of estimating the lower atmospheric refractivity （M profile） under nonstandard propagation conditions frequently encountered in low altitude maritime radar applications. The vertical structure of the refractive environment is modeled using five parameters and the horizontal structure is modeled using five parameters. The refractivity model is implemented with and without a priori constraint on the duct strength as might be derived from soundings or numerical weather-prediction models. An electromagnetic propagation model maps the refractivity structure into a replica field. Replica fields are compared with the observed clutter using a squared-error objective function. A global search for the 10 environmental parameters is performed using genetic algorithms. The inversion algorithm is implemented on the basis of S-band radar sea-clutter data from Wallops Island, Virginia （SPANDAR）. Reference data are from range-dependent refractivity profiles obtained with a helicopter. The inversion is assessed （i） by comparing the propagation predicted from the radar-inferred refractivity profiles with that from the helicopter profiles, （ii） by comparing the refractivity parameters from the helicopter soundings with those estimated. This technique could provide near-real-time estimation of ducting effects.

Observed characteristics of atmospheric ducts over the South China Sea in autumn

The observed characteristics of lower atmospheric ducts over the South China Sea(SCS) were analyzed based on Global Position Systerm(GPS) radiosonde data collected four times daily during autumn open cruises from 2006 to 2012.Duct occurrence,thickness,and strength over the SCS were about 40%,150-m thick,and 8 M units,respectively,which were larger than during the summer monsoon period.Most ducts occurred at heights <1 500 m and these ducts easily trap electromagnetic wave clusters with wavelengths <2 m.Diurnal variation of the SCS ducts appeared evident.They occurred more often at midnight at higher altitudes(about 1 100 m),with a thickest layer of about 145 m and less frequently during the evening at lower altitudes(about 800 m),with a thinnest layer of about 125 m.Moreover,ducts during the daytime at a mean height of about 900 m,with the greatest strength of about 10 M units.Furthermore,all duct variables observed over the SCS in autumn decreased from north to south.These findings are useful not only in the design of radar and communication systems,but also for evaluating possible effects of anomalous propagation on meteorological radar and military applications.

Estimation of co-channel interference between cities caused by ducting and turbulence

With the rapid development of the fifth-generation(5 G)mobile communication technology,the application of each frequency band has reached the extreme,causing mutual interference between different modules.Hence,there is a requirement for detecting filtering and preventing interference.In the troposphere,over-the-horizon propagation occurs in atmospheric ducts and turbulent media.The effects of both ducting and turbulence can increase the probability of occurrence of long-distance co-channel interference(CCI),in turn,severely affecting the key performance indicators such as system access,handover and drop.In the 5 G era,to ensure communication channels and information security,CCI must be reduced.This paper introduces a scattering parabolic equation algorithm for calculating signal propagation in atmospheric ducts on irregular terrain boundaries.It combines Hitney’s radio physical optical model and Wagner’s nonuniform turbulent scattering model for calculating the tropospheric scattering in an evaporation duct or a surface-based duct.The new model proposes a tropospheric scattering parabolic equation algorithm for various tropospheric duct environments.Finally,as a specific case,the topographical boundaries between several cities in the East China Plain were considered,and the over-the-horizon propagation loss was simulated for various ducting and turbulent environments.The simulation results were used to evaluate whether CCI would occur between cities in a specific environment.

Refractivity estimation from radar sea clutter

This paper addresses the problem of estimating lower atmospheric refractivity under the nonstandard propagation conditions frequently encountered in low altitude maritime radar applications. The vertical structure of the refractive environment is modeled by using a five-parameter model, and the horizontal structure is modeled as range-independent. The electromagnetic propagation in the troposphere is simulated by using a split-step fast Fourier transform based on parabolic approximation to the wave equation. A global search marked as a modified genetic algorithm （MGA） for the 5 environmental parameters is performed by using a genetic algorithm （GA） integrated with a simulated annealing technique. The retrieved results from simulated runs demonstrate the ability of this method to make atmospheric refractivity estimations. A comparison with the classical GA and the Bayesian Markov Chain Monte Carlo （Bayesian- MCMC） technique shows that the MGA can not only shorten the inverse time but also improve the inverse precision. For real data cases, the inversion values do not match the reference data very well. The inverted profile, however, can be used to synoptically describe the real refractive structure.

Anomalous propagation conditions of electromagnetic wave observed over Bosten Lake, China in July and August, 2014

Atmospheric duct is a common phenomenon over large bodies of water, and it can significantly affect the performance of many radio systems. In this paper, a two-month（in July and August, 2014） sounding experiment in ducting conditions over Bosten Lake was carried out at a littoral station（41.89°N, 87.22°E） with high resolution GPS radiosondes, and atmospheric ducts were observed for the first time in this area. During the two months, surface and surface-based ducts occurred frequently over the Lake. Strong diurnal variations in ducting characteristics were noticed in clear days. Ducting occurrence was found at its lowest in the early morning and at its highest（nearly 100%） in the afternoon. Duct strength was found increasing from early morning to forenoon, and reaching its maximum in the afternoon. But contrarily, duct altitude experienced a decrease in a clear day. Then the meteorological reasons for the variations were discussed in detail, turbulent bursting was a possible reason for the duct formation in the early morning and the prevailing lake-breeze front was the main reason in the afternoon. The propagation of electromagnetic wave in a ducting environment was also investigated. A raytracing framework based on Runge–Kutta method was proposed to assess the performance of radio systems, and the precise critical angle and grazing angle derived from the ray-tracing equations were provided. Finally, numerical investigations on the radar performance in the observed ducting environments have been carried out with high accuracy, which demonstrated that atmospheric ducts had made great impacts on the performance of radio systems. The range/height errors for radar measurement induced by refraction have also been presented, too, which shows that the height errors were very large for trapped rays when the total range was long enough.

A New Evaporation Duct Climatology over the South China Sea

The climatology of evaporation ducts is important for shipborne electromagnetic system design and application. The evaporation duct climatology that is currently used for such applications was developed in the mid 1980s; this study presents efforts to improve it over the South China Sea （SCS） by using a state- of-the-art evaporation duct model and an improved meteorology dataset. This new climatology provides better evaporation duct height （EDH） data over the SCS, at a higher resolution of 0.312°×0.313°. A comparison between the new climatology and the old one is performed. The monthly average EDH in the new climatology is between 10 and 12 m over the SCS, higher than that in the old climatology. The spatiotemporal characteristics of the evaporation duct over the SCS in different months are analyzed in detail, based on the new climatology.

Numerical Study on the Impacts of the Bogus Data Assimilation and Sea Spray Parameterization on Typhoon Ducts

The Weather Research and Forecasting model version 3.2 （WRF v3.2） was used with the bogus data assimilation （BDA） scheme and sea spray parameterization （SSP）, and experiments were conducted to assess the impacts of the BDA and SSP on prediction of the typhoon ducting process induced by Typhoon Mindule （2004）. The global positioning system （GPS） dropsonde observations were used for comparison, The results show that typhoon ducts are likely to form in every direction around the typhoon center, with the main type of ducts being elevated duct. With the BDA scheme included in the model initialization, the model has a better performance in predicting the existence, distribution, and strength of typhoon ducts. This improvement is attributed to the positive effect of the BDA scheme on the typhoon＇s ambient boundary layer structure. Sea spray affects typhoon ducts mainly by changing the latent heat （LH） flux at the air-sea interface beyond 270 km from the typhoon center. The strength of the typhoon duct is enhanced when the boundary layer under this duct is cooled and moistened by the sea spray; otherwise, the typhoon duct is weakened. The sea spray induced changes in the air-sea sensible heat （SH） flux and LH flux are concentrated in the maximum wind speed area near the typhoon center, and the changes are significantly weakened with the increase of the radial range.

Maintenance and Sudden Change of a Strong Elevated Ducting Event Associated with High Pressure and Marine Low-Level Jet

Capture of a strong elevated ducting event,especially its maintenance and sudden change,is of great value to airborne radar to achieve its beyond-the-line-of-sight detection.However,the knowledge is not easily accessible over the open ocean and hence very rare.During the Air–Sea Interaction Survey(ASIS)over the western North Pacific(WNP)in May 2016,a strong elevated ducting event with a long-life period and sudden change in its evolution was observed.Measurements from the ASIS,images from the Himawari-8 satellite,reanalysis data from the ECMWF,and Weather Research and Forecasting(WRF)model,were used to analyze the maintenance and sudden change of this strong ducting event,together with the model performance on simulating it.The results showed that the maintenance of strong elevated ducts,with their tops ranging from 750 to 1050 m and average strength of approximately 38 M units,was caused by a strong dry air mass capping over the wet marine atmospheric boundary layer(MABL),together with the subsidence inversion associated with high pressure.The WRF model performs well in simulating them.However,a sudden increase in duct height with a slight decrease of strength was recorded by the subsequent GPS radiosonde,which was finally contributed to the mechanical turbulent inversion and hydrolapse associated with the marine low-level jet(MLLJ).The height of the maximum horizontal wind speed(Umh)of the MLLJ corresponds well with the bottom of the trapping layer.However,these jet-relevant ducts are generally weak and it is difficult to accurately simulate them by using the mesoscale numerical model,since the wind-shear produced eddies are too small to be properly parameterized.

ANALYSIS ON CHARACTERISTICS OF ATMOSPHERIC DUCT AND ITS EFFECTS ON THE PROPAGATION OF ELECTROMAGNETIC WAVE

On the basis of introducing the basic categories of atmospheric refraction and their existing conditions,the forming processes of three kinds of atmospheric ducts are expounded.Several main characteristics of atmospheric duct are summarized and analyzed,and field sounding data from the WEstern North-Pacific cloud-radiation EXperiment(WENPEX)and meteorological data around the Xisha sea area are used to validate these characteristics.Meanwhile the sensitivities of the evaporation duct height to the variations of atmospheric humidity.the air-sea temperature difference.and horizontal wind speed are examined.With the analysis of the effect of atmospheric duct on the propagation of electromagnetic wave.the maximum trapped-wavelength and the critical emitting angle of elevation for electromagnetic wave which can form duct propagation are derived. At the same time the four kinds of necessary conditions for electromagnetic wave to form duct propagation are brought forward.The effects of atmospheric duct on ultrashort wave propagation, radar observation.short wave communication etc.are also discussed.

Atmospheric Ducting Effect in Wireless Communications:Challenges and Opportunities

Atmospheric ducting has a significant impact on electromagnetic wave propagation.Radio signals that are trapped and guided by the atmospheric duct can travel a much longer distance over the horizon with lower attenuation since the signal power does not spread isotropically through the atmosphere.Atmospheric ducting brings both challenges and opportunities to wireless communications.On one hand,the signals propagating in the atmospheric duct may interfere with a receiver far away as remote co-channel interference.On the other hand,a point-to-point link can be established directly through the atmospheric duct to enable beyond line-of-sight communications.In this article,the formation of the atmospheric duct and its effects on radio wave propagation are first overviewed.Then solutions and standardization activities in the 3rd Generation Partnership Project(3GPP)to mitigate atmospheric duct induced remote interference are presented.Finally,the applications and design challenges of atmospheric duct enabled beyond line-of-sight communications are reviewed and future research directions are suggested.

Analysis and prediction of 100 km-scale atmo-spheric duct interference in TD-LTE networks

Atmospheric ducts are horizontal layers that occur under certain weather conditions in the lower atmosphere.Radio signals guided in atmospheric ducts tend to experience less attenuation and spread much farther,i.e,hundreds of kilometers.In a large-scale deployed TD-LTE(Time Division Long Term Evolution)network,atmospheric ducts cause faraway downlink wireless signals to propagate beyond the designed protection distance and interfere with local uplink signals,thus resulting in a large outage probability.In this paper,we analyze the characteristics of ADI atmospheric duct interference(Atmospheric Duct Interference)by the use of real network-side big data from the current operated TD-LTE network owned by China Mobile.The analysis results yield the time varying and directional characteristics of ADI.In addition,we proposed an SVM(Support Vector Machine)-classi er based spacial prediction method of ADI by machine learning over combination of real network-side big data and real meteorological data.Furthermore,an implementation of ADMM(Alternating Direction Methods of Multipliers)framework is proposed to implement a distributed SVM prediction scheme,which reduces data exchange among di erent regions/cities,maintains similar prediction accuracy and is thus of a more practical use to operators.