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Using Data Assimilation to Reconstruct High‐Latitude Polar Cap Patches

Thu, 06/04/2020 - 19:00
Abstract

Discrete high‐density plasma structures in the Earth's ionosphere that convect across the polar cap from the dayside to nightside are known as polar cap patches. This high‐latitude phenomenon can interfere and disrupt satellite and high‐frequency (HF) communications when the associated sharp electron density gradients are encountered, and therefore, accurate modeling and forecasting of such events would be greatly beneficial. In this study, we have utilized the assimilative Global Positioning System Ionospheric Inversion (GPSII) method to reconstruct the high‐latitude ionosphere utilizing data from Global Navigation Satellite System (GNSS) receivers, vertical ionosondes, the Resolute Bay Incoherent Scatter Radar (RISR‐N), in situ satellite data, and Super Dual Auroral Radar Network (SuperDARN) radars. The novel method of assimilating RISR‐N and SuperDARN ground scatter measurements helps to increase the limited number of observations at high latitudes. The reconstructed polar cap patches are shown to correspond with ground‐ and spaced‐based observations, illustrating the ability of utilizing GPSII to study the complex high‐latitude region.

FFT Based Multiband Spectrum Sensing in SIMO In‐band Full‐Duplex Cognitive Radio Networks

Mon, 06/01/2020 - 16:05
Abstract

This paper presents fast Fourier transform (FFT) based multiband spectrum sensing over multipath Rayleigh frequency selective fading channels in single input multiple output (SIMO) in‐band full‐duplex (FD) cognitive radio (CR) networks (FDCRNs) under residual self interference (RSI). In this work, first multiband energy detection using Neyman Pearson criterion is proposed in FDCRNs under RSI, where the secondary user is equipped with multiple receive antennas to exploit spatial diversity. Next, a two dimensional averaging is done to overcome spectrum leakage problem occurring due to FFT operation in OFDM system. The closed form expressions for average probability of detection and probability of false alarm are derived for SIMO FDCRNs under RSI. Further, RSI cancellation is performed employing noise robust wavelet decomposition based least square scheme and the corresponding simulation studies indicate that the proposed algorithm further improves the detection performance in SIMO FDCRNs.

Multi‐dimensional Channel Characteristics Analysis in High‐Speed Train Scenarios

Thu, 05/28/2020 - 17:36
abstract

LTE for Railways (LTE‐R) is a next‐gen communication network dedicated to railway services, enabling high‐speed, reliable and intelligent communications to ensure safety and efficiency for rail passengers. The wireless channel between the train and the ground is a key challenge in network design and optimization. The high‐speed train (HST) and its surrounding scenarios bring non‐stationarity and unique radio propagation characteristics to the HST channel. A comprehensive and in‐depth analysis of channel characteristics is the basis of channel modeling. In this paper, based on the measurement‐validation ray‐tracing (RT) simulator, the quasi‐stationary intervals are presented first to reasonably quantify channel statistical parameters. Next, the time‐varying multi‐dimensional spectra of the channels in three typical HST scenarios are shown, including the power delay profile (PDP), the arrival/departure angular spectrum, and the Doppler spectrum. Moreover, the corresponding channel characteristic parameters are extracted, such as the root‐mean‐square (RMS) delay spread, angular spread, and Doppler spread. Based on multi‐dimensional channel characteristic analysis, combined with multi‐path geometric parameters provided by RT, we extract significant scatterers, and mine key physical factors that affect radio propagation in HST scenarios. This work lays a solid foundation for accurate time‐varying HST channel modeling.

Experimental Studies on Energy and Eigenvalue based Spectrum Sensing Algorithms using USRP Devices in OFDM Systems

Thu, 05/28/2020 - 17:31
abstract

In this paper, first, energy detection (ED) based spectrum sensing using NI USRP 2942R software defined radio platform has been implemented. It is observed that in practical scenario ED scheme gives poor performance at low gain (G) values. To overcome the shortcomings of energy detection, we propose eigenvalue based detection of the primary user (PU) signal, where, the ratio of the maximum eigenvalue to the average eigenvalue is used to detect the PU signal in both the single and multiple antenna systems/SISO and MIMO based CR user. The analytical expression of the performance metric (probability of detection (P d )) has been derived. Further, the experimental studies show that proposed technique gives optimum (P d ) in both SISO and MIMO case. It has been observed that the proposed technique outperforms the ED based detection even if the Tx‐Rx separation increases.

Gaussian Process Regression for Estimating EM Ducting Within the Marine Atmospheric Boundary Layer

Thu, 05/28/2020 - 16:19
Abstract

We show that Gaussian process regression (GPR) can be used to infer the electromagnetic (EM) duct height within the marine atmospheric boundary layer (MABL) from sparsely sampled propagation factors within the context of bistatic radars. We use GPR to calculate the posterior predictive distribution on the labels (i.e . duct height) from both noise‐free and noise‐contaminated array of propagation factors. For duct height inference from noise‐contaminated propagation factors, we compare a naïve approach, utilizing one random sample from the input distribution (i.e . disregarding the input noise), with an inverse‐variance weighted approach, utilizing a few random samples to estimate the true predictive distribution. The resulting posterior predictive distributions from these two approaches are compared to a “ground truth” distribution, which is approximated using a large number of Monte‐Carlo samples. The ability of GPR to yield accurate and fast duct height predictions using a few training examples indicates the suitability of the proposed method for real‐time applications.

Evaluation of EAR Spaced‐Antenna Performance Using Multiple Receiving Antennas Orientations

Thu, 05/28/2020 - 16:10
abstract

Equatorial Atmosphere Radar (EAR) is a very high frequency (VHF) Doppler radar with an active phased‐array antenna system operating at 47 MHz. It had originally been equipped with a single receiving channel system since its establishment in 2001 at the equator in Kototabang, West Sumatra, Indonesia (0.20°S, 100.32°E). Recent progress has enabled the implementation of a spaced‐antenna (SA) method on the EAR through the development of a multichannel receiver using universal software radio peripheral (USRP) and GNU Radio. However, this approach exhibits limited height observation and horizontal wind estimation accuracy. Here, we present comparison and analysis of EAR SA performance with five different orientations, taking into consideration the size of the receiving antennas and their separation distance. Experiments with the chosen configurations were carried out between April 2019 and September 2019, and the horizontal wind profiles were estimated using Full Correlation Analysis (FCA) and compared with the EAR standard data. In addition, FCA with the least squares method is carried out for all configurations with the aim of improving the estimation accuracy. Based on the results, the configuration with the largest aperture shows a clear advantage over the other four configurations but with limited improvement in terms of maximum observable height.

Issue Information

Tue, 05/26/2020 - 19:00

No abstract is available for this article.

A Numerical Model of CPR of Rough Surface With Discrete Scatterers for Analysis of Mini‐RF Data

Fri, 05/22/2020 - 19:00
Abstract

Circular polarization ratio (CPR) was regarded as an important index for detecting water ice in the permanently shaded region (PSR) of the Moon poles. However, many studies have intuitively described that the double‐bounce scatte ring caused by dihedral consisting of rock facets and the lunar rough surface may yield high CPR. Under a large local incidence angle, single scattering is reduced. Double‐bounce scattering of the dihedral governs the echoes and leads to an enhanced CPR. In this paper, a numerical model of the lunar rough surface with discrete scatterers, for example, rock bodies, is developed. The bidirectional analytic ray tracing (BART) method is applied to numerically solve high‐order scattering of this surface/rocks model. The lunar surface is modeled by the Digital Elevation Model (DEM) data from Lunar Reconnaissance Orbiter (LRO) Lunar Orbiter Laser Altimeter (LOLA). This paper quantitatively analyzes how the surface topography, rocks, radar local incidence, etc, affect the CPR. It is found that at a small local incident angle, the single scattering is usually dominant and results in a small CPR. When the local incident angle becomes large, the radar wave reflected in the specular direction is more likely to be reflected again and increases the CPR.

Comparison of Surface Radio Refractivity Variability in the Northern and Southern of Quebec, Canada

Wed, 05/20/2020 - 13:51
Abstract

A 39 years of archived meteorological data measured at two stations located in the northern and southern parts of the Quebec, Canada is used to estimating the surface refractivity and its dry and wet components. The results of the comparison of the obtained estimates showed that for all months the values of the dry component are higher in the northern part, whereas that the values of the wet component are higher in the southern part. Due to this, for several months of the year, the values of the surface refractivity are higher in the northern part and for the remaining months in the southern part. Moreover, in both parts, August is the month where the highest values of the surface refractivity were recorded. In this particular month, the slope of the surface refractivity trend in the northern is several times higher than that in the southern part. The obtained results show that the performance of the used direct smoothing forecasting technique depends on the deviation between the values of N of the current year and the previous year.

Estimation of turbulence parameters using ARIES ST Radar and GPS radiosonde measurements: First results from the Central Himalayan region

Wed, 05/20/2020 - 13:49
Abstract

Turbulence in the atmosphere plays vital role in controlling the surface, lower and upper tropospheric dynamics. Here, we have utilized a newly installed ARIES ST Radar at the high altitude subtropical site in the central Himalayan region (Nainital, 29.4oN, 79.5oE, 1793m amsl) for the first ever estimation of turbulence parameters from this unique location. We have used radar observations made in years 2017 and 2019 with simultaneous and co‐located GPS radiosonde observations. In this context, turbulence parameters like turbulent kinetic energy dissipation rate, and eddy diffusion coefficient due to thermal, and momentum fluctuations, have been determined by using (i) wind variance, (ii) Doppler spectral width and (iii) backscatter signal power methods as well as synergistic radiosonde measurements using Thorpe length scale method. The kinetic energy dissipation rate and eddy diffusivity coefficients was found to be as high as 10‐2 m2 s‐3 and 102.6 m2 s‐1 respectively. Statistical distribution of turbulence parameters derived from radar and radiosonde were found to agree reasonably well in terms of measures of central tendency. The refractive index structure constant (Cn 2) shows a decreasing tendency with height and it is found to vary as large as 10‐14 to as small as 10‐19 m‐2/3. Range and temporal variation of SNR indicated the existence of a stable layer around 8 km height. It is also evident from the present study that the turbulence parameters at this central Himalayan region of complex terrain are higher by one order of magnitude than those reported from the southern part of India.

UHF Propagation Through a Trunk Dominated Forest

Wed, 05/20/2020 - 13:49
Abstract

Transport theory is used to calculate the intensity of a wave propagating though a trunk dominated forest. The trunks are replaced by parallel infinitely long dielectric cylinders and a vertically polarized plane wave is normally incident on the layer of these randomly distribution parallel cylinders. The problem can be reduced to a two dimensional transport problem that can be solved by the eigenvalue technique for the coherent, incoherent and total intensity of the propagating wave. Using the assumption that the distribution of trunks is sparse and that the trunks locations are independent from one another, the probability density function (pdf) of the total and incoherent intensity as a function of depth into the layer can be found. To verify these results, a Monte‐Carlo (MC) simulation is performed in the low frequency limit which takes the effect of multiple scattering into account. The results show that there is a very close correspondence between the transport and MC simulation findings; the coherent, incoherent and the total intensity for these two methods agree very closely as a function of distance into the slab. In addition, the pdf’s for these three quantities also agree with the MC based histograms. One sees that as the wave propagates into the layer, the Rician distribution for the magnitude tends to a Rayleigh pdf as the coherent wave decays.

Long‐term observations of stratosphere‐troposphere exchange using MST Radar and Aura MLS measurements over a tropical station Gadanki

Wed, 05/20/2020 - 08:51
Abstract

This paper presents the climatology of stratospheric intrusion into the troposphere during the Indian Summer Monsoon (ISM) observed using the mesosphere‐stratosphere‐troposphere (MST) radar located at Gadanki (13.5oN, 79.2oE). The most significant and new observation is the presence of enhanced signal‐to‐noise ratio (SNR) of 3 dB and half‐power full spectral width of > 0.2 ms‐1 in the vicinity of tropopause during the ISM. Downdrafts (updrafts) are dominated in the vicinity of tropopause from April to June (July to March). The result of stratospheric air intrusion is also supported with ten years of ozone measurements obtained from Aura‐MLS and five years of in situ ozonesonde observations. Detailed analysis shows that the horizontal advection along with turbulence in the vicinity of tropopause caused by the tropical easterly jet and tropopause altitude variability are the prime candidates for stratosphere to troposphere transport of ozone. In contrast, the tropical tropopause temperature plays a significant role in the troposphere to stratosphere transport of water vapour during the ISM. The significance of the present study is to qualitatively constitute the climatology of these exchange processes over Gadanki using Indian MST radar.

An Eigenmode Correlation‐Based Algorithm for Approaching Antenna Optimal Currents With Multiple Feeds

Sat, 05/16/2020 - 19:00
Abstract

A feeding algorithm has been proposed for the excitation of the optimal electric current of Rayleigh quotient form optimization problems. Modal weighting coefficients of the corresponding generalized eigenvalue problem are calculated to form the correlation information between the desired and all other unwanted modes. Based on this information, multiple feeds are arranged to approximate the desired current distributions. The eigencurrent distribution is also utilized for some shape modification to the radiator for a possible feed number reduction. Three canonical optimization problems for electrically small antennas, minimum Q , maximum G /Q , and maximum G are studied and discussed. Several numerical examples with a certain arbitrary shape and electrical size are given. With the proposed feeding algorithm, calculated and simulated current distributions and performance indices are close to the theoretical optimum solution. Finally, a practical feeding network design for a classic characteristic mode problem is shown as a validation.

A New Method for Analyzing the Attenuation Characteristics of Satellite Radar Altimeter Signals Due to Rainfall Based on a Multilayer Medium Model

Tue, 05/12/2020 - 19:00
Abstract

Rainfall has an attenuation of backscatter coefficient of the sea surface and a change in the sea surface roughness, and these effects give rise to some errors in retrieving the sea surface wind speed, the significant wave height, and wave slope. It is meaningful to make considerable efforts to study the attenuation of radio waves caused by rainfall. In this article, a new model of analyzing the attenuation characteristics of satellite radar altimeter pulse signals because of rainfall is presented. First, the model of the equivalent permittivity of rainfall is calculated and presented. The imaginary part of the equivalent permittivity is studied when radio frequency and rainfall rate vary, respectively. Second, a new theoretical model and method of analyzing the effect of rainfall on satellite radar altimeter pulses is presented based on a multilayer‐medium model with the equivalent permittivity of rainfall. On the other hand, some existing models of computing rainfall attenuation characteristics of radar signals are studied and improved to some extent. Finally, some attenuation characteristics of radar signals due to rainfall are calculated by those models. The calculated results show that the attenuation characteristics of radar altimeter pulse signals are all in good agreement with those by other models. The results computed by the multilayer‐medium model can provide a good theoretical explanation and understanding for these attenuation characteristics of radar pulse signals and can also give some data support and corrections for the measured oceanic parameters by the satellite radar altimeter.

Thank You to Our 2019 Reviewers

Wed, 05/06/2020 - 19:00
Radio Science, Volume 55, Issue 5, May 2020.

Evaluation of Spatio‐Temporal Characteristics of Different Zenith Tropospheric Delay Models in Antarctica

Fri, 05/01/2020 - 19:00
Abstract

Zenith tropospheric delay (ZTD) is one of the main error sources in space geodetic techniques, such as Global Positioning System (GPS) and satellite altimetry. To qualitatively and quantitatively determine the most suitable model for Antarctica, we analyze the accuracy and applicability of nine models (UNB3m, EGNOS, GPT2 + Saastamoinen, GPT2w + Saastamoinen, GPT3 + Saastamoinen, GPT2 + Hopfield, GPT2w + Hopfield, GPT3 + Hopfield, and IGGtropSH) in Antarctica using 8 years of GPS‐derived ZTD time series from 65 stations. The results show that the GPT2/2w/3 + SAAS models are better than the other six models, with a bias of 0.2, −0.22, and −0.29 cm and root mean square (RMS) of 2.33, 2.31, and 2.36 cm. Based on the decimeter bias and RMS, the UNB3m model and EGNOS model present the worst performance in Antarctica. There are regional characteristics of bias and RMS in the nine models. The GPT2/2w/3 + SAAS models have the smallest regional deviation, and the bias and RMS between subregions (Antarctic Peninsula, Amundsen Sea Embayment, Ross Ice Shelf, Inland area of West Antarctica, Filchner‐Ronne Ice Shelf, and coastal East Antarctica) are all at the 0.2 and 0.7 cm levels, respectively. The GPT2/2w/3 + HOP models have the largest regional deviation, with regional bias and RMS at the levels of 8 and 6 cm, respectively. Our results suggest that the uncertainty of ice sheet elevation derived from satellite altimetry may be partly caused by the spatial‐related bias and error in the ZTD corrections. The bias and RMS of six GPT combined models and the IGGtropSH model present limited seasonal changes, indicating that these models can simulate the seasonal characteristics of ZTD better. The time series of the bias and RMS values of the EGNOS and UNB3m models show obvious seasonal characteristics, which may contaminate the annual ice sheet elevation by approximately 5 cm if used as ZTD corrections.

Evaluation of Spatio‐Temporal Characteristics of Different Zenith Tropospheric Delay Models in Antarctica

Fri, 05/01/2020 - 18:12
Abstract

Zenith tropospheric delay (ZTD) is one of the main error sources in space geodetic techniques, such as Global Positioning System (GPS) and satellite altimetry. To qualitatively and quantitatively determine the most suitable model for Antarctica, we analyze the accuracy and applicability of nine models (UNB3m, EGNOS, GPT2 + Saastamoinen, GPT2w + Saastamoinen, GPT3 + Saastamoinen, GPT2 + Hopfield, GPT2w + Hopfield, GPT3 + Hopfield, and IGGtropSH) in Antarctica using 8 years of GPS‐derived ZTD time series from 65 stations. The results show that the GPT2/2w/3 + SAAS models are better than the other six models, with a bias of 0.2, −0.22, and −0.29 cm and root mean square (RMS) of 2.33, 2.31, and 2.36 cm. Based on the decimeter bias and RMS, the UNB3m model and EGNOS model present the worst performance in Antarctica. There are regional characteristics of bias and RMS in the nine models. The GPT2/2w/3 + SAAS models have the smallest regional deviation, and the bias and RMS between subregions (Antarctic Peninsula, Amundsen Sea Embayment, Ross Ice Shelf, Inland area of West Antarctica, Filchner‐Ronne Ice Shelf, and coastal East Antarctica) are all at the 0.2 and 0.7 cm levels, respectively. The GPT2/2w/3 + HOP models have the largest regional deviation, with regional bias and RMS at the levels of 8 and 6 cm, respectively. Our results suggest that the uncertainty of ice sheet elevation derived from satellite altimetry may be partly caused by the spatial‐related bias and error in the ZTD corrections. The bias and RMS of six GPT combined models and the IGGtropSH model present limited seasonal changes, indicating that these models can simulate the seasonal characteristics of ZTD better. The time series of the bias and RMS values of the EGNOS and UNB3m models show obvious seasonal characteristics, which may contaminate the annual ice sheet elevation by approximately 5 cm if used as ZTD corrections.

Long‐Range Longitudinal Electric Wave in Vacuum Radiated by Electric Dipole: Part I

Tue, 04/28/2020 - 19:00
Abstract

In this work, by using the assumptions that wavelength is much smaller than charge separation distance of an electric dipole, which in turn is much smaller than a distance up to the point of observation, the new results for radiation of an electric dipole were obtained. These results generalize and extend the standard classical solution, and they indicate that under the above assumptions, the electric dipole emits both long‐range longitudinal electric and transverse electromagnetic waves. For a specific values of the dipole system parameters, the longitudinal and transverse electric fields are displayed. Total power emitted by electric and electromagnetic waves are calculated and compared. It was shown that under the standard assumption of charge separation distance being much smaller than wavelength, (a) classical solution correctly describes the transverse electromagnetic waves only; (b) longitudinal electric waves are nonnegligible; (c) total radiated power is proportional to the fourth degree of frequency and to the second degree of the charge separation distance; and (d) transverse component of our solution reduces to classical solution. In case wavelength is much smaller than charge separation distance, (a) the classical solution is not valid, and it overestimates the total radiated power; (b) longitudinal electric waves are dominant and transverse electromagnetic waves are negligible; (c) total radiated power is proportional to the third degree of frequency and to the charge separation distance; and (d) most of the power is emitted in a narrow beam along the dipole axis; thus, emission of waves is focused as with lasers.

Long‐Range Longitudinal Electric Wave in Vacuum Radiated by Electric Dipole: Part I

Tue, 04/28/2020 - 19:00
Abstract

In this work, by using the assumptions that wavelength is much smaller than charge separation distance of an electric dipole, which in turn is much smaller than a distance up to the point of observation, the new results for radiation of an electric dipole were obtained. These results generalize and extend the standard classical solution, and they indicate that under the above assumptions, the electric dipole emits both long‐range longitudinal electric and transverse electromagnetic waves. For a specific values of the dipole system parameters, the longitudinal and transverse electric fields are displayed. Total power emitted by electric and electromagnetic waves are calculated and compared. It was shown that under the standard assumption of charge separation distance being much smaller than wavelength, (a) classical solution correctly describes the transverse electromagnetic waves only; (b) longitudinal electric waves are nonnegligible; (c) total radiated power is proportional to the fourth degree of frequency and to the second degree of the charge separation distance; and (d) transverse component of our solution reduces to classical solution. In case wavelength is much smaller than charge separation distance, (a) the classical solution is not valid, and it overestimates the total radiated power; (b) longitudinal electric waves are dominant and transverse electromagnetic waves are negligible; (c) total radiated power is proportional to the third degree of frequency and to the charge separation distance; and (d) most of the power is emitted in a narrow beam along the dipole axis; thus, emission of waves is focused as with lasers.

Comment on “Additional Boundary Condition for Electric Quadrupolar Continua Derived from Maxwell's Differential Equations” by A.D. Yaghjian and M.G. Silveirinha

Fri, 04/17/2020 - 10:18
Abstract

The accuracy of the fundamental electric quadrupolar constitutive relation used in the paper by Yaghjian and Silveirinha (2016, https://doi.org/10.1002/2016RS006066) is determined and used to improve upon the derivation of one of the boundary conditions for electric quadrupolar media. In addition, three typographical errors in the aforementioned paper are noted.

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