Based on the values of k and α given by ITU-R for the power-law relationship of specific rain attenuation γR=kRα, the analytic expressions for k and α are regressed as a function of frequency and are in high agreement with the values tabulated. The specific rain attenuation calculated by the analytic expressions are also in high agreement with those by the values of k and α tabulated. Comparisons with other analytic expressions show that the ones in this paper are more accuracy and simple.

Analytic Specific Attenuation Model for Rain for Use in Prediction Methods

In this article, we trace the significant milestones in the field of parabolic equation (PE) modeling, which is applied to tropospheric groundwave propagation, as well as the latest achievements in recent years. We divide these achievements into several independent topics: the PE framework, PE algorithms, PE boundary conditions, and some specific propagation modeling issues. By summarizing the research results for each module and outlining the unique functions of different solution methods, we can clearly and effectively grasp the development of PE modeling in tropospheric groundwave propagation, thus promoting further studies in this field.

Applying the Parabolic Equation to Tropospheric Groundwave Propagation: A review of recent achievements and significant milestones.

The evaporation duct which forms above the ocean surface has a significant influence on electromagnetic wave propagation above 2 GHz over the ocean. The effects of horizontal inhomogeneity of evaporation duct on electromagnetic wave propagation are investigated, both in numerical simulation and experimental observation methods, in this paper. Firstly, the features of the horizontal inhomogeneity of the evaporation duct are discussed. Then, two typical inhomogeneous cases are simulated and compared with the homogeneous case. The result shows that path loss is significantly higher than that in the homogeneous case when the evaporation duct height (EDH) at the receiver is lower than that at the transmitter. It is also concluded that the horizontal inhomogeneity of the evaporation duct has a significant influence when the EDH is low or when the electromagnetic wave frequency is lower than 13 GHz. Finally, experimental data collected on a 149-km long propagation path in the South China Sea in 2013 are used to verify the conclusion. The experimental results are consistent with the simulation results. The horizontal inhomogeneity of evaporation duct should be considered when modeling electromagnetic wave propagation over the ocean.

https://iopscience.iop.org/article/10.1088/1674-1056/24/4/044102/pdf

Experimental verification of effect of horizontal inhomogeneity of evaporation duct on electromagnetic wave propagation

/pdf/rain-induced-attenuation-studies-for-v-band-satellite-1jig5f86qj.pdf

Rain induced attenuation studies for V-band satellite communication in tropical region

Radio frequency propagation for wireless sensor networks in agricultural environments faces challenges due to placement of nodes for wide-area mesh coverage and reliable link quality above crop canopies. Environmental conditions may also have a role in receiver signal strengths. IEEE 802.15.4/ZigBee XBee Pro 2.4GHz wireless sensor network devices were tested to determine distance and height limitations on signal strength. Testing of signal strength and link quality was performed to simulate effects of changing crop canopy heights. Data indicated attenuation and signal strength variance were dependent on line of sight (LOS) losses and heights less than the Fresnel zone radius. Testing of receiver signal strength during heavy precipitation indicated non-uniform losses and variance in signal strength across available frequency channels.

Results of Wireless Sensor Network Transceiver Testing for Agricultural Applications

The maritime tropospheric duct is a low-altitude anomalous refractivity structure over the ocean surface, and it can significantly affect the performance of many shore-based/shipboard radar and communication systems. We propose the idea that maritime tropospheric ducts can be retrieved from ocean forward-scattered low-elevation global positioning system (GPS) signals. Retrieval is accomplished by matching the measured power patterns of the signals to those predicted by the forward propagation model as a function of the modified refractivity profile. On the basis of a parabolic equation method and bistatic radar equation, we develop such a forward model for computing the trapped propagation characteristics of an ocean forward-scattered GPS signal within a tropospheric duct. A new GPS scattering initial field is defined for this model to start the propagation modeling. A preliminary test on the performance of this model is conducted using measured data obtained from a 2009-experiment in the South China Sea. Results demonstrate that this model can predict GPS propagation characteristics within maritime tropospheric ducts and serve as a forward model for duct inversion.

http://iopscience.iop.org/article/10.1088/1674-1056/21/10/109202/pdf

Propagation modeling of ocean-scattered low-elevation GPS signals for maritime tropospheric duct inversion

Millimeter wave applications are becoming increasingly considered and exploited in order to satisfy the demand for new communications systems, active and passive remote sensing, etc. Fog may be one of the dominant factors in determining the reliability of millimeter wave systems, especially in coastal areas where dense moist fog with high liquid water content and larger drop size happen frequently. Clouds are similar to fog, the attenuation due to clouds may be a factor of importance especially for microwave systems well above 10 GHz or low-availability systems.

Millimeter-wave attenuation due to fog and clouds

Rain attenuation is one of the dominant factors in determining the reliability of microwave and millimeter systems; the specific rain attenuation is a fundamental quantity in calculation of rain attenuation statistics for terrestrial and earth-space paths. The power-law relationship of specific rain attenuation y/sub R/ (dB/km) and rain rate R (mm/h), y/sub R/ = kR/sup a/ is widely used and the values of k and a are usually tabulated for specific frequencies. The values tabulated are particularly convenient for estimation of specific attenuation in experimental applications or link designs at specific frequency, and the interpolated values should be used for other frequencies. However, It would be quite useful for system studies requiring calculations at many frequencies to have simple analytic expressions which give results in good agreement with the values tabulated. Regression to determine the relationships between the parameters, k and a, and frequency has been done and the regressed expressions given.

An analytic model of specific attenuation due to rain

Radio wave propagation test is introduced in this paper. It was held in the sea area near Qingdao city, and involved different band including L band, S band, C band and X band. Using the path loss model given in the International Telecommunication Union (ITU) recommendation propagation 1411, we derived the characteristic parameters such as path loss exponent and shadow fading for different frequencies. The statistic propagation model can be used for providing a reference for ship information communication.

Radio wave propagation characteristics measurement and modeling over the sea

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.

Zhao Zhen-wei

Papers

Propagation modeling of ocean-scattered low-elevation GPS signals for maritime tropospheric duct inversion

Millimeter-wave attenuation due to fog and clouds

An analytic model of specific attenuation due to rain

Radio wave propagation characteristics measurement and modeling over the sea

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