Abstract: This work is devoted to estimation of the additional absorption of millimeter and submillimeter wavelengths in water vapor arising from collisional interaction of molecules due to the induced dipole moment. Absorption is modeled on the basis of ab initio data on the magnitude of the water molecule dipole moment at high densities, and common knowledge of the water vapor absorption spectrum. Using the model developed, we obtained a simple analytical expression for the absorption coefficient as a function of temperature, pressure, and frequency. Comparison of the results with known experimental data leads to the conclusion that in the range of pressures and temperatures typical of water vapor in the Earth’s atmosphere this type of absorption is negligible compared with the absorption arising due to association or dimerization of the water vapor molecules. PubDate: 2015-09-28

Abstract: This paper aims at analyzing the broadband part of electromagnetic emission from thunderclouds in a frequency range of tens of kilohertz to hundreds of megahertz. A model of the intracloud lightning discharge formation is presented. The lightning formation is described as a stochastic growth of the branching discharge channels, which is determined by the electrostatic field. The dynamics of the electric field and of the charge distribution over the lightning structure is calculated deterministically. The effect of the initial charge density in the cloud and the parameters of the conducting channels on spatio-temporal characteristics of the currents and structure of the lightning discharge is studied. The discharge radio emission is calculated by summing up the radiation fields of each channel at the observation point. The standard model for a separate discharge current is adopted, and the electromagnetic radiation in the far zone is estimated. It is found that the obtained frequency spectra exhibit a universal power-law behavior. The results of the modeling agree with known experimental data. PubDate: 2015-09-26

Abstract: We propose a new method for determining the wind-velocity vector above the ocean surface using the data of a polarimetric synthetic aperture radar. The preliminary calculations show that for wind waves, the location of the maximum in the radar image is unambiguously related to the wind velocity, whereas the wind direction is retrieved with an uncertainty of 180°, which is related to the central symmetry of the image spectrum. To eliminate the ambiguity when determining the wind direction, a criterion based on the information on the sign of the coefficient of correlation among the complex signals on the co- and cross polarizations is used. It is shown that using the polarimetric radar, it is theoretically possible to obtain information on both the wind velocity and direction without exact radar calibration. PubDate: 2015-09-26

Abstract: We present for the first time the experimental data on the frequency of ion–neutral collisions at the altitudes of the ionospheric E layer, which were obtained by the method of resonance scattering of the radio waves by artificial periodic irregularities of the ionospheric plasma. The measurements were carried out in different time periods from 1990 to 2012. Time and altitude dependences of the collision frequency are given. The dependence of the collision frequency on the solar and geomagnetic activity has been analyzed. PubDate: 2015-09-26

Abstract: We introduce the notion of a quasi-ellipsoidal three-dimensional optical pulse beam with a diffuse boundary and solve the problem about its propagation in free space. The quality of the diffracted pulse is characterized by two parameters responsible for distortions in the transverse intensity distribution and blurring of the entire pulse. Imposing constraints on these parameters, one can find the maximum distance which the pulse can propagate without critically strong distortions and, consequently, determine the required accuracy of the longitudinal positioning of the elements of the optical scheme which transmits the pulse. PubDate: 2015-09-26

Abstract: In the studies of the data received from DEMETER (orbit altitude above the Earth is about 700 km), we detected for the first time electromagnetic perturbations, which are due to the ionospheric modification by HAARP, a high-power high-frequency transmitter, simultaneously in the extremely low-frequency (ELF, below 1200 Hz) and very low-frequency (VLF, below 20 kHz) ranges. Of the thirteen analyzed flybys of the satellite above the heated area, the ELF/VLF signals were detected in three cases in the daytime (LT = 11–12 h), when the minimum distance between the geomagnetic projections of the satellite and the heated area center on the Earth’s surface did not exceed 31 km. During the nighttime flybys, the ELF/VLF perturbations were not detected. The size of the perturbed region was about 100 km. The amplitude, spectrum, and polarization of the ELF perturbations were analyzed, and their comparison with the characteristics of natural ELF noise above the HAARP transmitter was performed. In particular, it was shown that in the daytime the ELF perturbation amplitude above the heated area can exceed by a factor of 3 to 8 the amplitude of natural ELF noise. The absence of the nighttime records of artificial ELF/VLF perturbations above the heated area can be due to both the lower frequency of the heating signal, at which the heating occurs in the lower ionosphere, and the higher level of natural noise. The spectrum of the VLF signals related to the HAARP transmitter operation had two peaks at frequencies of 8 to 10 kHz and 15 to 18 kHz, which are close to the first and second harmonics of the lower-hybrid resonance in the heated area. The effect of the whistler wave propagation near the lower-hybrid resonance region on the perturbation spectrum recorded in the upper ionosphere for these signals has been demonstrated. In particular, some of the spectrum features can be explained by assuming that the VLF signals propagate in quasiresonance, rather than quasilongitudinal, regime. It is noted that the profile and dynamics of the ELF perturbation frequency spectrum conform to the assumption of their connection with quasistatic small-scale electron-density inhomogeneities occurring in the heated region and having lifetimes of a few seconds or more. The possible mechanisms of the ELF/VLF perturbation formation in the ionospheric plasma above the high-latitude HAARP facility at the DEMETER flyby altitudes are discussed. PubDate: 2015-09-26

Abstract: We generalize the version of the method of discrete sources, which was proposed earlier for numerical solution of the problem of scattering of electromagnetic radiation by a structure consisting of a finite number of three-dimensional smooth impedance bodies, to the case of a structure consisting of a finite number of impedance and magnetodielectric bodies. The possibilities of the developed computer program are briefly described. Some results of calculating the scattering cross sections of two structures, one of which consists of a perfectly conducting spheroid and a dielectric spheroid with identical geometric parameters, and another, of two identical impedance spheroids and a dielectric sphere, are presented. PubDate: 2015-09-26

Abstract: We consider an adaptive antenna array, which ensures the maximum output ratio of the signal power to the average noise power. Two algorithms for the adaptive processing of the signal in the power-vector basis are proposed. For each algorithm, the regularized estimates of the weight vector are obtained using a limited number of input-process samples, which can be both greater and smaller (the short-sample case) than the number of array elements. The results of simulating the adaptive signal processing, which demonstrate a high signal-processing efficiency in the considered array, are presented. PubDate: 2015-09-26

Abstract: The well-known experiments performed by Pound and Rebka already in the 1960s confirmed the effect of gravitational time dilation, which had been predicted earlier within the framework of the general relativity theory. However, since photon exchange occurred in the course of these experiments on comparing the frequencies of nuclear resonance fluorescence at various altitudes, the reasons underlying the origin of this effect are explained in the literature by two different and, in fact, alternative presumed physical phenomena. According to the first explanation, clocks locate higher run faster, which is due to an increase in the gravitational potential with increasing distance from the Earth, whereas ascending and descending photons do not change their frequency (by the same clock, e.g., that of the so-called outside observer). According to the second explanation, the clock rate is the same at different altitudes, but the ascending photons undergo a redshift since they lose their energy, while the descending photons undergo a blueshift since they acquire energy. Other combined interpretations of the gravitational time dilation, which presume that the both phenomena exist simultaneously, are proposed in the literature. We propose an experiment with two clocks being active hydrogen masers, one of which is located at the bottom of a high-rise building, and the other, on the top of the building. In this case, time is measured by the first and second clocks during a sufficiently long time interval. After that, the masers are placed at one point, and their indications are compared. In this case, the photon exchange is not required for comparison of the clock readings, and, therefore, the method proposed allows one to reveal the actual reason of the effect under consideration. Numerical estimations are made, which allow for the accompanying effects influencing the measurement accuracy. Critical analysis of the earlier experiments shows that they are either equivocal, or are not absolutely impeccable from the methodology viewpoint. PubDate: 2015-09-26

Abstract: We analyze the results of the radio-occultation experiments which were carried out for six years in two equatorial regions of the lower ionosphere. The features of the decimeter radio-wave amplitude variations are considered for the case of remote sensing of the different sporadic structures along the radio paths between two satellites. The diurnal dependences of the height and thickness of the Es layer are presented for different time intervals. It is shown that in different days in the nighttime the Es-layer plasma structures can exist in the form of a single layer or in the form of two layers simultaneously. The first layer is located at an average altitude of 116 km, while the second one, at 96 km. It was found that in the daytime the height of the first layer decreases, while in the evening, irregular structures are formed at altitudes distributed randomly between 90 and 100 km. The amplitude variations of the sounding signals are discussed for cases where the distance (in the perigee) of the radio ray path from the Earth’s surface is between 70 and 85 km in the mesosphere. Statistics of the sporadic structure occurrence is given for the regions located in Africa and Indonesia. PubDate: 2015-09-26

Abstract: We have developed and tested experimentally a method for measuring optical wave fields, which is based on diffraction of the optical wave field at two complementary screens. An optical scheme of the experimental setup, which implements this method, has been developed, as well as the experimental procedure used to measure the phase of the optical wave field. The main parameters of the method, such as accuracy and spatial resolution, were studied experimentally. The developed optical scheme was calibrated, which allowed eliminating the systematic error of phase measurements introduced by the scheme elements. PubDate: 2015-09-26

Abstract: In the second part of the work, which is dedicated to the methods of studying the wave characteristics, we present the results of measuring three-dimensional spectra of the water-surface height distributions in the closed sea- and lake-water areas with low-level waves. The data on the wave spectra is obtained on the basis of processing the wave video images using the energy and correlation approaches. On the whole, the obtained information on the multidimensional characteristics of the waves agrees with the theoretical concepts and the results of other studies. PubDate: 2015-09-26

Abstract: We consider the method of constructing the suboptimal filter on the basis of approximating the a posteriori probability density of the multidimensional Markov process by the Pearson distributions. The proposed method can efficiently be used for approximating asymmetric, excessive, and finite densities. PubDate: 2015-09-26

Abstract: We consider the soliton dynamics within the framework of an extended nonlinear Schrödinger equation with pseudo stimulated scattering, which occurs from the damped low-frequency waves, and the spatially inhomogeneous cubic nonlinearity. It is shown that the pseudo stimulated scattering, which leads to a shift of the spectrum of the soliton wave numbers to the long-wavelength region, and the nonlinearity, which increases with the coordinate and shifts the soliton spectrum to the short-wavelength region, can be in balance. The soliton solution, which results from this balance, is explicitly obtained. PubDate: 2015-09-26

Abstract: Using the process model, we describe the phase, amplitude, polarization, and spatial characteristics of the parametric scatterer. The mathematical model of the parametric scatterer, which is developed on the basis of its equivalent circuit, is also discussed. The relation between the parameters of the process and mathematical models of the parametric scatterer is shown. The transient processes during simultaneous action of the pump- and synchronization-signal radio pulses on the parametric scatterer are studied. We show that it is expedient to use the synchronization radio pulse at the reply-signal frequency not only for disambiguation of the initial phase of the reply signal, but also for quick excitation of the parametric circuit. PubDate: 2015-09-26

Abstract: We develop a new method for electromagnetic computer tomography of distributed subsurface inhomogeneities and holography (i.e., retrieval of the form) of internally homogeneous subsurface objects. The method is based on solving the inverse problem of near-field scattering with allowance for the data of multifrequency measurements of the two-dimensional distribution of the scattered-field complex amplitudes along the medium surface over the region of inhomogeneities. PubDate: 2015-07-24

Abstract: We present the results of studying theoretically of propagation of plane longitudinal acoustic waves in homogeneous media with different-modulus elastic nonlinearity and relaxation. Exact analytical relations are obtained for the profiles of stationary waves and self-similar pulsed and periodic waves propagating in such media with no shape variations. PubDate: 2015-07-24

Abstract: It is shown that to use the maximum share of the energy of a unipolar ultrashort electric pulse, its duration and shape, as well as the transmitting antenna parameters should, be related to the receiver center frequency and passband in a certain manner. Distortions introduced by the propagation effects to the received-radiation spectrum shape increase with broadening radiation and receiver frequency bands. PubDate: 2015-07-24

Abstract: Characteristics of the wave disturbances of the ionospheric electron number density were measured using the Kharkov incoherent scatter radar. The disturbance generation accompanied the SURA heating of the near-Earth plasma by high-power periodic radiation. The distance between the heater and the radar was about 960 km. The possibility of generating ionospheric wave disturbances with a period of 20 to 30 min in the internal gravity wave range was confirmed. The disturbance propagation velocity was near 320–400 m/s, and the relative amplitude of the electron density variation was 1–10%. The wave disturbances appeared in the altitude range 145–235 km. Aperiodic bursts of the electron number density with a relative amplitude of up to 5–10% were detected after the first switch-ons of periodic radiation in the 30-min heating — 30-min pause regime at altitudes of 145 to 310 km. The observation results generally conform to the synchronous observation data obtained using the Kharkov vertical-sounding Doppler radar and a network of ionosondes. PubDate: 2015-07-24

Abstract: We propose a method for determining the mutual time delay during the propagation of signals with pseudorandom frequency hopping in different channels. A modified algorithm for calculating the uncertainty function, which permits calculation parallelization, is used to compensate for the influence of the Doppler effect during the signal recording. The results of studying the efficiency of the proposed method are presented. PubDate: 2015-07-24