Analysis of the response of an HF radio signal to ionospheric plasma disturbances caused by acoustic shock waves

We analyze the form of the response of an HF radio signal scattered by the nonstationary disturbances of the electron density N_e caused by acoustic shock-wave disturbances in the upper atmosphere from rockets in the active section of the trajectory. A typical picture of the manifestation of additional modes in the spectrum of an oblique Doppler HF sounding signal is presented. The evolution of the signal response under different conditions of the experiment is discussed. Siberian Physicotechnical at Tomsk State University, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 1, pp. 36–44, January, 1999.     

Spectrum of signal scattered by anisotropic wandering irregularities

The problem of radio-wave scattering by anisotropic wandering irregularities is examined. Allowance for the strong anisotropy of the irregularities simplifies the problem and allows a simple formula to be derived for calculation of the Doppler spectrum of a scattered signal. The calculated spectra are similar in form to the experimental spectra of radio aurora.     

Measuring the characteristics of backscattering of sound on a rough surface in the near-field zone of a phased array

The paper presents the results of an experiment on measuring the characteristics of backscattering of sound waves by a rough surface. Measurements were conducted in the near zone of a vertical array, which made it possible with a high degree of accuracy to control the propagation conditions and the angles of incidence of an acoustic wave onto the surface. Tonal signals were emitted in a constant mode at frequencies of 0.5–3.5 kHz. The Doppler spectrum of the scattered signal was analyzed in detail, the spectral component corresponding to Bragg scattering was isolated, and the width of this component was determined. The possibilities of calculating the scattered field using two forms of the sea state spectrum are studied and compared: the two-dimensional spatiotemporal sea state spectrum, which was measured optically, and the conventional one-dimensional time spectrum, measured with a single surveying mark.     

On the possibility of reconstructing an anisotropic wind wave spectrum by the method of double-position sonar

We investigate the possibility of reconstructing the wind wave spectrum, with anisotropy taken into account, by the method of ocean acoustic sounding, using horizontally deployed antennas in the continuous mode of operation. This method uses marrow-beam horizontally spaced antennas for radiating a monochromatic sound signal and receiving signals scattered by the surface. By this method, we can localize a definite area of the scattering surface and reconstruct the wind wave spectrum owing to the direct dependence of the wind wave harmonic, which forms the scattered signal, on the position of this area relative to the radiator and the receiver. Expressions that relate the energy spectrum of the scattered signal formed at the receiver output to the wind wave spectrum are found. On the basis of these expressions, an algorithm has been developed for gaining information both about the spatial isotropic spectrum of wind waves and about the dependence of the angular spectrum on the value of the wind wave vector and its direction relative to the wind velocity.Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, Nos. 1–2, pp. 139–145, January–February, 1995.     

Studies of the Irregular Structure of the Ionosphere using Scattering of Radio Waves on Artificial Periodic Inhomogeneities

We present new results of our studies of the irregular structure of the ionosphere using artificial periodic inhomogeneities (APIs) of the ionospheric plasma. The observations were carried out from 9:00 to 17:00 in August 10–12, 1999 with a height step of 0.7 km and digital registration and real-time processing of the signal quadratures. It is shown that in many cases, the amplitude of the scattered signal is determined by the interference of radio waves scattered on APIs and on natural ionospheric formations including sporadic layers and large-scale natural irregularities. This allows one to study the irregular structure of the lower ionosphere by analyzing height-time dependences of the amplitude and phase of the scattered signal.     

EFFECTS OF THE LENGTH SCALE OF FREE-STREAM TURBULENCE AND CYLINDER SIZE ON LOCAL HEAT TRANSFER IN LAMINAR SEPARATED FLOWS

An experimental study has been conducted to investigate the combined influence of length scale of free-stream turbulence, A, and cylinder diameter, D, on heal transfer from slightly heated circular cylinders in cross flow. By using a hot-wire anemometer, spectrum analysis of its signal with a Fourier analyzer is employed to investigate the separated shear layer formed behind the circular cylinder. A resistance thermometer is used to measure the time-averaged temperature behind the cylinder and the power-spectral density of the temperature fluctuation in the thermal boundary layer. It is found that (I) the Nusselt number at the rear stagnation point varies with the relative scale A / D, at the same Reynolds number, (2) the laminar-to-turbulence transition region in the separated shear layer moves in the streamwise direction with the change in the length-scale ratio, and (3) a streamwise shift of the transition region in the separated shear layer causes a substantial increase in the power spectrum of the temperature fluctuation. A correlation equation with A/ Das a parameter is derived to predict the heat transfer rate at the rear stagnation point.     

Sounding of an artificially perturbed ionosphere by means of an ionosonde/position finder with chirp modulation of the signal

We describe the operation of an ionosonde/position finder with chirp modulation of the signal. The first results of measuring the characteristics of short-wave radio signals scattered by artificial small-scale inhomogeneities, which were obtained by means of an ionosonde/position finder on the IZMIRAN—“SURA”—Rostov-on-Don path are presented. It was found that under certain ionospheric conditions, the angular and frequency selection of the scattered signals take place, in which case the signals are observed simultaneously in several frequency intervals (mainly, in three, namely, 6–9.5 MHz, 10–12 MHz, and 15–18 MHz) with different angles of incidence of radio waves in the vertical plane. In this case, the incidence angles were 20◦–35◦, 18◦–32◦, and 10◦–20◦ from the horizon for the first, second, and third frequency interval, respectively. Ionograms of oblique sounding were modeled allowing for the scattering of radio waves by artificial small-scale inhomogeneities. It is shown that at frequencies from 10 to 12 MHz, aspect conditions are fulfilled for the signals ducting along the high-angle beam (Pedersen mode). At frequencies 15–18 MHz (higher than the maximum observable frequency of the forward signal on the path IZMIRAN—Rostov-on-Don), aspect scattering conditions are fulfilled for the signals incident on a scattering area in the ascending part of the trajectory. At low frequencies 6–9.5 MHz (below the maximum observed frequency of the forward signal on the IZMIRAN—Rostov-on-Don path), the observable additional signals are caused by the scattering of radio waves by artificial inhomogeneities with subsequent relfection of the scattered signal from the Earth on the “SURA”—Rostov-on-Don path. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 4, pp. 267–278, April 2009.     

脉冲相干激光雷达测距信号研究

对脉冲激光雷达外差测距信号进行了研究，理论上，采用调Q激光脉冲的数值计算波形，研究了脉冲激光经远处目标漫反向后进行外差接收的波形及其傅里叶变换频谱成分。实验上，研究了可调谐电光调Q射频激励波导CO2激光器脉冲激光经目标反射后的外差波形及其傅里叶变换频谱成分，并计算了目标的距离，理论分析与实验结果一致。     

A multiphoton treatment of near resonant light scattering in intense fields

The scattering by a two-state atom of monochromatic light of arbitrary intensity and detuning, is treated by solving Schrödinger's equation directly for the state of the scattered field. The calculation is performed in a basis of dressed atom states, which include to all orders the coupling of the incident field to the atom. Amplitudes describing sequences of scattering events are found by a nonperturbative method. A scattered intensity spectrum, directly related to the rate of change of energy in any given scattered field mode, is constructed in terms of bilinear products of the amplitudes representing all possible sequences of photon emission, and in the steady state limit the spectrum is found to be identical to the widely quoted results of Mollow. A discussion is devoted to understanding in physical terms the various quantities appearing in the expression for the intensity spectrum.     

等离子体中X射线透过率分析及潜在通信应用研究

X射线具有波长短、光子能量高等特点,有望在等离子体环境中实现信息的有效传输.本文首先采用基于连续介质中的WKB分层法,研究了黑障条件下, X射线在非均匀等离子体鞘套中的透过率特性,仿真了不同等离子体电子密度和碰撞频率下X射线信号的透过率,理论上证明了X射线可用于黑障区信息传输的可行性.其次通过搭建环形扩散辉光放电等离子体发生器及实验验证系统,进行了国内外首次X射线穿过等离子体鞘套的验证实验.实验结果表明,等离子体对X射线信号的透过率存在一定程度的衰减,透过等离子体前后的X射线信号能谱轮廓相似度优于95.5%,能谱峰值点的偏移量小于1.3%.此外,在原有理论模型的基础上,考虑等离子中的粒子与X射线的碰撞、吸收效应,优化了X射线在等离子体中的透过率模型,与传统的理论方法相比,该模型可对实验现象进行更好的解释.同时计算了X射线在临近空间的透过率,并分析了X射线通信所能达到的潜在指标.这些结果有望为解决黑障区信号传输提供一定的理论与实验依据.     

Signal area estimation based on deep learning

In many practical application scenarios, radio communication signals are commonly represented as a spectrogram, which represents the signal strength measured at multiple discrete time instants and frequency points within a specific time interval and frequency band, respectively. In the context of spectrum occupancy measurements, the notion of Signal Area (SA) is defined as the rectangular region in the time–frequency domain where a signal is assumed to be present. Signal Area Estimation (SAE) is an important functionality in spectrum-aware wireless systems where spectrum usage monitoring is required. However, the conventional approaches to SAE have a limited estimation accuracy, in particular at low SNR. In this work, a novel technique for SAE is proposed using Deep Learning based on Artificial Neural Network (DL-ANN) for enhanced extraction of SA information from radio spectrograms. The performance of the proposed DL-ANN method is evaluated both with software simulations and hardware experiments, and the results are compared with several conventional methods from the literature, showing significant performance improvements. A key feature of the proposed method is the improvement in the SAE accuracy compared to other existing methods (in particular in the low SNR regime) and the capability to extract the location of the detected SAs automatically. Overall, the proposed technique is a promising solution for the automatic processing of radio spectrograms in spectrum-aware wireless systems.     

Laser scattering with a rapidly tuned dye laser

A facility is described for the measurement of the total spectrum produced by laser radiation scattered from a plasma during one laser pulse. The dye laser is electrooptically tuned by a high frequency voltage applied to a modified Lyot filter within its cavity. The scattered spectrum is registrated together with the laser reference signal by a transient recorder and processed afterwards. Both measuring time and inaccuracy could be reduced drastically. Scattering experiments have been accomplished in a H₂ cascade of 5 mm diameter arc at atmospheric pressure, and at 14 and 20 A, respectively. For this arc very precise spectroscopic results are available for checking the accuracy of the scattering measurements. Both the spectroscopic line and continuum experiments yield a temperature which lies between electron and ion temperature if there is no local thermal equilibrium, whereas the pure electron temperature is provided by the scattered spectrum. The agreement between spectroscopic and scattering results within the high error limits is the experimental proof for the applicability of this new scattering technique which requires only about one hundredth of the measuring time, as compared with the usual shot-to-shot registration.     

Inelastic scattering of 185 MeV protons from Mg and Al

A magnetic spectrometer was used for the energy analysis of protons scattered from targets of magnesium (natural isotopic composition) and aluminium. The mean energy of the incident protons in the targets was 185 MeV. A total energy resolution of 350 keV (FWHM) was achieved, which made possible the observation of the excitation of a large number of discrete levels. Energy spectra were measured in the angular region of 4° to 40° (lab system).

The results are presented partly in the form of tables giving measured excitation energies and maximum cross sections for resolved levels and partly in the form of graphs of angular distributions of the differential cross sections.

A qualitative discussion of the results is given in terms of the multipolarities of the transitions involved and comparisons are made with similar results from other experiments in inelastic scattering and in a few cases with theoretical predictions.     

Spatial-frequency characteristics of radio emission induced by interaction of an extensive air shower with the Earth’s surface

The spatial directional pattern of the radio emission induced by interaction of the excess electrons of an extensive air shower with the Earth’s surface was found in the approximation of perfect soil conductance. The results made it possible to determine the frequency range (≈0.2–1 MHz), within which the radio emission of the shower is maximum, provided that this emission mechanism is valid. In addition, it became possible to explain the previously observed lack of direct proportionality between the shower energy and the radio signal amplitude. It was found that this disproportionality is caused mainly by the high directivity of low-frequency (0.2–3 MHz) radiation patterns within a wide range of the values of the axial tilt.     

Radiophysical and radio astronomical diagnostics of ionospheric effects induced by a ground-based infrasonic transmitter (preliminary results)

We present results of preliminary studies aimed at detection of weak ionospheric disturbances induced by acoustic emission of a ground-based controlled transmitter. Radio astronomical and radiophysical facilities based on the decameter radio telescope URAN-3 were used in these experiments. Three methods were applied in this study: occultation of the disturbed region by radio emission from discrete cosmic sources, scattering of sounding radio waves from the perturbed ionospheric region, and weakly-oblique sounding of the ionosphere. It is shown that the parameters of transmitted, scattered, and reflected signals are well correlated with the parameters of the acoustic radiation, and that the weak ionospheric disturbances detected in our experiments are actually induced by the acoustic radiation. G. V. Karpenko Physico-Mechanical Institute of the National Academy of Sciences of Ukraine, Khar'kov, Ukraine. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 8, pp. 785–798, August 1999.     

Modeling the recorded spectrum and reconstructing the transfer function of the wideband ionospheric HF radio channel in the case of chirp sounding

We model theoretically the received spectrum in the case of sounding of the ionospheric HF radio channel by a chirp signal. It is shown that the result of processing of an individual time sample of the received signal is equivalent to the sounding of the radio channel by a complex narrow-band pulsed signal such that the group delays of its propagation modes determine the maxima in the received spectrum. We analyze the quadrature components of realizations of the received signal at the intermediate frequency at the bandpass-filter output in the receiving channel of the chirp ionosonde. The results of our analysis show the possibility of reconstructing the transfer function of a HF radio channel in the sounding-frequency band for the delay range determined by the characteristics of the intermediate-frequency bandpass filter. We propose a method for reconstructing the transfer function of the ionospheric radio channel, which involves supplementing the circuit of primary processing of the signal by a corrective digital filter with specified amplitude-frequency and phase-frequency characteristics. The proposed method can be used for all operating regimes of the chirp ionosonde in the case of digital recording and processing of signals. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 5, pp. 387–395, May 2007.     

Efficiency of sequential resonance compression of radio pulses

A study is made of the efficiency of forming high-power wide-band and ultrawide-band radio pulses by a sequence of resonance compression steps. An analysis is made of the compression of radio pulses with a rectangular envelope in a chain consisting of two or three compressors, and also in a chain where the output signal from the first stage has an exponential trailing edge and the other stages have rectangular envelopes. The maximum energy storage efficiency is determined for a cavity excited by a signal with an exponential trailing edge. Zh. Tekh. Fiz. 69, 131–133 (April 1999)     

Method of Self-Mixing in the Spectroscopy of Quasielastically Scattered Laser Radiation

Interaction of a semiconductor laser with its self-radiation quasielastically scattered in the environment is considered. It is established that at small coefficients of coupling of the laser with the scattering medium the spectral density of the power of an optoelectronic signal in the laser faithfully reproduces the shape of the scattered-radiation spectrum at the Doppler-shift frequencies. This makes it possible to measure the spectrum with a resolution characteristic for optical homodynation by recording the optoelectronic signal.     

Influence of ionospheric irregularities on the form of radio signal scattering spectrum in over-the-horizon radar sounding of the rough sea surface

Abstract

This paper is concerned with the backscattering of HF radio waves from the rough sea surface, which have propagated through the ionosphere with random large-scale irregularities.

For the sake of simplicity, it is assumed in calculations that the rough sea surface is a perfectly conducting surface with the known Philips power spectrum of irregularities. Ionospheric irregularities of a random medium that are isotropic and single-scale ones, with a Gaussian spectrum, are considered within the limits of the hypothesis of frozen-in irregularities.

Within the first approximation of perturbation theory, using, as the incident wave and the Green function, their geometrical-optics approximations, we obtained the expression for the backscattering spectrum of the ionospheric chirp radio signal with a Gaussian envelope. The expression involves the parameters of the receive–transmit antenna, the signal, the propagation medium, and of the scattering surface. Numerical simulation was used to investigate the influence of all the above-mentioned parameters on the backscattering spectrum. It is shown that travel of ionospheric irregularities has the largest influence on the scattering spectrum, the signal parameters mainly determine the size of the scattering area in the range, and the form of the coherent integration window determines the form of the received signal and can distort it.     

利用空间外差光谱技术进行紫外高分辨率大气散射信号探测

羟基OH对于人类理解中间层化学成分非常重要,它是大气光化学反应中重要的氧化剂,OH在308 nm波段受到太阳能量激发,发射出OH A2Σ＋-X２Π（0,0）荧光信号。为了探测中间层大气中OH自由基的紫外共振荧光发射信号,从复杂背景信号中分离目标信号,研制了中高层大气OH自由基超分辨空间外差光谱仪,光谱范围为308.2～309.8 nm,光谱分辨率为0.008 25 nm。临边观测主要探测大气散射信号,能量来源为大气中的粒子,包括大气分子与气溶胶、云等对太阳能量的散射作用。中高层大气OH自由基超分辨空间外差光谱仪基于空间外差光谱技术,可以在设计的闪耀波长范围内获得极高的光谱分辨率,适用于大气成分的精细探测。通过在前置或后置光学系统中加入柱面镜,总视场内的场景被分成多个视场切片,每一个视场切片的干涉图分别成像到对应的探测器行上。利用空间外差光谱仪具有空间维分层成像功能,临边观测时可以同时获取不同高度层大气吸收光谱的散射辐射信号,无需像传统临边探测遥感器在不同高度层进行扫描来获取大气高度维的廓线信息。为了验证中高层大气OH自由基超分辨空间外差光谱仪的临边散射信号探测能力与对观测几何的敏感性,进行了地面临边观测实验,探测紫外308 nm波段大气散射信号。模拟临边观测几何,选取晴朗无云的一天,在空旷场地对大气散射信号进行观测。由于仪器基于空间外差光谱技术,需要对干涉数据进行干涉误差修正与光谱复原。对一段观测时间内间隔10分钟的干涉数据进行光谱复原并定标,得到最终临边观测光谱。由于散射信号的主要来源为大气分子对太阳光的散射作用,因此光谱中应包含太阳光谱高分辨率精细特征信息。从高分辨率太阳光谱中选取三个特征信息窗,分析观测光谱中对应波段,三个特征信息窗完全匹配,验证了中高层大气OH自由基超分辨空间外差光谱仪的超高分辨率光谱探测能力和光谱精细信息提取能力。将太阳辐射计实时测量获得的气溶胶光学厚度及根据观测时间计算的太阳天顶角与太阳方位角输入辐射传输模型SCIATRAN,结合对应日期与经纬度的大气廓线数据库,得到模拟光谱,将实测结果与辐射传输模型结果进行比对,两者残差较小。实测结果与模拟结果存在的残差,可能是由于大气环境参数并没有完全符合实测状态,后续可使用当地实时温湿压廓线对模拟数据库进行替换,使辐射传输模型更接近实际状态。与辐射传输模型对比的结果验证了中高层大气OH自由基超分辨空间外差光谱仪的散射信号探测能力与对观测几何的敏感性,验证了在轨探测多谱段、宽谱段大气散射光谱与OH目标信号的可行性,为在轨探测OH目标信号提供了理论与实验基础。