Research on Continuous Wave Electromagnetic Effect in Swept Frequency Radar

In order to establish the prediction model of radar equipment in multisource complex electromagnetic environment, the blocking effect and false alarm interference effect caused by single-frequency CW (continuous wave) electromagnetic interference on typical radar equipment are studied. Taking a certain sweep radar as the research object, the equivalent injection test of EMI (electromagnetic interference) is carried out. Based on the theory of radar front door coupling, the interference mechanism of EMI to radar receiver RF front end is revealed, and the variation law of blocking target and false alarm target level is analyzed. The results show that, under the single-frequency CW-EMI, the target echo level decreases with the increase of the interference field strength, and the false alarm level increases with the increase of the interference field strength. The blocking jamming sensitive bandwidth is about f 0 ± 200 MHz , and the false alarm jamming sensitive bandwidth is about f 0 ± 80 MHz .

RECORDING OF DIFFRACTION GRATINGS WITH AN ACTIVE STABILIZATION SCHEME OF INTERFERENCE FIELD

The paper describes a modernized optoelectronic system for stabilizing the interference pattern during exposure of a holographic grating. The results of applying the extreme control system to stabilize the interference field when recording holographic gratings of high optical quality are presented. Thin chalcogenide layers of the composition As2S3 were used as the recording medium. When using the stabilization system, a monotonic increase in the diffraction efficiency of the gratings from the recording time is observed and a low level of spurious scattering is recorded for the recorded gratings. The scheme was experimentally tested when recording holographic gratings up to 60x60 mm2 in size and exposure time up to 30 minutes. The use of an active stabilization scheme will make it possible to record large-size gratings using low-power lasers without the use of additional complex systems for protecting optical circuits from vibration.

Large wood hydraulics - a fluvial process of growing interest

<p>In the last decade, the perception of large wood in rivers has shifted from a hazard perspective towards a valuable and required component of the river ecosystem. Consequently, there is a demand to quantify and predict the effects of large wood on flow, morphology and retention.</p><p>The research programme ‘Large Wood Hydraulics’ investigates the flow and turbulence characteristics of instream large wood. Within the programme, field measurements and lab experiments are conducted and cover different wood types (tree morphology, branching pattern), their position / orientation in the cross-section and single or multiple elements (wake interference). Field measurements were carried out in river Mulde, Germany within the BMBF-project ‘Wilde Mulde’ and flume experiments in the hydraulics lab of  TU Vienna.</p><p>The aim of the study is to predict the effects of different wood configurations to promote the use of wood in river restoration schemes.</p>

Способ компенсации интерференционного поля станционных радиопомех в коротковолновых широкополосных каналах радиосвязи

В работе представлены результаты экспериментальных исследований пространственно-корреляционных свойств узкополосных станционных помех коротковолнового диапазона. По результатам обработки экспериментальных данных получены обобщающие закономерности пространственно-корреляционных свойств интерференционного поля узкополосных станционных помех, определяющие возможность компенсации их влияния при обработке широкополосных сигналов в коротковолновых каналах радиосвязи, использующих цифровые антенные решетки с пространственно-корреляционной обработкой сигналов. С учетом возможностей компенсации интерференционного поля узкополосных станционных помех, исследована возможность повышения помехоустойчивости и скорости передачи информации в ионосферных каналах радиосвязи за счет передачи широкополосных сигналов с применением OFDM модуляции, более адаптируемой к условиям дисперсионных искажений и временного рассеяния сигналов, возникающих при распространении коротких волн. Результаты моделирования показали потенциальную возможность обеспечения повышенной скорости передачи информации в коротковолновых каналах с пространственно-корреляционной обработкой сигналов с заданной помехоустойчивостью при малых отношениях уровней сигнал/шум в точке приема, обеспечиваемой при меньших ограничениях выбора рабочей частоты, по сравнению с возможностями новых разработок скоростных коротковолновых модемов, в условиях ограниченности частотного ресурса коротковолнового диапазона из-за большой загруженности работой территориально-разнесенных станций.The experimental studies results of the spatial-correlation properties of narrow-band short-wave station interference are presents. Based on the results of processing the experimental data generalizing regularities of the interference field spatial-correlation properties of narrow-band station noise have been obtained. These regularities determine the possibility of compensating for their influence during processing broadband signals in radio channels using digital antenna arrays with spatial-correlation signal processing. Taking into account the possibilities of compensating for the interference field of narrow-band noise, the possibility of increasing the information transfer rate by transmitting wide-band signals using modulation with OFDM, which is more adaptable to the conditions of dispersion distortion and temporal dispersion of signals arising from the propagation of short waves in ionospheric communication channels, has been studied. The simulation results showed the potential for providing an increased information transfer rate in short-wave radio channels with spatial-correlation signal processing with a given noise immunity at low signal-to-noise levels at the receiving point, provided with less restrictions on the choice of operating frequency, compared with the capabilities of new developments of high-speed HF modems, in conditions of limited frequency resource of the HF band due to the heavy workload of geographically dispersed stations.

Automatic Detection of Near-Surface Targets for Unmanned Aerial Vehicle (UAV) Magnetic Survey

Great progress has been made in the integration of Unmanned Aerial Vehicle (UAV) magnetic measurement systems, but the interpretation of UAV magnetic data is facing serious challenges. This paper presents a complete workflow for the detection of the subsurface objects, like Unexploded Ordnance (UXO), by the UAV-borne magnetic survey. The elimination of interference field generated by the drone and an improved Euler deconvolution are emphasized. The quality of UAV magnetic data is limited by the UAV interference field. A compensation method based on the signal correlation is proposed to remove the UAV interference field, which lays the foundation for the subsequent interpretation of UAV magnetic data. An improved Euler deconvolution is developed to estimate the location of underground targets automatically, which is the combination of YOLOv3 (You Only Look Once version 3) and Euler deconvolution. YOLOv3 is a deep convolutional neural network (DCNN)-based image and video detector and it is applied in the context of magnetic survey for the first time, replacing the traditional sliding window. The improved algorithm is more satisfactory for the large-scale UAV-borne magnetic survey because of the simpler and faster workflow, compared with the traditional sliding window (SW)-based Euler method. The field test is conducted and the experimental results show that all procedures in the designed routine is reasonable and effective. The UAV interference field is suppressed significantly with root mean square error 0.5391 nT and the improved Euler deconvolution outperforms the SW Euler deconvolution in terms of positioning accuracy and reducing false targets.

Fraunhofer Diffraction

We will develop a simple derivation of the Huygens-Fresnel integral based on an application of Huygens’ Principle and on the addition of waves to calculate an interference field starting with two apertures as in Young’s two slit experiment extending to N apertures and then a continuum distribution. A detailed look is made of the obliquity factor and a constant value is derived to be used in the simple derivation. We use one dimensional theory for most of the discussion but do present the results of diffraction from a circular aperture as it will be needed in our later discussion of imaging. A second description of the propagation of light, useful when using laser light sources, the gaussian wave, is introduced and examples are given of the use of the theory in geometrical optics and laser design.

An Aeromagnetic Compensation Method Based on a Multimodel for Mitigating Multicollinearity

Aeromagnetic surveys play an important role in geophysical exploration and many other fields. In many applications, magnetometers are installed aboard an aircraft to survey large areas. Due to its composition, an aircraft has its own magnetic field, which degrades the reliability of the measurements, and thus a technique (named aeromagnetic compensation) that reduces the magnetic interference field effect is required. Commonly, based on the Tolles–Lawson model, this issue is solved as a linear regression problem. However, multicollinearity, which refers to the case when more than two model variables are highly linearly related, creates accuracy problems when estimating the model coefficients. The analysis in this study indicates that the variables that cause multicollinearity are related to the flight heading. To take this point into account, a multimodel compensation method is proposed. By selecting the variables that contribute less to the multicollinearity, different sub-models are built to describe the magnetic interference of the aircraft when flying in different orientations. This method restricts the impact of multicollinearity and improves the reliability of the measurements. Compared with the existing methods, the proposed method reduces the interference field more effectively, which is verified by a set of airborne tests.