We suggest an explanation of a sharp increase in the abundance of cosmogenic radiocarbon found in tree rings dated AD 775. The increase could originate from high-energy irradiation of the atmosphere by a galactic gamma-ray burst. We argue that, unlike a cosmic ray event, a gamma-ray burst does not necessarily result in a substantial increase in long-lived 10 Be atmospheric production. At the same time, the 36 Cl nuclide would be generated in the amounts detectable in the corresponding ice core samples from Greenland and Antarctica. These peculiar features allow experimental discrimination of nuclide effects caused by gamma-ray bursts and by powerful proton events.
In modern conditions, it becomes necessary to create security systems, surveillance systems, anti-terrorist systems that carry out covert detection and surveillance of small-sized ground objects, including biological ones.
Traditionally used single-position radars are ineffective in conditions of a large number of reflections that interfere with and low speed of movement of detected objects (people). The use of several such radars is impractical due to their rather high complexity and cost. In addition, it is impossible to ensure the secrecy of such systems. The construction of radar surveillance systems in the form of semi-active bistatic, including educational, radar systems is promising for the described conditions. One of the important issues in the construction of semi-active bistatic systems is the substantiation of the parameters of external illumination signals and the assessment of the attainable characteristics of such systems when using them.
The analysis and definition of the requirements for the characteristics of the illumination signals is carried out. In addition, consider the features of using signals from modern emitting systems in semi-active radars. The basic parameters of the signals are given – the bandwidth, the pulse duration (spectrum width), the power at the transmitter output, the frequency range in which the system operates. The advantages and disadvantages of semi-active radar stations (SA RS), which use such signals, are described.
Variants of semi-active bistatic systems with external illumination are determined. The widespread use of modern digital language and telecommunication systems provides the SA RS with effective illumination signals with good correlation properties, which makes it possible to obtain the necessary technical characteristics in a variety of application conditions
The emergence of new means of attack, reconnaissance and methods of sabotage imposes special requirements on the technical means of protecting important state facilities (ISF). Modern trends in the construction of ISF physical protection systems are the integration of engineering barriers, perimeter signaling and detection tools. Detection tools should provide covert receipt of information about the approach of the intruder in "distant" intrigues. To do this, it is possible to use technical means built on the principle of semi-active bistatic radar with an external illumination source. However, in order to identify intruders in the ISF protection zone, it is necessary to have a priori information about the radar visibility of the combined location objects. The combined object is typically a complex object having both metallic and dielectric elements.
To this end, a technique has been developed for estimating the radar cross-section (RCS) of combined objects in the field of external illumination. The electromagnetic field (EMF) scattered by a combined object in the meter and decimeter wavelength ranges is calculated as a coherent sum of fields, taking into account their phase, scattered by its metal and dielectric elements. This made it possible to take into account the electromagnetic interaction of the elements of the combined object. The method of integral equations (IE) was used to find the current density and magnetic field strength.
The scatter diagrams of the person-intruder, the person-intruder in personal armor protection (PAP) under different conditions of irradiation and reception and illumination frequencies are obtained and analyzed. This made it possible to evaluate the effect of metallic elements on the scatter diagram of the combined object.
The obtained a priori information is of significant practical importance at the stage of optimizing signal processing algorithms and designing new means of covert detection
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