Dirty thunderstorms caused by volcano explosive eruptions in Kamchatka by the data of electromagnetic radiation

During volcano eruptions, so called dirty thunderstorms are the sources of electromagnetic radiation. They are caused by ash-gas clouds formed during explosive eruptions. Thunderstorm activity in an ash-gas cloud during volcano eruption is monitored by radio equipment. The VLF direction finder, located at Paratunka, monitors thunderstorm activity in the region of Kamchatka Peninsula including dirty thunderstorms accompanying explosive eruptions of Shiveluch and Bezymyanniy volcanoes. In the paper, we analyze records of electromagnetic radiation associated with dirty thunderstorms occurring during volcano eruptions from 2017 to 2020. During that period 24 eruptions of Shiveluch volcano and 5 eruptions of Bezymyanniy volcano occurred. Seventeen and three of them, respectively, caused dirty thunderstorms. Two-stage scenario of development is typical for all the dirty thunderstorms. The first stage lasts for 5–7 minutes and accompanies eruptive column development. However, if the eruption begins according to a smooth scenario, the first stage may be weak. The second stage lasts for 20–80 minutes and is associated with eruptive cloud formation and propagation. The intensity of this dirty thunderstorm stage depends on eruption power as well as on the interaction of an eruptive cloud during its propagation with the clouds of meteorological origin. Based on the obtained data, that is indicated by the increase of cloud-to-cloud stroke number.

Evidence of turbulence in the stratosphere

Arnold (1954) has observed considerable turbulence in the stratosphere on four different occasions at Belmar, New Jersey, while tracking balloons with a telescope and a radio direction finder. The turbulence was so severe that the radiosonde separated from the balloon, though it was suspended with a cord with a nominal breaking strength of about 70 lbs. During three observations in June 1950, the instrument separated from the balloon at heights ranging from 28 to 32 km, while in the observation in October it separated at 24 km. He has estimated that a descending current of about 11 m. sec-1 could provide the necessary conditions for a free fall of the sonde of about 10 ft which could break the line.

Improved Unmanned Aerial Vehicle Noise Direction Finding System

The work is devoted to the development of the acoustic direction of creation of means of detection of unmanned aerial vehicles (UAVs). The work of these tools is based on the principles of noise direction finding with the use of such variable characteristics of the acoustic field as: sound intensity, frequency spectrum and spatial spectrum. The architecture of UAV detection devices on the acoustic field corresponds to the algorithms of reproduction in separate paths of the device of ideology of registration and control of dynamics of change of characteristic of an acoustic field which defines the specified change as the fact of detection. The technical implementation of the above detection devices is to create a path of parallel octave, ½ octave and ⅓ octave filters, a path of narrowband filtering and a path of detection by power (intensity). The ideology of construction of detection devices is based on variability and physical manifestations of changes in such characteristics of acoustic noise as: sound intensity in the space - time interval of observation, broadband filtering, narrowband filtering, correlation characteristics. To ensure the detection of acoustic power (or intensity) with subsequent measurement of the level, the counter-inclusion (by switching or using operational amplifiers) of the elements of the cross-shaped group is used. An important and new feature is that one of the linear discrete acoustic antennas with an enlarged base additionally has two more pressure receivers symmetrically relative to the phase center. For broadband filtration, a comb of ⅓ octave band and semi-octave filters is used. In turn, the path of the narrowband spectrum is an octave band filter and a unit for calculating the fast Fourier transform. The path of the correlation direction-finding method implements the determination of changes in the autocorrelation coefficient and the corresponding electrical parameter (say the current through the display circuit) in the processing path in situations of fixing the direction to the target. Therefore, the proposed system for detecting useful noise signals should contain four paths, the physical implementation of detection in which is performed by software implementation of detection algorithms and, threshold processing and indication of results In order to improve and increase the reliability of detection, the direction finder is supplemented by the path of detection on the mutual spectrum and the path of the correlation method of direction finding. The processing of input acoustic information of the type of specific noise-like signal is carried out by using the instrumental laboratory software package Lab View and Math Lab. We will add that the article contains theoretical and practical results of measurements of noise loading and range of action of a noise direction finder. Experimental studies in terms of detection and measurement of the main characteristics of the device were conducted in laboratory and field conditions. At the same time, the present demonstrates the rapid development of the UAV fleet, which determines the urgency of the work and the development of the device as a means of counteracting small aircraft of various recognitions is its goal.

Calculating the topocentric coordinates of the radio emission source according to the measurement results of the phase direction finder on board a mobile object

The algorithm to calculate the azimuth and the elevation angle on the source of radio emission in the topocentric system of coordinates is suggested according to the measurements done by the phase direction finder located on board a mobile object. The position of an aerial system direction finder to the earth topocentric system of coordinates can be changed. The change in the position of the aerial system influences the accuracy of calculating the bearings. The method to reduce the errors of bearing by iteration method is considered. The checking procedure of the algorithm by mathematical modelling is carried out.

Performance characteristics of acoustic direction finders of localized broadband signal sources

In this paper, we substantiate main performance characteristics of the regression algorithm of a two-channel direction finder of localized sources of broadband signal against the background of interference distributed in space, invariant to radiated power and supply voltage. We analyze mutual statistical characteristics of broadband signals in a two-channel direction finder. Based on the method of canonical decomposition in complex form, we show the cross-correlation function of processes at the outputs of direction finder antennas when operating on a localized signal source against the background of interference distributed in space. For invariance of performance characteristics, we consider the application of sign transformation to signals and analyze the dependence of a cross-correlation function of the input signals after the sign transformation at different signal-to-noise ratios. We show the formation of a directivity pattern in a correlation direction finder with signal-to-noise ratio more than 1. For direction-finding of localized signal source, we substantiated a regression algorithm with discrete-analog signal processing, where sign processing based on standard digital hardware components is used. The invariance of the algorithm to supply voltage is shown by representing Boolean functions as expressions of conjunction, disjunction, and negation. The regression algorithm is substantiated in the time domain. We obtain the expressions for mean and variance of the calculated statistics for direction-finding of localized signal source against the background of interference distributed in space. We show the possibility of formation of a directivity pattern with completely suppressed side lobes. The algorithm functions at signalto-noise ratios up to 1. The algorithms can be used in passive acoustic and hydroacoustic direction finders, as well as direction finders with ultra-wideband signals with computer-based signal processing.

The spatial configuration control for the mobile digital direction finder system

A promising direction related to determining the location of radio sources is the use of mobile digital direction finders. Their use is most effective when such direction finders form a system of information-related meters localized in a mobile coordinate system and able to move in it. Depending on the variation of the electromagnetic environment (the termination of radiation by some sources, the appearance of other sources of radio emission, their movement, etc.), the positions of the separated digital direction finders inside such a system should change. To ensure the effective functioning of the measuring system, the paper considers the problem of synthesizing control of the spatial configuration of digital direction finders, the solution of which provides maximum accuracy in determining the coordinates of the location of radio sources. It is shown that the specified problem belongs to the class of active experiments optimization problems or problems of trajectory control of observations.

DIFFERENTIAL PHASE DIRECTION FINDING ERRORS FOR EMITTERS WITH PHASE-ANGLE DEPENDENCE

Выведены формульные соотношения для расчета ошибок пеленгования парного излучателя с использованием разностно-фазового пеленгатора. Оценено влияние различных параметров парного излучателя на величину ошибки пеленгования этого излучателя. Formula relations for calculating the direction finding errors of a paired transmitter using a phase difference direction finder are derived. The influence of various parameters of a paired radiator on the magnitude of the direction finding error of this radiator is estimated.