Observation of quadrocopters by radar with long-term coherent signal accumulation

2021 ◽  
Author(s):  
A.А. Lavrov ◽  
I.К. Antonov ◽  
A.А. Kasaikin ◽  
V.G. Ovchinnikov ◽  
M.S. Ogorodnikov
Keyword(s):  
Wavelength Range ◽  
Pulse Signal ◽  
Coherence Time ◽  
Chirp Pulse ◽  
Coherent Signal ◽  
Coherent Accumulation ◽  
Spectral Components ◽  
Probing Signal ◽  
Coherent Pulse

The article discusses the experimentally obtained characteristics of radar signals reflected from small-sized aerial targets such as a quadrocopter, with their long-term coherent accumulation. A brief description of the structural diagram of the experimental radar and its characteristics is given. The radar operates in the ten-centimeter wavelength range and emits a coherent-pulse signal. The duration of the emitted chirp pulse is 1 μs with a compression ratio of 15. Algorithms for primary processing of signals in a computer are given, including compression of chirp signals and spectral analysis of the received implementation, which is equivalent to its coherent accumulation. The parameters of the generated radar image are determined. The characteristics of the targets used - the small-sized quadcopters Mavic and Phoenix – are given. As a result of the experiments, it was shown that the tested small-sized air targets in the ten-centimeter wavelength range of the probing signal have their own coherence time sufficient for the coherent accumulation of the signal reflected from them for a time of at least 0.2 seconds. The Mavic does not produce reflections from its rotating rotors. The main rotor of the Phoenix quadcopter creates spectral components in the image, concentrated along the speed axis in the form of maxima symmetrically located relative to the central mark of the target. The presence of this feature of the signal allows you to identify the type of target, highlight the target against the background of birds, and detect a stationary, hovering target. It is shown that the features of signals reflected from the ground, with long-term coherent accumulation, allow providing the minimum speed of the detected target, measured in fractions of a meter per second.

scholarly journals Model and long-term coherent accumulation basic algorithm for the reflected signal with non-zero higher derivative range to radar target

Doklady BGUIR ◽  
2021 ◽  
Vol 19 (2) ◽  
pp. 49-57
Author(s):  
S. V. Kozlov ◽  
Le Van Cuong
Keyword(s):  
Matched Filter ◽  
Radar Target ◽  
Complex Frequency ◽  
Repetition Period ◽  
Target Movement ◽  
Basic Algorithm ◽  
Coherent Accumulation ◽  
Phase Alignment ◽  
Reflected Signal

The purpose of the work was to substantiate a mathematical model of the signal reflected from moving radar target at the time of its observation, which determines the need to take into account the range migration and its derivatives up to the third order, inclusive, and the Doppler frequency migration, and the basic algorithm of long-term coherent accumulation for the reflected signal. The algorithm provides for the calculation of the “fast” spectra samples, within each repetition period, time, the phase alignment of the spectra samples by multiplying by the correcting phase factors determined by the expected parameters of the target movement and the number of the repetition period, the summation of the spectral samples in the “slow” time, the multiplication of the result by complex frequency response of a matched filter of a single signal and performing an inverse Fourier transform. The performance of the algorithm is illustrated by the results of computer simulation.

scholarly journals Long-time coherent accumulation algorithms for reflected signal with non-zero higher derivatives of the range to radar target in the spectral domain

Doklady BGUIR ◽  
2021 ◽  
Vol 19 (5) ◽  
pp. 35-44
Author(s):  
S. V. Kozlov ◽  
Van Cuong Le
Keyword(s):  
Fourier Transform ◽  
Matched Filter ◽  
Repetition Period ◽  
Coherent Accumulation ◽  
Uncertainty Function ◽  
Long Time ◽  
Higher Derivatives ◽  
Range Migration ◽  
The Difference

The purpose of the article is to present computationally economical algorithms for long-term coherent accumulation of signals reflected from a point target with compensation for range and frequency migration and accumulation of signals in the spectral region. The algorithms include intra-period processing with simultaneous correction of range and frequency migration and inter-period processing with coherent accumulation of signals at the output of intra-period processing. In the first variant of the algorithm, intra-period processing is implemented by calculating the spectra of the received signals in each repetition period, multiplying the samples of the spectra by the samples of the amplitude-phase-frequency characteristic of the matched filter of a single signal and correcting phase coefficients determined by the number of the repetition period and the values of the range derivatives, and the inverse Fourier transform of the transformed spectra. The difference between the second version of the algorithm at the stage of intraperiod processing is the correction of only the quadratic and subsequent components of the range and frequency migration and the use of the keystone transformation, which eliminates the linear range migration. Coherent accumulation for both variants is realized due to the fast Fourier transform of the signal samples over the repetition periods for all samples over the range. The concept of “rough speed resolutionˮ is introduced, which determines the arrangement of channels when compensating for range migration. The uncertainty function in the coordinates “velocity–acceleration” is obtained. The equivalence of the two variants of the algorithm is shown and estimates for the required number of receiver channels are given. The simulation results confirming the operability of the proposed algorithms are presented.

scholarly journals Heart Rate Monitoring Sensor Based on Singlemode-Multimode-Singlemode Fiber

2019 ◽  
Vol 10 (2) ◽  
pp. 186-193
Author(s):  
Ninik Irawati ◽  
Agus Muhamad Hatta ◽  
Yoseph Gita Yhun Yhuwana ◽  
Sekartedjo
Keyword(s):  
Heart Rate ◽  
High Stability ◽  
Pulse Signal ◽  
Fiber Structure ◽  
Heart Rate Monitoring ◽  
Structure Changes ◽  
Optical Output ◽  
Structure Monitoring ◽  
Electrocardiogram Ecg

AbstractThe singlemode-multimode-singlemode (SMS) fiber structure for a heart rate monitoring is proposed and developed. An artificial electrocardiogram (ECG) signal is used to simulate the heart pulse at different rates ranging from 50 beats per minute (bpm) to 200 bpm. The SMS fiber structure is placed at the center of a loudspeaker and it senses the vibration of the pulse. The vibration of the pulse signal applied to the SMS fiber structure changes the intensity of the optical output power. The proposed sensor shows a linear frequency of the heart rate sensing range that matches well with the relevant heart rate from the artificial ECG. This work shows the capability of the SMS fiber structure monitoring the heart rate frequencies for a long term, high stability realization, and reproducibility, and being suitable for the observation in hospitals as well as in other environments.

Quantitative spectroscopy of the aurora. VI. The auroral spectrum from 275 to 815 nm observed by the OSIRIS spectrograph on board the Odin spacecraft

2010 ◽  
Vol 88 (8) ◽  
pp. 559-567 ◽  
Author(s):  
R. L. Gattinger ◽  
A. Vallance Jones ◽  
D. A. Degenstein ◽  
E. J. Llewellyn
Keyword(s):  
Wavelength Range ◽  
Polar Region ◽  
Spectral Response ◽  
Reference Spectrum ◽  
Digital Format ◽  
Atomic Lines ◽  
Scanning Systems ◽  
Imaging Spectrograph ◽  
Potential Use

Terrestrial auroral spectra over the 275 to 815 nm wavelength range have been recorded by the OSIRIS imaging spectrograph on board the Odin spacecraft. The spectra are from the dark polar region and are averaged over limb tangent altitudes from 100 to 105 km. All wavelengths are exposed simultaneously, thus avoiding the effect of temporal intensity variations inherently present in spectrally scanning systems. Particular care has been taken to quantify the relative spectral sensitivity over the entire wavelength range, and there is an estimated 5% precision in the measurements. To maintain accurate on-orbit spectral calibrations, an atmospheric radiation model with multiple Rayleigh scatter is employed to regularly update the OSIRIS spectral response throughout the mission. A calibrated auroral spectrum is presented, together with matching synthetic spectra for many of the observed features, for potential use as a reference spectrum in general atmospheric research. The relative intensities of the brighter auroral band systems and atomic lines are reviewed. Finally, the observed spectrum is made freely available in digital format in long term archives.

scholarly journals Излучательная рекомбинация, захват носителей заряда на ловушки и релаксация фототока в PbSnTe : In с составом вблизи инверсии зон

2018 ◽  
Vol 52 (7) ◽  
pp. 694
Author(s):  
Д.В. Ищенко ◽  
И.Г. Неизвестный
Keyword(s):  
Experimental Data ◽  
Fermi Level ◽  
Wavelength Range ◽  
Radiative Recombination ◽  
Recombination Lifetime ◽  
Disordered Structure ◽  
Wide Wavelength Range ◽  
High Photosensitivity

AbstractBased on the notions that PbSnTe:In is a direct-gap semiconductor, the radiative-recombination lifetime is calculated, and the photocurrent relaxation and dependences of the instantaneous electron and hole lifetime are calculated under the assumption that PbSnTe:In is a disordered structure containing capture centers. These calculations explain such experimentally observed peculiarities of PbSnTe:In as a high photosensitivity in a wide wavelength range, pinning of the Fermi level, and long-term photocurrent relaxation. Calculations are also compared with experimental data and the possible parameters of photodetectors are evaluated.

scholarly journals PERIODIC AND SPORADIC VARIATIONS IN THE SPECTRAL FLUX DENSITY OF THE CAS A SUPERNOVA REMNANT

2020 ◽  
Vol 25 (4) ◽  
pp. 268-275
Author(s):  
A. A. Gorbunov ◽  
◽  
M. I. Ryabov ◽  
A. L. Sukharev ◽  
V. V. Bezrukovs ◽  
...  
Keyword(s):  
Solar Activity ◽  
Flux Density ◽  
Wavelength Range ◽  
Radio Astronomy ◽  
Supernova Remnant ◽  
Radiation Flux ◽  
National Academy Of Sciences ◽  
Spectral Flux ◽  
Cas A

Purpose: Based on the long-term study data in all radio spectrum ranges, the nature of deviations of spectral flux density of the Cas A supernova remnant from the tendency of its secular decrease is considered. The aim of this work is determining the presence of quasiperiodic variations and sporadic changes in the Cas A spectral radiation flux density depending on frequency. Design/methodology/approach: The main database is using the published results obtained with the method of absolute measurements of the Cas A spectral radiation flux density in a wide range from millimeter to decimeter wavelengths, as well as the results obtained with the method of relative measurements of the ratio of the flux densities of the Cas A supernova remnant and radio galaxy Cyg A, this latter being used as a reference source in the meter wavelength range. For making comparison with the aforesaid data obtained with different methods, the results of a long-term monitoring (since 1987) of the variation of the ratio of the spectral flux densities of Cas A and Cyg A made with the URAN-4 radio telescope of the Institute of Radio Astronomy of the National Academy of Sciences of Ukraine at 25 MHz were used. Findings: As a result of the analysis of the observed data for the Cas A radiation flux density in the entire radio wavelength range, the existence of quasiperiodic variations in the range from millimeter to meter wavelengths within 2 to 9 years has been noted. The reason for the detected quasiperiodic variations can be the processes in the Cas A remnant itself. In the decameter wavelength range, according to monitoring data obtained with the URAN-4 radio telescope, the seasonal-diurnal and long-term variations are noted, being associated with changes in the ionosphere state in the solar activity cycle, with some weak appearance of the secular decrease of the Cas A radiation flux. The presence of sporadic variations in the ratio of the spectral flux densities of Cas A and Cyg A is associated with the effect of the increased solar activity. For explaining the lowering of the Cas A spectral flux density to the Cyg A level and maintaining the excess of the Cas A flux at decameter waves, the quasi-simultaneous observations made with radiotelescopes for different wavelength ranges will be required. Conclusions: The evolution of the Cas A supernova remnant remains the focus of interest of current research efforts. An intriguing moment was the discovery of a point X-ray source in the center of radio source Cas A as a possible supernova remnant. The role of this source in the Cas A radio flux secular decrease and in its variations needs to be clarified. A detailed analysis of the long-term data and making quasi-simultaneous observations will allow to reveal the processes occurring in the radio source itself and to determine the influence of the ionosphere state on the results of measurements. A joint program is suggested for observations of Cas A and Cyg A flux variations with the RT-32 and RT-16 radio telescopes, the LOFAR element of the Ventspils International Radio Astronomy Center (Latvia), and the URAN, UTR-2 and GURT radio telescopes of the Institute of Radio Astronomy of the National Academy of Sciences of Ukraine. Key words: Cas A; secular radiation flux decrease; supernova remnant; ionosphere; solar activity

scholarly journals Acoustic-phonetic and auditory mechanisms of adaptation in the perception of sibilant fricatives

2019 ◽  
Author(s):  
Eleanor Chodroff ◽  
Colin Wilson
Keyword(s):  
White Noise ◽  
Short Term ◽  
Contextual Variation ◽  
Average Spectrum ◽  
Significant Difference ◽  
Spectral Components ◽  
Mechanisms Of Adaptation ◽  
Sibilant Fricatives ◽  
Contextual Adaptation

Listeners are highly proficient at adapting to contextual variation when perceiving speech. The present study examined the effects of brief speech and non-speech contexts on the perception of sibilant fricatives. We explored three theoretically motivated accounts of contextual adaptation based on phonetic cue calibration, phonetic covariation, and auditory contrast. Under the cue calibration account, listeners adapt by estimating a talker-specific average for each phonetic cue or dimension; under the cue covariation account, listeners adapt by exploiting consistencies in how the realization of speech sounds vary across talkers; under the auditory contrast account, adaptation results from (partial) masking of spectral components that are shared by adjacent stimuli. The spectral center of gravity, a phonetic cue to fricative identity, was manipulated for several types of context sound: /z/-initial syllables, /v/-initial syllables, and white noise matched in long-term average spectrum (LTAS) to the /z/-initial stimuli. Listeners’ perception of the /s/–/ʃ/ contrast was significantly influenced by /z/-initial syllables and LTAS-matched white noise stimuli, but not by /v/-initial syllables. No significant difference in adaptation was observed between exposure to /z/-initial syllables and matched white noise stimuli, and speech did not have a considerable advantage over noise when the two were presented consecutively within a context. The pattern of findings is most consistent with the auditory contrast account of short-term perceptual adaptation. The cue covariation account makes accurate predictions for speech contexts, but not for non-speech contexts or the absence of a speech vs. non-speech difference.

scholarly journals Long-term variability of H2O masers in YSOs

2002 ◽  
Vol 206 ◽  
pp. 51-54 ◽  
Author(s):  
Riccardo Valdettaro ◽  
Francesco Palla ◽  
Jan Brand ◽  
Riccardo Cesaroni ◽  
Giovanni Comoretto ◽  
...  
Keyword(s):  
Stellar Mass ◽  
Young Stellar Objects ◽  
Frequency Of Occurrence ◽  
Velocity Range ◽  
Stellar Objects ◽  
Spectral Components ◽  
The Relationship ◽  
Maser Sources ◽  
Water Maser

A sample of 14 water maser sources associated with young stellar objects (YSOs) has been monitored over 13 years with the Medicina 32-m antenna. The YSOs have been selected with bolometric luminosities from 20 L⊙ to 2 × 106 L⊙ with the aim of investigating the relationship between H2O maser variability and stellar mass. The results are presented in various graphical forms which allow to follow the variation of the different spectral components. In particular, four quantities have been considered in our analysis: the intensity of the maser lines as a function of time and velocity; the flux integrated over the observed velocity range as a function of time; the maximum flux ever observed at each velocity; and the frequency of occurrence of the maser emission at any given velocity.

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