Atmospheric Attenuation Coefficient Research Articles

Первые результаты инфракрасной съемки с БПЛА термальных объектов Курильских островов в 2023 г.

For monitoring hard-to-reach thermal facilities, remote surveillance techniques from unmanned aerial vehicles (UAVs) equipped with a thermal infrared camera represent a progressive platform for rapid information collection. This paper presents the first results of such an application of UAVs to study five thermal objects on the Kuril Islands. Four of them (Kipyashchaya Riwer on Iturup Island, Lake Biryuzovoye on Simushir Island, Yankich Island and Yurieva River on Paramushir Island) are associated with active volcanoes. Heat maps with precise geographical reference have been obtained for all sections of gas hydrothermal discharge. For Kipyashchaya River and Yankich Island verification of air thermometry by ground data was performed and real atmospheric attenuation coefficients were obtained for different flight altitudes under observed meteorological conditions. The first data on the parameters of the thermal plume from the hot Yurievа River flowing into the Sea of Okhotsk were obtained.

Research on multi-dimensional micro-motion feature extraction of moving targets

The micro-Doppler effect is a physical phenomenon generated by the micro-motion of objects and their components, which have a significant influence on improving radar detection and resolution capability and also enhancing the radar imaging and target recognition performance. The extraction of micro-Doppler frequency, as a commonly used time-frequency analysis tool, is of great significance in extracting and reconstructing the signal with micro-motion targets. The micro-motion characteristics for moving targets can be verified by using simulation through combining the theory of micro-Doppler effect with the frequency domain model of electromagnetic waves. The simulation research on the micro-motion characteristics of a three-dimensional target is conducted by using the finite element method. The influences of environmental conditions such as relative humidity, visibility, and the presence or absence of turbulence on echo intensity and time-frequency relationship are investigated theoretically. The simulation results indicate that parameters such as relative humidity and visibility, which affect the atmospheric attenuation coefficient, can reduce echo intensity and the period of time-frequency curve. By triggering off beam drift in the transmission path, turbulence can lead to “frequency shift deformation” of the time-frequency curve, degrading the extraction of target motion attitude. A motion attitude classification method is proposed in order to study the micro-Doppler effect better. According to whether the frequency shift changes with time, the motion attitude can be divided into frequency shift time-invariant motion and time-variant motion. Frequency shift time-variant motion includes translation, rolling and vibration. Vibration and rolling are motions that periodically change with time, requiring the comparison of instantaneous frequency shifts at any three times within a cycle. Translation is a time-variant motion with irregular frequency shifts over time, which involves studying instantaneous frequency shifts at any three times. Transient frequency shifts should be analyzed and compared at different times for these motions. The frequency shift time-invariant motion is mainly rotation obtained experimental results indicate that the amplitude, plus-minus, and spectral width of frequency shift at different positions are aimed at inverting the target shape, attitude, direction and velocity. Demodulating one-dimensional data obtained from the FFTshift function can obtain the time-frequency-intensity relationship. This multi-parameter analysis method is a multi-dimensional processing method widely used in the fields of radar, sonar, and communication. The above research is conductive to the measurement of target macroscopic shape properties and the extraction of microscopic motion information, which lays the foundation for radar detection and recognition.

A modified acoustic-turbulent scattering model for long-range propagation with wind tunnel validation

We present a newly developed ‘bridging’ model to quantify turbulent effects on long-range acoustic propagation in the atmosphere. The bridging model is incorporated into an existing validated Burgers’ equation solver. The new model combines the scattering model of Ostashev and Wilson and a traditional refraction model for acoustic-turbulent interaction. A new attenuation coefficient is obtained that is consistent with the atmospheric attenuation coefficient via integration of energy loss over all scattering angles. To validate and quantify the effect of the new model, we conduct a series of propagation experiments in the National Science Foundation funded University of Florida Boundary Layer Wind Tunnel. A synthetic noise signal propagates through the tunnel, which has controllable boundary layer turbulent statistics via fan speeds and hundreds of individually controlled roughness elements. We compare predictions of the bridging model, Ostashev and Wilson’s model, and the experiments of the wind tunnel. Also, we perform example long-range predictions using the new model and Ostashev and Wilson’s model with a synthetic tornadic infrasound signal. A sensitivity test of model parameters is performed. We show that for particular atmospheric conditions and turbulent statistics, the bridging model has particular advantages with minimal additional computational expense.

Deceiving ability of typical natural objects used for false target in laser decoy jamming

Aiming at the application of natural objects false target in laser decoy jamming, its deceiving ability characterized by decoy airspace was calculated and analyzed. On the premise of full considering the reflection characteristics of target, the intensity of jamming-indicating laser, atmospheric laser attenuation coefficient, and other factors, the analysis model of decoy jamming ability for false target was established under the condition of suppression coefficient K (≥1). Furthermore, the effectual decoy airspace of common natural objects was analyzed under typical condition. The results show that the effective cheating airspace of false target is closely related to the type of targets, and the deceiving ability of vegetation, gravel and diffuse reflection objects is enhanced in turn under the same conditions. There exists a mirror reflection component that is much smaller than the diffuse reflection component in the decoy airspace of vegetation and gravel natural objects, and the variation of the incident angle of jamming laser has obvious influence on the distribution of effectual decoy airspace. However, there is no obvious trend change rule for the decoy airspace of vegetation targets with the incidence angle. The research results are instructive for the reasonable application of typical natural objects used for false target.

Performance Investigation of OFDM-FSO System under Diverse Weather Conditions of Bangladesh

Free space optical (FSO) communication systems which are deployed for last mile access, being considered as a suitable alternative technology for optical fiber networks. It is one of the emerging technologies for broadband wireless connectivity which has also been receiving growing attention due to high data rate transmission capability with low installation cost and license free spectrum. However, the widespread use of FSO technology has been hampered by the randomly time varying characteristics of propagation path mainly due to atmospheric turbulence, sensitivity to diverse weather conditions and the nonlinear responsivity of laser diode. This paper presents the performance investigation of an OFDM-FSO system over atmospheric turbulence channels under diverse weather conditions of Bangladesh. The channel is modeled with gamma-gamma distribution using 16-QAM modulation format and 4×4 multiple transceiver FSO system. All possible challenges are imposed on the system performance such as atmospheric attenuation, turbulence, pointing error, geometric loss etc. The refractive index structure parameter and atmospheric attenuation coefficient for different weather conditions are calculated by using the data, collected from Bangladesh Meteorological Department. The acquired results can be fruitful for scheming, forecasting and assessing the OFDM-FSO system’s ability to transmit wireless services over turbulent FSO links under actual conditions of Bangladesh.

SNR and transmission error rate for remote laser communication system in real atmosphere channel

Performance of remote laser communication system fluctuates greatly due to influence by atmospheric turbulence, it is difficult to assess its system error performance effectively. On the basis of the atmospheric attenuation channel and atmospheric turbulence channel, this paper establishes the integrated computation signal-to-noise ratio(SNR) function and transmission error rate function under the condition of atmospheric attenuation and the atmospheric turbulence, analyzes the affecting factors of the transmission error rate under two kinds of channel in remote transmission, calculates the relation between atmospheric attenuation coefficient and haze particle size under different visibility in atmospheric attenuation channel, as well as the relationship between the optimal threshold and intensity fluctuation under different transmitting powers in atmospheric turbulence channel. Through the test in atmospheric turbulence channel, results show that light intensity fluctuation is the main factor causing low system performance within a certain range of background noise, the new calculation method of SNR makes the variation between the actual system bit error rate and the achievable minimum bit error rate in theory several orders of magnitude. The models can effectively assess the performance of laser communication system under atmospheric attenuation and atmospheric turbulence, and provide a reference for relevant researches.

Super-sensitive detection of quantum interferometer in atmospheric environment

With squeezed states or entangled states being the source, quantum metrology, imaging and sensing can break the standard quantum limit (SQL), even reach the Heisenberg limit (HL), which is difficult to achieve by traditional methods. However, the photon loss or phase fluctuation caused by the atmospheric attenuation and turbulence cannot be ignored in the actual application. Atmospheric transmittance and phase fluctuation are related to the detection distance, and the phase sensitivity becomes worse as the distance increases. As the functions of distance, the photon loss and phase fluctuation are uniformly expressed according to the introduction of atmospheric attenuation coefficient, turbulence structure constant and receive aperture size in this paper. The density matrixes and phase sensitivities of N00N states and M&M′ states in the atmospheric environment are proposed in terms of distance variables. Then the quantitative computation of super-sensitive distance is carried out. SQL-contour is proposed to describe the super-sensitive ability of the quantum interferometer for the affection from both photon loss and phase fluctuation. The simulation results show that, in atmospheric environment the super-sensitive distance can reach hundreds of meters. M&M′ states with less total photon number are more likely to reflect the advantage of super-sensitivity. SQL-contour can provide references for interferometric source choosing.

Maximum detection range limitation of pulse laser radar with Geiger-mode avalanche photodiode array

When designing and evaluating the performance of laser radar system, maximum detection range achievable is an essential parameter. The purpose of this paper is to propose a theoretical model of maximum detection range for simulating the Geiger-mode laser radar’s ranging performance. Based on the laser radar equation and the requirement of the minimum acceptable detection probability, and assuming the primary electrons triggered by the echo photons obey Poisson statistics, the maximum range theoretical model is established. By using the system design parameters, the influence of five main factors, namely emitted pulse energy, noise, echo position, atmospheric attenuation coefficient, and target reflectivity on the maximum detection range are investigated. The results show that stronger emitted pulse energy, lower noise level, more front echo position in the range gate, higher atmospheric attenuation coefficient, and higher target reflectivity can result in greater maximum detection range. It is also shown that it’s important to select the minimum acceptable detection probability, which is equivalent to the system signal-to-noise ratio for producing greater maximum detection range and lower false-alarm probability.

Computation of the Total Acoustic Atmospheric Attenuation Coefficient Aα for Several Acoustic Sources in Tikrit City

In this work, the attenuation coefficients Aα had determined for different acoustic source by the air atmosphere for one day in Tikrit city, based on an analytical method which employed on several empirical equations that taking in consideration the various meteorological conditions in which the climate elements changed in additional to frequencies sources. The results shows the atmospheric attenuation is sensitive to the composition of air, particularly to the wide varying concentration of water vapor and temperature where the air temperature play and frequency variation are dominate that controlling the values of Aα.

Study on survival function of noise quantum channel and its simulation

In order to build a quantum signaling network with high survivability, quantum channel survival function and survivability of signaling network have been proposed based on the concept of fidelity. The survival coefficient in optical fiber or free space is analyzed, fidelity in noisy quantum channel with the decoherence mechanisms is calculated and survival function test model is proposed. Simulation analysis shows that, by reducing the quantum state transition rate, controlling fiber attenuation coefficient and atmospheric attenuation coefficient, decreasing the time of quantum states evolution, and setting quantum repeaters, we can construct a high survivability of quantum channel and provide a theoretical foundation for the formulation of quantum entanglement signaling network standard.

Performance analysis of a free-space terrestrial optical system in the presence of absorption, scattering, and pointing error

Performance analysis has been carried out to evaluate the performance of a free-space optical terrestrial system using on-off keying in the presence of scattering and absorption due to atmospheric gas molecules and aerosols, and pointing error phenomenon due to the link missalignment. It is found that in order to achieve a bit error rate (BER) of 10−9 at a visibility of 1.9 km, a 13.2 dB power penalty is incurred for atmospheric channel in haze condition and for atmospheric channel in rain condition, a heavy rainfall rate of 25 mm/h produces a high atmospheric attenuation coefficient α, and thus almost 18 dB power penalty is induced to achieve a BER of 10−9. However, for the atmospheric channel in a fog condition, the visibility can reach 1.1 km and induces a power penalty of 25 dB to maintain the BER of 10−9. The power penalty increases when the visibility is reduced, rainfall intensity increased, and an additional power penalty of more than 25 dB is incurred in the presence of pointing error for atmospheric channel of 1.3 km visibility in a light fog condition compared to clear weather condition.

Inter-comparison of thermal and optical methods for determination of atmospheric black carbon and attenuation coefficient from an urban location in northern India

The simultaneous measurements of black carbon (BC, based on Aethalometer) and elemental carbon (EC, using thermo-optical EC–OC analyzer) in airborne particles collected from an urban location (Kanpur) in northern India are reported here. The strategy for site-selection is most relevant in order to assess the relative dominance of emissions from coal-fired industries, fossil–fuel combustion and biomass burning on the seasonal variability of EC (BC) concentrations. An inter-comparison of the analytical data ( n = 32) suggests that BC mass concentration is ∼ 20% higher than that of EC. However, attenuation coefficient ( b ATN) measured by the two analytical instruments shows good agreement (slope = 0.97, n = 27), establishing the validity of b ATN derived from thermo-optical EC–OC analyzer. Furthermore, slope (20.7 m 2 g − 1 ) of a linear-fit to the data ( n = 48, R 2 = 0.86) for surface EC concentration (EC s ≤ 8 μg C cm − 2 ) and optical-attenuation (ATN ≤ 180) measured at 678 nm on thermo-optical analyzer provides an independent and novel way of determining the “site-specific” attenuation cross-section ( σ ATN).

Does a Model-Scale Nozzle Emit the Same Jet Noise as a Jet Engine?

A careful experimental study has been carried out to verify whether a model-scale nozzle produces the same jet noise as a jet engine, with the twin goals of 1) validating the practice of carrying out jet noise research at model scale for full-scale applications, and 2) aiding the identification of jet noise in measured total spectra from jet engines, which have contributions from several noise sources. A special test was carried out to measure pure jet noise from a low-bypass ratio jet engine at all the angles. Aeroacoustic measurements were made from model-scale nozzles at the Boeing Low-Speed Aeroacoustic Facility at the same operating conditions as the jet engine. Many issues that are pertinent for the comparison of scaled model data with engine data have been investigated thoroughly. These include the requirements of the instrumentation system for model and engine tests, suitable methodology for the calculation of the atmospheric attenuation coefficients, propagation effects, data repeatability, scaling of jet noise spectra, effects of the disparate Reynolds numbers and mixing perimeters between model nozzles and engines, etc. The data indicate that the weather corrections are accurate even at very high frequencies of interest in model tests. A new phenomenon of nonlinear propagation effects is identified for subsonic heated jets when the convective Mach number exceeds unity. The convective Mach number is shown to be a better indicator of nonlinear processes than high sound amplitudes,as has been believed in the past As demonstrated, with the proper scaling factors, both narrowband and one-third-octave jet spectra can be collapsed. The concept of increasing the shear perimeter for achieving better mixing and hence reducing noise has no merit, even at supercritical pressure ratios. Excellent agreement between scaled model and engine spectra is demonstrated at all angles and frequencies for a variety of power levels; thus, it is possible to acquire high-quality spectra at high frequencies, provided proper care is taken. Finally, the major conclusion from the preceding results is that jet noise research carried out at model scale is applicable to jet engines.

Application of Atmospheric Attenuation Correction in Scaling Jet Spectra

S CALE model tests of exhaust nozzles are usually carried out to establish the characteristics of jet noise because of significantly lower cost relative to full-scale engine tests. Model tests also allow the flexibility to independently control and vary the jetMach number and jet total temperature, which is not possible with jet engines. Further, acoustic data may be acquired in a controlled anechoic environment with systematic parametric variation. Much of the knowledge on jet noise gained in the last six decades has come mainly from scale model tests conducted at various laboratories. Suitable theories that explain the observed characteristics, and scaling laws to collapse spectra, have also been attempted. To facilitate direct comparison of jet noise spectra obtained fromnozzles of different diameters and varying test-day weather conditions, the measured data must be normalized in some fashion. Recently, Viswanathan [1] investigated several issues that are relevant in the scaling ofmodel scale spectra so as to permit comparisonwith engine noise. Some of these issues addressed include the requirements of the instrumentation system for model and engine tests, a suitable methodology for the calculation of the atmospheric attenuation coefficients, the propagation effects, the repeatability of data, the effects of the disparate Reynolds numbers, etc. It was clearly demonstrated that 1) spectra obtained with nozzles of different diameters can be collapsed perfectly at all frequencies; and 2) a model scale nozzle emits the same jet noise as a jet engine. Viswanathan [2] developed new scaling laws based on the explicit recognition that 1) the variation of the overall sound power level with jet velocity has a weak dependence on jet stagnation temperature ratio; and 2) the variation of the overall sound pressure level with velocity at every radiation angle is a function of jet stagnation temperature ratio. Excellent collapse of the spectra over the entire measured frequency range, at various jet stagnation temperature ratios and at several radiation angles, has been shown in [1–4]. However, some confusion still prevails on the application of the atmospheric absorption corrections in the scaling of spectra. It is well established that the amplitude of acoustic waves is attenuated by the atmosphere during sound propagation. It is also well known that the effect of atmospheric absorption is a strong function of frequency, with the coefficients of absorption increasing with increasing frequency. Several methods have been developed for calculating the absorption coefficients. It was shown in [1] that the method due to Shields and Bass [5] is best suited for the high frequencies of interest in model tests. Some clarification on the proper application of the atmospheric corrections, with concrete examples, is provided in this paper.

Methodology for generation of heliostat field layout in central receiver systems based on yearly normalized energy surfaces

The heliostat field layout is an essential task for any solar tower plant optimization process. Radially staggered and other distributions are usually optimised by computer codes using different approaches. In most of those cases, due to the CPU time required, the heliostat field layout is optimised by several mathematical models and simplifications. With today’s computers, it is possible to calculate the yearly energy available at any point in a site for a given tower height, the yearly normalized energy surface (YNES). Yearly efficiency maps can be generated based on the cosine factor, the spillage factor and the atmospheric attenuation coefficient of the site using real Direct Normal Irradiance (DNI) data, within a reasonable computing time. It is therefore easy to find the place where the yearly energy available is the highest for location of the first heliostat. It is also possible to calculate the effect of shadowing and blocking by this heliostat on the YNES, so YNES can be re-calculated and the best position for the next heliostat can be found. Although this iterative method is time-consuming, it is worthwhile if either the efficiency of the solar plant can be increased or the capital cost reduced. This YNES-based layout generation method enables better flexibility than pre-determined gridding strategies such as used in DELSOL. The paper includes a description of the optimization procedure.

Ground-level enhancements during solar cycle 23: results from SVIRCO, LOMNICKY STIT and LARC neutron monitors

The list of Ground-Level Enhancements (GLEs) occurring during the on-going solar cycle (no. 23) is used to show that they are absent during a time interval of the maximum phase in which a relative reduction in the sunspot area extent occurs. This period refers to October 2000 to March 2001 and it is associated with the concept of the Gnevyshev Gap, introduced 10 years ago by the Rome cosmic ray group. Also, effects of the Gnevyshev Gap in the solar cycle modulation of the atmospheric attenuation coefficient for Rome neutron monitor during the past solar cycle (no. 22) are illustrated. Moreover, it is suggested that GLE data files should be prepared by using the appropriate attenuation coefficient for each level of solar activity.

Assessment of lidar inversion errors for homogeneous atmospheres

The inversion of lidar returns from homogeneous atmospheres has been done customarily through the well-known slope method. The logarithmic operation over the range-corrected and system-normalized received signal used in this method introduces a bias in the statistics of the noise-affected processed signal that can severely distort the estimates of the atmospheric attenuation and backscatter coefficients under measurement. It is shown that a fitting of the theoretically expected exponential signal to the range-corrected received one, using as the initial guess the results provided by the slope method and a least-squares iterative procedure, can yield enhanced accuracy under low signal-to-noise ratios and especially in moderate-to-high extinction conditions.

Reconstruction and analysis of meteorological data for energy balances over the Venetian Lagoon and its hinterland

In order to compute the fluxes of net radiation and the energy balance of the Venetian Lagoon and its hinterland, it is necessary to know the solar input. To this end, the seasonal variation of the global solar radiation over a 10-year period has been analyzed. The normalized daily transparency coefficients and the atmospheric attenuation coefficients, as well as the net radiative fluxes over both the lagoon and the land, have been computed and are discussed in terms of the local dynamic climatology. The results are particularly interesting because of their practical applications, which include air pollution studies, emission strategy, thermal pollution of shallow waters, local climatology, and the preservation of works of art.

Contribution of Particles Pollution to Visibility

The contribution of particulate pollution to the visibility is demonstrated by applying a pulsed GaAs laser. The density of the "cloud" and the atmospheric attenuation coefficient were also determined. According to the definitions of multiple scattering, it was found that this process governs, in this case, the interaction between the laser light and the particles in the cloud.

Atmospheric Scattering Coefficients in the Visible and Infrared Regions

Atmospheric spectral attenuation coefficients have been measured in ten narrow wavelength bands between 0.4 and 2.3 μ for a variety of weather conditions for two overwater, sea-level paths of 5.5 and 16.3 km. The wavelength bands were chosen so as to avoid molecular absorption and were isolated by interference filters. A 60-in.-diameter high-intensity source and a 24-in.-diameter narrow-field receiver were combined to yield relative scattering attenuation coefficients (σ) as a function of wavelength λ. These were then scaled using values obtained at one wavelength with a visual telephotometer. Logσ vs logλ curves show a wide range of slopes and shapes, with a tendency toward less slope in the infrared (indicating that σ is becoming independent of λ in the infrared). Some correlation with relative humidity was found for relative humidities greater than 70%. An anomalous slope reversal between 1.68 and 2.27 μ is discussed, and a possible explanation for the reversal is given as selective scattering by the aerosol at these wavelengths.