Статті в журналах з теми "Vertical signal attenuation"
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1
Berne, A., G. Delrieu, and H. Andrieu. "Estimating the Vertical Structure of Intense Mediterranean Precipitation Using Two X-Band Weather Radar Systems." Journal of Atmospheric and Oceanic Technology 22, no. 11 (November 1, 2005): 1656–75. http://dx.doi.org/10.1175/jtech1802.1.
Повний текст джерелаАнотація:
Abstract The present study aims at a preliminary approach of multiradar compositing applied to the estimation of the vertical structure of precipitation—an important issue for radar rainfall measurement and prediction. During the HYDROMET Integrated Radar Experiment (HIRE’98), the vertical profile of reflectivity was measured, on the one hand, with an X-band vertically pointing radar system, and, on the other hand, with an X-band RHI scanning protocol radar. The analysis of the raw data highlights the effects of calibration and attenuation problems affecting the measurements of both radar systems. Once the two radar systems have been intercalibrated, various attenuation correction techniques are applied. The comparison of raw, intercalibrated, and corrected radar measurements for the two radar systems stresses the importance of calibration and attenuation correction. The applied corrections improve the consistency of the vertical profile of reflectivity that is measured by the two radar systems. However, a significant uncertainty remains when strong radar signal attenuations occur.
2
Vaňková, Irena, Keith W. Nicholls, Surui Xie, Byron R. Parizek, Denis Voytenko, and David M. Holland. "Depth-dependent artifacts resulting from ApRES signal clipping." Annals of Glaciology 61, no. 81 (April 2020): 108–13. http://dx.doi.org/10.1017/aog.2020.56.
Повний текст джерелаАнотація:
AbstractSeveral autonomous phase-sensitive radio-echo sounders (ApRES) were deployed at Greenland glaciers to investigate ice deformation. Different attenuation settings were tested and it was observed that, in the presence of clipping of the deramped ApRES signal, each setting produced a different result. Specifically, higher levels of clipping associated with lower attenuation produced an apparent linear increase of diurnal vertical cumulative displacement with depth, and obscured the visibility of the basal reflector in the return amplitude. An example with a synthetic deramped signal confirmed that these types of artifacts result from the introduction of harmonics from square-wave-like features introduced by clipping. Apparent linear increase of vertical displacement with depth occurs when the vertical position of a near-surface internal reflector changes in time. Artifacts in the return amplitude may obscure returns from internal reflectors and the basal reflector, making it difficult to detect thickness evolution of the ice and to correctly estimate vertical velocities. Variations in surface melt during ApRES deployments can substantially modulate the received signal strength on short timescales, and we therefore recommend using higher attenuator settings for deployments in such locations.
3
Shen, Xi, and Defeng David Huang. "Retrieval of Raindrop Size Distribution Using Dual-Polarized Microwave Signals from LEO Satellites: A Feasibility Study through Simulations." Sensors 21, no. 19 (September 24, 2021): 6389. http://dx.doi.org/10.3390/s21196389.
Повний текст джерелаАнотація:
In this paper, a novel approach for raindrop size distribution retrieval using dual-polarized microwave signals from low Earth orbit satellites is proposed. The feasibility of this approach is studied through modelling and simulating the retrieval system which includes multiple ground receivers equipped with signal-to-noise ratio estimators and a low Earth orbit satellite communicating with the receivers using both vertically and horizontally polarized signals. Our analysis suggests that the dual-polarized links offer the opportunity to estimate two independent raindrop size distribution parameters. To achieve that, the vertical and horizontal polarization attenuations need to be measured at low elevation angles where the difference between them is more distinct. Two synthetic rain fields are generated to test the performance of the retrieval. Simulation results suggest that the specific attenuations for both link types can be retrieved through a least-squares algorithm. They also confirm that the specific attenuation ratio of vertically to horizontally polarized signals can be used to retrieve the slope and intercept parameters of raindrop size distribution.
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Wallis, Rory, and Hyunkook Lee. "Localisation of Vertical Auditory Phantom Image with Band-limited Reductions of Vertical Interchannel Crosstalk." Applied Sciences 10, no. 4 (February 21, 2020): 1490. http://dx.doi.org/10.3390/app10041490.
Повний текст джерелаАнотація:
Direct sound that is captured by the upper layer of a three-dimensional (3D) microphone array is typically regarded as vertical interchannel crosstalk (VIC), since it tends to produce an undesired effect of the sound source image being elevated from the ear-level loudspeaker layer position (0°) in reproduction. The present study examined the effectiveness of band-limited VIC attenuation methods on preventing the vertical image shift problem. In a subjective experiment, five natural sound sources were presented as vertically-oriented phantom images while using two stereophonic loudspeaker pairs elevated at 0° and 30° in front of the listener. The upper layer signal (i.e., VIC) was attenuated in various octave-band-dependent conditions that were based on vertical localisation thresholds obtained from previous studies. The results showed that it was possible to achieve the goal of panning the phantom image at the same height as the image produced by the main loudspeaker layer by attenuating only a single octave band with the centre frequency of 4 kHz or 8 kHz or multiple bands at 1 kHz and above. This has a useful practical implication in 3D sound recording and mixing where a vertically oriented phantom image is rendered.
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Kosteletskii, Valerii. "Cascade Configuration of Modal Filters for Power Bus Protection in Differential and Common Modes." International Journal of Circuits, Systems and Signal Processing 15 (July 20, 2021): 666–71. http://dx.doi.org/10.46300/9106.2021.15.74.
Повний текст джерелаАнотація:
The paper discusses the results of quasi-static simulation of two modal filter (MF) cascade configurations designed to attenuate an interference pulse in differential and common modes. The geometric parameters of the MF are optimized by heuristic search according to the amplitude minimization condition. The results of calculating the time responses to an ultrashort pulse (USP) and electrostatic discharge (ESD) are presented. The USP attenuation coefficient in the differential mode was 6.84 times for the horizontally placed cascades, and 6.94 times for the vertical configuration. In the common mode, the attenuation coefficient was 7.35 times for the horizontally placed cascades, and 7.57 times for the vertically placed cascades. For ESD, the attenuation coefficients were 1.51 times for the horizontally and 1.55 times for the vertically placed cascades in the differential and common modes. It was found that only the first spike is attenuated by the ESD excitation on the MF
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Maresh, Jennifer, Robert S. White, Richard W. Hobbs, and John R. Smallwood. "Seismic attenuation of Atlantic margin basalts: Observations and modeling." GEOPHYSICS 71, no. 6 (November 2006): B211—B221. http://dx.doi.org/10.1190/1.2335875.
Повний текст джерелаАнотація:
Paleogene basalts are present over much of the northeastern Atlantic European margin. In regions containing significant thicknesses of layered basalt flows, conducting seismic imaging within and beneath the volcanic section has proven difficult, largely because the basalts severely attenuate and scatter seismic energy. We use data from a vertical seismic profile (VSP) from well 164/07-1 that penetrated [Formula: see text] of basalt in the northern Rockall Trough west of Britain to measure the seismic attenuation caused by the in-situ basalts. The effective quality factor [Formula: see text] of the basalt layer is found from the VSP to be 15–35, which is considerably lower (more attenuative) than the intrinsic attenuation measured on basalt samples in the laboratory. We then run synthetic seismogram models to investigate the likely cause of the attenuation. Full waveform 1D modeling of stacked sequences of lava flows based on rock properties from the same well indicates that much of the seismic attenuation observed from the VSP can be accounted for by the scattering effects of multiple thin layers with high impedance contrasts. Phase-screen seismic modeling of the rugose basalt surface at the top-of-basalt sediment interface, with the magnitude and wavelength of the relief constrained by a 3D seismic survey around the well, suggests that surface scattering from this interface plays a much smaller role than internal scattering in attenuating the seismic signal as it passes through the basalt sequence.
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Wang, Yanghua. "Stable Q analysis on vertical seismic profiling data." GEOPHYSICS 79, no. 4 (July 1, 2014): D217—D225. http://dx.doi.org/10.1190/geo2013-0273.1.
Повний текст джерелаАнотація:
Vertical seismic profiling (VSP) provides a direct observation of seismic waveforms propagating to various depths within the earth’s subsurface. The [Formula: see text] analysis or attenuation ([Formula: see text]) analysis based on direct comparison between individual waveforms at different depths, however, suffers from the problem of instability commonly due to fluctuations inherent in the frequency spectrum of each waveform. To improve the stability, we considered frequency and time variations and conducted [Formula: see text] analysis on an integrated observation. First, we transformed the time- (or depth-) frequency-domain spectrum to a 1D attenuation measurement with respect to a single variable, the product of time and frequency. Although this 1D measurement has a higher signal-to-noise ratio than the 2D spectrum in the time-frequency domain, it can also be used to further generate a stabilized compensation function. Then, we implemented two [Formula: see text]-analysis methods by data fitting (in a least-squares sense) to either the attenuation measurement or the data-driven gain function. These two methods are theoretically consistent and practically robust for conducting [Formula: see text] analysis on field VSP data.
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Nikahd, Ali, Mazlan Hashim, and Mohammad Jafar Nazemosadat. "A Review of Uncertainty Sources on Weather Ground-Based Radar for Rainfall Estimation." Applied Mechanics and Materials 818 (January 2016): 254–71. http://dx.doi.org/10.4028/www.scientific.net/amm.818.254.
Повний текст джерелаАнотація:
Efforts in hydrometeorology are concentrated on finding the causes of the ground based radar uncertainty sources for rainfall estimation recently. The error sources are interactions between radar with atmosphere and topography. Radar singly often covers systematic error whereas atmospheric and topographic errors are relevant to location and precipitation pattern. This article reviews uncertainty sources on weather ground-based radar in order to rainfall estimation that have been discussed in nine main categories includes; the range effects, radar signal attenuation, beam blockage, vertical air motion and precipitation drift, ground clutter, anomalous propagation, vertical variability of the precipitation system, variability of the Z-R relationship and bright band. Topographic errors such as ground clutter and beam blockage primarily can be eliminated by attentive in site selection. Atmospheric errors such as vertical air motion and precipitation drift can filter or eliminated by calibration methods. Systematic errors include radar signal attenuation and anomalous propagation is the result of structural changes in the radar waves in space. Thus, this review is explored the characteristics of uncertainty error resources and a comprehensive appraisal of experimental procedures is provided.
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Borel, Andžej. "DEVELOPMENT AND INVESTIGATION OF INPUT AMPLIFIER FOR THE OSCILOSCOPE." Mokslas - Lietuvos ateitis 12 (January 20, 2020): 1–5. http://dx.doi.org/10.3846/mla.2020.11420.
Повний текст джерелаАнотація:
Digital oscilloscope’s structure has analog signal acquisition circuit, which transforms signal’s amplitude to fit ADC dynamic range. This circuit is commonly called oscilloscope’s vertical or front-end amplifier. Difficulty in designing front-end amplifiers in GHz range largely affects higher frequency range oscilloscope’s price. This work is focused on designing a front-end amplifier using discrete and openly sold components. We propose a design for attenuator, buffer, variable gain circuits. Amplifier’s prototype is designed. Main characteristics of the amplifier were measured. Measured bandwidth is 3 GHz. Amplifier’s gain and attenuation can support vertical scale sensitivity range from 10 mV/div to 1 V/div. Step response distortion is under 10 %. SMD and PTH relay model attenuators were evaluated. In this paper we review oscilloscope’s front-end purpose and structure. We review amplifiers design and provide the results of experimental measurements.
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Protat, Alain, Surendra Rauniyar, Julien Delanoë, Emmanuel Fontaine, and Alfons Schwarzenboeck. "W-Band (95 GHz) Radar Attenuation in Tropical Stratiform Ice Anvils." Journal of Atmospheric and Oceanic Technology 36, no. 8 (August 2019): 1463–76. http://dx.doi.org/10.1175/jtech-d-18-0154.1.
Повний текст джерелаАнотація:
AbstractAttenuation of the W-band (95 GHz) radar signal by atmospheric ice particles has long been neglected in cloud microphysics studies. In this work, 95-GHz airborne multibeam cloud radar observations in tropical stratiform ice anvils are used to estimate vertical profiles of 95-GHz attenuation. Two techniques are developed and compared, using very different assumptions. The first technique examines statistical reflectivity differences between repeated aircraft passes through the same cloud mass at different altitudes. The second technique exploits reflectivity differences between two different pathlengths through the same cloud, using the multibeam capabilities of the cloud radar. Using the first technique, the two-way attenuation coefficient produced by stratiform ice particles ranges between 1 and 1.6 dB km−1 for reflectivities between 13 and 18 dBZ, with an expected increase of attenuation with reflectivity. Using the second technique, the multibeam results confirm these high attenuation coefficient values and expand the reflectivity range, with typical attenuation coefficient values of up to 3–4 dB km−1 for reflectivities of 20 dBZ. The potential impact of attenuation on precipitating-ice-cloud microphysics retrievals is quantified using vertical profiles of the mean and the 99th percentile of ice water content derived from noncorrected and attenuation-corrected reflectivities. A large impact is found on the 99th percentile of ice water content, which increases by 0.3–0.4 g m−3 up to 11-km height. Finally, T-matrix calculations of attenuation constrained by measured particle size distributions, ice crystal mass–size, and projected area–size relationships are found to largely underestimate cloud radar attenuation estimates.
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Touzeau, Alexandra, Amaëlle Landais, Samuel Morin, Laurent Arnaud, and Ghislain Picard. "Numerical experiments on vapor diffusion in polar snow and firn and its impact on isotopes using the multi-layer energy balance model Crocus in SURFEX v8.0." Geoscientific Model Development 11, no. 6 (June 20, 2018): 2393–418. http://dx.doi.org/10.5194/gmd-11-2393-2018.
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Abstract. To evaluate the impact of vapor diffusion on isotopic composition variations in snow pits and then in ice cores, we introduced water isotopes in the detailed snowpack model Crocus. At each step and for each snow layer, (1) the initial isotopic composition of vapor is taken at equilibrium with the solid phase, (2) a kinetic fractionation is applied during transport, and (3) vapor is condensed or snow is sublimated to compensate for deviation to vapor pressure at saturation. We study the different effects of temperature gradient, compaction, wind compaction, and precipitation on the final vertical isotopic profiles. We also run complete simulations of vapor diffusion along isotopic gradients and of vapor diffusion driven by temperature gradients at GRIP, Greenland and at Dome C, Antarctica over periods of 1 or 10 years. The vapor diffusion tends to smooth the original seasonal signal, with an attenuation of 7 to 12 % of the original signal over 10 years at GRIP. This is smaller than the observed attenuation in ice cores, indicating that the model attenuation due to diffusion is underestimated or that other processes, such as ventilation, influence attenuation. At Dome C, the attenuation is stronger (18 %), probably because of the lower accumulation and stronger δ18O gradients.
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Shrestha, Sujan, and Dong-You Choi. "Rain Attenuation Study over an 18 GHz Terrestrial Microwave Link in South Korea." International Journal of Antennas and Propagation 2019 (March 31, 2019): 1–16. http://dx.doi.org/10.1155/2019/1712791.
Повний текст джерелаАнотація:
Absorption of microwave radio frequency signal by atmospheric rain and losses is prevalent at frequencies above 5 GHz. The functioning frequencies of 18 GHz are taken for the point-to-point microwave link system. This paper presents studies on rain attenuation at 18 GHz, which specifies minimum performance parameters for terrestrial fixed service digital radio communication equipment. It presents a 3.2 km experimental link at 18 GHz between Khumdang (Korea Telecom, KT station) and Icheon (National Radio Research Agency, RRA station). The received signal data for rain attenuation and the rain rate were collected at 10-second intervals over three year’s periods from 2013 to 2015. During the observation period, rain rates of about 50 mm/hr and attenuation values of 33.38 dB and 21.88 dB occurred for 0.01% of the time for horizontal and vertical polarization. This paper highlights the discussion and comparison of ITU-R P.530-16, Moupfouma, Silva Mello, and Abdulrahman models and proposed an attenuation prediction approach where it presents the relationship between theoretical specific rain attenuation as specified by ITU-R P.838-3, γ%p, and effective specific rain attenuation, γeff. Additionally, it studies 1-minute rain rates derived from higher time integration of 5-minute, 10-minute, 20-minute, 30-minute, and 60-minute instances which are obtained from experimental 1-minute rainfall amounts that are maintained by the Korea Meteorological Administration (KMA). The effectiveness of the proposed approach is further analyzed for 38 and 75 GHz links which shows better prediction capability. Particularly, in an 18 GHz link under horizontal polarization, ITU-R P. 530-16 shows the relative error margin of 71%, 60%, and 38% where as 64%, 49%, and 42% were obtained under vertical polarization for 0.1%, 0.01%, and 0.001% of the time, respectively. The limitation of research lies on the experimental system that is set up in only one location; however, the preliminary results indicate the application of a suitable 1-minute rain attenuation model for a specific site. The method provides useful information for microwave engineers and researchers in making decisions over the choice of the most suitable rain attenuation prediction for terrestrial links operating in the South Korea region, particularly for lower frequency ranges.
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Feltane, S., S. Yahyaoui, A. Hafsaoui, and A. Boussaid. "Signal processing application for vibration generated by blasting in tunnels." Naukovyi Visnyk Natsionalnoho Hirnychoho Universytetu, no. 5 (2020): 54–60. http://dx.doi.org/10.33271/nvngu/2021-5/054.
Повний текст джерелаАнотація:
Purpose. To study the vibrations waves generated by blasting in a tunnel using the signal processing tools. Methodology. Field tests are carried out to measure vibration wave during blasting operations at different locations in the tunnel and its immediate environment. Results of the measurements are processed by the autocorrelation method, which consists of filtering based on signal shape recognition. A comparison is accomplished between the peak particle velocities (PPV) measured and those obtained after filtering. Findings. The results obtained after filtering gave a significant reduction in PPV of the measured vibration amplitudes in comparison to those obtained after treatment for the three components: longitudinal, transversal and vertical ones. Good knowledge of vibration source is important for amplitude attenuation regarding the observed difference between the recorded seismogram during explosion of a single unit charge and other standard explosions. Originality. The work introduces signal processing methods for filtering vibration signals related to blasting, which is insufficiently studied. Practical value. This study shows that the treatment of blasting vibrations by a filtering method should reduce the peak velocity of the particles by separating the signals and eliminating the interference in the initial signal.
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CARTA, CORRADO, MUNKYO SEO, and MARK RODWELL. "A MIXED-SIGNAL ROW/COLUMN ARCHITECTURE FOR VERY LARGE MONOLITHIC mm-WAVE PHASED ARRAYS." International Journal of High Speed Electronics and Systems 17, no. 01 (March 2007): 111–14. http://dx.doi.org/10.1142/s012915640700431x.
Повний текст джерелаАнотація:
The range of mm-wave radio communications is severely constrained by high losses arising from the short wavelength and from atmospheric attenuation. Large phased arrays can overcome these limitations, but it is very difficult to realize them using present monolithic beamsteering IC architectures. We propose an alternative architecture for large monolithic phased arrays. The beam is steered in altitude and in azimuth by separately imposing vertical and horizontal phase gradients. This choice reduces IC complexity, making large arrays feasible. Since extensive digital processing provides robust amplitude control and reduces die area, the LOs are processed as digital signals. Being very sensitive to compression, the IF signals are processed as analog signals and distributed by means of synthetic transmission-line buses. With careful frequency planning, this mixed-signal approach can allow large phased arrays to operate at frequencies much higher than those achievable with pure analog design.
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Jun, Hyunggu, Hyeong-Tae Jou, Chung-Ho Kim, Sang Hoon Lee, and Han-Joon Kim. "Random noise attenuation of sparker seismic oceanography data with machine learning." Ocean Science 16, no. 6 (November 11, 2020): 1367–83. http://dx.doi.org/10.5194/os-16-1367-2020.
Повний текст джерелаАнотація:
Abstract. Seismic oceanography (SO) acquires water column reflections using controlled source seismology and provides high lateral resolution that enables the tracking of the thermohaline structure of the oceans. Most SO studies obtain data using air guns, which can produce acoustic energy below 100 Hz bandwidth, with vertical resolution of approximately 10 m or more. For higher-frequency bands, with vertical resolution ranging from several centimeters to several meters, a smaller, low-cost seismic exploration system may be used, such as a sparker source with central frequencies of 250 Hz or higher. However, the sparker source has a relatively low energy compared to air guns and consequently produces data with a lower signal-to-noise (S∕N) ratio. To attenuate the random noise and extract reliable signal from the low S∕N ratio of sparker SO data without distorting the true shape and amplitude of water column reflections, we applied machine learning. Specifically, we used a denoising convolutional neural network (DnCNN) that efficiently suppresses random noise in a natural image. One of the most important factors of machine learning is the generation of an appropriate training dataset. We generated two different training datasets using synthetic and field data. Models trained with the different training datasets were applied to the test data, and the denoised results were quantitatively compared. To demonstrate the technique, the trained models were applied to an SO sparker seismic dataset acquired in the Ulleung Basin, East Sea (Sea of Japan), and the denoised seismic sections were evaluated. The results show that machine learning can successfully attenuate the random noise in sparker water column seismic reflection data.
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Short, David A., Robert Meneghini, Amber E. Emory, and Mathew R. Schwaller. "Reduction of Nonuniform Beamfilling Effects by Multiple Constraints: A Simulation Study." Journal of Atmospheric and Oceanic Technology 32, no. 11 (November 2015): 2114–24. http://dx.doi.org/10.1175/jtech-d-15-0021.1.
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AbstractA spaceborne precipitation radar samples the vertical structure of precipitating hydrometeors from the top down. The viewing geometry and operating frequency result in certain limitations and opportunities. Among the limitations is attenuation of the radar signal that can cause the measured radar reflectivity factor to be substantially less than the desired quantity, the true radar reflectivity factor. Another error source is the spatial variability in precipitation rates that occurs at scales smaller than the sensor field of view (FOV), giving rise to the nonuniform beamfilling (NUBF) effect. The opportunities arise when the radar return from the surface can be used to obtain constraints on the path-integrated attenuation (PIA) for use in hybrid attenuation correction algorithms. The surface return can also provide some information on the degree of NUBF at off-nadir viewing angles. In this paper ground-based radar data are used to simulate spaceborne radar data at nadir and off-nadir viewing angles at Ku band and Ka band and to test attenuation correction algorithms in the presence of nonuniform beamfilling. The cross-FOV gradient in PIA is found to be an important characteristic for describing the performance of attenuation correction algorithms.
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Bickel, S. H., and R. R. Natarajan. "Plane‐wave Q deconvolution." GEOPHYSICS 50, no. 9 (September 1985): 1426–39. http://dx.doi.org/10.1190/1.1442011.
Повний текст джерелаАнотація:
Often the information content of measured signals from distance sources is hidden, because the signal distorts, weakens, and loses resolution as it propagates. For seismic energy traveling in the earth, these propagation effects can be approximated by the constant (frequency‐independent) Q model for attenuation and dispersion. For a propagating plane wave, this model leads to a spatial attenuation factor that is an unbounded function of frequency. Consequently, the broadband inverse of the constant-Q filter does not exist. For a fixed distance between the source and receiver the effects of the propagation path can be deconvolved (removed) within the seismic band by reversing the propagation of the plane wave. This propagation reversal is done by a time reversal with Q replaced by —Q, thereby changing absorption to gain in the complex wavenumber. Normally, measured seismic traces contain returns from a variety of depths. The interference of waves with different amounts of attenuation complicates the inversion process. From a superposition of plane waves with reversed propagation, a general inverse to an attenuation earth filter is proposed. To account for the increased attenuation with depth, the plane‐wave inverse filter is now time‐varying. This time‐varying inverse filter has a simple Fourier integral representation where the wavenumber is complex, and the direction of propagation is chosen such that the wave is growing rather than attenuating with distance. To control the wavelet side lobes a frequency‐domain window function (Hanning window) is applied to the trace. This two‐step plane‐wave deconvolution scheme was demonstrated to be superior to conventional deconvolution procedures. Tests with field data indicate the method is effective in removing attenuation effects from both VSP (Vertical Seismic Profile) and surface measurements. Phase distortions are eliminated and interference between events is reduced within the seismic band. This inverse is nearly exact for events where the time‐bandwidth (propagation time‐signal bandwidth) product is less than the effective Q. For depths where the time‐bandwidth product is greater than [Formula: see text] large wavelet side lobes appear. The wavelet side lobes can be partially suppressed by tapering the edges of the spectrum. However, the large side lobes of wavelets from shallow reflectors limit the bandwidth that can be recovered from the deeper events to aproximately [Formula: see text], where t is the propagation time to the event. Advances in the inversion algorithm (e.g., a Wiener filter could be used in place of the Hanning window to control side lobes) could probably improve upon our results, but in most cases even a small amount of measurement noise limits the reflection sequences to time‐bandwidth products that are less than twice the effective Q.
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Samad, Md Abdus, Feyisa Debo Diba, and Dong-You Choi. "Rain Attenuation Scaling in South Korea: Experimental Results and Artificial Neural Network." Electronics 10, no. 16 (August 22, 2021): 2030. http://dx.doi.org/10.3390/electronics10162030.
Повний текст джерелаАнотація:
Scaling rain attenuation parameters will significantly benefit the quick monitoring of rain attenuation in a particular channel with previously known results or in situ setup attenuation measurements. Most of the rain attenuation scaling techniques have been derived for slant links. In this study, we also applied frequency and polarization scaling techniques for terrestrial link applications. We collected real measured datasets from research paper publications and examined those datasets using International Telecommunication Union-Radiocommunication sector (ITU-R) models (P.530-17, P.618-13). Our analyzed results show that existing long-term frequency and polarization scaling rain attenuation models (ITU-R P.618-13 for slant links and ITU-R P.530-17 for terrestrial links) show reduced performance for frequency and polarization scaling measured locations in South Korea. Hence, we proposed a new scaling technique using artificial neural networks from the measured rain attenuation data of slant and terrestrial links in South Korea. The experimental results confirm that the proposed Artificial Neural Network (ANN)-based scaling model shows satisfactory performance to predict attenuation for frequency and vertical polarization scaling.
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Campos, Edwin F., Wayne Hocking, and Frédéric Fabry. "Evaluating the Effects of Height-Variable Reflectivity and Antenna Sidelobes on the Radar Equation." Journal of Atmospheric and Oceanic Technology 25, no. 8 (August 1, 2008): 1469–76. http://dx.doi.org/10.1175/2007jtecha941.1.
Повний текст джерелаАнотація:
Abstract Using radar observations to quantify precipitation intensity requires the intervention of the radar equation, which converts the precipitation signal into reflectivity units. This equation generally assumes that the reflectivity is uniform within each sampling gate and that the sidelobes of the antenna pattern are negligible. The purpose here is to provide a more realistic approach that eliminates these assumptions when computing profiles of precipitation intensity (by using a height-variable reflectivity and antenna pattern of significant sidelobes to compute profiles of a radar reflectivity factor). To achieve this, simultaneous observations of collocated vertically pointing radars operating in the VHF and X bands were obtained. Raindrop measurements were used to correct for attenuation in the precipitation signal at the X band. Then the precipitation signal in the VHF radar was simulated by combining this X-band signal and the VHF antenna pattern into a general version of the radar equation. The simulated precipitation signal at VHF compares well with actual measurements of the rain signal (range gates centered at 2.5, 3.0, and 3.5 km) by the VHF radar, and this validates the analysis methods. In conclusion, the analysis indicates that VHF reflectivity at gates above the melting layer is artificially enhanced by the precipitation signal collected in the sidelobe direction. Similar enhancement will be expected wherever there is a strong vertical gradient of reflectivity (i.e., on the order of 10 dB km−1 or larger).
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Merker, C., G. Peters, M. Clemens, K. Lengfeld, and F. Ament. "A novel approach for absolute radar calibration." Atmospheric Measurement Techniques Discussions 8, no. 2 (February 5, 2015): 1671–95. http://dx.doi.org/10.5194/amtd-8-1671-2015.
Повний текст джерелаАнотація:
Abstract. The theoretical framework of a novel approach for absolute radar calibration is presented and its potential analysed by means of synthetic data to lay out a solid basis for future practical application. The method presents the advantage of an absolute calibration with respect to the directly measured reflectivity, without needing a previously calibrated reference device. It requires a setup comprising three radars: two devices oriented towards each other, measuring reflectivity along the same horizontal beam and operating within a strongly attenuated frequency range (e.g. K or X band) and one vertical reflectivity and drop size distribution (DSD) profiler below this connecting line, which is to be calibrated. The absolute determination of the calibration factor is based on attenuation estimates. Using synthetic, smooth and geometrically idealised data calibration is found to perform best using homogeneous precipitation events with rain rates high enough to ensure a distinct attenuation signal (approx. 30 dBZ). Furthermore, the choice of the interval width (in measuring range gates) around the vertically pointing radar, needed for attenuation estimation, is found to have an impact on the calibration results. Further analysis is done by means of synthetic data with realistic, inhomogeneous precipitation fields taken from measurements. A calibration factor is calculated for each considered case using the presented method. Based on the distribution of the calculated calibration factors, the most probable value is determined by estimating the mode of a fitted shifted logarithmic normal distribution function. After filtering the data set with respect to rain rate and inhomogeneity and choosing an appropriate length of the considered attenuation path, the estimated uncertainty of the calibration factor is in the order of 1%. Considering stability and accuracy of the method, an interval of 8 range gates on both sides of the vertically pointing radar is most appropriate for calibration.
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Chun, Kin-Yip, Gordon F. West, Richard J. Kokoski, and Claire Samson. "A novel technique for measuring Lg attenuation—results from Eastern Canada between 1 to 10 hz." Bulletin of the Seismological Society of America 77, no. 2 (April 1, 1987): 398–419. http://dx.doi.org/10.1785/bssa0770020398.
Повний текст джерелаАнотація:
Abstract Spectral amplitudes of regionally recorded Lg waves are studied in detail between 0.6 and 10 Hz, using vertical-component, velocity seismograms of the Eastern Canada Telemetered Network stations and a supplementary Seismic Research Observatory-type station at Glen Almond (GAC), Québec. We find that the site responses vary among these stations by more than a factor of 3 within the frequency range of interest. Furthermore, they are found to be strongly frequency dependent. Consequently, it is essential that they be taken into consideration in studies of Lg wave attenuation and Lg source spectra of regionally recorded seismic events. We present a new method of measuring interstation surface wave attenuation, which is closely related to the conventional two-station method. While retaining all the desirable features of the conventional two-station method, the new technique, which we will call the “reversed two-station method,” allows simple, direct (one-parameter) determination of the Lg wave attenuation from sparse spectral data in a manner unaffected by station site effects and associated instrument error. The reversed two-station method is successfully tested over weakly attenuating, short (53 to 210 km) interstation paths in eastern Canada, a difficult experimental condition by normal standards. The Lg attenuation coefficient (0.6 to 10 Hz) in eastern Canada is found to be frequency dependent and of the form γ(f) = 0.0008 f0.81 km−1. At higher frequencies, the Lg attenuation appears to be essentially frequency independent. This latter finding is preliminarily interpreted as evidence that regionally recorded Lg waves in the Canadian Shield are, as in the case of Lg waves propagating through the structurally complex Appalachian Province, contaminated by the high-frequency coda of Sn waves. The Lg contamination over the shield paths becomes severe starting at 14 Hz, twice the frequency above which the Lg signal propagating over the Appalachian Province becomes completely dominated by non-Lg arrivals.
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Xue, Ya-Juan, Jun-Xing Cao, and Xing-Jian Wang. "Inverse Q filtering via synchrosqueezed wavelet transform." GEOPHYSICS 84, no. 2 (March 1, 2019): V121—V132. http://dx.doi.org/10.1190/geo2018-0177.1.
Повний текст джерелаАнотація:
We have developed and applied an inverse [Formula: see text]-filter formulation using synchrosqueezed wavelet transforms for the compensation of attenuating and dispersive media. A damping criterion concerning the reconstruction of the effective components for controlling noise amplification and the separation of the noise and signal in the synchrosqueezed wavelet domain is generated. The proposed method provides stable attenuation compensation without decreasing the seismic vertical and lateral resolution. The best property of the proposed method, unlike conventional inverse [Formula: see text]-filtering methods, is that it carries out amplitude compensation for the effective components located at some time samples in the time-frequency domain. The spectral reconstruction contributes to the reconstruction of the trace in the time domain and suppresses the ambient noise located at high frequencies at later times, especially suppressing the ambient noise within the main frequency band. It is not a noise-level-dependent method. We validated our approach with synthetic and real data. The comparison of the proposed method with the conventional stabilized inverse [Formula: see text]-filtering method is also carried out to illustrate the particular features of the proposed method. The examples demonstrate that our proposed method can effectively compensate for the amplitude attenuation by suppressing the ambient noise and further provide seismic images at high resolution while highlighting the effective details. Furthermore, it is a robust and easily tunable algorithm.
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Merker, C., G. Peters, M. Clemens, K. Lengfeld, and F. Ament. "A novel approach for absolute radar calibration: formulation and theoretical validation." Atmospheric Measurement Techniques 8, no. 6 (June 22, 2015): 2521–30. http://dx.doi.org/10.5194/amt-8-2521-2015.
Повний текст джерелаАнотація:
Abstract. The theoretical framework of a novel approach for absolute radar calibration is presented and its potential analysed by means of synthetic data to lay out a solid basis for future practical application. The method presents the advantage of an absolute calibration with respect to the directly measured reflectivity, without needing a previously calibrated reference device. It requires a setup comprising three radars: two devices oriented towards each other, measuring reflectivity along the same horizontal beam and operating within a strongly attenuated frequency range (e.g. K or X band), and one vertical reflectivity and drop size distribution (DSD) profiler below this connecting line, which is to be calibrated. The absolute determination of the calibration factor is based on attenuation estimates. Using synthetic, smooth and geometrically idealised data, calibration is found to perform best using homogeneous precipitation events with rain rates high enough to ensure a distinct attenuation signal (reflectivity above ca. 30 dBZ). Furthermore, the choice of the interval width (in measuring range gates) around the vertically pointing radar, needed for attenuation estimation, is found to have an impact on the calibration results. Further analysis is done by means of synthetic data with realistic, inhomogeneous precipitation fields taken from measurements. A calibration factor is calculated for each considered case using the presented method. Based on the distribution of the calculated calibration factors, the most probable value is determined by estimating the mode of a fitted shifted logarithmic normal distribution function. After filtering the data set with respect to rain rate and inhomogeneity and choosing an appropriate length of the considered attenuation path, the estimated uncertainty of the calibration factor is of the order of 1 to 11 %, depending on the chosen interval width. Considering stability and accuracy of the method, an interval of eight range gates on both sides of the vertically pointing radar is most appropriate for calibration in the presented setup.
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Richter, K., N. Stelling, and H. G. Maas. "Correcting attenuation effects caused by interactions in the forest canopy in full-waveform airborne laser scanner data." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XL-3 (August 11, 2014): 273–80. http://dx.doi.org/10.5194/isprsarchives-xl-3-273-2014.
Повний текст джерелаАнотація:
Full-waveform airborne laser scanning offers a great potential for various forestry applications. Especially applications requiring information on the vertical structure of the lower canopy parts benefit from the great amount of information contained in waveform data. To enable the derivation of vertical forest canopy structure, the development of suitable voxel based data analysis methods is straightforward. Beyond extracting additional 3D points, it is very promising to derive the voxel attributes from the digitized waveform directly. For this purpose, the differential backscatter cross sections have to be projected into a Cartesian voxel structure. Thereby the voxel entries represent amplitudes of the cross section and can be interpreted as a local measure for the amount of pulse reflecting matter. However, the "history" of each laser echo pulse is characterized by attenuation effects caused by reflections in higher regions of the crown. As a result, the received waveform signals within the canopy have a lower amplitude than it would be observed for an identical structure without the previous canopy structure interactions (Romanczyk et al., 2012). If the biophysical structure is determined from the raw waveform data, material in the lower parts of the canopy is thus under-represented. <br><br> To achieve a radiometrically correct voxel space representation the loss of signal strength caused by partial reflections on the path of a laser pulse through the canopy has to be compensated. In this paper, we present an integral approach correcting the waveform at each recorded sample. The basic idea of the procedure is to enhance the waveform intensity values in lower parts of the canopy for portions of the pulse intensity, which have been reflected (and thus blocked) in higher parts of the canopy. The paper will discuss the developed correction method and show results from a validation both with synthetic and real world data.
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Reine, Carl, Roger Clark, and Mirko van der Baan. "Robust prestack Q-determination using surface seismic data: Part 1 — Method and synthetic examples." GEOPHYSICS 77, no. 1 (January 2012): R45—R56. http://dx.doi.org/10.1190/geo2011-0073.1.
Повний текст джерелаАнотація:
The accurate determination of seismic attenuation, or [Formula: see text], is useful for signal enhancement and reservoir characterization. To arrive at the necessary accuracy however, a number of issues must be addressed in the measurement technique. Specifically, spectral interference from closely spaced reflections is a major concern, in addition to the assumptions and errors associated with the raypath geometries of the reference and measured reflections. We have developed a robust method for measuring attenuation from prestack surface seismic gathers that helps minimize these issues. In our prestack [Formula: see text]-inversion technique; the presence of spectral interference was first reduced by making use of a variable-window time-frequency transform. To minimize the effects of the remaining interference, we then made use of an inversion scheme operating simultaneously in the frequency and traveltime-difference coordinates. A by-product of this inversion was a collection of the frequency-independent amplitude changes, which in the absence of geometric spreading, contains valuable amplitude variation with angle information, free from attenuation amplitude losses. Furthermore, under the assumption of locally 1D velocity and attenuation distributions, we made use of the [Formula: see text] transform to operate on traces of constant horizontal slowness. This allowed angle-dependent effects in the overburden such as attenuation anisotropy and source or receiver directivity to be eliminated. In the second part of our study, published separately, this technique was also demonstrated upon a shallow 3D seismic survey, and the measurements compared to another Q-estimation technique, as well as measurements from a vertical seismic profile.
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Wang, Yanghua. "Quantifying the effectiveness of stabilized inverse Q filtering." GEOPHYSICS 68, no. 1 (January 2003): 337–45. http://dx.doi.org/10.1190/1.1543219.
Повний текст джерелаАнотація:
Applying inverse Q filtering to surface seismic data may minimize the effect of dispersion and attenuation and hence improve the seismic resolution. In this case study, a stabilized inverse Q filter is applied to a land seismic data set, for which the prerequisite reliable earth Q function is estimated from the vertical seismic profile (VSP) downgoing wavefield. The paper focuses on the robust estimate of Q values from VSP data and on the quantitative evaluation of the effectiveness of the stabilized inverse Q filtering approach. The quantitative evaluation shows that inverse Q filtering may flatten the amplitude spectrum, strengthen the time‐variant amplitude, increase the spectral bandwidth, and improve the signal‐to‐noise (S/N) ratio. A parameter measuring the resolution enhancement is defined as a function of the changes in the bandwidth and the S/N ratio. The stabilized inverse Q filtering algorithm, which may provide a stable solution for compensating the high‐frequency wave components lost through attenuation, has positive changes in both the bandwidth and the S/N ratio, and thereby enhances the resolution of the final processed seismic data.
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Liu, Dong, Cao, and Su. "Applications of QC and Merged Doppler Spectral Density Data from Ka-Band Cloud Radar to Microphysics Retrieval and Comparison with Airplane in Situ Observation." Remote Sensing 11, no. 13 (July 4, 2019): 1595. http://dx.doi.org/10.3390/rs11131595.
Повний текст джерелаАнотація:
The new Chinese Ka-band solid-state transmitter cloud radar (CR) uses four operational modes with different pulse widths and coherent integration and non-coherent integration numbers to meet long-term cloud measurement requirements. The CR and an instrument-equipped aircraft were used to observe clouds and precipitation on the east side of Taihang Mountain in Hebei Province in 2018. To resolve the data quality problems caused by attenuation in the precipitation area; we focused on developing an algorithm for attenuation correction based on rain drop size distribution (DSD) retrieved from the merged Doppler spectral density data of the four operational modes following data quality control (QC). After dealiasing Doppler velocity and removal of range sidelobe artifacts; we merged the four types of Doppler spectral density data. Vertical air speed and DSD are retrieved from the merged Doppler spectral density data. Finally, we conducted attenuation correction of Doppler spectral density data and recalculated Doppler moments such as reflectivity; radial velocity; and spectral width. We evaluated the consistencies of reflectivity spectra from the four operational modes and DSD retrieval performance using airborne in situ observation. We drew three conclusions: First, the four operational modes observed similar reflectivity and velocity for clouds and low-velocity solid hydrometeors; however; three times of coherent integration underestimated Doppler reflectivity spectra for velocities greater than 2 m s−1. Reflectivity spectra were also underestimated for low signal-to-noise ratios in the low-sensitivity operational mode. Second, QC successfully dealiased Doppler velocity and removed range sidelobe artifacts; and merging of the reflectivity spectra mitigated the effects of coherent integration and pulse compression on radar data. Lastly, the CR observed similar DSD and liquid water content vertical profiles to airborne in situ observations. Comparing CR and aircraft data yielded uncertainty due to differences in observation space and temporal and spatial resolutions of the data.
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St. George, L., S. H. Roy, J. Richards, J. Sinclair, and S. J. Hobbs. "Surface EMG signal normalisation and filtering improves sensitivity of equine gait analysis." Comparative Exercise Physiology 15, no. 3 (July 1, 2019): 173–85. http://dx.doi.org/10.3920/cep190028.
Повний текст джерелаАнотація:
Low-frequency noise attenuation and normalisation are fundamental signal processing (SP) methods for surface electromyography (sEMG), but are absent, or not consistently applied, in equine biomechanics. The purpose of this study was to examine the effect of different band-pass filtering and normalisation conventions on sensitivity for identifying differences in sEMG amplitude-related measures, calculated from leading (LdH) and trailing hindlimb (TrH) during canter, where between-limb differences in vertical loading are known. sEMG and 3D-kinematic data were collected from the right Biceps Femoris in 10 horses during both canter leads. Peak hip and stifle joint angle and angular velocity were calculated during stance to verify between-limb biomechanical differences. Four SP methods, with and without normalisation and high-pass filtering, were applied to raw sEMG data. Methods 1 (M1) to 4 (M4) included DC-offset removal and full-wave rectification. Method 2 (M2) included additional normalisation relative to maximum sEMG across all strides. Method 3 (M3) included additional high-pass filtering (Butterworth 4th order, 40 Hz cut-off), for artefact attenuation. M4 included the addition of high-pass filtering and normalisation. Integrated EMG (iEMG) and average rectified value (ARV) were calculated using processed sEMG data from M1 – M4, with stride duration as the temporal domain. sEMG parameters, within M1 – M4, and kinematic parameters were grouped by LdH and TrH and compared using repeated measures ANOVA. Significant between-limb differences for hip and stifle joint kinematics were found, indicating functional differences in hindlimb movement. M2 and M4, revealed significantly greater iEMG and ARV for LdH than TrH (P<0.01), with M4 producing the lowest P-values and largest effect sizes. Significant between-limb differences in sEMG parameters were not observed with M1 and M3. The results indicate that equine sEMG SP should include normalisation and high-pass filtering to improve sensitivity for identifying differences in muscle function associated with biomechanical changes during equine gait.
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Brisbourne, Alex M., Michael Kendall, Sofia-Katerina Kufner, Thomas S. Hudson, and Andrew M. Smith. "Downhole distributed acoustic seismic profiling at Skytrain Ice Rise, West Antarctica." Cryosphere 15, no. 7 (July 23, 2021): 3443–58. http://dx.doi.org/10.5194/tc-15-3443-2021.
Повний текст джерелаАнотація:
Abstract. Antarctic ice sheet history is imprinted in the structure and fabric of the ice column. At ice rises, the signature of ice flow history is preserved due to the low strain rates inherent at these independent ice flow centres. We present results from a distributed acoustic sensing (DAS) experiment at Skytrain Ice Rise in the Weddell Sea sector of West Antarctica, aimed at delineating the englacial fabric to improve our understanding of ice sheet history in the region. This pilot experiment demonstrates the feasibility of an innovative technique to delineate ice rise structure. Both direct and reflected P- and S-wave energy, as well as surface wave energy, are observed using a range of source offsets, i.e. a walkaway vertical seismic profile, recorded using fibre optic cable. Significant noise, which results from the cable hanging untethered in the borehole, is modelled and suppressed at the processing stage. At greater depth where the cable is suspended in drilling fluid, seismic interval velocities and attenuation are measured. Vertical P-wave velocities are high (VINT=3984±218 m s−1) and consistent with a strong vertical cluster fabric. Seismic attenuation is high (QINT=75±12) and inconsistent with previous observations in ice sheets over this temperature range. The signal level is too low, and the noise level too high, to undertake analysis of englacial fabric variability. However, modelling of P- and S-wave travel times and amplitudes with a range of fabric geometries, combined with these measurements, demonstrates the capacity of the DAS method to discriminate englacial fabric distribution. From this pilot study we make a number of recommendations for future experiments aimed at quantifying englacial fabric to improve our understanding of recent ice sheet history.
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Boran-Keshishian, A. L., A. A. Alekseev, V. V. Popov, and A. I. Kondratyev. "Stability and increased radio communication coverage of sea area infrastructure measurement antennas." Journal of Physics: Conference Series 2061, no. 1 (October 1, 2021): 012025. http://dx.doi.org/10.1088/1742-6596/2061/1/012025.
Повний текст джерелаАнотація:
Abstract This research presents a modified method of signal amplification over layered surfaces of absolutely thin ice over marine waters on condition of stable operation of communication networks, necessary for deployment of Big Information Management Communication Systems and the concept of E-Navigation development. The method was first tested when deploying a GMSSB(b) network in the Azov-Black Sea region. Peculiarity of radio wave behavior during propagation over thin layered ice is that mutual phase ratios make a part of field energy “sticking” to the surface and propagating along it, thus creating a surface wave effect. At that, attenuation function is above one, and the field may increase with distance, even above design limits, breaking the proportionality law of reduction with distance. There are several details requiring clarification and adjustments to local conditions.In the MF and LF radio bands, solid surface and sea water are good conductors of electromagnetic flow. Thus, antenna fields for radio communications are located immediately above the surface for reception and transmission of vertical polarization signals, while field calculations are conducted with an elementary dipole.
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Li, Yuan, Baomin Wang, Shao-Yi Lee, Zhijie Zhang, Ye Wang, and Wenjie Dong. "Micro-Pulse Lidar Cruising Measurements in Northern South China Sea." Remote Sensing 12, no. 10 (May 25, 2020): 1695. http://dx.doi.org/10.3390/rs12101695.
Повний текст джерелаАнотація:
A shipborne micro-pulse lidar (Sigma Space Mini-MPL) was used to measure aerosol extinction coefficient over the northern region of the South China Sea from 9 August to 7 September 2016, the first time a mini-MPL was used for aerosol observation over the cruise region. The goal of the experiment was to investigate if the compact and affordable mini-MPL was usable for aerosol observation over this region. The measurements were used to calculate vertical profiles of volume extinction coefficient, depolarization ratio, and atmospheric boundary layer height. Aerosol optical depth (AOD) was lower over the southwest side of the cruise region, compared to the northeast side. Most attenuation occurred below 3.5 km, and maximum extinction values over coastal areas were generally about double of values offshore. The extinction coefficients at 532 nm (aerosol and molecular combined) over coastal and offshore areas were on average 0.04 km−1 and 0.02 km−1, respectively. Maximum values reached 0.2 km−1 and 0.14 km−1, respectively. Vertical profiles and back-trajectory calculations indicated vertical and horizontal layering of aerosols from different terrestrial sources. The mean volume depolarization ratio of the aerosols along the cruise was 0.04. The mean atmospheric boundary layer height along the cruise was 653 m, with a diurnal cycle reaching its mean maximum of 1041 m at 12:00 local time, and its mean minimum of 450 m at 20:00 local time. Unfortunately, only 11% of the measurements were usable. This was due to ship instability in rough cruise conditions, lack of stabilization rig, water condensation attached to the eye lens, and high humidity attenuating the echo signal. We recommend against the use of the mini-MPL in this cruise region unless substantial improvements are made to the default setup, e.g., instrument stabilization, instrument protection cover, and more theoretical work taking into account atmospheric gas scattering or absorption.
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Richter, K., R. Blaskow, N. Stelling, and H. G. Maas. "REFERENCE VALUE PROVISION SCHEMES FOR ATTENUATION CORRECTION OF FULL-WAVEFORM AIRBORNE LASER SCANNER DATA." ISPRS Annals of Photogrammetry, Remote Sensing and Spatial Information Sciences II-3/W5 (August 19, 2015): 65–72. http://dx.doi.org/10.5194/isprsannals-ii-3-w5-65-2015.
Повний текст джерелаАнотація:
The characterization of the vertical forest structure is highly relevant for ecological research and for better understanding forest ecosystems. Full-waveform airborne laser scanner systems providing a complete time-resolved digitization of every laser pulse echo may deliver very valuable information on the biophysical structure in forest stands. To exploit the great potential offered by full-waveform airborne laser scanning data, the development of suitable voxel based data analysis methods is straightforward. Beyond extracting additional 3D points, it is very promising to derive voxel attributes from the digitized waveform directly. However, the ’history’ of each laser pulse echo is characterized by attenuation effects caused by reflections in higher regions of the crown. As a result, the received waveform signals within the canopy have a lower amplitude than it would be observed for an identical structure without the previous canopy structure interactions (Romanczyk et al., 2012). <br><br> To achieve a radiometrically correct voxel space representation, the loss of signal strength caused by partial reflections on the path of a laser pulse through the canopy has to be compensated by applying suitable attenuation correction models. The basic idea of the correction procedure is to enhance the waveform intensity values in lower parts of the canopy for portions of the pulse intensity, which have been reflected in higher parts of the canopy. To estimate the enhancement factor an appropriate reference value has to be derived from the data itself. Based on pulse history correction schemes presented in previous publications, the paper will discuss several approaches for reference value estimation. Furthermore, the results of experiments with two different data sets (leaf-on/leaf-off) are presented.
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Shell, Karen M., Simon P. de Szoeke, Michael Makiyama, and Zhe Feng. "Vertical Structure of Radiative Heating Rates of the MJO during DYNAMO." Journal of Climate 33, no. 12 (June 15, 2020): 5317–35. http://dx.doi.org/10.1175/jcli-d-19-0519.1.
Повний текст джерелаАнотація:
AbstractThe vertical structure of radiative heating rates over the region of the tropical Indian Ocean associated with the MJO during the DYNAMO/ARM MJO Investigation Experiment is presented. The mean and variability of heating rates during active, suppressed, and disturbed phases are determined from the Pacific Northwest National Laboratory Combined Remote Sensing Retrieval (CombRet) from Gan Island, Maldives (0.69°S, 73.15°E). TOA and surface fluxes from the CombRet product are compared with collocated 3-hourly CERES SYN1deg Ed4A satellite retrievals. The fluxes are correlated in time with correlation coefficients around 0.9, yet CombRet time-mean OLR is 15 W m−2 larger. Previous work has suggested that CombRet undersamples high clouds, due to signal attenuation by low-level clouds and reduced instrument sensitivity with altitude. However, mean OLR differs between CombRet and CERES for all values of OLR, not just the lowest values corresponding to widespread high clouds. The discrepancy peaks for midrange OLR, suggestive of precipitating, towering cumulus convective clouds, rather than stratiform cirrus clouds. Low biases in the cloud-top height of thick clouds substantially contribute to the overestimate of OLR by CombRet. CombRet data are used to generate composite shortwave and longwave atmospheric heating rate profiles as a function of the local OLR. Although there is considerable variability in CombRet not directly related to OLR, the time–height structure of mean heating rate composites generated using OLR as the interpolant is broadly representative of tropical convective variability on intraseasonal time scales.
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Aslan, Toprak, Olli Peltola, Andreas Ibrom, Eiko Nemitz, Üllar Rannik, and Ivan Mammarella. "The high-frequency response correction of eddy covariance fluxes – Part 2: An experimental approach for analysing noisy measurements of small fluxes." Atmospheric Measurement Techniques 14, no. 7 (July 28, 2021): 5089–106. http://dx.doi.org/10.5194/amt-14-5089-2021.
Повний текст джерелаАнотація:
Abstract. Fluxes measured with the eddy covariance (EC) technique are subject to flux losses at high frequencies (low-pass filtering). If not properly corrected for, these result in systematically biased ecosystem–atmosphere gas exchange estimates. This loss is corrected using the system's transfer function which can be estimated with either theoretical or experimental approaches. In the experimental approach, commonly used for closed-path EC systems, the low-pass filter transfer function (H) can be derived from the comparison of either (i) the measured power spectra of sonic temperature and the target gas mixing ratio or (ii) the cospectra of both entities with vertical wind speed. In this study, we compare the power spectral approach (PSA) and cospectral approach (CSA) in the calculation of H for a range of attenuation levels and signal-to-noise ratios (SNRs). For a systematic analysis, we artificially generate a representative dataset from sonic temperature (T) by attenuating it with a first order filter and contaminating it with white noise, resulting in various combinations of time constants and SNRs. For PSA, we use two methods to account for the noise in the spectra: the first is the one introduced by Ibrom et al. (2007a) (PSAI07), in which the noise and H are fitted in different frequency ranges, and the noise is removed before estimating H. The second is a novel approach that uses the full power spectrum to fit both H and noise simultaneously (PSAA21). For CSA, we use a method utilizing the square root of the H with shifted vertical wind velocity time series via cross-covariance maximization (CSAH,sync). PSAI07 tends to overestimate the time constant when low-pass filtering is low, whilst the new PSAA21 and CSAH,sync successfully estimate the expected time constant regardless of the degree of attenuation and SNR. We further examine the effect of the time constant obtained with the different implementations of PSA and CSA on cumulative fluxes using estimated time constants in frequency response correction. For our example time series, the fluxes corrected using time constants derived by PSAI07 show a bias between 0.1 % and 1.4 %. PSAA21 showed almost no bias, while CSAH,sync showed bias of ±0.4 %. The accuracies of both PSA and CSA methods were not significantly affected by SNR level, instilling confidence in EC flux measurements and data processing in set-ups with low SNR. Overall we show that, when using power spectra for the empirical estimation of parameters of H for closed-path EC systems the new PSAA21 outperforms PSAI07, while when using cospectra the CSAH,sync approach provides accurate results. These findings are independent of the SNR value and attenuation level.
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Dang, Ruijun, Yi Yang, Hong Li, Xiao-Ming Hu, Zhiting Wang, Zhongwei Huang, Tian Zhou, and Tiejun Zhang. "Atmosphere Boundary Layer Height (ABLH) Determination under Multiple-Layer Conditions Using Micro-Pulse Lidar." Remote Sensing 11, no. 3 (January 29, 2019): 263. http://dx.doi.org/10.3390/rs11030263.
Повний текст джерелаАнотація:
Accurate estimation of the atmospheric boundary layer height (ABLH) is critically important and it mainly relies on the detection of the vertical profiles of atmosphere variables (temperature, humidity,’ and horizontal wind speed) or aerosols. Aerosol Lidar is a powerful remote sensing instrument frequently used to retrieve ABLH through the detection of the vertical distribution of aerosol concentration. A challenge is that cloud, residual layer (RL), and local signal structure seriously interfere with the lidar measurement of ABLH. A new objective technique presenting as giving a top limiter altitude is introduced to reduce the interference of RL and cloud layer on ABLH determination. Cloud layers are identified by looking for the rapid increase and sharp attenuation of the signal combined with the relative increase in the signal. The cloud layers weather overlay are classified or are decoupled from the ABL by analyzing the continuity of the signal below the cloud base. For cloud layer capping of the ABL, the limiter is determined to be the altitude where a positive signal gradient first occurs above the cloud upper edge. For a cloud that is decoupled from the ABL, the cloud base is considered to be the altitude limiter. For RL in the morning, the altitude limiter is the greatest positive gradient altitude below the RL top. The ABLH will be determined below the top limiter altitude using Haar wavelet (HM) and the curve fitting method (CFM). Besides, the interference of local signal noise is eliminated through consideration of the temporal continuity. While comparing the lidar-determined ABLH by HM (or CFM) and nearby radiosonde measurements of the ABLH, a reasonable concordance is found with a correlation coefficient of 0.94 (or 0.96) and 0.79 (or 0.74), presenting a mean of the relative absolute differences with respect to radiosonde measurements of 10.5% (or 12.3%) and 22.3% (or 17.2%) for cloud-free and cloudy situations, respectively. The diurnal variations in the ABLH determined from HM and CFM on four selected cases show good agreement with a mean correlation coefficient higher than 0.99 and a mean absolute bias of 0.22 km. Also, the determined diurnal ABLH are consistent with surface turbulent kinetic energy (TKE) combined with the time-height distribution of the equivalent potential temperature.
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Kavanagh, Justin J., Steven Morrison, and Rod S. Barrett. "Lumbar and cervical erector spinae fatigue elicit compensatory postural responses to assist in maintaining head stability during walking." Journal of Applied Physiology 101, no. 4 (October 2006): 1118–26. http://dx.doi.org/10.1152/japplphysiol.00165.2006.
Повний текст джерелаАнотація:
The purpose of this study was to examine how inducing fatigue of the 1) lumbar erector spinae and 2) cervical erector spinae (CES) muscles affected the ability to maintain head stability during walking. Triaxial accelerometers were attached to the head, upper trunk, and lower trunk to measure accelerations in the vertical, anterior-posterior, and mediolateral directions during walking. Using three accelerometers enabled two adjacent upper body segments to be defined: the neck segment and trunk segment. A transfer function was applied to root mean square acceleration, peak power, and harmonic data derived from spectral analysis of accelerations to quantify segmental gain. The structure of upper body accelerations were examined using measures of signal regularity and smoothness. The main findings were that head stability was only affected in the anterior-posterior direction, as accelerations of the head were less regular following CES fatigue. Furthermore, following CES fatigue, the central nervous system altered the attenuation properties of the trunk segment in the anterior-posterior direction, presumably to enhance head stability. Following lumbar erector spinae fatigue, the trunk segment had greater gain and increased regularity and smoothness of accelerations in the mediolateral direction. Overall, the results of this study suggest that erector spinae fatigue differentially altered segmental attenuation during walking, according to the level of the upper body that was fatigued and the direction that oscillations were attenuated. A compensatory postural response was not only elicited in the sagittal plane, where greater segmental attenuation occurred, but also in the frontal plane, where greater segmental gain occurred.
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Avitabile, Gianfranco, Antonello Florio, Vito Leonardo Gallo, Alessandro Pali, and Lorenzo Forni. "An Optimization Framework for the Design of High-Speed PCB VIAs." Electronics 11, no. 3 (February 6, 2022): 475. http://dx.doi.org/10.3390/electronics11030475.
Повний текст джерелаАнотація:
Signal integrity represents a key issue in all modern electronic systems, which are strongly dominated by the extreme component density usually employed on PCBs and the associated increase in the interconnection density. The use of multi-layer structures with microstrips connected by various types of Vertical Interconnect Accesses (VIAs) calls for design strategies that reduce the impedance mismatch and signal attenuation. The paper proposes a thorough analysis of the effects associated with the VIA geometry and presents a parametric evaluation of them. The obtained results represent the starting point for a possible design procedure that manages the geometric aspects of differential VIAs, aiming to optimize their electrical performance while reducing their occupation of PCB area. The optimization technique considers a differential VIA as a four-port circuit whose characteristics are evaluated with suitable Figures of Merit (FoMs), thus striving for an optimal design obtained with closed-loop iterations. The analysis is performed in both the time (TDR: Time-Domain Reflectometry) and frequency domains (S and Z parameters), thus allowing a dramatic reduction in the number of cases to be analyzed. The procedure is thoroughly described and validated using simulation results.
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Gurevich, Boris, and Roman Pevzner. "How frequency dependency of Q affects spectral ratio estimates." GEOPHYSICS 80, no. 2 (March 1, 2015): A39—A44. http://dx.doi.org/10.1190/geo2014-0418.1.
Повний текст джерелаАнотація:
Because seismic amplitudes can be affected by purely geometrical factors, attenuation is often estimated not from amplitudes but from the evolution of the amplitude spectra of the waveform. Such estimation methods (e.g., the spectral ratio method and the centroid frequency shift method) assume that the quality factor [Formula: see text] is constant (independent of frequency) in the frequency band of the signal. If this assumption is violated, then [Formula: see text] estimates become biased. In particular, when the frequency dependency of [Formula: see text] is a power law [Formula: see text], then [Formula: see text] is systematically under- or overestimated by a factor of [Formula: see text]. The errors are larger for larger values of [Formula: see text], particularly when [Formula: see text] is negative. In particular, if [Formula: see text], the frequency content of the signal does not change, and [Formula: see text] is estimated to be infinite, regardless of the true value of [Formula: see text]. To avoid these systematic errors, it is necessary to monitor the evolution of frequency content and amplitude with distance. Zero-offset vertical seismic profile data from the North West Shelf of Australia revealed the decay of the signal amplitude with depth that can be explained by a combination of intrinsic constant [Formula: see text] and a frequency-independent factor, which in turn is caused by the geometric spreading plus transmission loss due to variations of acoustic impedance on a scale larger than the dominant wavelength in the signal.
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Amundsen, Lasse, and Rune Mittet. "Estimation of phase velocities and Q‐factors from zero‐offset, vertical seismic profile data." GEOPHYSICS 59, no. 4 (April 1994): 500–517. http://dx.doi.org/10.1190/1.1443612.
Повний текст джерелаАнотація:
In seismic processing, we face the problem of characterizing the effect of anelastic attenuation on the seismic signal during propagation. To solve this problem, approximate physical properties of the porous fluid‐filled rock are needed. We give a strategy for estimating effective parameters governing absorption and dispersion of waves in viscoelastic media by inverting zero‐offset vertical seismic profiling (VSP) data acquired in a medium with plane horizontal layers. The VSP data are filtered such that all energy except for the direct downgoing wave and the primary reflected wave from each interface is zeroed. This procedure requires a model with layer thicknesses greater than a minimum limit. A stack of thin layers must be replaced by a layer with average physical properties and with thickness exceeding the required minimum. The model parameter vector is partitioned into two vectors. The first contains the frequency‐dependent complex propagation velocity in each layer, and is evaluated over the frequency band where the signal‐to‐noise ratio is acceptable. In the second vector, the geophone‐to‐formation coupling factors, which are assumed to be frequency‐independent, are gathered. It is straightforward to determine both the frequency‐dependent phase velocities and the frequency‐dependent quality (Q‐) factors from the frequency‐dependent propagation velocities. We assume that layer boundaries and layer densities can be obtained from well logs. We give the equations for a simplified forwardmodeling scheme and the equations for the solution of the nonlinear inverse problem. The algorithm is applied to both synthetic and real data. Inversion of synthetic data shows that the phase velocities can be satisfactorily estimated, and that Q‐factors below approximately 50 are well‐resolved, even for large errors in the geophone‐to‐formation coupling factors. The estimated phase velocities from the real data behave fairly stable as a function of frequency. The results for the quality factors are less conclusive, but the low Q‐factors may be of correct size.
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Swanston, Alastair M., Michael D. Mathias, and Craig A. Barker. "Wide-azimuth TTI imaging at Tahiti: Reducing structural uncertainty of a major deepwater subsalt field." GEOPHYSICS 76, no. 5 (September 2011): WB67—WB78. http://dx.doi.org/10.1190/geo2010-0393.1.
Повний текст джерелаАнотація:
The Tahiti field is a recent major development in the deepwater Gulf of Mexico. The field’s prolific Miocene reservoir section lies below a thick salt canopy with structural dips as high as 80 degrees, adjacent to a near-vertical salt root. Successful appraisal and initial development was enabled by interpretation of proprietary depth imaging products generated from narrow-azimuth seismic data. However, reservoir-scale mapping and fault definition remained problematic due to seismic imaging and illumination challenges. In 2009–2010, the Tahiti partnership initiated a reimaging project using multiclient wide-azimuth seismic data. The project employed current technologies for multiple attenuation, tilted transverse isotropy velocity modeling, and migration. Increased azimuthal coverage and inherent multiple suppression provided by wide azimuth acquisition delivered significant imaging enhancements. Advanced noise and multiple attenuation techniques provided cleaner data with improved signal-to-noise. Earth models representing multiazimuth subsurface velocities and anisotropy parameters calibrated to well control with detailed salt interpretation resulted in higher confidence structural imaging. Comparison of Gaussian beam, one-way wave equation, and reverse time migration algorithms shows that reverse time migration generally provides superior subsalt and salt-body data quality, with improved event positioning, higher resolution, and enhanced steep dip imaging. The resulting seismic volumes enable accurate mapping of reservoir horizons and faulting. This will improve resource determination and future well placement in the next phase of field development.
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Chen, Peng, Delu Pan, Zhihua Mao, and Hang Liu. "A Feasible Calibration Method for Type 1 Open Ocean Water LiDAR Data Based on Bio-Optical Models." Remote Sensing 11, no. 2 (January 17, 2019): 172. http://dx.doi.org/10.3390/rs11020172.
Повний текст джерелаАнотація:
Accurate calibration of oceanic LiDAR signals is essential for the accurate retrieval of ocean optical properties. Nowadays, there are many methods for aerosol LiDAR calibration, but fewer attempts have been made to implement specific calibration methods for oceanic LiDAR. Oceanic LiDAR often has higher vertical resolution, needs greater signal dynamic range, detects several orders of magnitude lower less depth of penetration, and suffers from the effects of the air-sea interface. Therefore the calibration methods for aerosol LiDAR may not be useful for oceanic LiDAR. In this paper, we present a new simple and feasible approach for oceanic LiDAR calibration via comparison of LiDAR backscatter against calculated scatter based on iteratively bio-optical models in clear, open ocean, Type 1 water. Compared with current aerosol LiDAR calibration methods, it particularly considers geometric losses and attenuation occurring in the atmosphere-sea interface. The mean relative error percentage (MREP) of LiDAR calibration constant at two different stations was all within 0.08%. The MREP between LiDAR-retrieved backscatter, chlorophyll after using LiDAR calibration constant with inversion results of measured data were within 0.18% and 1.39%, respectively. These findings indicate that the bio-optical methods for LiDAR calibration in clear ocean water are feasible and effective.
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Theodoreson, Mark D., Ausrine Zykaite, Michael Haley, and Saroj Meena. "Case of non-alcoholic Wernicke’s encephalopathy." BMJ Case Reports 12, no. 11 (November 2019): e230763. http://dx.doi.org/10.1136/bcr-2019-230763.
Повний текст джерелаАнотація:
A 61-year-old obese man presented with 8-week history of nausea and occasional vomiting. He reported poor appetite and unintentional weight loss of more than 20 kg of his body mass. A week after admission, he developed double vision and unsteady gait. Neurological examination revealed isolated sixth cranial nerve palsy on the left side with horizontal nystagmus that progressed to bilateral lateral gaze palsy with normal vertical gaze. Brain MR revealed T2/fluid attenuation inversion recovery (FLAIR) high signal in mammillary bodies, tectum of the midbrain and the periaqueductal grey matter. He was diagnosed with Wernicke’s encephalopathy (WE). WE is a medical emergency that carries high mortality yet can be often under-diagnosed in the non-alcoholic patient. Varied presentation and absence of alcohol dependence lowers the degree of suspicion and this was true in this case. The patient was given intravenous thiamine and made a rapid and dramatic recovery.
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van Verseveld, Willem J., Holly R. Barnard, Chris B. Graham, Jeffrey J. McDonnell, J. Renée Brooks, and Markus Weiler. "A sprinkling experiment to quantify celerity–velocity differences at the hillslope scale." Hydrology and Earth System Sciences 21, no. 11 (November 27, 2017): 5891–910. http://dx.doi.org/10.5194/hess-21-5891-2017.
Повний текст джерелаАнотація:
Abstract. Few studies have quantified the differences between celerity and velocity of hillslope water flow and explained the processes that control these differences. Here, we asses these differences by combining a 24-day hillslope sprinkling experiment with a spatially explicit hydrologic model analysis. We focused our work on Watershed 10 at the H. J. Andrews Experimental Forest in western Oregon. Celerities estimated from wetting front arrival times were generally much faster than average vertical velocities of δ2H. In the model analysis, this was consistent with an identifiable effective porosity (fraction of total porosity available for mass transfer) parameter, indicating that subsurface mixing was controlled by an immobile soil fraction, resulting in the attenuation of the δ2H input signal in lateral subsurface flow. In addition to the immobile soil fraction, exfiltrating deep groundwater that mixed with lateral subsurface flow captured at the experimental hillslope trench caused further reduction in the δ2H input signal. Finally, our results suggest that soil depth variability played a significant role in the celerity–velocity responses. Deeper upslope soils damped the δ2H input signal, while a shallow soil near the trench controlled the δ2H peak in lateral subsurface flow response. Simulated exit time and residence time distributions with our hillslope hydrologic model showed that water captured at the trench did not represent the entire modeled hillslope domain; the exit time distribution for lateral subsurface flow captured at the trench showed more early time weighting.
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Linville, A. Frank, and Robert A. Meek. "A procedure for optimally removing localized coherent noise." GEOPHYSICS 60, no. 1 (January 1995): 191–203. http://dx.doi.org/10.1190/1.1443746.
Повний текст джерелаАнотація:
Primary reflections in seismic records are often obscured by coherent noise making processing and interpretation difficult. Trapped water modes, surface waves, scattered waves, air waves, and tube waves to name a few, must be removed early in the processing sequence to optimize subsequent processing and imaging. We have developed a noise canceling algorithm that effectively removes many of the commonly encountered noise trains in seismic data. All currently available techniques for coherent noise attenuation suffer from limitations that introduce unacceptable signal distortions and artifacts. Also, most of those techniques impose the dual stringent requirements of equal and fine spatial sampling in the field acquisition of seismic data. Our technique takes advantage of characteristics usually found in coherent noise such as being localized in time, highly aliased, nondispersive (or only mildly so), and exhibit a variety of moveout patterns across the seismic records. When coherent noise is localized in time, a window much like a surgical mute is drawn around the noise. The algorithm derives an estimate of the noise in the window, automatically correcting for amplitude and phase differences, and adaptively subtracts this noise from the window of data. This signal estimate is then placed back in the record. In a model and a land data example, the algorithm removes noise more effectively with less signal distortion than does f-k filtering or velocity notch filtering. Downgoing energy in a vertical seismic profile (VSP) with irregular receiver spacing is also removed.
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Kyrölä, E., J. Tamminen, V. Sofieva, J. L. Bertaux, A. Hauchecorne, F. Dalaudier, D. Fussen, et al. "Retrieval of atmospheric parameters from GOMOS data." Atmospheric Chemistry and Physics Discussions 10, no. 4 (April 19, 2010): 10145–217. http://dx.doi.org/10.5194/acpd-10-10145-2010.
Повний текст джерелаАнотація:
Abstract. The Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument on board the European Space Agency's ENVISAT satellite measures attenuation of stellar light in occultation geometry. Daytime measurements also record scattered solar light from the atmosphere. The wavelength regions are the ultraviolet-visible band 248–690 nm and two infrared bands at 755–774 nm and at 926–954 nm. From UV-Visible and IR spectra the vertical profiles of O3, NO2, NO3, H2O, O2 and aerosols can be retrieved. In addition there are two 1 kHz photometers at blue 473–527 nm and red 646–698 nm. Photometer data are used to correct spectrometer measurements for scintillations and to retrieve high resolution temperature profiles as well as gravity wave and turbulence parameters. Measurements cover altitude region 5–150 km. Atmospherically valid data are obtained in 15–100 km. In this paper we present an overview of the GOMOS retrieval algorithms for stellar occultation measurements. The low signal-to-noise ratio and the refractive effects due to the point source nature of stars have been important drivers in the development of GOMOS retrieval algorithms. We present first the Level 1b algorithms that are used to correct instrument related disturbances in the spectrometer and photometer measurements The Level 2 algorithms deal with the retrieval of vertical profiles of atmospheric gaseous constituents, aerosols and high resolution temperature. We divide the presentation into correction for refractive effects, high resolution temperature retrieval and spectral/vertical inversion. The paper also includes discussion about the GOMOS algorithm development, expected improvements, access to GOMOS data and alternative retrieval approaches.
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Kyrölä, E., J. Tamminen, V. Sofieva, J. L. Bertaux, A. Hauchecorne, F. Dalaudier, D. Fussen, et al. "Retrieval of atmospheric parameters from GOMOS data." Atmospheric Chemistry and Physics 10, no. 23 (December 14, 2010): 11881–903. http://dx.doi.org/10.5194/acp-10-11881-2010.
Повний текст джерелаАнотація:
Abstract. The Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument on board the European Space Agency's ENVISAT satellite measures attenuation of stellar light in occultation geometry. Daytime measurements also record scattered solar light from the atmosphere. The wavelength regions are the ultraviolet-visible band 248–690 nm and two infrared bands at 755–774 nm and at 926–954 nm. From UV-Visible and IR spectra the vertical profiles of O3, NO2, NO3, H2O, O2 and aerosols can be retrieved. In addition there are two 1 kHz photometers at blue 473–527 nm and red 646–698 nm. Photometer data are used to correct spectrometer measurements for scintillations and to retrieve high resolution temperature profiles as well as gravity wave and turbulence parameters. Measurements cover altitude region 5–150 km. Atmospherically valid data are obtained in 15–100 km. In this paper we present an overview of the GOMOS retrieval algorithms for stellar occultation measurements. The low signal-to-noise ratio and the refractive effects due to the point source nature of stars have been important drivers in the development of GOMOS retrieval algorithms. We present first the Level 1b algorithms that are used to correct instrument related disturbances in the spectrometer and photometer measurements The Level 2 algorithms deal with the retrieval of vertical profiles of atmospheric gaseous constituents, aerosols and high resolution temperature. We divide the presentation into correction for refractive effects, high resolution temperature retrieval and spectral/vertical inversion. The paper also includes discussion about the GOMOS algorithm development, expected improvements, access to GOMOS data and alternative retrieval approaches.
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Cohee, Brian P., and Thorne Lay. "Modeling teleseismic SV waves from underground explosions with tectonic release: Results for Southern Novaya Zemlya." Bulletin of the Seismological Society of America 78, no. 3 (June 1, 1988): 1158–78. http://dx.doi.org/10.1785/bssa0780031158.
Повний текст джерелаАнотація:
Abstract Detailed forward modeling of long-period shear waves for two large underground explosions at the Southern Novaya Zemlya test site indicates that the appropriate equivalent double-couple orientation for the tectonic release radiation is vertical strike-slip. Previous studies of observed teleseismic SH waveforms and SV amplitudes for the 27 October 1973 and 2 November 1974 events using geometric ray theory could not distinguish between vertical strike-slip and 45°-dipping thrust geometries. Either mechanism can match the observed four-lobed SH radiation pattern, and the two-lobed SV amplitude pattern can be produced by interference with an appropriate size explosion pS signal. However, the complexity of the observed SV waveforms arising from Sp conversions near the receiver, diffracted Sp, and shear-coupled PL phases is not accounted for in the ray theory synthetics. Incorporating more realistic Green's functions using Baag and Langston's (1985b) WKBJ spectral method allows more complete modeling of the SV signals. Due to differences in frequency content between the explosion and double-couple SV waveforms, constructive interference occurs more efficiently than destructive interference when the two signals are linearly superimposed. As a result, using tectonic release moments determined from the SH waves and the optimum F factors required to match the SV amplitude patterns, the waveforms produced by the strike-slip and thrust orientations differ substantially at some azimuths. The strike-slip solution yields a consistently superior match to the data. Using the EU2 model of Lerner-Lam and Jordan (1987) for the source region and either EU2 or TNA (Grand and Helmberger, 1984) for the receiver structure, together with an attenuation model similar to SL8, we obtain a double-couple moment, M0 = 3.2 × 1024 dyne-cm and explosion source strength, ψ∞ = 3.8 ± 0.5 × 1011 cm3 for the 27 October 1973 event, and M0 = 1.7 × 1024 dyne-cm and ψ∞ = 2.0 ± 0.3 × 1011 cm3 for the 2 November 1974 event. Complete waveform modeling of SV signals can thus provide improved constraints on tectonic release radiation and explosion source strength.
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Riedel, M., G. Bellefleur, S. R. Dallimore, A. Taylor, and J. F. Wright. "Amplitude and frequency anomalies in regional 3D seismic data surrounding the Mallik 5L-38 research site, Mackenzie Delta, Northwest Territories, Canada." GEOPHYSICS 71, no. 6 (November 2006): B183—B191. http://dx.doi.org/10.1190/1.2338332.
Повний текст джерелаАнотація:
Amplitude and frequency anomalies associated with lakes and drainage systems were observed in a 3D seismic data set acquired in the Mallik area, Mackenzie Delta, Northwest Territories, Canada. The site is characterized by large gas hydrate deposits inferred from well-log analyses and coring. Regional interpretation of the gas hydrate occurrences is mainly based on seismic amplitude anomalies, such as brightening or blanking of seismic energy. Thus, the scope of this research is to understand the nature of the amplitude behavior in the seismic data. We have therefore analyzed the 3D seismic data to define areas with amplitude reduction due to contamination from lakes and channels and to distinguish them from areas where amplitude blanking may be a geologic signal. We have used the spectral ratio method to define attenuation (Q) over different areas in the 3D volume and subsequently applied Q-compensation to attenuate lateral variations ofdispersive absorption. Underneath larger lakes, seismic amplitude is reduced and the frequency content is reduced to [Formula: see text], which is half the original bandwidth. Traces with source-receiver pairs located inside of lakes show an attenuation factor Q of [Formula: see text], approximately half of that obtained for source-receiver pairs situated on deep, continuous permafrost outside of lakes. Deeper reflections occasionally identified underneath lakes show low-velocity-related pull-down. The vertical extent of the washout zones is enhanced by acquisition with limited offsets and from processing parameters such as harsh mute functions to reduce noise from surface waves. The strong attenuation and seismic pull-down may indicate the presence of unfrozen water in deeper lakes and unfrozen pore water within the sediments underlying the lakes. Thus, the blanking underneath lakes is not necessarily related to gas migration or other in situ changes in physical properties potentially associated with the presence of gas hydrate.
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Denisenkov, D. A., V. Y. Zhukov, and G. G. Shchukin. "MESOCYCLONE OBSERVATION BY MULTI-PARAMETER METEOROLOGICAL RADAR." HYDROMETEOROLOGY AND ECOLOGY. PROCEEDINGS OF THE RUSSIAN STATE HYDROMETEOROLOGICAL UNIVERSITY, no. 58 (2020): 9–19. http://dx.doi.org/10.33933/2074-2762-2020-58-9-19.
Повний текст джерелаАнотація:
The article deals in detail with the case of observation of a cloud array characterized by a large (15 km) height of the upper boundary of cloud cover and the presence of areas with radar reflectivity of more than 60 dBZ by the DMRL-S meteorological radar installed in Valday (Novgorod region). Integrated application of the estimates of all measured parameters makes it possible to identify in this array the area where a rare weather phenomenon - a supercell - develops. The fact of formation of the hail area of large size is ascertained. It leads to the effect of depolarization attenuation - negative values of differential reflectivity of the echo signal of the meteorological targets. The coordinates of vertical flows are determined by analyzing data on the cross-correlation coefficient of polarization constituents of received signal. Then the obtained result is compared with the one obtained by means of estimations of the average radial velocity of particles, their much coincidence being shown. At an altitude of 5 km, areas with sharp local speed changes are observed, indicating the existence of strong vortices. Sequential analysis of the data obtained during the whole time of existence of the supercell leads to identification of a zone 5 km in diameter with a “jump” of magnitude radial velocity of particles in a layer 1 km high at a distance of 100 km. The scale of this zone, its location and the magnitudes of the parameters of the signal received from it indicate the formation of another rare weather phenomenon in it – the mesocyclone
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Qamar, Faizan, MHD Nour Hindia, Kaharudin Dimyati, Kamarul Ariffin Noordin, Mohammed Bahjat Majed, Tharek Abd Rahman, and Iraj Sadegh Amiri. "Investigation of Future 5G-IoT Millimeter-Wave Network Performance at 38 GHz for Urban Microcell Outdoor Environment." Electronics 8, no. 5 (May 3, 2019): 495. http://dx.doi.org/10.3390/electronics8050495.
Повний текст джерелаАнотація:
The advent of fifth-generation (5G) systems and their mechanics have introduced an unconventional frequency spectrum of high bandwidth with most falling under the millimeter wave (mmWave) spectrum. The benefit of adopting these bands of the frequency spectrum is two-fold. First, most of these bands appear to be unutilized and they are free, thus suggesting the absence of interference from other technologies. Second, the availability of a larger bandwidth offers higher data rates for all users, as there are higher numbers of users who are connected in a small geographical area, which is also stated as the Internet of Things (IoT). Nevertheless, high-frequency band poses several challenges in terms of coverage area limitations, signal attenuation, path and penetration losses, as well as scattering. Additionally, mmWave signal bands are susceptible to blockage from buildings and other structures, particularly in higher-density urban areas. Identifying the channel performance at a given frequency is indeed necessary to optimize communication efficiency between the transmitter and receiver. Therefore, this paper investigated the potential ability of mmWave path loss models, such as floating intercept (FI) and close-in (CI), based on real measurements gathered from urban microcell outdoor environments at 38 GHz conducted at the Universiti Teknologi Malaysia (UTM), Kuala Lumpur campus. The measurement data were obtained by using a narrow band mmWave channel sounder equipped with a steerable direction horn antenna. It investigated the potential of the network for outdoor scenarios of line-of-sight (LOS) and non-line-of-sight (NLOS) with both schemes of co- (vertical-vertical) and cross (vertical-horizontal) polarization. The parameters were selected to reflect the performance and the variances with other schemes, such as average users cell throughput, throughput of users that are at cell-edges, fairness index, and spectral efficiency. The outcomes were examined for various antenna configurations as well as at different channel bandwidths to prove the enhancement of overall network performance. This work showed that the CI path loss model predicted greater network performance for the LOS condition, and also estimated significant outcomes for the NLOS environment. The outputs proved that the FI path loss model, particularly for V-V antenna polarization, gave system simulation results that were unsuitable for the NLOS scenario.