Time Difference Of Localization Research Articles

A Pulse‐Type Hardware Level Difference Detection Model Based on Sound Source Localization Mechanism in the Barn Owl

SUMMARYAuditory information processing is very important in the darkness where vision information is extremely limited. Barn owls have an excellent hearing information processing function. Barn owls can detect a sound source with high accuracy to within less than two degrees in both the vertical and horizontal directions. When they perform sound source localization, barn owls use the interaural time difference for localization in the horizontal plane, and the interaural level difference for localization in the vertical plane. We are constructing a two‐dimensional sound source localization model using pulse‐type hardware neuron models based on sound source the localization mechanism of barn owl for the purpose of engineering application. In this paper we propose a pulse‐type hardware model for level difference detection based on sound source the localization mechanism of the barn owl. First, we discuss the response characteristics of the mathematical model for level difference detection. Next we discuss the response characteristics of the hardware mode. The results show clearly that this proposed model can be used as a sound source localization model for the vertical direction.

A Pulse-type Hardware External Nucleus of the Inferior Colliculus Model for 2-D Sound Source Localization Based on Auditory Sense Mechanism of Barn Owl

Hearing information is very important role in visual information limited. Sound source localization is nominated for particularly ability in a hearing information processing. Barn owls have excellent processing for hearing. We propose a hardware model which construct by auditory sense mechanism of barn owls. In this paper, we consider the model of external nucleus of the inferior colliculus (hereafter “ICx”), which locate the source of a sound by interaural time difference (hereafter “ITD”) for localization in the horizontal direction, and interaural level difference (hereafter “ILD”) for localization in the vertical direction. As a result, we show clearly that the detection position of an ITD model and detection position of an ILD model can converge. Also the output position of ICx model change with the position of sound source.

Localization of humpback whale signals with two directional frequency analysis and recording sonobouys

For many years, the navy has used directional frequency analysis and recording (DIFAR) sonobouys to record and track ships. DIFAR sonobouys compute acoustic particle velocity for two bimodal perpendicular hydrophone elements, which, with a magnetic compass, gives a directional bearing to the sound recorded on a third omnidirectional hydrophone. Use of DIFAR represents an easily deployable alternative method to standard time-difference of arrival localization with towed or bottom-mounted hydrophone arrays. In this study, we used two tethered DIFAR sonobouys to record and track playbacks of humpback whale song. GPS positions of playbacks were recorded. Digital signals were recorded at the sonobouy before multiplexing. Song units were recorded on both sonobouys, and then matched between sonobouys using time from the sonobouy GPS. To localize the signals, azimuths from the DIFAR sonobouys were combined with the time difference of arrival parabola to create a three-dimensional likelihood surface that gives the probabilities that a signal originated at a specific point in space. The locations with maximum likelihood were used to estimate source level of whale calls, and singing whales were tracked over time. Comparisons will be made between DIFAR methods and GPS locations from the playback boat, to ground-truth this localization methodology.

Intercalibrating Microwave Satellite Observations for Monitoring Long-Term Variations in Upper- and Midtropospheric Water Vapor*

Abstract This paper analyzes the growing archive of 183-GHz water vapor absorption band measurements from the Advanced Microwave Sounding Unit B (AMSU-B) and Microwave Humidity Sounder (MHS) on board polar-orbiting satellites and document adjustments necessary to use the data for long-term climate monitoring. The water vapor channels located at 183.31 ± 1 GHz and 183.31 ± 3 GHz are sensitive to upper- and midtropospheric relative humidity and less prone to the clear-sky sampling bias than infrared measurements, making them a valuable but underutilized source of information on free-tropospheric water vapor. A method for the limb correction of the satellite viewing angle based upon a simplified model of radiative transfer is introduced to remove the scan angle dependence of the radiances. Biases due to the difference in local observation time between satellites and spurious trends associated with satellite orbital drift are then diagnosed and adjusted for using synthetic radiative simulations based on the Interim European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-Interim). The adjusted, cloud-filtered, and limb-corrected brightness temperatures are then intercalibrated using zonal-mean brightness temperature differences. It is found that these correction procedures significantly improve consistency and quantitative agreement between microwave radiometric satellite observations that can be used to monitor upper- and midtropospheric water vapor. The resulting radiances are converted to estimates of the deep-layer-mean upper- and midtropospheric relative humidity, and can be used to evaluate trends in upper-tropospheric relative humidity from reanalysis datasets and coupled ocean–atmosphere models.

The Diurnal Variation of Geo‐Electric Field Along the Longitude and Latitude Chains in China Mainland

AbstractThis paper studied the time and frequency characteristics of the geo‐electric field diurnal variation along two longitude chains and two latitude chains in China mainland, using the data of geo‐electric field observed at 37 stations along the chains. The following significant results are obtained. The diurnal variation at most stations appears as semi‐diurnal waves twice a day, near before and after the noon; in descending order of the FFT amplitude spectrums, the main periods of the diurnal variation are 12.4 h/12 h, 8 h, 24 h, etc., which are in accordance with the periods of the tidal harmonic components; the diurnal variation changes with latitude as the wave crest‐to‐trough amplitude gradually becomes bigger/smaller with reduced/increased latitude of the station, and also varies with longitude as the phase difference agrees with the local‐time difference between the stations along the same latitude. Furthermore, the amplitude of the diurnal variation is related with the Loyd season, which reduces orderly in J‐, E‐ and D‐seasons. The possible reasons which cause the main periodic components of the diurnal variation have been discussed, as a result, it is believed that the variation of the ground eddy current intensity caused by lunisolar tidal forces and the space electromagnetic activity aroused by the solar wind jointly produce the semi‐diurnal period components of the geo‐electric diurnal variation.

Latitudinal variation of F2-region response to geomagnetic disturbance

The effect of geomagnetic storms on the F2 region was studied by calculating the deviation, ΔfoF2, of foF2 during 40 magnetic storms, ranging from moderate (Dst<−50nT) to very intense (Dst<−200nT) of the 21st solar cycle. In order to study the variation of storm-time foF2 with latitude, season and storm strength, ionosonde data were obtained from eight stations spanning a latitudinal range of +60–−60°. The stations chosen lay in a narrow longitudinal range of 140–151°, so that local time difference between the stations is practically negligible. The features exhibited by positive and negative phases were essentially different. The storm time ΔfoF2 clearly exhibited a latitudinal variation and this variation were found to be coupled with the seasonal variation. As for the variation with storm intensity, though ΔfoF2 was found to vary even between two storms of almost equal intensity, the amplitude of a positive or negative phase, |ΔfoF2max| showed a distinct upper limit for each intensity category of storms.

Radiometric comparison of Mars Climate Sounder and Thermal Emission spectrometer measurements

Mars Climate Sounder (MCS) nadir oriented thermal infrared and solar channel measurements are compared with Thermal Emission Spectrometer (TES) measurements across multiple Mars years. Thermal infrared measurements were compared by convolving the TES data using the MCS spectral band passes. The MCS solar channel measurements were calibrated using Compact Reconnaissance Imaging Spectrometer for Mars observations to provide the proper gain factor (3.09×10−3Wsr−1m−2μm−1). The comparisons of the datasets show that day and night surface and atmospheric temperatures are within 3K over the course of 5 martian years, after accounting for the local time differences. Any potential interannual variations in global average temperature are masked by calibration and modeling uncertainties. Previous work attributed apparent interannual global surface and atmospheric temperature variations to major dust storm activity; however, this variation has since been attributed to a calibration error in the TES dataset that has been corrected. MCS derived Lambert albedos are slightly higher than TES measurements acquired over the same season and locations. Most of this difference can be attributed to the spectral response functions of MCS and TES. Consistent with previous work, global albedo is highly variable (∼6%) and this variability must be taken into account when determining long term global trends. Vertical aerosol distributions were also derived from the calibrated MCS visible channel limb measurements, demonstrating the utility of the MCS visible channel data for monitoring of aerosols.

View‐angle‐dependent AIRS cloudiness and radiance variance: Analysis and interpretation

AbstractUpper tropospheric clouds play an important role in the global energy budget and hydrological cycle. Significant view‐angle asymmetry has been observed in upper‐level tropical clouds derived from 8 years of Atmospheric Infrared Sounder (AIRS) 15 µm radiances. Here we find that the asymmetry also exists in the extratropics. It is larger during day than that during night, more prominent near elevated terrain, and closely associated with deep convection and wind shear. The cloud radiance variance, a proxy for cloud inhomogeneity, has consistent characteristics of the asymmetry to those in the AIRS cloudiness. The leading causes of the view‐dependent cloudiness asymmetry are the local time difference and small‐scale organized cloud structures. The local time difference (1–1.5 h) of upper‐level clouds between two AIRS outermost views can create parts of the observed asymmetry. On the other hand, small‐scale tilted and banded structures of the upper‐level clouds can induce about half of the observed view‐angle‐dependent differences in the AIRS cloud radiances and their variances. This estimate is inferred from analogous study using microwave humidity sounder radiances observed during the period of time when there were simultaneous measurements at two different view‐angles from NOAA‐18 and NOAA‐19 satellites. The existence of tilted cloud structures and asymmetric 15 µm and 6.7 µm cloud radiances implies that cloud statistics would be view‐angle‐dependent, and should be taken into account in radiative transfer calculations, measurement uncertainty evaluations and cloud climatology investigations. In addition, the momentum forcing in the upper troposphere from tilted clouds is also likely asymmetric, which can affect atmospheric circulation anisotropically.

Research on Method for Obtaining Time Difference of Localization of Transformer PD Source

Ultrasonic positioning accuracy of transformer partial discharge is not high. The main reason is that it is difficult to obtain accurate time difference of the ultrasonic signals reaching two different sensors, especially when the signal-to-noise ratio is not high enough. To solve this problem, Hilbert-Huang transform (HHT) is applied in signal processing to extract the precise moment, and in this way the precise time difference is easily obtained. The signal-to-noise ratio (SNR) of received signal is low, and even worse PD signal is drowned in the strong interference signal. For this, the method named fast independent component analysis (FastICA) is applied in ultrasonic signal denoising before obtaining the time difference. FastICA is not effective in separating the ultrasonic signal from the separated components and in order to solve the problem, envelope identification method is proposed in this paper. In the method, the upper envelope of the signal waveform is sampled and the average of the sampling points is calculated to extract the ultrasonic signal. The numerical result confirmed the practicality of all the mentioned methods.

一种基于相频函数关系的双基时差定位方法

基于相、频、时三者之间的函数关系，提出了一种有助于改善现有多站时差无源定位性能的定位算法。相对于现有的平面三站时差定位方法，这种先通过频移到相差的函数变换，再利用相差和时差间的关系，将原先仅能用于机载的测距公式转化为与探测平台运动状态无关的双基时差定位方法具有更高的测量精度，避免了对高重频信号测量的定位解模糊，同时相距较远的两主基站间的时间基准可以要求不同步，这无疑有利于站址的选择。仿真结果验证了该算法的有效性。 This paper presents a location algorithm which can help to improve existing performance of multistation time difference location based on the function relationship among phase shift, Doppler shift and time difference. New method uses the relationship between phase difference and time difference based on the function transforms from Doppler shift into phase shift. Finally, the ranging formula that only can apply to airborne platform can be translated into the double station time difference location method which is not associated with the motion state of detection platform. As compared to existing three stations time difference location method in two-dimension plane, the double station time difference location method can heighten measurement accuracy and avoid the time difference ambiguity introduced by high PRF signal. At the same time, it also has the characteristics that the time reference between two major base stations can be deranged, and that looking for the building position of base station is more convenient. Simulation result proves the availability of the algorithm.

运动平台上时差变化率的相差检测

提出了一种利用机载短基线阵列，以及通过多通道相移测量获得时差变化率的新方法。由相差与时差定位方程即可解出基于相差检测的时差表示式，通过微分，并利用相移与频移间的函数关系即可得到仅基于相差检测的时差变化率。另一方面，如对测向公式进行微分运算，则又可得到仅基于频差检测的时差变化率。模拟计算验证了所导出的时差变化率测算公式都是正确性的。初步的误差分析说明，由于分母上具有量级很大的光速，故基于相差或频差的时差变化率的检测应具有较高的测量精度。新方法将能用于解决在机载平台上时差变化率难以实时检测的问题。 A new method for detection of time difference rate using short baseline array on airborne platform is presented by measuring the phase shift in multichannel way. The time difference expression based on phase difference measurement can be solved according to phase difference and time difference location equation. Further, the time difference rate based on phase difference measurement can be derived by differential and making use of the functional relationship between phase shift and Doppler shift. On the other hand, the time difference rate based on frequency difference measurement can be obtained if we do the differential analyzer for direction finding formula. The analog calculation validates that derived formula of time difference rate are all correct. The elementary error analysis shows that the measurement accuracy of time difference rate based on phase difference or frequency difference is higher for having the light velocity whose order of magnitude is enormous in denominator of formula. The major contribution in this paper is that the time difference rate on airborne platform can be in real time detected by phase interferometry with short-baseline array.

Two GABAA responses with distinct kinetics in a sound localization circuit

The temporal characteristics and functional diversity of GABAergic inhibition are determined by the spatiotemporal neurotransmitter profile, intrinsic properties of GABAA receptors, and other factors. Here, we report two distinct GABAA responses and the underlying mechanisms in neurons of the chicken nucleus laminaris (NL), the first encoder of interaural time difference for sound localization in birds. The time course of the postsynaptic GABAA currents in NL neurons, recorded with whole-cell voltage clamp, differed between different characteristic frequency (CF) regions. Compared to low-CF (LF) neurons, middle/high-CF (MF/HF) neurons had significantly slower IPSCs, with a 2.6-fold difference in the decay time constants of spontaneous IPSCs and a 5.3-fold difference in the decay of IPSCs elicited by single-pulse stimulus. Such differences were especially dramatic when IPSCs were elicited by train stimulations at physiologically relevant frequencies, and at high stimulus intensities. To account for these distinct GABAA responses, we showed that MF/HF neurons exhibited more prominent asynchronous release of GABA. Supporting this observation, replacement of extracellular Ca2+ with Sr2+ increased the decay of IPSCs in LF neurons, and EGTA-AM reduced the decay of IPSCs in MF/HF neurons. Furthermore, pharmacological evidence suggests that GABA spillover plays a greater role in prolonging the IPSCs of MF/HF neurons. Consequently, under whole-cell current clamp, synaptically released GABA produced short- and long-lasting suppression of the neuronal excitability of LF and MF/HF neurons, respectively. Taken together, these results suggest that the GABAergic inputs to NL neurons may exert a dynamic modulation of interaural time difference (ITD) coding in a CF-dependent manner.

Her2-enriched breast cancer brain metastases exhibit resistance to Gamma Knife radiosurgery: findings from a single institutional series review

This study aims to assess the outcomes and prognostic/predictive factors of overall survival and local control in patients with a diagnosis of brain metastasis from a breast cancer primary who underwent Gamma Knife radiosurgery (GKRS) as part of intracranial treatment. A total of 69 patients were identified who were treated with GKRS for one to four brain metastases from breast cancer as a primary diagnosis. A total of 176 metastases were treated at diagnosis or as salvage treatment. Differences in overall survival time (OS) and local control time (LC) after GKRS between groups were assessed. The median follow-up was 9.2 months (range 3–90.5 months). The median OS for this cohort was 13.4 months (range 0.5–90.5 months). The median LC was 15.8 months. For a given metastasis, univariate analysis showed that LC was significantly correlated with the dose density (DD, ratio of GKRS dose to metastasis volume, [gray per cubic centimeters]). Additionally, human epidermal growth factor receptor 2 (HER2) enrichment predicted for worse local control on univariate analysis [HR 2.18; 95 % CI 1.047–4.532] (p = 0.037). With DD as a continuous variable, the only independent and significant predictive factors were the DD [HR: 0.99; 95%CI: 0.984–0.998] (p = 0.009) and HER2-enriched subtype [HR = 2.25; 95 % CI = 1.074–4.728] (p = 0.032) after accounting for dose, metastasis volume, whole-brain radiotherapy (WBRT), and other subtypes. DD was then examined as a binary categorical variable whether or not a metastasis was treated to, at least, the median DD delivered across the cohort. With the cutoff set at this median, a DD value of 36 Gy/c3, the independent and significant predictive factor again was the DD [HR: 3.49; 95%CI: 1.45–8.40] (p = 0.005) in favor of metastases receiving at least 36 Gy/c3. Additionally, HER2 enrichment was significant when DD was examined as a binary variable, predicting for worse LC [HR 2.20; 95 % CI: 1.048–4.636] (p = 0.037). The median LC for metastasis receiving <36 Gy/c3 is 18.7 months vs. median not reached in those receiving at least 36 Gy/c3 (p < 0.001). For HER2-enriched metastases, a DD ≥36 Gy/c3 resulted in a 14 % failure rate (10-month actuarial), compared to that of 0 % observed in non-HER2-enriched subtypes. The ratio of dose delivered with GKRS to metastasis volume was significantly correlated with LC, with values ≥36 Gy/c3 improving LC. This effect was significantly diminished in HER2 subtypes, and a required higher DD for improved control, suggesting these metastases may be intrinsically resistant to radiosurgery.

Time difference localization in the presence of outliers

In this work we examine new ways to solve a time-difference-of-arrival (TDOA) localization problem when the set of measurements is contaminated by outliers. The proposed method relies on the minimization of an Lp-norm based cost function with p∈(0,1]. This norm is known to provide robustness against outliers. Some known positioning method can eventually successfully locate an emitter in the presence of outlier measurements, but it is at the expense of huge computational costs due to multi-dimensional grid search. We propose in this paper a way to dramatically lighten the computational load by reducing the problem to a few linear searches. Even if 70% of the measurements are outliers, the proposed positioning method provides high accuracy location estimates, while keeping the computational load very low. Optionally, the location estimates can be used to identify and reject outliers from the data set, which can then serve as an input of any common TDOA positioning method to obtain refined location estimates. Numerical examples corroborate our results, both in terms of accuracy and of computational time.

Adaptive Line Enhancement for Improved Uplink Time Difference of Arrival Localization

The problem of locating mobile stations (MS) in cellular systems based on uplink time difference of arrival (UTDOA) of MS signal at spatially separated base stations with known locations is addressed in this paper. Multipath fading and channel noise are the main factors resulting in inaccurate mobile station position estimation. Therefore, use of the normalized least mean square (NLMS) algorithm based adaptive line enhancer (ALE) followed by a correlator is proposed to obtain more precise time difference of arrival (TDOA) estimation. The proposed technique applies the ALE as a pre-filter to signal cross correlation, leading to improved accuracy in TDOA estimation and consequently more precise positioning of MS. The robustness of the proposed technique is examined and analyzed through computer simulations. Simulation results indicate superior performance of the proposed ALE-UTDOA estimator over the conventional cross correlation method.

Application of quantum neural networks in localization of acoustic emission

Due to defects of time-difference of arrival localization, which influences by speed differences of various model waveforms and waveform distortion in transmitting process, a neural network technique is introduced to calculate localization of the acoustic emission source. However, in back propagation (BP) neural network, the BP algorithm is a stochastic gradient algorithm virtually, the network may get into local minimum and the result of network training is dissatisfactory. It is a kind of genetic algorithms with the form of quantum chromosomes, the random observation which simulates the quantum collapse can bring diverse individuals, and the evolutionary operators characterized by a quantum mechanism are introduced to speed up convergence and avoid prematurity. Simulation results show that the modeling of neural network based on quantum genetic algorithm has fast convergent and higher localization accuracy, so it has a good application prospect and is worth researching further more.

Reconstructing echolocation behavior using time difference of arrival localization and a distributed microphone array as a virtual Telemike.

Bats use echolocation to probe their 3-D environment. New techniques in distributed microphone array processing allow us to record echolocation behavior, reconstruct the flight paths, and generate an acoustic record of individual bats flying the laboratory or the field. Probabilistic methods of time difference of arrival localization allow us to follow bats navigating in flight room mazes, foraging in the wild and using active sonar in the presence of possible jamming from conspecifics. By reversing the localization operation, we back out the changing propagation times of the sounds emitted by bats flying fast in three dimensions. Through beamforming, we then create an amplified acoustic track that follows the reference frame of the bat, amounting to a virtual Telemike based on consensus data from the microphone array. Spatial tracking and virtual on-board recording allow us to ask new questions about the spectral and temporal strategies employed by echolocating bats and to model the neural and perceptual natures of sonar. [Work supported by ONR and NSF.]

A combined gene and cell therapy approach for restoration of conduction

Abnormal conduction underlies both bradyarrhythmias and re-entrant tachyarrhythmias. However, no practical way exists for restoring or improving conduction in areas of conduction slowing or block. This study sought to test the feasibility of a novel strategy for conduction repair using genetically engineered cells designed to form biological "conducting cables." An in vitro model of conduction block was established using spatially separated, spontaneously contracting, nonsynchronized human embryonic stem cell-derived cardiomyocytes clusters. Immunostaining, dye transfer, intracellular recordings, and multielectrode array (MEA) studies were performed to evaluate the ability of genetically engineered HEK293 cells, expressing the SCN5A-encoded Na(+) channel, to couple with cultured cardiomyocytes and to synchronize their electrical activity. Connexin-43 immunostaining and calcein dye-transfer experiments confirmed the formation of functional gap junctions between the engineered cells and neighboring cardiomyocytes. MEA and intracellular recordings were performed to assess the ability of the engineered cells to restore conduction in the co-cultures. Synchronization was defined by establishment of fixed local activation time differences between the cardiomyocytes clusters and convergence of their activation cycle lengths. Nontransfected control cells were able to induce synchronization between cardiomyocytes clusters separated by distances up to 300 μm (n = 21). In contrast, the Na(+) channel-expressing cells synchronized contractions between clusters separated by up to 1,050 μm, the longest distance studied (n = 23). Finally, engineered cells expressing the voltage-sensitive K(v)1.3 potassium channel prevented synchronization at any distance. Genetically engineered cells, transfected to express Na(+) channels, can form biological conducting cables bridging and coupling spatially separated cardiomyocytes. This novel cell therapy approach might be useful for the development of therapeutic strategies for both bradyarrhythmias and tachyarrhythmias.

A Clustering Detection Algorithm of Stationary Target for Passive Time Difference Location System

A Clustering Detection Algorithm of Stationary Target for Passive Time Difference Location System

Positioning of Acoustic Emission Source by Using Sub-gradient Projection Based on Energy Attenuation Model

Because of containing several model waveforms, the source rub-impact acoustic emission(AE) signal transmitting in complicated body will cause waveform distortion for varying transmission speed of each model and dispersion effect. It is difficult to achieve exact source location by traditional time difference location. An energy attenuation model is established on the basis of the characteristic of approximately inverse ratio between propagation energy and source distance, the location of the AE source is limited in a hypersphere in which the circle centre and radius are all the energy ratio functions of a sensors pair, and uses adaptive sub-gradient projection to approximate to the source location. As the method is based on energy ratio instead of energy, the location accuracy will not be significantly affected even if the energy of AE source has a significant change. When multiple sensors pairs are installed more hyperspheres can be decided, so this method is also applicable to positioning array composed of multiple sensors. The experiment results show that this algorithms has higher location accuracy than Time Delay Estimation algorithm, it also has good convergence and lower computation complexity.