Short Arrays Research Articles

Macrovibrissae and microvibrissae inversion and lateralization in elephants.

Elephants are known for strongly lateralized trunk behaviors, but the mechanisms driving elephant lateralization are poorly understood. Here, we investigate features of elephant mouth organization that presumably promote lateralization. We find the lower jaw of elephants is of narrow width, but is rostrally strongly elongated even beyond the jaw bone. Elephant lip vibrissae become progressively longer rostrally. Thus, elephants have two lateral dense, short microvibrissae arrays and central, less dense long macrovibrissae. This is an inversion of the ancestral mammalian facial vibrissae pattern, where central, dense short microvibrissae are flanked by two lateral macrovibrissae arrays. Elephant microvibrissae have smaller follicles than macrovibrissae. Similar to trunk-tip vibrissae, elephant lip microvibrissae show laterally asymmetric abrasion. Observations on Asian zoo elephants indicate lateralized abrasion results from lateralized feeding. It appears that the ancestral mammalian mouth (upper and lower lips, incisors, frontal microvibrissae) is shaped by oral food apprehension. The elephant mouth organization radically changed, however, because trunk-mediated feeding replaced oral apprehension. Such elephant mouth changes include the upper lip-nose fusion to the trunk, the super-flexible elongated lower jaw, the loss of incisors, and lateral rather than frontal microvibrissae. Elephants' specialization for lateral food insertion is reflected by the reduction in the centering effects of oral food apprehension and lip vibrissae patterns.

An application of a beamforming technique, linear acoustic array and robot for pipe condition localization

Pipe inspection robots with sensors significantly enhance the maintenance of water systems by enabling early defect detection and reducing the risks of leaks and environmental damage. This paper introduces a sparse representation acoustic beamformer designed to locate artefacts within pipes using a short linear microphone array on a robot. The primary contributions include: (i) a new acoustic beamforming approach based on sparse representation that accurately predicts pipe conditions with a localization error within 3 % of the sensing distance; (ii) an enhanced beamforming algorithm combining plane wave and first non-axisymmetric mode, extending the frequency range from < 1300 Hz to < 2200 Hz in a 150 mm diameter pipe (an increase by 1.69 times), effectively managing unwanted acoustic reverberations and distinguishing blockages from lateral connections; and (iii) a novel robust algorithm predicting pipe length with an error margin within 2 %. This research advances acoustic sensing technologies for autonomous mobile robots inspecting buried pipes.

Research and application on in-situ monitoring of strata movement in submarine cold seeps area based on three-dimensional MEMS sensor network

Accurate monitoring of strata movement is crucial for understanding the geomorphological evolution of the cold seeps. However, the complex environments and inherent challenges of deep-sea operations present significant obstacles for existing observation methods. In this paper, we present a strata movement monitoring system based on a three-dimensional micro-electromechanical system (MEMS) sensor network that includes multiple short and long sensor arrays. The movement vector is reconstructed using triaxial-acceleration and cubic Hermite interpolation. In laboratory simulations with vertical and horizontal displacement of 250 mm and 100 mm, respectively, the root mean square error of the reconstruction model is 3.74 mm. Two sensor arrays were deployed and operated for 4 days in cold seeps in South China Sea, and the observed displacement showed micro-tremors, and the displacement ranges in the x- and y- directions were (−0.4 mm, 0.18 mm) and (−0.43 mm, 0.19 mm), respectively. These results affirm the feasibility of the proposed system.

An X/Ku‐band shared aperture antenna with open, short, and load‐ended series‐feed center‐fed chebyshev amplitude distribution array for AIR‐BORNE‐synthetic aperture radar

AbstractThis article presents a dual‐band shared aperture antenna array designed for ASAR applications. The antenna array comprises eight elements for Chebyshev array configurations in both X/Ku‐bands. The proposed array achieves a scanning angle of ±25° by employing an interelement spacing of 0.7 λ. The layout mitigates mutual coupling effects and provides good isolation performance between the X‐ and Ku‐band antenna arrays across all synthesis techniques. Adopting the open, short, and load antenna array achieves different side lobe level (SLL) performances, &gt;−25 dB. The isolation between bands and between the three conditions is quantified as follows: S16 = S61 = −68 dB, S15 = S51 = −55 dB, S12 = S21 = −46 dB, S43 = S34 = −49 dB, and S56 = S65 = −43 dB. The SLL values for each synthesis technique in the X/Ku‐band are as follows: Chebyshev simulated and measured results for open‐ended (X/Ku‐band: −26/−24 dB/−27/−26.8 dB). Furthermore, the antenna array achieves maximum realized gains in different positions (0°, 5°, 10°, 15°, 20°, 25°) in the X/Ku‐band. The gains for each synthesis technique are as follows: Chebyshev (The measured gain of this X/Ku‐band is high around 16.2/16.5 dBi (open‐ended), 13.1/14.2 dBi (short‐ended), and 15.3/15.2 dBi (load‐ended). The antenna array exhibits a comparatively wide impedance bandwidth Chebyshev (X/Ku‐band: 100/230 MHz).

Strain and Temperature Sensing Based on Different Temperature Coefficients fs-FBG Arrays for Intelligent Buoyancy Materials.

The temperature and strain fields monitoring during the preparation process of buoyancy materials, as well as the health status after molding, are important for mastering the mechanical properties of buoyancy materials and ensuring the safety of operators and equipment. This paper proposes a short and high-density femtosecond fiber Bragg grating (fs-FBG) array based on different temperature coefficients fibers. By optimizing the parameters of femtosecond laser point-by-point writing technology, high-performance fs-FBG arrays with millimeter level gating length and millimeter level spatial resolution were prepared on two types of fibers. These were successfully embedded in buoyancy materials to achieve in-situ online monitoring of the curing process and after molding. The experimental results show that the fs-FBG array sensor has good anti-chirp performance and achieves online monitoring of millimeter-level spatial resolution. Intelligent buoyancy materials can provide real-time feedback on the health status of equipment in harsh underwater environments. The system can achieve temperature monitoring with an accuracy of 0.56 °C and deformation monitoring with sub-millimeter accuracy; the error is in the order of micrometers, which is of great significance in the field of deep-sea exploration.

Centromere diversity: How different repeat-based holocentromeres may have evolved.

In addition to monocentric eukaryotes, which have a single localized centromere on each chromosome, there are holocentric species, with extended repeat-based or repeat-less centromeres distributed over the entire chromosome length. At least two types of repeat-based holocentromeres exist, one composed of many small repeat-based centromere units (small unit-type), and another one characterized by a few large centromere units (large unit-type). We hypothesize that the transposable element-mediated dispersal of hundreds of short satellite arrays formed the small centromere unit-type holocentromere in Rhynchospora pubera. The large centromere unit-type of the plant Chionographis japonica is likely a product of simultaneous DNA double-strand breaks (DSBs), which initiated the de novo formation of repeat-based holocentromeres via insertion of satellite DNA, derived from extra-chromosomal circular DNAs (eccDNAs). The number of initial DSBs along the chromosomes must be higher than the number of centromere units since only a portion of the breaks will have incorporated eccDNA at an appropriate position to serve as future centromere unit sites. Subsequently, preferential incorporation of the centromeric histone H3 variant at these positions is assumed. The identification of repeat-based holocentromeres across lineages will unveil the centromere plasticity and elucidate the mechanisms underlying the diverse formation of holocentromeres.

Performance of an approximate Bayes factor based detector for environmentally informed active sonar

Developed here are a space of approximate Bayes Factor (BF) inference processors for high frequency broadband active sonar with short vertical arrays operating in shallow water ocean waveguides that exploit relatively depth invariant modes of propagation. The relevant information regarding the refractive media, rough surface and volume reverberation are incorporated to build the marginal likelihoods under each of the composite hypotheses of null and alternative. Acoustic scattering from a mobile object of interest under depth uncertainty characterizes the compound alternative hypothesis. Approximations are presented and inferences regarding the presence of the mobile body of interest are determined against a composite null hypothesis of reverberation and ambient acoustic noise. The approximate BF processor is shown to be a time-varying quadratic form of array observations over the beam-delay space. We demonstrate the sub-space processing of depth invariant modes at range and illustrate the BF inferential approach on a few representative waveguides. Performance in classic terms of probability of detection as a function of false alarm rate are presented. [This work supported by the Office of Naval Research.]

Fast deconvolved beamforming For arbitrary arrays based on beam-domain sparse Bayesian learning

Aiming at the problem that the conventional deconvolved beamforming methods cannot be directly applied to the specific array with a shift-variant point spread function and also have considerable computational workload, a deconvolved beamforming method for arbitrary arrays based on beam-domain sparse Bayesian learning(SBL) is proposed. First, generalized convolution model for arbitrary arrays in beam-domain is derived. Conventional beamforming is used to obtain several complex output beams. Then, to improve the accuracy of direction of arrival(DOA) estimation, the off-grid SBL method which adopts a coarse grid and takes the sampled positions in the coarse grid as the adjustable parameters is applied to achieve deconvolution of complex output beams. Controlling the number of output beams from the conventional beamforming can accelerate the off-grid SBL method while maintaining reasonable accuracy. The simulation results show that the proposed method provides enhanced recovery performance and higher DOA estimation accuracy comparable to the traditional SBL beamforming method in element domain at the same grid interval. Especially for short and dense arrays, it can achieve a decrease in computational complexity by one to two orders of magnitude with the same accuracy.

Enhanced boiling heat transfer on three-dimensional hybrid micropillar array surfaces

Boiling heat transfer is widely used in numerous industrial systems because of its excellent heat dissipation performance. The critical heat flux (CHF) represents the upper limit of efficient heat removal. The most widely applied CHF model is Zuber's hydrodynamic instability model, which posits that the interference between vapor and liquid counterflows results in the CHF. In this paper, a three-dimensional (3D) hybrid micropillar array surface for hindering the liquid–vapor interface is proposed to enhance the CHF and heat transfer coefficient (HTC). The 3D hybrid surface comprises a tall hydrophobic (HB) pillar array surrounded by a short hydrophilic (HP) pillar array. The tall HB pillar array acts as a potential nucleation site for increasing the HTC, and the short HP pillar array acts as a wicking structure for facilitating liquid rewetting. In addition, the height difference between the HB and HP pillar arrays can potentially reduce the interference between liquid and vapor counterflows and increase the CHF. Relative to a plain silica surface, the 3D hybrid surface increases the CHF and HTC by 107% and 360%, respectively. Theoretical modeling suggests that the CHF on the 3D hybrid surface was still limited by pool hydrodynamics.

Contribution of the satellitome to the exceptionally large genome of dinoflagellates: The case of the harmful alga Alexandrium minutum

Dinoflagellates are known to possess an exceptionally large genome organized in permanently condensed chromosomes. Focusing on the contribution of satellite DNA (satDNA) to the whole DNA content of genomes and its potential role in the architecture of the chromosomes, we present the characterization of the satellitome of Alexandriun minutum strain VGO577. To achieve this, we analyzed Illumina reads using graph-based clustering and performed complementary bioinformatic analyses. In this way, we discovered 180 satDNAs occupying 17.38 % of the genome. The 12 most abundant satDNAs represent the half of the satellitome but no satDNA is overrepresented, with the most abundant contributing ∼1.56 % of the genome. The largest repeat unit is 517 bp long but more than the half of the satDNAs (101) have repeat units shorter than 20 bp. We used FISH to map a selected set of 26 satDNAs. Although some satDNAs generate discrete hybridization signals at specific chromosomal locations (hybridization sites, HS), our cytological analysis showed that most satDNAs are dispersed throughout the genome, probably forming short arrays. Two satDNAs co-localize with the 45S rDNA. With the exception of telomeric DNA, no other satDNA yields HS on all chromosomes. In addition, we analyzed nine satDNAs yielding HS in VGO577 in four other A. minutum strains. Polymorphism at the intraspecific level was found for the presence/absence and/or abundance of some satDNAs, suggesting the amplification/deletion of these satDNAs following geographic separation or during culture maintenance of the strains. We also discuss how these results contribute to the understanding of chromosome architecture and evolution of dinoflagellate genomes.

Quantifying ATP-Independent Nucleosome Chaperone Activity with Single-Molecule Methods.

The dynamics of histone-DNA interactions govern chromosome organization and regulates the processes of transcription, replication, and repair. Accurate measurements of the energies and the kinetics of DNA binding to component histones of the nucleosome under a variety of conditions are essential to understand these processes at the molecular level. To accomplish this, we employ three specific single-molecule techniques: force disruption (FD) with optical tweezers, confocal imaging (CI) in a combined fluorescence plus optical trap, and survival probability (SP) measurements of disrupted and reformed nucleosomes. Short arrays of positioned nucleosomes serve as a template for study, facilitating rapid quantification of kinetic parameters. These arrays are then exposed to FACT (FAcilitates Chromatin Transcription), a non-ATP-driven heterodimeric nuclear chaperone known to both disrupt and tether histones during transcription. FACT binding drives off the outer wrap of DNA and destabilizes the histone-DNA interactions of the inner wrap as well. This reorganization is driven by two key domains with distinct function. FD experiments show the SPT16 MD domain stabilizes DNA-histone contacts, while the HMGB box of SSRP1 binds DNA, destabilizing the nucleosome. Surprisingly, CI experiments do not show tethering of disrupted histones, but increased rates of histone release from the DNA. SI experiments resolve this, showing that the two active domains of FACT combine to chaperone nucleosome reassembly after the timely release of force. These combinations of single-molecule approaches show FACT is a true nucleosome catalyst, lowering the barrier to both disruption and reformation.

The nature and organization of satellite DNAs in Petunia hybrida, related, and ancestral genomes.

The garden petunia, Petunia hybrida (Solanaceae) is a fertile, diploid, annual hybrid species (2n=14) originating from P. axillaris and P. inflata 200 years ago. To understand the recent evolution of the P. hybrida genome, we examined tandemly repeated or satellite sequences using bioinformatic and molecular cytogenetic analysis. Raw reads from available genomic assemblies and survey sequences of P. axillaris N (PaxiN), P. inflata S6, (PinfS6), P. hybrida (PhybR27) and the here sequenced P. parodii S7 (PparS7) were used for graph and k-mer based cluster analysis of TAREAN and RepeatExplorer. Analysis of repeat specific monomer lengths and sequence heterogeneity of the major tandem repeat families with more than 0.01% genome proportion were complemented by fluorescent in situ hybridization (FISH) using consensus sequences as probes to chromosomes of all four species. Seven repeat families, PSAT1, PSAT3, PSAT4, PSAT5 PSAT6, PSAT7 and PSAT8, shared high consensus sequence similarity and organisation between the four genomes. Additionally, many degenerate copies were present. FISH in P. hybrida and in the three wild petunias confirmed the bioinformatics data and gave corresponding signals on all or some chromosomes. PSAT1 is located at the ends of all chromosomes except the 45S rDNA bearing short arms of chromosomes II and III, and we classify it as a telomere associated sequence (TAS). It is the most abundant satellite repeat with over 300,000 copies, 0.2% of the genomes. PSAT3 and the variant PSAT7 are located adjacent to the centromere or mid-arm of one to three chromosome pairs. PSAT5 has a strong signal at the end of the short arm of chromosome III in P. axillaris and P.inflata, while in P. hybrida additional interstitial sites were present. PSAT6 is located at the centromeres of chromosomes II and III. PSAT4 and PSAT8 were found with only short arrays. These results demonstrate that (i) repeat families occupy distinct niches within chromosomes, (ii) they differ in the copy number, cluster organization and homogenization events, and that (iii) the recent genome hybridization in breeding P. hybrida preserved the chromosomal position of repeats but affected the copy number of repetitive DNA.

Beam-domain deconvolution beamforming algorithm based on compressive sensing

Deconvolution beamforming is often used to improve the azimuth resolution in target detection. However, most traditional deconvolution beamforming algorithms require the array directivity function to be shift-invariant, which are suitable for specific arrays such as linear arrays and circular arrays. A beam-domain deconvolution beamforming method suitable for arbitrary array is proposed based on compressive sensing. First, conventional beamforming is used to obtain several complex beam outputs, then the Sparse Bayesian Learning (SBL) reconstruction algorithm is applied to the beam-domain model to achieve deconvolution of complex beam outputs. The deconvolution process leads to more accurate estimation for the Direction Of Arrival (DOA) for target signals. The proposed method can also effectively reduce the computational complexity of the algorithm by controlling the number of output beams from the conventional beamforming and is applicable for both non coherent and coherent signals. The simulation and experiment results show that the proposed algorithm has azimuth resolution performance comparable to the traditional element-domain SBL beamforming algorithm, and is superior to the conventional beamforming and Minimum Variance Distortionless Response (MVDR) algorithms. When applied to short and dense arrays, the computation complexity of the proposed algorithm is significantly lower than that of the traditional element-domain SBL beamforming algorithm.

Azimuthal, range, and depth tracking of marine mammal sounds using a drifting acoustic vector sensor and hydrophone array platform

Deep-water acoustic tracking of marine mammals typically requires correlating hydrophone signals across both short and large-aperture hydrophone arrays. Here, we demonstrate how a single drifting, depth-controlled platform can obtain two and three-dimensional positional fixes of marine mammal sounds using an acoustic vector sensor and short-aperture arrays, both mounted on an autonomous drifting platform. In February and June 2023 two autonomous opto-acoustic drifters were deployed 50km off San Diego, CA at 250 m depth in 1030 m deep water. Both drifters were equipped with a CTD and acoustic recording system comprised of a 1.75 m aperture vertical hydrophone array, a tetrahedral hydrophone array, and either a 2-D Geospectrum M-35 or 3-D Wilcoxon VS-209 acoustic vector sensor. Throughout the two to three-day deployments, all acoustic sensors detected numerous marine mammal calls, including humpback whales and a pod of common dolphins. Estimates of azimuth and elevation were obtained from the simultaneously sampled acoustic vector sensor and hydrophone arrays, while multi-path and cross-platform processing were employed to extract range information. The results suggest that sparse deployments of drifting vector sensor platforms may be able to map biological distributions over spatial scales that would otherwise require larger numbers of hydrophone-only platforms. [Work supported by ONR TFO.]

Source localization in deep water with a towed array from UUV

Unmanned Underwater Vehicle (UUV) can work in larger depth. If a towed array applied on UUV, it can detect the acoustics signals from a target in the direct arrival zone with lower transmission loss in deep water. Based on sound field characteristics in deep water, a source detection scheme with multiple UUVs is proposed. The aperture of sonar array is limited by the carrying capacity of UUV. Therefore, a passive aperture extension with sparse Bayesian learning (SBL) is proposed for a moving short array to improve the performance of direction-of-arrival estimation by constructing a larger virtual aperture. The phase correction factors and bearings of different targets are estimated simultaneously by SBL. The experiment results show that the method extends the aperture effectively and obtains higher azimuth resolution and accuracy for the direction-of-arrival (DOA) estimation than the Conventional Beamforming (CBF). The detection of an underwater target by using a towed array from UUV is possible. [Work supported by the National Natural Science Foundation of China, Grant No. U22A2012.]

Evolution of speech perception in patients with ossified cochlea and short array cochlear implant

Background: Short array cochlear implant is indicated as rehabilitation in patients with severe to profound deafness, especially when there is cochlear ossification. In these cases, with reduced intracochlear patency, total insertion becomes more difficult, requiring the use of this type of electrode (15 mm). Few studies have been published to evaluate auditory performance, presenting controversial audiological results.Aims/Objectives: To report the speech perception of users of cochlear implants (CI) with short array. Material and Methods: A retrospective analysis of medical records of patients who underwent surgery for cochlear implantation with a short array, between 2009 and 2020, at the Hospital for Rehabilitation of Craniofacial Anomalies, University of São Paulo (HRAC-USP) was carried out. Results: There was performance evolution in the speech perception tests in the data analysis. Meningitis and congenital hearing loss were the main indications for CI in the sample. Conclusion. CI with a short array is an alternative in the management of patients with a history of cochlear ossification and severe or profound sensorineural hearing loss. Significance: To demonstrate the evolution of speech perception tests with short array cochlear implant in patients with or without ossified cochlea and its characteristics for application in clinical practice.

High-resolution frequency-difference beamforming for a short linear array.

Conventional beamforming (CBF) is a commonly employed approach for detecting and estimating the direction-of-arrival (DOA) of acoustic signals in underwater environments. However, CBF becomes ambiguous due to spatial aliasing when the received signal's half wavelength is smaller than the array spacing. Frequency-difference beamforming (FDB) allows for processing data in the lower frequency Δf without encountering spatial aliasing by utilizing the product of array data at frequency f with its complex conjugate at frequency f+Δf. However, lower frequency results in a wider mainlobe, which can lead to poorer DOA performance for short arrays. In this paper, a fourth-order cumulants FDB method and a conjugate augmented FDB method are proposed to extend an M-element uniform linear array to 2M-1 and 4M-3 elements. The proposed methods generate narrower beams and lower sidelobe levels than the original FDB for short arrays with large spacing. And by setting the signal subspace dimension reasonably, the proposed methods can improve the weak target detection ability under strong interference compared with FDB. Last, we verify the excellent performance of the proposed methods through simulations and experimental data.

Comparing linear and non-linear models to estimate the appropriate cochlear implant electrode array length—are current methods precise enough?

PurposeIn cochlear implantation with flexible lateral wall electrode arrays, a cochlear coverage (CC) range between 70% and 80% is considered ideal for optimal speech perception. To achieve this CC, the cochlear implant (CI) electrode array has to be chosen according to the individual cochlear duct length (CDL). Here, we mathematically analyzed the suitability of different flexible lateral wall electrode array lengths covering between 70% and 80% of the CDL.MethodsIn a retrospective cross-sectional study preoperative high-resolution computed tomography (HRCT) from patients undergoing cochlear implantation was investigated. The CDL was estimated using an otosurgical planning software and the CI electrode array lengths covering 70–80% of the CDL was calculated using (i) linear and (ii) non-linear models.ResultsThe analysis of 120 HRCT data sets showed significantly different model-dependent CDL. Significant differences between the CC of 70% assessed from linear and non-linear models (mean difference: 2.5 mm, p < 0.001) and the CC of 80% assessed from linear and non-linear models (mean difference: 1.5 mm, p < 0.001) were found. In up to 25% of the patients none of the existing flexible lateral wall electrode arrays fit into this range. In 59 cases (49,2%) the models did not agree on the suitable electrode arrays.ConclusionsThe CC varies depending on the underlying CDL approximation, which critically influences electrode array choice. Based on the literature, we hypothesize that the non-linear method systematically overestimates the CC and may lead to rather too short electrode array choices. Future studies need to assess the accuracy of the individual mathematical models.

Lunar active seismic profiler for investigating shallow substrates of the Moon and other extraterrestrial environments

To investigate the structures and properties of shallow material in extraterrestrial environments, we have developed a lunar active seismic profiler (LASP), which integrates active seismic sources and receivers in a short (~1 m) array that can be deployed on a rover. The small active source generates a chirp waveform that sweeps over a wide frequency range (20–250 Hz). The receivers are coupled to the ground by their own weight, but nevertheless deliver acceptable performance. We improve the signal-to-noise ratio of the seismic signal by stacking waveforms, enabling a minimal source to support the exploration of geological substrates. By processing shot gather of the LASP data, we calculated a dispersion curve of surface waves and obtained an accurate S-wave velocity profile from surface to 1 m depth. The results suggest that regions with even small amounts of subsurface ice (~0.5 wt%) can be identified in LASP results by their anomalously high S-wave velocity. Field experiments demonstrate that the LASP can support estimates of 3D S-wave velocity distributions and the identification of a buried geological boundary. The LASP also detected different degrees of compaction at the experimental site. If two rovers carry these profilers, or if a single rover combines one with a separately deployed receiver or active seismic source, seismic refraction and seismic reflection analyses can be conducted simultaneously in addition to surface wave analyses. These seismic surveys for longer-offset data achieve the exploration of deeper substrates in extraterrestrial settings such as the Moon, Mars, and other solid bodies.

Quality influencing factors of dispersion curves from short period dense arrays based on a convolutional neural network across the north section of the Xiaojiang fault area

The number of dispersion curves increases significantly when the scale of a short-period dense array increases. Owing to a substantial increase in data volume, it is important to quickly evaluate dispersion curve quality as well as select the available dispersion curve. Accordingly, this study quantitatively evaluated dispersion curve quality by training a convolutional neural network model for ambient noise tomography using a short-period dense array. The model can select high-quality dispersion curves that exhibit a ≤ 10% difference between the results of manual screening and the proposed model. In addition, this study established a dispersion curve loss function by analyzing the quality of the dispersion curve and the corresponding influencing factors, thereby estimating the number of available dispersion curves for the existing observation systems. Furthermore, a Monte Carlo simulation experiment is used to illustrates the station-pair interval distance probability density function, which is independent of station number in the observational system with randomly deployed stations. The results suggested that the straight-line length should exceed 15 km to ensure that loss rate of dispersion curves remains < 0.5, while maintaining the threshold ambient noise tomography accuracy within the study area.