High Spatial Accuracy Research Articles

Создание виртуальных моделей местности при проектировании портовых комплексов по данным лидарной съемки

The design of port complexes is a process that requires considering geographical and economic features of the territory. It is necessary to aggregate the characteristics of coastal landscapes, seascapes, artificial elements, dangerous objects, etc. The experience of implementing such projects (for example, in Sabetta) suggests that all participants in the design process need highly precise geographical information to optimize the location of coastal facilities, infrastructure solutions, power supply lines, water conduits, product pipelines, and related structures. As for now, the best method of geoinformation support of such projects is LIDAR (with simultaneous nadir and perspective aerial surveys). In the future, these materials, combined with space-based remote sensing data on the surrounding areas, would be used for creating virtual models with tools adapted for users with an average and low-level GIS data experience. Nowadays geoinformation systems have a number of disadvantages. First and foremost, it is difficult for non-specialists to master them. Full-featured GIS packages are expensive and cannot be used by a significant number of specialists, dispersed over various settlements only using high-speed internet connections (designing port complexes requires the efforts of heterogeneous specialists living in different cities and working in different industries). The approach proposed in this paper allows to solve this problem without using GIS packages. We consider it possible to use virtual environments that are closed from editing and access to the source data. An area of 2400 km² in the territory of Kamchatka Peninsula near Bechevinka Bay was chosen as a test site. The resulting virtual model of the territory of the future port complex is a convenient tool for increasing the spatial awareness of users, closed from unauthorized access. The work has successfully achieved the functionality and usability of this model on conventional computers, combined with the high spatial accuracy of the model.

Seagrass restoration monitoring and shallow-water benthic habitat mapping through a photogrammetry-based protocol

Seagrasses rank among the most productive yet highly threatened ecosystems on Earth. Loss of seagrass habitat because of anthropogenic disturbances and evidence of their limited resilience have provided the impetus for investigating and monitoring habitat restoration through transplantation programmes. Although Structure from Motion (SfM) photogrammetry is becoming a more and more relevant technique for mapping underwater environments, no standardised methods currently exist to provide 3-dimensional high spatial resolution and accuracy cartographic products for monitoring seagrass transplantation areas. By synthesizing various remote sensing applications, we provide an underwater SfM-based protocol for monitoring large seagrass restoration areas. The data obtained from consumer-grade red-green-blue (RGB) imagery allowed the fine characterization of the seabed by using 3D dense point clouds and raster layers, including orthophoto mosaics and Digital Surface Models (DSM). The integration of high spatial resolution underwater imagery with object-based image classification (OBIA) technique provided a new tool to count transplanted Posidonia oceanica fragments and estimate the bottom coverage expressed as a percentage of seabed covered by such fragments. Finally, the resulting digital maps were integrated into Geographic Information Systems (GIS) to run topographic change detection analysis and evaluate the mean height of transplanted fragments and detect fine-scale changes in seabed vector ruggedness measure (VRM). Our study provides a guide for creating large-scale, replicable and ready-to-use products for a broad range of applications aimed at standardizing monitoring protocols in future seagrass restoration actions.

Fabrication and evaluation of bilateral Helmholtz radiofrequency coil for thermo-stable breast image with reduced artifacts.

PurposeThe positron emission tomography (PET)‐magnetic resonance (MR) system is a newly emerging technique that yields hybrid images with high‐resolution anatomical and metabolic information. With PET‐MR imaging, a definitive diagnosis of breast abnormalities will be possible with high spatial accuracy and images will be acquired for the optimal fusion of anatomic locations. Therefore, we propose a PET‐compatible two‐channel breast MR coil with minimal disturbance to image acquisition which can be used for simultaneous PET‐MR imaging in patients with breast cancer.Materials and MethodsFor coil design and construction, the conductor loops of the Helmholtz coil were tuned, matched, and subdivided with nonmagnetic components. Element values were optimized with an electromagnetic field simulation. Images were acquired on a GE 600 PET‐computed tomography (CT) and GE 3.0 T MR system. For this study, we used the T1‐weighted image (volunteer; repetition time (TR), 694 ms; echo time (TE), 9.6 ms) and T2‐weighted image (phantom; TR, 8742 ms; TE, 104 ms) with the fast spin‐echo sequence.ResultsThe results of measuring image factors with the proposed radiofrequency (RF) coil and standard conventional RF coil were as follows: signal‐to‐noise ratio (breast; 207.7 vs. 175.2), percent image uniformity (phantom; 89.22%–91.27% vs. 94.63%–94.77%), and Hounsfield units (phantom; ‐4.51 vs. 2.38).ConclusionsOur study focused on the feasibility of proposed two‐channel Helmholtz loops (by minimizing metallic components and soldering) for PET‐MR imaging and found the comparable image quality to the standard conventional coil. We believe our work will help significantly to improve image quality with the development of a less metallic breast MR coil.

Modeling of wastewater treatment processes with hydrosludge.

The pressure for Water Resource Recovery Facilities (WRRF) operators to efficiently treat wastewater is greater than ever because of the water crisis, produced by the climate change effects and more restrictive regulations. Technicians and researchers need to evaluate WRRF performance to ensure maximum efficiency. For this purpose, numerical techniques, such as CFD, have been widely applied to the wastewater sector to model biological reactors and secondary settling tanks with high spatial and temporal accuracy. However, limitations such as complexity and learning curve prevent extending CFD usage among wastewater modeling experts. This paper presents HydroSludge, a framework that provides a series of tools that simplify the implementation of the processes and workflows in a WRRF. This work leverages HydroSludge to preprocess existing data, aid the meshing process, and perform CFD simulations. Its intuitive interface proves itself as an effective tool to increase the efficiency of wastewater treatment. PRACTITIONER POINTS: This paper introduces a software platform specifically oriented to WRRF, named HydroSludge, which provides easy access to the most widespread and leading CFD simulation software, OpenFOAM. Hydrosludge is intended to be used by WRRF operators, bringing a more wizard-like, automatic, and intuitive usage. Meshing assistance, submersible mixers, biological models, and distributed parallel computing are the most remarkable features included in HydroSludge. With the provided study cases, HydroSludge has proven to be a crucial tool for operators, managers, and researchers in WRRF.

Perception and Performance of Electrical Stimulation for Proprioception.

Proprioception, yielding awareness of the body's position and motion in space, is typically lacking in prostheses and supernumerary limbs. Electrical stimulation is one technique that may provide these devices with proprioception. This paper first investigates how the modalities of electrotactile cues, such as frequency and intensity, are perceived. Using the results, we designed and compared several comfortable and perceptible feedback mappings for spatial cues. Two experiments were conducted using a 16-electrode bracelet worn above the elbow to provide electrical stimuli. We found that subjects could localize the stimulating electrode with a precision of ±1 electrode (110 mm) in all feedback conditions. Moreover, within the range of pulse intensities perceived as comfortable, the participants' performance was more sensitive to changes in frequency than in intensity. The highest performance was obtained for the condition which increased both intensity and frequency with radial distance. These results suggest that electrical stimulation can be used for artificial proprioceptive feedback, which can ensure a comfortable and intuitive interaction and provides high spatial accuracy.

Sparsity-enhanced equivalent source method for acoustic source reconstruction via the Generalized Minimax-Concave penalty

The Equivalent Source Method (ESM) is a powerful technique for acoustic source reconstruction, which has been widely used in noise control and machinery fault detection. Because the inverse acoustic source reconstruction problem is typically ill-conditioned, regularization techniques are often adopted in ESM to achieve meaningful solutions. Based on the sparse distribution assumption of acoustic sources, sparse regularization can be utilized in ESM to promote the spatial resolution of reconstructed results. Existing sparse ESMs often adopt convex l1 norm or nonconvex lp norm as the regularization terms. However, l1 norm-regularized ESM suffers from an insufficient sparsity-inducing problem, which decreases the spatial resolution and reconstruction accuracy. Meanwhile, reconstructed results of lp norm-regularized ESM are often unstable due to multiple local minimas. In this paper, a sparsity-enhanced ESM is proposed, which introduces a nonconvex Generalized Minimax-Concave (GMC) penalty into ESM as the regularization term. The GMC penalty can enhance the sparsity of solutions and simultaneously maintain the convexity of the overall objective function in acoustic source reconstruction. Consequently, the GMC penalty-regularized ESM can improve the spatial resolution and reconstruction accuracy of the reconstructed results. To solve the acoustic source reconstruction problem rapidly, a computation framework based on Alternating Direction Method of Multipliers (ADMM) is derived. Simulation studies indicate that the proposed method can improve the acoustic source reconstruction accuracy in a wide frequency band, compared with existing l1 and lp norm-regularized ESMs. Two experimental cases further verify that the proposed sparsity-enhanced ESM can effectively reconstruct the acoustic sources with high spatial resolution and reconstruction accuracy at higher frequencies.

4D line-scan hyperspectral imaging

This paper proposes a 4D line-scan hyperspectral imager that combines 3D geometrical measurement and spectral detection with high spectral resolution and spatial accuracy. We investigated the geometrical optical model of a camera attaching with a spectrograph, theoretically explored the mathematical model for line-scan fringe projection profilometry, and established the 3D reconstruction and calibration methods under this proposed line-scan high-dimensional imaging system. The spectral resolution of the system is 2.8 nm, and the spatial root-mean-square-error is 0.0895 mm when measuring a standard sphere with a diameter of 40.234 mm. We measure a colored statue to showcase the intensity change along the dimension of wavelength. In addition, the quality and defect of the spinach leaves are inspected based on spectral data and depth data, which demonstrates the potential application of the system in the food industry.

A Simulation Study of Ultra-relativistic Jets–I. A New Code for Relativistic Hydrodynamics

Abstract In an attempt to investigate the structures of ultra-relativistic jets injected into the intracluster medium (ICM) and the associated flow dynamics, such as shocks, velocity shear, and turbulence, we have developed a new special relativistic hydrodynamic (RHD) code in the Cartesian coordinates, based on the weighted essentially non-oscillatory (WENO) scheme. It is a finite difference scheme of high spatial accuracy, which has been widely employed for solving hyperbolic systems of conservation equations. The code is equipped with different WENO versions, such as the fifth-order accurate WENO-JS, WENO-Z, and WENO-ZA, and different time-integration methods, such as the fourth-order accurate Runge–Kutta (RK4) and strong stability preserving RK (SSPRK), as well as the implementation of the equations of state (EOSs) that closely approximate the EOS of the single-component perfect gas in relativistic regimes. In addition, it incorporates a high-order accurate averaging of fluxes along the transverse directions to enhance the accuracy of multidimensional problems, and a modification of eigenvalues for the acoustic modes to effectively control the carbuncle instability. Through extensive numerical tests, we assess the accuracy and robustness of the code, and choose WENO-Z, SSPRK, and the EOS suggested in Ryu et al. as the fiducial setup for simulations of ultra-relativistic jets. The results of our study of ultra-relativistic jets using the code is reported in an accompanying paper.

Pseudospectral methods with PML for nonlinear Klein-Gordon equations in classical and non-relativistic regimes

Two different Perfectly Matched Layer (PML) formulations with efficient pseudo-spectral numerical schemes are derived for the standard and non-relativistic nonlinear Klein-Gordon equations (NKGE). A pseudo-spectral explicit exponential integrator scheme for a first-order formulation and a linearly implicit preconditioned finite-difference scheme for a second-order formulation are proposed and analyzed. To obtain a high spatial accuracy, new regularized Berm\'udez type absorption profiles are introduced for the PML. It is shown that the two schemes are efficient, but the linearly implicit scheme should be preferred for accuracy purpose when used within the framework of pseudo-spectral methods combined with the regularized Berm\'udez type functions. In addition, in the non-relativistic regime, numerical examples lead to the conclusion that the error related to regularized Berm\'udez type absorption functions is insensitive to the small parameter $\varepsilon$ involved in the NKGE. The paper ends by a two-dimensional example showing that the strategy extends to the rotating NKGE where the vortex dynamics is very well-reproduced.

Accuracy Assessment of UAV-Photogrammetric-Derived Products Using PPK and GCPs in Challenging Terrains: In Search of Optimized Rockfall Mapping

Unmanned aerial photogrammetric surveys are increasingly being used for mapping and studying natural hazards, such as rockfalls. Surveys using unmanned aerial vehicles (UAVs) can be performed in remote, hardly accessible, and dangerous areas, while the photogrammetric-derived products, with high spatial and temporal accuracy, can provide us with detailed information about phenomena under consideration. However, as photogrammetry commonly uses indirect georeferencing through bundle block adjustment (BBA) with ground control points (GCPs), data acquisition in the field is not only time-consuming and labor-intensive, but also extremely dangerous. Therefore, the main goal of this study was to investigate how accurate photogrammetric products can be produced by using BBA without GCPs and auxiliary data, namely using the coordinates X0, Y0 and Z0 of the camera perspective centers computed with PPK (Post-Processing Kinematic). To this end, orthomosaics and digital surface models (DSMs) were produced for three rockfall sites by using images acquired with a DJI Phantom 4 RTK and the two different BBA methods mentioned above (hereafter referred to as BBA_traditional and BBA_PPK). The accuracy of the products, in terms of the Root Mean Square Error (RMSE), was computed by using verification points (VPs). The accuracy of both BBA methods was also assessed. To test the differences between the georeferencing methods, two statistical test were used, namely a paired Student’s t-test, and a non-parametric Wilcoxon signed-rank. The results show that the accuracy of the BBA_PPK is inferior to that of BBA_traditional, with the total RMSE values for the three sites being 0.056, 0.066, and 0.305 m, respectively, compared to 0.019, 0.036 and 0.014 m obtained with BBA_traditional. The accuracies of the BBA methods are reflected in the accuracy of the orthomosaics, whose values for the BBA_PPK are 0.039, 0.043 and 0.157 m, respectively, against 0.029, 0.036 and 0.020 m obtained with the BBA_traditional. Concerning the DSM, those produced with the BBA_PPK method present accuracy values of 0.065, 0.072 and 0.261 m, respectively, against 0.038, 0.060 and 0.030 m obtained with the BBA_traditional. Even though that there are statistically significant differences between the georeferencing methods, one can state that the BBA_PPK presents a viable solution to map dangerous and exposed areas, such as rockfall transit and deposit areas, especially for applications at a regional level.

High Accuracy Ultrafast Spatiotemporal Pump-Probe Measurement of Electrical Thermal Transport in Thin Film Gold.

A high resolution spatiotemporal ultrafast pump-probe system is developed to examine the interactions and transport phenomena between the electrical and the lattice thermal subsystems during ultrafast laser-matter interactions. This system incorporates an ultrafast pump-probe scheme with a stationary probe beam that interrogates the response to a spatial scanning pump beam, providing a full spatiotemporal mapping of a material's response due to an ultrafast pump excitation. The material's response, which is highly sensitive to its transport properties, is measured with a high spatial accuracy of up to ±10 nm and subpicosecond time resolution. Details of achieving this high spatial accuracy are described, and a study of the ultrafast transport processes in thin film gold is demonstrated. With the aid of transport and optical response models, the electrical thermal transport properties of gold and the electron-lattice coupling constant are simultaneously determined.

Can no-bubble methane seeps affect biological traits of benthic macroinvertebrates in coastal systems?

Methane seep studies often target sites where methane gas is actively bubbling from the sea floor to the water column. However, gas bubbles often remain trapped in surficial seabed sediments, especially in coastal systems; notably few ecological studies exist for these systems. These environments form patches on the seafloor in the Bahia Blanca estuary that, based on taxonomic analysis, represent a distinct benthic habitat. Here we examine whether taxonomic changes in benthic communities associated with trapped methane gas bubbles are related to functional changes. We found significant differences in biological traits of macroinvertebrates weighted by abundance and by species between two sites differing in gas presence and between spring and winter seasons. Compared with the control (no gas) site, the gas site had subsurface-deposit feeders and large sessile animals partially calcified with suspension-feeding mode. In contrast, at the control site the small and non-calcified animals are discretely motile, building burrows and tubes and feeding on surface deposit material. Trapped methane gas, detected with seismic methods, changes biological traits in benthic fauna and can lead to alteration of some ecosystem functions. This suggests the utility of high-resolution seismic methods for detect these benthic habitats with high spatial accuracy, and a need to further understanding of ecosystem processes associated with gas presence in the context of both direct anthropogenic and climate-change pressures.

Improvement of sensitivity and specificity for laminar BOLD fMRI with double spin-echo EPI in humans at 7 T

Mapping mesoscopic cortical functional units such as columns or laminae is increasingly pursued by ultra-high field (UHF) functional magnetic resonance imaging (fMRI). The most popular approach for high-resolution fMRI is currently gradient-echo (GE) blood oxygenation level-dependent (BOLD) fMRI. However, its spatial accuracy is reduced due to its sensitivity to draining vessels, including pial veins, whereas spin-echo (SE) BOLD signal is expected to have higher spatial accuracy, albeit with lower sensitivity than the GE-BOLD signal. Here, we introduce a new double spin-echo (dSE) echo-planar imaging (EPI) method to improve the sensitivity of SE-BOLD contrast by averaging two spin-echoes using three radiofrequency pulses. Human fMRI experiments were performed with slices perpendicular to the central sulcus between motor and sensory cortices at 7 T during fist-clenching with touching. First, we evaluated the feasibility of single-shot dSE-EPI for BOLD fMRI with 1.5mm isotropic resolution and found that dSE-BOLD fMRI has higher signal-to-noise ratio (SNR), temporal SNR (tSNR), and higher functional sensitivity than conventional SE-BOLD fMRI. Second, to investigate the laminar specificity of dSE-BOLD fMRI, we implemented a multi-shot approach to achieve 0.8-mm isotropic resolution with sliding-window reconstruction. Unlike GE-BOLD fMRI, the cortical profile of dSE-BOLD fMRI peaked at ~ 1.0mm from the surface of the primary motor and sensory cortices, demonstrating an improvement of laminar specificity in humans over GE-BOLD fMRI. The proposed multi-shot dSE-EPI method is viable for high spatial resolution UHF-fMRI studies in the pursuit of resolving mesoscopic functional units.

Measurement of real phase distribution of a vortex beam propagating in free space based on an improved heterodyne interferometer

This paper proposes an improved heterodyne interferometer to measure the real phase distribution of vortex beams propagating in free space. The fundamental mode Gaussian beam passes through the vortex phase plate and has one or more phase transitions of 2π along the angular direction. Such vortex beams undergo phase distortion during transmission, and their complex phase distribution is difficult to measure. The improved heterodyne interferometer proposed in this study successfully measures the phase distortion, demonstrating high spatial resolution and phase measurement accuracy. Both the theoretical and the experimental results show that in the process of free space propagation, the phase jump intersection boundary transforms from a straight line into a twisted line and that the phase distribution gradually becomes a spiral phase distribution followed by a ring intensity distribution corresponding to further increase in the propagation distance. The proposed method is estimated to be capable of predicting the variation of the vortex beams based on the research conducted on the interaction between the vortex beams and the atmospheric turbulence.

High spatial resolution photo mosaicking for the monitoring of coralligenous reefs

Coralligenous reefs are characterized by large bathymetric and spatial distribution, as well as heterogeneity; in shallow environments, they develop mainly on vertical and sub-vertical rocky walls. Mainly diver-based techniques are carried out to gain detailed information on such habitats. Here, we propose a non-destructive and multi-purpose photo mosaicking method to study and monitor coralligenous reefs developing on vertical walls. High-pixel resolution images using three different commercial cameras were acquired on a 10 m2 reef, to compare the effectiveness of photomosaic method to the traditional photoquadrats technique in quantifying the coralligenous assemblage. Results showed very high spatial resolution and accuracy among the photomosaic acquired with different cameras and no significant differences with photoquadrats in assessing the assemblage composition. Despite the large difference in costs of each recording apparatus, little differences emerged from the assemblage characterization: through the analysis of the three photomosaics twelve taxa/morphological categories covered 97–99% of the sampled surface. Photo mosaicking represents a low-cost method that minimizes the time spent underwater by divers and capable of providing new opportunities for further studies on shallow coralligenous reefs.

A kinematic model-based analysis framework for 3D Cine-DENSE-validation with an axially compressed gel phantom and application in sheep before and after antero-apical myocardial infarction.

Myocardial strain is increasingly used to assess left ventricular (LV) function. Incorporation of LV deformation into finite element (FE) modeling environment with subsequent strain calculation will allow analysis to reach its full potential. We describe a new kinematic model-based analysis framework (KMAF) to calculate strain from 3D cine-DENSE (displacement encoding with stimulated echoes) MRI. Cine-DENSE allows measurement of 3D myocardial displacement with high spatial accuracy. The KMAF framework uses cine cardiovascular magnetic resonance (CMR) to facilitate cine-DENSE segmentation, interpolates cine-DENSE displacement, and kinematically deforms an FE model to calculate strain. This framework was validated in an axially compressed gel phantom and applied in 10 healthy sheep and 5 sheep after myocardial infarction (MI). Excellent Bland-Altman agreement of peak circumferential (Ecc ) and longitudinal (Ell ) strain (mean difference = 0.021 ± 0.04 and -0.006 ± 0.03, respectively), was found between KMAF estimates and idealized FE simulation. Err had a mean difference of -0.014 but larger variation (±0.12). Cine-DENSE estimated end-systolic (ES) Ecc , Ell and Err exhibited significant spatial variation for healthy sheep. Displacement magnitude was reduced on average by 27%, 42%, and 56% after MI in the remote, adjacent and MI regions, respectively. The KMAF framework allows accurate calculation of 3D LV Ecc and Ell from cine-DENSE.

Contribution of spectroscopic magnetic resonance imaging to target volume delineation in Gamma Knife Radiosurgery: Myth or reality?

Brain malignancies are still associated with poor prognosis despite multimodal radiosurgical therapeutic approach using Gamma Knife (GK), CyberKnife (CK), and linear accelerator-based technologies [1]. These advances have significantly improved the treatment outcome. However, the surgical and radiosurgical concept is still “image-guided”, and the success is closely related to precise tumor volume definition. The gross tumor volume (GTV) is defined as the visible contrast- enhancing lesion on magnetic resonance (MR) images with high three-dimensional spatial accuracy. Target delineation requires always both T2-weighted and volumetric T1-weighted sequences. T2-weighted fluid attenuated inversion recovery (FLAIR) sequences analyze the lesions surrounding brain tissues [2,3]. Objective assessment of apparently healthy tissue surrounding brain tumors seems to be a considerable factor interfering not only with the radiosurgical procedure, but also with the recurrence rate and overall survival. Several studies identified infiltrative spectroscopic pattern of the perilesional edema in more than 96% of high-grade gliomas cases and in 11,5% of patients with brain metastasis [4]. Moreover, some autopsy series of brain metastases confirmed infiltrative growth in radiologically healthy surrounding tissues in more than 60% of cases. This unseen malignant component is responsible of 80 % of “early recurrence” which should be considered as natural evolution of the main tumor [5]. In the management of high grade gliomas, the radiosurgeons are faced either to carcinologic incomplete procedures or to overestimated target irradiation with unbalanced benefit/risk action mostly related to radiation-induced brain necrosis [6]. The delineation of clinical target volume (CTV) which is defined as the volume of tissue that contains the GTV and any microscopic tumor or paths of spread, became a standard for any radio-surgical planning. Since a decade, the magnetic resonance spectroscopy (MRS) was standardized in the target volume assessment. The aim is to establish a metabolic lesional cartography. It had been reported that choline/ N- acetylaspartate (NAA) multivoxel MR spectroscopy index higher that 2,5 is in favor of malignancy in glioma with sensitivity of 90 % and specificity of 85 % [7]. However, NAA/Creatine (Cr) and Choline/Cr ratios are more relevant in the analysis of perilesional edema in brain metastasis cases. The introduction of MRS metabolic cartography concept, the use of relevant metabolite and adapted metabolites ratio estimation contributed to precision in radiosurgery. However, MRS is not used for target delineation for Gamma Knife radiosurgical treatment because of its incompatibility with the Leksell Gamma Knife planning software. Recently, we described the development of the first software allowing the integration of metabolic cartography based on multivoxel spectroscopic MRI in the radiosurgical planning for Leksell Gamma Knife Radiosurgery. The few existing meta-analysis could not lead to gold standard volume delineation techniques despite objective advance in imaging assessment [8,9]. Prospective studies using multimodal imaging data will help to overcome this insufficiency for target delineation in radiosurgery

GPU accelerated voxel-based machining simulation

The simulation of subtractive manufacturing processes has a long history in engineering. Corresponding predictions are utilized for planning, validation and optimization, e.g., of CNC-machining processes. With the up-rise of flexible robotic machining and the advancements of computational and algorithmic capability, the simulation of the coupled machine-process behaviour for complex machining processes and large workpieces is within reach. These simulations require fast material removal predictions and analysis with high spatial resolution for multi-axis operations. Within this contribution, we propose to leverage voxel-based concepts introduced in the computer graphics industry to accelerate material removal simulations. Corresponding schemes are well suited for massive parallelization. By leveraging the computational power offered by modern graphics hardware, the computational performance of high spatial accuracy volumetric voxel-based algorithms is further improved. They now allow for very fast and accurate volume removal simulation and analysis of machining processes. Within this paper, a detailed description of the data structures and algorithms is provided along a detailed benchmark for common machining operations.

Development of an Image Registration Technique for Fluvial Hyperspectral Imagery Using an Optical Flow Algorithm.

Fluvial remote sensing has been used to monitor diverse riverine properties through processes such as river bathymetry and visual detection of suspended sediment, algal blooms, and bed materials more efficiently than laborious and expensive in-situ measurements. Red–green–blue (RGB) optical sensors have been widely used in traditional fluvial remote sensing. However, owing to their three confined bands, they rely on visual inspection for qualitative assessments and are limited to performing quantitative and accurate monitoring. Recent advances in hyperspectral imaging in the fluvial domain have enabled hyperspectral images to be geared with more than 150 spectral bands. Thus, various riverine properties can be quantitatively characterized using sensors in low-altitude unmanned aerial vehicles (UAVs) with a high spatial resolution. Many efforts are ongoing to take full advantage of hyperspectral band information in fluvial research. Although geo-referenced hyperspectral images can be acquired for satellites and manned airplanes, few attempts have been made using UAVs. This is mainly because the synthesis of line-scanned images on top of image registration using UAVs is more difficult owing to the highly sensitive and heavy image driven by dense spatial resolution. Therefore, in this study, we propose a practical technique for achieving high spatial accuracy in UAV-based fluvial hyperspectral imaging through efficient image registration using an optical flow algorithm. Template matching algorithms are the most common image registration technique in RGB-based remote sensing; however, they require many calculations and can be error-prone depending on the user, as decisions regarding various parameters are required. Furthermore, the spatial accuracy of this technique needs to be verified, as it has not been widely applied to hyperspectral imagery. The proposed technique resulted in an average reduction of spatial errors by 91.9%, compared to the case where the image registration technique was not applied, and by 78.7% compared to template matching.

Characterizing the three‐dimensional distribution of schooling reef fish with a portable multibeam echosounder

AbstractMultispecies schools of small planktivorous fishes are important constituents of reefs and coastal infrastructure; however, determining the extent and distribution of these schools is challenging. Here, we describe a novel use of a low‐cost portable multibeam echosounder from a small vessel, which can concurrently measure detailed bathymetry and the distribution of mid‐water targets with high spatial accuracy, regardless of light availability or water clarity. Fish abundance and biomass are not easily quantified by multibeam echosounders, so we developed a new metric for delineating the gridded horizontal distribution of school thickness, and assessed the metric's efficacy by examining its correlation with mean volume backscattering strength derived from a calibrated 38 kHz split‐beam echosounder (R = 0.67). We measured the distribution of fish school thickness around clusters of large concrete modules of an artificial reef using a multibeam echosounder, complemented with underwater video to aid species identification. The mean distribution of school thickness was mapped around the reef field with generalized additive mixed models. Model spatial predictions indicated schools aggregated around module clusters, rather than individual modules. Dynamic schools of fish in relatively shallow coastal waters (~ 30 m) can be surveyed over 400,000 m2 at 3 m s−1 in just 60 min. Portable multibeam echosounders are an accessible and valuable addition to quantifying the dynamic distributions of coastal fishes around features with high vertical relief.