Large Coverage Research Articles

Flood Mapping of Synthetic Aperture Radar (SAR) Imagery Based on Semi-Automatic Thresholding and Change Detection

Synthetic aperture radar (SAR) technology has become an important means of flood monitoring because of its large coverage, repeated observation, and all-weather and all-time working capabilities. The commonly used thresholding and change detection methods in emergency monitoring can quickly and simply detect floods. However, these methods still have some problems: (1) thresholding methods are easily affected by low backscattering regions and speckle noise; (2) changes from multi-temporal information include urban renewal and seasonal variation, reducing the precision of flood monitoring. To solve these problems, this paper presents a new flood mapping framework that combines semi-automatic thresholding and change detection. First, multiple lines across land and water are drawn manually, and their local optimal thresholds are calculated automatically along these lines from two ends towards the middle. Using the average of these thresholds, the low backscattering regions are extracted to generate a preliminary inundation map. Then, the neighborhood-based change detection method combined with entropy thresholding is adopted to detect the changed areas. Finally, pixels in both the low backscattering regions and the changed regions are marked as inundated terrain. Two flood datasets, one from Sentinel-1 in the Wharfe and Ouse River basin and another from GF-3 in Chaohu are chosen to verify the effectiveness and practicality of the proposed method.

Aerodynamic effects of an offshore floating photovoltaic platform undergoing pitch and heave motions

The offshore floating photovoltaic (OFPV) platform is a renewable energy generation system that has gained attention in recent years due to several advantages. OFPV exhibits higher sensitivity to wind loads than other offshore platforms, owing to its lightweight design and large aerial coverage. In contrast to the fixed photovoltaic systems, the OFPV platforms experience continuous oscillations induced by waves, which significantly influence the aerodynamic characteristics. In this study, the aerodynamic effects of an oscillating OFPV are investigated using the computational fluid dynamics (CFD) simulation method, including the three-dimensional effects, the Reynolds number effects, and the aerodynamic loads with various kinematic parameters. Some major findings are as follows. Firstly, a large-scale tip vortex exists when OFPV oscillates in pitch and heavy directions, which cannot be detected in two-dimensional simulations. Consequently, the lift coefficient, CL, and the drag coefficient, CD, are highly overestimated in 2-D simulation. Secondly, CL and CD decrease significantly as the Reynolds number increases for cases where Re < 106 while there is only a slight decrease for Re > 106. Thirdly, the aerodynamic forces are highly related to the amplitude of the pitch motion and the phase lag between the pitch and the heave motions. A fitting formula is proposed to calculate CL and CD based on the maximum angle of attack. Lastly, the evolution of the flow fields around the oscillating OFPV is analyzed. The separation of the leading edge mainly causes the aerodynamic force.

A Combination of Remote Sensing Datasets for Coastal Marine Habitat Mapping Using Random Forest Algorithm in Pistolet Bay, Canada

Marine ecosystems serve as vital indicators of biodiversity, providing habitats for diverse flora and fauna. Canada’s extensive coastal regions encompass a rich range of marine habitats, necessitating accurate mapping techniques utilizing advanced technologies, such as remote sensing (RS). This study focused on a study area in Pistolet Bay in Newfoundland and Labrador (NL), Canada, with an area of approximately 170 km2 and depths varying between 0 and −28 m. Considering the relatively large coverage and shallow depths of water of the study area, it was decided to use airborne bathymetric Light Detection and Ranging (LiDAR) data, which used green laser pulses, to map the marine habitats in this region. Along with this LiDAR data, Remotely Operated Vehicle (ROV) footage, high-resolution multispectral drone imagery, true color Google Earth (GE) imagery, and shoreline survey data were also collected. These datasets were preprocessed and categorized into five classes of Eelgrass, Rockweed, Kelp, Other vegetation, and Non-Vegetation. A marine habitat map of the study area was generated using the features extracted from LiDAR data, such as intensity, depth, slope, and canopy height, using an object-based Random Forest (RF) algorithm. Despite multiple challenges, the resulting habitat map exhibited a commendable classification accuracy of 89%. This underscores the efficacy of the developed Artificial Intelligence (AI) model for future marine habitat mapping endeavors across the country.

Preliminary Geological Mapping, Petrographic, and Structural Studies of Precambrian Basement Complex Rocks in Part of Chulwe-Matale, South Kivu, DR Congo

A geological map is a veritable planning tool for the economic development of any nation. This map contains the distribution of various types of bedrock in the area. A geological map of Congo’s geographic landmass has been produced since 1974 with the recently updated map of Kivu (Eastern part of Congo) in February 2018. This map largely omits some local geology of interest, possibly owing to its large area coverage. Thus, local geologic mapping must be encouraged to bridge this lacuna; the focus of this study. Field traversing and rock sample collections were carried out and thin sections of the different rock types were prepared and mounted on glass slides for microscopic observation. Geological mapping revealed that the study area is made of ferruginous, graphitic sandstone schists and quartzite with interbedded metadoleritic sills. The petrographic studies revealed the mineral assemblages of quartz-feldspars-muscovite and olivine-pyroxene and plagioclase feldspars respectively for the first and the second group geological units. The structural investigations come out of two deformation phases: the strike-slip type would be at the origin of the cleavages and folds. It’s related to the D1 of the Kibarian orogeny. The second is an extensive phase responsible for the NW-SE fracturation mapped in the study area. The Matale discordance crosses all these lithologies, a later phase is possible. This discontinuity would have acted in the region studied by switching the lithology units from NE-SW to ENE-WSW orientation. This research recommends that the Chulwe-Matale formations would be typical of the Lower Kibarian (Bugarama group) but the geochronology and geochemical data are lacking to confirm this hypothesis.

Functional ultrasound neuroimaging reveals mesoscopic organization of saccades in the lateral intraparietal area of posterior parietal cortex.

The lateral intraparietal cortex (LIP) located within the posterior parietal cortex (PPC) is an important area for the transformation of spatial information into accurate saccadic eye movements. Despite extensive research, we do not fully understand the functional anatomy of intended movement directions within LIP. This is in part due to technical challenges. Electrophysiology recordings can only record from small regions of the PPC, while fMRI and other whole-brain techniques lack sufficient spatiotemporal resolution. Here, we use functional ultrasound imaging (fUSI), an emerging technique with high sensitivity, large spatial coverage, and good spatial resolution, to determine how movement direction is encoded across PPC. We used fUSI to record local changes in cerebral blood volume in PPC as two monkeys performed memory-guided saccades to targets throughout their visual field. We then analyzed the distribution of preferred directional response fields within each coronal plane of PPC. Many subregions within LIP demonstrated strong directional tuning that was consistent across several months to years. These mesoscopic maps revealed a highly heterogenous organization within LIP with many small patches of neighboring cortex encoding different directions. LIP had a rough topography where anterior LIP represented more contralateral upward movements and posterior LIP represented more contralateral downward movements. These results address two fundamental gaps in our understanding of LIP's functional organization: the neighborhood organization of patches and the broader organization across LIP. These findings were achieved by tracking the same LIP populations across many months to years and developing mesoscopic maps of direction specificity previously unattainable with fMRI or electrophysiology methods.

Understanding bottom and surface marine heatwaves along the continental shelf of China

Marine heatwaves (MHWs) have become longer and more frequent over the past century under anthropogenic climate change, with devastating impacts on marine ecosystems. Surface MHWs (SMHWs) and their drivers have been extensively studied using satellite sea surface temperature data, yet the mechanism and characteristics of subsurface MHWs, especially bottom MHWs (BMHWs) along continental shelves, remain unclear. Based on a high-resolution ocean reanalysis dataset, we compare SMHWs and BMHWs along the continental shelf of China and find that BMHWs are typically longer (0–16 d) and more intense (0 °C–50 °C days) than SMHWs. The categorizing of both the BMHW and SMHW shows that moderate and strong events commonly occur in most areas with relatively large spatial coverage, whereas severe and extreme events occur with relatively small spatial coverage. There is a clear negative relationship between the BMHW intensity and ocean depth along the continental shelf, while the BMHW annual days and ocean depth are positively correlated in the Bohai and East China Seas. Generally, BMHWs and SMHWs occur more frequently in shallow coastal regions where the mixed layer depth is more likely to extend to the seafloor, resulting in high BMHW and SMHW synchrony. In addition to spatial coherence, there is a good temporal correspondence between BMHWs and SMHWs across the continental shelf of China from 1993 to 2020.

Token-based deep reinforcement learning for Heterogeneous VRP with Service Time Constraints

Heterogeneous Vehicle Routing aims to construct routes for various vehicles while optimizing an objective with a series of constraints. However, existing deep reinforcement learning-based methods often ignore the service time constraints, which prohibits vehicles from leaving current nodes until the service time is met. This limitation restricts their practical application. To address these concerns, we introduce the Heterogeneous Vehicle Routing Problem with Service Time Constraints (HVRP-STC) and formulate it as a Markov Decision Process with Service Time Constraints. We propose a novel deep reinforcement learning-based model, Token-based Deep Reinforcement Learning (TDRL), to solve this problem.To provide sufficient and timely information for decision making, we design a State Token Coding (STC) mechanism that encodes and updates individual and overall vehicle and node states as tokens of different types. To determine the pairs of vehicles and nodes and generate actions, we propose a Heterogeneous Decoder (HD) with a vehicle-selector and multiple vehicle-specific node-selectors. This decouples the vehicle-node selection tasks and customizes the task of choosing nodes to visit for individual vehicles, better catering to the heterogeneous nature of HVRP-STC.We evaluate the proposed method on four types of datasets with instances of different sizes, large spatial coverage, and varied mathematical model. Our results show that TDRL consistently outperforms state-of-the-art DRL methods. We will release the datasets and the source code of this benchmark with the paper via https://github.com/Vision-Intelligence-and-Robots-Group/ToDRL.

Cross-method Analysis of Corotation Radii Data Set for Spiral Galaxies

A corotation radius is a key characteristic of disk galaxies that is essential to determine the angular speed of the spiral structure Ω p , and therefore understand its nature. In the literature, there are plenty of methods to estimate this value, but do these measurements have any consistency? In this work, we collected a data set of corotation radius measurements for 547 galaxies, 300 of which had at least two values. An initial analysis reveals that most objects have rather inconsistent corotation radius positions. Moreover, a significant fraction of galactic disks is distinguished by a large error coverage and almost uniform distribution of measurements. These findings do not have any relation to spiral type, Hubble classification, or presence of a bar. Among other reasons, obtained results could be explained by the transient nature of spirals in a considerable part of galaxies. We have made our collected data sample publicly available, and have demonstrated on one example how it could be useful for future research by investigating a winding time value for a sample of galaxies with possible multiple spiral arm patterns.

Flexible thin-layer plasma sterilizer based on polyimide and efficacy evaluation under bending deformation

Cold atmospheric pressure plasma is receiving attention in biomedical treatment for its non-thermal, dry-type, and high-efficiency disinfection effects on bacteria, fungi, and viruses, compared to typical sterilization methods, such as pasteurization, chemical solutions, and ultraviolet radiation. There are great demands of plasma decontamination on the surface of complex 3D objects, with the request of large coverage, convenience, and uniformity, which still remains a challenge for the current plasma devices. In this work, a flexible thin-layer plasma source for sterilization is developed based on a polyimide substrate, and its plasma generation process is characterized by experiment and simulation. The influences of bending deformation are studied and evaluated by electrical waveforms, heat radiation, and ozone production, of which the mechanisms are further explained. Results illustrate that the variation in electron impact ionization induced by different curvatures is the main cause leading to the change in microparticle production, thus affecting the macroscopic properties of plasmas. Activations of the plasma sterilizer for 30 and 120 s reduce both S. aureus and P. aeruginosa on the flat surface by around 2.5 and 5 log colony forming units (CFU). However, the plasma sterilization effect decreases with an extent of about 1 log CFU when treating the curved surface, while being regained after conforming the plasma sterilizer to the curved surface. This kind of plasma generator offers significant flexibility and efficacy, being promising for the treatment of objects with irregular surfaces in future plasma biomedicine and material processing.

Improved fusion model for generating hourly fine scale land surface temperature data under all-weather condition

Existing Land Surface Temperature (LST) fusion models encounter some challenges due to missing data, complex weather areas, and rapid land cover changes. To overcome these limitations, we proposed the Integrated SpatioTemporal Fusion Algorithm (ISFAT). ISFAT is developed based on contemporary fusion models but in addition incorporates data from partially contaminated LSTs using the masked weight function. This helps to predict fine-scale LST on prediction date while considering error resulting from landcover changes between the base and prediction date. This algorithm also factors in the calculation of model residuals, which are distributed back to the predicted fine-scale LST using the thin-plate spline function. The fine-scale LST on prediction can thereafter employed for predicting hourly fine-scale LST images by integrating a coarse resolution LST with hourly temporal resolution. Compared to contemporary LST fusion models, ISFAT demonstrates superior performance, with mean average differences of 0.1 K and 0.27 K over SADFAT and STITFM, respectively. Additionally, diurnal LST predictions from ISFAT compare well with air temperatures from automatic weather stations. Notably, on February 18, 2020, ISFAT effectively optimized fine-scale LST for Hong Kong, achieving an RMSE of 3.33 K, despite the limitation of cloud cover in the base date. The newly developed ISFAT could facilitate better LST retrieval over a large spatial coverage under different degrees of cloud contamination.

Accelerated 3D metabolite T1 mapping of the brain using variable-flip-angle SPICE.

To develop a practical method to enable 3D T1 mapping of brain metabolites. Due to the high dimensionality of the imaging problem underlying metabolite T1 mapping, measurement of metabolite T1 values has been currently limited to a single voxel or slice. This work achieved 3D metabolite T1 mapping by leveraging a recent ultrafast MRSI technique called SPICE (spectroscopic imaging by exploiting spatiospectral correlation). The Ernst-angle FID MRSI data acquisition used in SPICE was extended to variable flip angles, with variable-density sparse sampling for efficient encoding of metabolite T1 information. In data processing, a novel generalized series model was used to remove water and subcutaneous lipid signals; a low-rank tensor model with prelearned subspaces was used to reconstruct the variable-flip-angle metabolite signals jointly from the noisy data. The proposed method was evaluated using both phantom and healthy subject data. Phantom experimental results demonstrated that high-quality 3D metabolite T1 maps could be obtained and used for correction of T1 saturation effects. In vivo experimental results showed metabolite T1 maps with a large spatial coverage of 240 × 240 × 72 mm3 and good reproducibility coefficients (< 11%) in a 14.5-min scan. The metabolite T1 times obtained ranged from 0.99 to 1.44 s in gray matter and from 1.00 to 1.35 s in white matter. We successfully demonstrated the feasibility of 3D metabolite T1 mapping within a clinically acceptable scan time. The proposed method may prove useful for both T1 mapping of brain metabolites and correcting the T1-weighting effects in quantitative metabolic imaging.

Optimising collection geometry for long‐range synthetic aperture sonar interferometry

AbstractInterferometric synthetic aperture sonar (SAS) is a technique to image and map the seabed in very high resolution. For large area coverage rate systems with hundreds of metres swath width, the achievable performance varies significantly over the swath. The performance is a function of system, collection geometry, and seabed type. A model is suggested to optimise the collection geometry for maximising area coverage rate given certain optimisation criteria, such as observation geometry, signal‐to‐noise ratio, depth measurement accuracy, and coverage within swath. The model is fitted to measurements (or calibrated) through a simple procedure. Specifically, the effect of vehicle altitude during the interferometric SAS data collection is studied. A novel model on data collected by a HUGIN Superior autonomous underwater vehicle carrying a HISAS 1032 Dual Rx interferometric SAS is demonstrated. The authors show that optimising the collection geometry, and in this case specifically the vehicle altitude, significantly improves the overall performance.

High-precision Lamb wave evaluation for corrosion damage with model-based Bayesian Optimization and Gaussian meta-modeling strategy

The presence of corrosion damage in metallic structures is a critical problem affecting system safety, which poses challenges for structural maintenance. Ultrasonic Lamb wave testing has shown many benefits, including high sensitivity and a large coverage area. However, multiple external factors are causing a mismatch between the imaging result and the actual damage. This study proposes a Bayesian Optimization-based model calibration framework, incorporating a Gaussian process (GP) measurement model, for accurate corrosion damage quantification. In this method, one critical problem is obtaining the high-fidelity Finite Element Method (FEM) model. The initial FEM model usually has inevitable modeling errors due to necessary simplifications and idealized constraints. Here we introduced Bayesian Optimization by which the numerical model could be calibrated. The calibrated FEM model, which had fewer discrepancies with actual experiments, could generate high-fidelity signals corresponding to various damage severity. Then, the GP measurement model outputted the mean and variance of the corrosion width and depth corresponding to the differences between experiment signals and model outputs. The inversion of damage information from the established GP model was accomplished by the genetic algorithm. Hence, both the damage size and depth could be evaluated with high accuracy. Once the corrosion information along different propagation paths was obtained, it can be combined with the location of the corrosion damage center for locating the edge points of the corrosion damage. In the end, the edge points were fitted using the least square algorithm. Validations were experimentally performed, and the detection result showed good consistency with the actual damage.

Polydopamine Adhesion: Catechol, Amine, Dihydroxyindole, and Aggregation Dynamics.

While polydopamine (PDA) possesses the surface-independent adhesion property of mussel-binding proteins, significant differences exist between them. Particularly, PDA's short and rigid backbone differs from the long and flexible protein sequence of mussel-binding proteins. Given that adhesion relies on achieving a conformal contact with large surface coverage, PDA has drawbacks as an adhesive. In our study, we investigated the roles of each building block of PDA to build a better understanding of their binding mechanisms. Initially, we anticipated that catecholamine oligomers form specific binding with substrates. However, our study showed that the universal adhesion of PDA is initiated by the solubility limit of growing oligomers by forming agglomerates, complemented by multiple binding modes of catechol. Notably, in the absence of amines, poly(catechol) either remained in solution or formed minor suspensions without any surface coating, underscoring the essential role of amines in the adhesion process by facilitating insoluble aggregate formation. To substantiate our findings, we induced poly(catechol) aggregation using quaternized poly(4-vinylpyridine) (qPVP), leading to subsequent surface adhesion upon agglomerate formation.

Integrating geospatial data and street‐view imagery to reconstruct large‐scale 3D urban building models

Abstract3D urban building modeling is a vital foundational step for building Digital Twins and Smart Cities. In response to existing challenges, such as high time costs, complex production processes, and low consistency with real‐world textures in large‐scale 3D urban building modeling methods, this research proposes a reconstructing 3D urban building models (3DUBM) approach that integrates geospatial data and street view. The approach achieves an enhanced generation of large‐scale 3DUBMs. Based on open geospatial data and street‐view imagery (SVI), the approach was tested in modeling experiments conducted in Shanghai, Hongkong, and Nanjing. Furthermore, a dataset covering unique blocks of 30 cities in China was constructed to demonstrate the approach's characteristics of large coverage, high time efficiency, high model quality and low economic cost. The accuracy of texture mapping from SVI to 3DUBM reached 85%. This achievement has significant economic value in bridging the gap in the production of large‐scale and low‐cost 3DUBM data, promoting the construction of Digital Twins, Smart Cities, and Real‐world 3D modeling.

Highly aligned pyrolytic graphite blades for neutron monochromatization

Highly aligned pyrolytic graphite blades for neutron monochromatization have been fabricated successfully from smaller commercial highly oriented pyrolytic graphite (HOPG) crystals. These blades of a large coverage area, 136 mm wide × 2 mm high, are achieved with minimum increase of the mosaic over that of the original HOPG crystal. A specialized crystal cleavage device and soldering device are developed for the fabrication process. Furthermore, an optimized intermittent mode of the radio frequency magnetron sputtering technique is employed to deposit indium on HOPG crystals. The devices and procedure reported here could be applied to the development of the focusing monochromators and analyzers in neutron scattering instruments using a sizable neutron beam.

Volumetric Analysis of a Novel Chimeric Gracilis and Profunda Artery Perforator Flap.

The presence of a chimeric gracilis and profunda artery perforator (PAP) flap with a common arterial pedicle has been demonstrated on computed tomography angiography in up to 59% of patients and confirmed in a cadaveric model. Already utilized for head and neck reconstruction by Heredero et al, this novel flap could provide more volume than either flap alone which is advantageous, particularly in patients with sizable defects. The purpose of this study was to determine the average tissue volume that can be utilized from this chimeric flap. CT Angiogram imaging studies exhibiting chimeric flap anatomy were reviewed over a 7-year period at a single institution utilizing Visage Version 7.1, a radiology picture archiving and communication system. This software was used to trace the flap pedicles and to capture estimated soft tissue volumes of each respective flap. A total of 31 patients, consisting of 52 lower extremity gracilis and PAP chimeric flaps, underwent tissue volume analysis. The average total volume of soft tissue supplied by the gracilis flap was found to be 70.21 cm3 (standard deviation [SD] = 26.99). The average volume of the PAP flap was 31.73 cm3 (SD = 26.12). The average total volume captured by the chimeric gracilis and PAP flap was 101.94 cm3 (SD = 62.40). The potential soft tissue volume that can be harvested from a chimeric gracilis and PAP flap is significantly greater than solitary gracilis or PAP flaps. This chimeric flap may serve as a viable and advantageous reconstructive option for patients requiring large volume soft tissue coverage, particularly if other sizable options are not available.

Tracking the scaling of urban open spaces in China from 1990 to 2020

Urban open spaces (UOS) are crucial for urban life, offering benefits across individual and societal levels. However, the understanding of the systematic dynamic of UOS scaling with city size and its potential non-linear performance remains a limited clarity area. This study bridges this gap by integrating urban scaling laws with remote sensing data from 1990 to 2020, creating a framework to analyze UOS trends in China. Our findings reveal that UOS growth is sub-linear scaling with city size, exhibiting economies of scale with scaling exponents between 0.55 and 0.65 and suggesting potential shortages. The distribution structure of UOS across cities is becoming increasingly balanced, as indicated by the rising Zipf’s slope from 0.66 to 0.88. Southeastern coastal cities outperform, highlighting spatial variations and path dependency in UOS development. Additionally, using metrics of Scale-adjusted metropolitan indicator (SAMI) and the ratio of open space consumption to population growth rates (OCRPGR), we observe a trend towards more coordinated development between UOS and population, with a declining proportion of uncoordinated cities. Our long-term, large sample coverage study of UOS in China may offer positive significance for urban ecological planning and management in similar rapidly urbanizing countries, contributing to critical insights for quantifying and monitoring urban sustainable development.

Local and regional interactions between tidal stream turbines and coastal environment

An extended three-dimensional unstructured ocean model for simulating impacts of tidal stream turbines on tidal current, turbulence and surface waves has been applied to study the interactions between a tidal turbine farm and its surrounding environment. The present study aims to reveal three-dimensional local and regional changes due to the operation of a proposed turbine farm in natural coastal environment. Fine mesh size is assigned at the turbine farm location to capture the details of local wake dynamics, hydrodynamics and suspended sediment transport. Large geographic coverage of the model provides details of changes in regional features. Results showed that the proposed turbine farm comprised of 18 turbines (15–20 m in diameter) with approximately 20% power extraction from the average available power (averaged over five and half tidal cycles) led to local variation of surface elevation within the range of −10 to 3 mm, flow acceleration on both sides of the turbine farm, flow acceleration of ∼ 0.4 m/s near the bed in the vicinity of the turbine farm which caused bed shear stress to rise up to 2.5 N/m2 (corresponding to the critical stress of a range of fine gravel and finer sediment particles), locally increased TKE of 0.09 m2/s2, reduced wave height of 0.01–0.05 m, and upward sediment transport in the water column. On a regional scale, most of the changes on amplitude and phase of M2 constituent were observed within 10 km (∼ 15 times the array width) from the centre of the turbine farm, and the wake in terms of 95% flow rate recovery was found to be 9 km long (∼ 14 times the array width). Noticeable changes were also found in surface waves, bed shear stress and suspended sediment transport on regional scale as result of moderation in tidal and flow dynamics, although much less prominent than the local effects. It is recommended that consideration during the Environmental Impact Assessment stage of tidal stream energy projects should be given to an area that extends beyond the immediate vicinity of the planned turbine farm.

Seismic Data Acquisition Technology in Loess Mountainous Area of Ordos and Southern Jiangsu

The surface of the loess mountain area in southern Ordos is covered by a thick loess layer, and the seismic exploration process has poor excitation and reception effects of seismic waves, and the reflection energy of seismic waves in the target horizon is weak, and the quality of collected data is poor. According to the principle that high water saturation and good lithology of loess layer will be beneficial to seismic wave excitation, through the investigation of water saturation and lithology of loess layer in the study area, the best seismic wave excitation horizon and depth are determined, and the best single well excitation dose is determined according to practical experience. In the aspect of seismic wave receiving and recording, the basic flow of survey line layout is worked out, and the seismic wave acquisition scheme suitable for the study area is finally worked out by combining the seismic wave receiving scheme with small path distance, large offset distance and high coverage times.