Field Measurement Method Research Articles

A Review of Estimation Methods for Aboveground Biomass in Grasslands Using UAV

Grasslands are one of the world’s largest ecosystems, accounting for 30% of total terrestrial biomass. Considering that aboveground biomass (AGB) is one of the most essential ecosystem services in grasslands, an accurate and faster method for estimating AGB is critical for managing, protecting, and promoting ecosystem sustainability. Unmanned aerial vehicles (UAVs) have emerged as a useful and practical tool for achieving this goal. Here, we review recent research studies that employ UAVs to estimate AGB in grassland ecosystems. We summarize different methods to establish a comprehensive workflow, from data collection in the field to data processing. For this purpose, 64 research articles were reviewed, focusing on several features including study site, grassland species composition, UAV platforms, flight parameters, sensors, field measurement, biomass indices, data processing, and analysis methods. The results demonstrate that there has been an increase in scientific research evaluating the use of UAVs in AGB estimation in grasslands during the period 2018–2022. Most of the studies were carried out in three countries (Germany, China, and USA), which indicates an urgent need for research in other locations where grassland ecosystems are abundant. We found RGB imaging was the most commonly used and is the most suitable for estimating AGB in grasslands at the moment, in terms of cost–benefit and data processing simplicity. In 50% of the studies, at least one vegetation index was used to estimate AGB; the Normalized Difference Vegetation Index (NDVI) was the most common. The most popular methods for data analysis were linear regression, partial least squares regression (PLSR), and random forest. Studies that used spectral and structural data showed that models incorporating both data types outperformed models utilizing only one. We also observed that research in this field has been limited both spatially and temporally. For example, only a small number of papers conducted studies over a number of years and in multiple places, suggesting that the protocols are not transferable to other locations and time points. Despite these limitations, and in the light of the rapid advances, we anticipate that UAV methods for AGB estimation in grasslands will continue improving and may become commercialized for farming applications in the near future.

Optimization of Transducer Array for Cross-Sectional Velocity Field Reconstruction in Acoustic Tomography

As a part of industrial process tomography, acoustic tomography (AT) is a promising method for high-quality velocity field measurement, which is widely utilized in the monitoring of multiphase flow, atmospheric environment, and so on. However, subjected to the safety and reliability requirements of furnaces or industrial pipes, the number of installed transducers is restricted, which results in sparse valid data, and, thus, ill-posed and rank-deficient limited-data linear AT. Therefore, special attention should be given to the transducer arrangement in the framework construction module to maximize the reconstruction accuracy. Unlike methods that minimize relative reconstruction error including true value of interesting field, finding an alternative prior knowledge-based predictor that maps the reconstruction error is more practical and preferred. In this work, based on the prior information that the linear independence of vectors incorporates maximum measurement information, a linear independence degree (LID) metric is proposed to optimize the transducer array. It contains no prior information about flow velocity fields, which enables the procedure to be performed in an off-line mode. A covariance matrix adaptation evolution strategy (CMA-ES) algorithm is employed to solve this minimization problem. Proof-of-concept demonstrations, including representative synthetic vortical flow fields with a biased single vortex or with double vortices and experimental data-based velocity field, are performed by comparison with existing representative optimization strategies. Qualitative and quantitative results show the feasibility and robustness of the LID metric in improving imaging accuracy of arbitrary practical velocity fields based on AT. This prior metric is expected to provide guidance for better diagnosis of multiphase flow and optimization of industrial flow process.

Survey method for field measurement of rubber ball impact sound in reinforced concrete apartment houses in Korea – Based on the Korean measurement method

The rubber ball impact sound has been standardized by ISO 10140 series and ISO 16283-2 for laboratory and field measurements, respectively. The ISO 10052 standard specifies a survey method for the impact sound measurement using a tapping machine and a rubber ball. This study proposed measurement position for the survey method which is highly correlated with result based on the Korean Standards (KS) and the building regulation of South Korea for engineering method. The rubber ball impact sounds were measured in 79 reinforced concrete apartment houses, which have a centre point and four perimeter points for both exciting and receiving sounds. The proposed survey method was validated for only a specific type of apartment building layout and construction in the South Korean environment. The excitation and receiving points in the perimeter having the most similar characteristics to the results obtained using the Korean engineering methods were first selected. By combining the selected perimeter point and centre point for both the excitation and receiving sounds, the characteristics of each combination were compared with the results obtained using the Korean engineering method. When one excitation point or receiving point in the perimeter was added to the centre point for the proposed survey method, the difference between the measurement result using the engineering and proposed survey method decreased. The standard deviation of the difference between the SNQs of the proposed survey method and the Korean engineering method for measuring the rubber ball impact sound was smaller than 2 dB.

The In-Plane Magnetic Field Measurement Method of SC/MR Mixed Sensor and Its Three-Axis Magnetic Sensor With Integrated Magnetic Concentrator

Superconductor/magnetoresistance (SC/MR) mixed sensor has the advantage of ultrahigh sensitivity and is thought to be a promising candidate for weak magnetic field detection. However, it has no effect on the magnetic field in the superconducting flux-to-field transformation amplifier (SFTA) plane, which limits its applications in 3-D magnetic field detection. Here, we present a new architecture of SC/MR mixed sensor with only one integrated magnetic concentrator (IMC) to realize the in-plane magnetic field measurement. Firstly, the conversion efficiency, defined as the in-plane magnetic changing to the out-plane magnetic field by the IMC and SFTA of mixed sensor, was systematically studied by the finite element analysis method, the results show that the high conversion efficiency is from the combined action of superconducting diamagnetism and magnetic concentrator of soft magnetic materials. Then, a serial prototype mixed sensors with different IMC relative configuration sizes were prepared and their experimental performances were obtained. Indeed, the mixed sensor with IMC can simultaneously measure the in-plane and out-of-plane magnetic fields, furthermore, the conversion efficiency changes as the function of the relative configuration size is consistent well with the simulation result. Finally, a three-axis SC/MR mixed sensor scheme and its corresponding three-axis magnetic field decoupling method based on this method were also proposed, showing the obvious capability of three-axis magnetic field measurement. Our work is meaningful to the development of a three-axis weak magnetic field detection.

A Novel Transient Electric Field Measurement for Low Kerr Constant Liquid Dielectrics Based on Concave Spherical Mirror Conjugate Structure

This article proposes a Kerr effect electric field measurement method based on a concave spherical mirror conjugate structure (CSM CS) for a transient electric field in low Kerr constant liquid dielectrics. The accuracy of transient electric field measurement can be greatly improved in a limited space by multiple small-angle reflections. To verify the effect of the proposed structure, the electric field distribution is measured in propylene carbonate (PC) with a high Kerr constant at a switching overvoltage. The measurement results show that the electric field error of a PC under an extremely low electric field is only about 2%. The novel structure improves the electric field measurement accuracy of a liquid with a high Kerr constant. Then, the whole device is applied to the transformer oil, and the accuracy of the measured electric field is also greatly improved. At the same electrode size, the sensitivity of measuring the electric field with the proposed structure is three times that without it. The analysis results show that the introduction of the proposed structure has little effect on the electric field measurement. The proposal and application of the proposed CSM CS further expand the electric field measurement range based on the Kerr effect and improves the electric field measurement accuracy.

Three-dimensional temperature field measurement method based on light field colorimetric thermometry

This paper proposes a novel method for three-dimensional (3D) temperature measurement using light field colorimetric thermometry, aiming to overcome the challenges associated with the intricate system structure and the limited availability of 3D information in traditional radiation temperature measurement methods. Firstly, the correlation between corresponding image points and the positions of 3D object in the light field image system is analyzed using the ray tracing method. The 3D position acquisition model and the light field colorimetric thermometry model are established, enabling simultaneous acquisition of the spatial coordinates and radiometric information of the 3D object. Then, the light field camera radiation calibration experiment was conducted, and the 3D temperature field will be obtained by employing colorimetric thermometry for each corresponding image point of the same object point. Finally, the experiment employed a light field camera for temperature measurement and reconstruction of candle flames. The accuracy of the temperature measurement is 3.31%, thus confirming the feasibility and effectiveness of the proposed method.

Digital speckle photography in the presence of displacement gradients

Digital speckle photography is a displacement field measurement method that employs laser speckles as surface markers. Since the approach requires only one reference image without a preparation of the sample and provides a fast, single-shot measurement with interferometric precision, the method is applied for in-process measurements in manufacturing engineering. Due to highly localized loads, higher-order displacement gradients occur in manufacturing processes and it is an open research question how these gradients affect the measurement errors of digital speckle photography. We simulate isotropic Gaussian surface topographies, apply a displacement field and then generate laser speckle patterns, which are evaluated with digital image correlation and subsequently the resulting random and systematic errors of the displacement field are analyzed. We found that the random error is proportional to the first-order displacement gradient and results from decorrelation of the laser speckles. The systematic error is mainly caused by the evaluation algorithm and is linearly dependent on the second-order gradient and the subset size. We evaluated in-process displacement measurements of laser hardening, grinding and single-tooth milling where we determined the relative error caused by displacement gradients to be below 2.5% based on the findings from the simulative study.

Multiwaveform Current Transmitter for Induced Polarization Effects Surveying Based on the SQUID-TEM System

The induced polarization effects magnetic field measurement method based on the superconductive quantum interfere device (SQUID) and transient electromagnetic (TEM) system can improve the exploration accuracy of metal minerals. As the core component of the SQUID-TEM system based on magnetic source, the current transmitter should reach consensus in three key aspects: high power, controllable turn-off time and combined current waveforms. In order to solve the problem of single transmitting current waveform and uncontrollable turn-off time in traditional current transmitter, a topology structure of current transmitter with multiple waveform combinations in time domain is proposed in this paper. By using the passive multi-group clamp technology and RLC series resonance technology, the falling edge turn-off time of trapezoidal and triangular transmitting current can be controlled, and the pulse width of semi-sinusoidal transmitting current can be adjusted. The laboratory and field experiments are implemented to test the performance of the current transmitter. Compared with the commercial PROTEM67 transmitter, the test results show that it can successfully transmit three current waveforms and their combination waveforms, the current amplitude is more than 100A, and the transmitting current turn-off time is controllable. The field measurement response results show that the combined multi-waveform transmit system can effectively measure the induction field and the polarization field generated by the Cole-Cole polarization ring, which provides technical support for the high-precision detection of induction-polarization effects based on the SQUID-TEM system.

Discharging Phenomena in different types of Lightning

There are two charge regions and charges can transfer from one region to another region. For lightning discharging process, the centers of two charges are separated by different distances and air as an insulator between them. The methods of the process of charge formation in differ-ent types of lightning are different. In volcanic lightning, it form closer to the ground and dis-charging process occurs between the two charge regions as the normal thunderstorm lightning does. The steeped leader starts at the structure and propagates upward in nuclear lightning. Their direction of branching is also upward and the return strokes do not initiate from upward moving leaders. It is similar to upward initiated thunderstorm lightning flashes from tall struc-tures and forms in several kilometers. In Earthquake lightning, a shifting of the positive and negative charge centers in the material, which then results in an external electric field. Even the different lightning signatures have been observed in our scientific community, the thunderstorm lightning is frequently observed and measured by the different methods such as electric field measurement, magnetic field measurement, photography and so on. Here, the method of elec-tric field measurement is used to measure the thunderstorm lightning. In all cases of lightning, the discharge phenomena take place between two different charged regions. The two regions of positive charges and negative charges are separated by a certain distance and the air between them is an insulator. When the sufficient charges store in the two charge regions, voltage is de-veloped between them. If the potential developed is sufficient for the electric breakdown of the air, then lightning phenomena occur. Hence, the discharging phenomena occur between the positive and negative charge regions for the different types of lightning.

Determination of the Required Strength of Artificial Roof for the Underhand Cut-and-Fill Mine Using Field Measurements and Theoretical Analysis

For the underhand cut-and-fill mining method, to ensure safe and economic mining, a key issue is to correctly determine the required strength of the artificial roof made of cemented paste backfill (CPB). However, the determination of the required strength is typically based on historical experience and analytical beam formulas, resulting in the obtained required strength being unsuitable for the actual situation. Therefore, in order to determine the required strength of the CPB roof reasonably and accurately, field measurements based on sensors were proposed and carried out in the Jinchuan mine, and then formulas based on thick plate theory were derived to verify the measured results. The results show that the required strength obtained by field measurement is 0.325 MPa and that obtained by thick plate theory is 0.304 MPa, with an error of 6.78% between them, verifying the accuracy of the measurements. However, the strength standard currently used by Jinchuan is 0.59 MPa, which far exceeds the optimal strength and results in many additional, unnecessary expenses. To ensure economical mining, the span of the drift was enlarged from 5.0 m to 6.0 m based on the results of the actual measurements and the current production status of the mine. The measurements show that the maximum cumulative subsidence of the drift roof is 11.69 mm and the maximum convergence deformation of the sidewalls is 8.34 mm, which indicates that the stability of the span-enlarged drift is satisfactory. Meanwhile, enlarging the drift span allows for a 20% increase in production capacity per mining cycle. This field measurement method and theoretical analysis model can be used as an efficient guide to facilitate the design of underhand cut-and-fill mining.

Comparative Study of Laboratory Based Chlorophyll - A Determination Methods

Protecting the quality and quantity of the available surface water resources is one of the most important points. Water quality is a complex concept that includes the physical, chemical, biological and hydrological parameters of water. One of the most significant biological water quality parameters is the chlorophyll-a content. Several different laboratory and field measurement methods are used to determine the chlorophyll-a content of water samples. The most frequently used laboratory methods are the Felföldy 1987 and the ISO 10260:1992 methods. Among field determination methods, submersible probes are frequently used to measure the chlorophyll-a concentration. Previously mentioned methods are based on fluorescence techniques. The main aim of this recent study is to compare different laboratory chlorophyll-a determination methods. Among the applied approaches, the Felföldy 1987 method and the ISO 10260:1992 method were compared. Furthermore, we measured the effect of the different solvent on the determination methods. Based on this, we investigated the Felföldy determination method using different solvents (methanol substituted with ethanol). The measurements were carried out under the same conditions from samples of Chlorella vulgaris culture in three repetitions by preparing a dilution series.

Influence of double-line large-slope shield tunneling on settlement of ground surface and mechanical properties of surrounding rock and segment

The surface settlement formula of large slope tunnel is derived firstly. Then, the finite element model of shield tunnel is established by using ABAQUS software. Finally, the influences of tunnel slope, grouting pressure and shield tail clearance on ground surface settlement, and mechanical properties of surrounding rock and segments are studied by the field measurement and numerical simulation method. The results show that (1) For the slope is less than 4°, the slope increases by 1°, the settlement of ground surface increases by about 2.85 %, the shear stress of surrounding rock increases by about 4.5 kPa, and the tensile and circumferential stresses of segment increase by about 5 % and 3.1 %, respectively. (2) The proper grouting pressure is beneficial to the settlement of ground surface, and the mechanical properties of surrounding rock and segment. (3) For the shield tail clearance is less than 15 cm, the clearance increases by 1 cm, the settlement of ground surface increases by about 0.65 mm, the shear stress of surrounding rock increases by about 4.77 kPa, and the circumferential stress of segment reduces by about 0.02 MPa. Therefore, the grouting pressure with 200 kPa and the shield tail clearance with 10 cm are recommended.

Trampoline-Shaped Micro Electric-Field Sensor for AC/DC High Electric Field Measurement

The measurement of high electric field is widely used in applications such as power grid, electrical equipment, space launch, petroleum industry, and meteorological monitoring. Traditional electric field measurement methods, such as field mills, are bulky and cause electric field distortion. In this article, we presented a trampoline-shaped microelectric field sensor (E-sensor) based on microelectromechanical system (MEMS). The micro E-sensor uses the effect of electrostatic induction, which generates force that drives the vibration of a piezoresistive film and converts the electric field into a differential voltage signal. The presented E-sensor can measure both ac and dc high electric fields with relatively high resolution and wide range. Through experimental measurement, the device exhibits an ac resolution of 172 V/m/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> and a linear measurable electric field range of 312 V/m to over 700 kV/m. The presented E-sensor has good performance with mm-level size and low cost, which could be mass produced for broad applications.

Research on the Control of Mining Instability and Disaster in Crisscross Roadways

In order to solve the disaster caused by the instability of spatial crisscross roadways under the action of leading abutment pressure in the coal mine face, combined with a specific engineering example, the methods of theoretical analysis, numerical simulation and field measurement are adopted to simulate and analyze the stress mutual disturbance intensity and influence range of spatial crisscross roadways. The evolution law of the plastic zone in spatial crisscross roadways under the influence of mining is explored, and the key to mining instability control is made clear. The roof of the return air roadway, the shoulder angle of the two sides and the coal wall are the key parts of surrounding rock stability control. On this basis, the cooperative control scheme of changing the roadway section shape (straight wall semicircular arch), supporting (anchor cable and “U” section steel) and modifying (grouting) is put forward. Through the field measurement, within the influence range of the return air roadway, the displacement deformation of the top and bottom is less than 200 mm, which achieves the goal of roadway safety and stability. Furthermore, based on the theory of “butterfly plastic zone”, the mechanical mechanism of the overall instability of the spatial crisscross roadway is revealed; that is, during the advance of the working face, the advance mining stress is superimposed with the surrounding rock stress of the crisscross roadway, and the peak value of the partial stress of the surrounding rock mass of the crisscross roadway is increased. The expansion of the plastic zone is intensified, and beyond 7 m from the crisscross position, the shoulder angle of the two sides and the leading plastic zone of the coal wall of the working face are connected with each other, which leads to the overall failure and instability of the surrounding rock between the roadways at the intersection.

Machine learning for flow field measurements: a perspective

Advancements in machine-learning (ML) techniques are driving a paradigm shift in image processing. Flow diagnostics with optical techniques is not an exception. Considering the existing and foreseeable disruptive developments in flow field measurement techniques, we elaborate this perspective, particularly focused to the field of particle image velocimetry. The driving forces for the advancements in ML methods for flow field measurements in recent years are reviewed in terms of image preprocessing, data treatment and conditioning. Finally, possible routes for further developments are highlighted.

Experiment on Space-Time Evolution Characteristics of Deformation and Failure of Overlying strata in Longwall Mining of Steeply Dipping Coal Seam

Revealing the space-time evolution characteristics of overlying strata deformation and failure is the key for safe and efficient mining of steeply dipping coal seam. In this paper, based on the physical similarity simulation experiment and field measurement method, the non-uniform filling characteristics of gangue in gob and the roof migration law are comprehensively determined, the evolution characteristics and distribution patterns of the abutment pressure in the upper and lower sections, the distribution characteristics of the working resistance of the support, and the regional strata behavior law in the mining process are analyzed, and the technical measures for the stability control of the support in steeply dipping coal seam are put forward. Results shown: With the advancing distance increases, the accumulation range of gangue increases, and the inverted triangle airspace begins to appear repeatedly in the gob behind the support. In the deep gob, the angle between the gangue pile and the horizontal plane decreases continuously from the lower part to the upper part along the inclined direction. Horizontal displacement, vertical displacement and combined displacement of roof show an evolutionary trend of ‘increase – stability’. The peak displacement position moves from the upper part to the middle part of the working face, which is located at the hinge point between the broken block and the failure envelope surface. The evolution of abutment pressure of headgate and tailgate T-junction shows a trend of ‘increase – stability’. The peak and concentration coefficient at headgate T-junction are greater than tailgate T-junction. The load imbalance characteristics of the support in working face are obvious, and the basic characteristics along the inclined direction are the largest in the middle area, the second in the upper and the smallest in the lower area. The initial force and working resistance of support should be improved, and the position of the support should be adjusted in time in practical engineering. The results provide reference and guidance for practical production.

Hyperspectral imagery reveals large spatial variations of heavy metal content in agricultural soil - A case study of remote-sensing inversion based on Orbita Hyperspectral Satellites (OHS) imagery

The widespread heavy metal contamination in soil induced by extensive human disturbance has been a global significant issue because of its chronic toxic effects on human health. However, the establishment of effective monitoring and assessing methods for heavy metal content in the soil remain a long-term challenge due to the intrinsic limitation of the current multi-band remote sensing technology and field measurement methods. Prompted by this significant technique gap, we represent an implementation of remote-sensing inversion models based on hyperspectral imagery to reconstruct soil heavy metal contents within an experimental farmland located in Mianzhu city, Sichuan, China. We collected soil samples at the pre-defined sites, and measured soil heavy metal contents and soil spectrum in the laboratory condition. Meanwhile, we obtained Orbita Hyperspectral Satellites (OHS) imagery and quantified the associated vegetation indexes. The measured soil spectrum, bands of OHS, and the generated vegetation indexes were mathematically transformed to better represent their relations with soil heavy metal contents. Consequently, the most sensitive variables were selected as potent predictors of soil heavy metal contents in the inversion models. After evaluating the optimal inversion models for each heavy metal element, we implemented them to reconstruct the spatial patterns of soil heavy metal contents over the study landscape. We found obvious benefits of the remote sensing inversion model in predicting the spatial heterogeneity of heavy metal content within this small landscape patch. Specifically, the inversion model unraveled a normal distribution of heavy metal contents within the landscape, while the traditional spatial interpolation based on field measurements may suggest a largely skewed distribution. Compared with airborne-based studies, this study represents an application of spaceborne satellite data, which can be easily applied to a large spatial scale and long-term monitoring.

Flow Field Measurement and Display Technology Based on Hand-Held Probe

Measuring flow field information in wind tunnel is an indispensable basic condition for aerodynamic research. Traditional measuring equipments include phase Doppler particle analyzer, hot wire anemometer, particle image velocimeter, etc. Particle image velocimeter can visualize the flow field, but its installation and debugging are complicated. To obtain flow field information quickly and realize visualization, a kind of technology based on hand-held probe is designed. The velocity of the flow field is calculated by the probe, and the position and attitude information of the probe is obtained by a kind of visual measurement system (Optotrak system), The spatial velocity distribution is fused with the position and attitude information of the probe, and then the flow field in the test area is graphically displayed by interpolation with mathematical tools. By using this technique to carry out test in wind tunnels, taking segment of the airfoil as the test object, and the dynamic measurement of the probe at the rear of the airfoil, the complex vortical flow generated by segment of the airfoil is successfully plotted. The test result shows the device used in this technology is simple in structure and flexible in use and can quickly acquire flow field information, which provides a new method and idea for flow field measurement.

Energy Consumption of Indonesian Red Cross (PMI) Building at Wonosobo Regency

Energy use in health buildings is inevitable due to building functions that must protect specific equipment or parts. One of the health buildings, namely the Indonesian Red Cross (PMI) building, serves to draw people's blood. The use of artificial ventilation must be used to support the function of the PMI building. The study aimed to determine the use or energy consumption of the Indonesian Red Cross (PMI) building in the Wonosobo Regency. The study used the field measurement method for one day. The data collection method also uses the observation method to describe the space and activities in the building. Data analysis uses graphs and compares the outside and inside of the building. AC specifications are also displayed to know how much energy is used. The results showed that the energy consumption of air conditioning in the Wonosobo PMI building was not too large, considering that only specific spaces were used. The outside area is quite remarkable and supports the AC setting, which is not too strong.

A photographic transect method for field measurement of vegetation cover along an ecotone gradient in a desert environment

Vegetation cover is essential to the ecologic and biogeochemical functioning of drylands. These systems are marked by spatiotemporal variation in vegetation cover and biomass. Regular monitoring of vegetation cover in drylands is critical for their conservation and management. This study examines the effectiveness of photo-based grid point intercept field survey for quantifying vegetation characteristics in drylands. The field data provides ground truth data for space borne remote sensing to analyze changes in vegetation cover. The study integrates rapid field photo sampling, GPS, and GIS to maximize raw data collection in the field and allow for subsequent sampling in the laboratory setting. Paired T-tests and simple linear regression were employed to assess sample size. Quantification of vegetation cover using minimum distance (MD), spectral angle mapper (SAM), and support vector machine (SVM) automated classification were assessed using visual sampling as a reference. Fifty sampling points are sufficient for quantifying vegetation cover of steppe, but are less adequate for desert steppe. The assessment of automated classifications of photo plots revealed that SAM outperformed both MD and SVM. Photo-based Grid-point Intercept provides a cost- and time-effective technique for data collection to support satellite and air platform remote sensing analysis of vegetation dynamics.