Ultrasonic Imaging of a Crack Using Modified Time Reversal

2016 ◽  
Vol 846 ◽  
pp. 553-558
Author(s):  
Jed Guinto ◽  
Philippe Blanloeuil ◽  
Chun H. Wang ◽  
Francis Rose ◽  
Martin Veidt
Keyword(s):  
Time Reversal ◽  
Computational Simulation ◽  
Field Measurements ◽  
Tone Burst ◽  
Data Matrix ◽  
Accurate Estimation ◽  
Diffraction Tomography ◽  
Static Data ◽  
Reconstruction Quality ◽  
Scatter Field

A majority of the research in Structural Health Monitoring focuses on detection of damage. This paper presents a method of imaging crack damage in an isotropic material using the Time Reversal imaging algorithm. Inputs for the algorithm are obtained via computational simulation of the propagation field of a crack in a medium under tone-burst excitation. The approach is similar to existing techniques such as Diffraction Tomography which makes use of the multi-static data matrix constructed using scatter field measurements from the computational simulation. Results indicate excellent reconstruction quality and accurate estimation of damage size.

scholarly journals An automated procedure for estimating the leaf area index (LAI) of woodland ecosystems using digital imagery, MATLAB programming and its application to an examination of the relationship between remotely sensed and field measurements of LAI

2008 ◽  
Vol 35 (10) ◽  
pp. 1070 ◽  
Author(s):  
Sigfredo Fuentes ◽  
Anthony R. Palmer ◽  
Daniel Taylor ◽  
Melanie Zeppel ◽  
Rhys Whitley ◽  
...  
Keyword(s):  
Leaf Area Index ◽  
Leaf Area ◽  
Gap Analysis ◽  
Digital Camera ◽  
Field Measurements ◽  
Accurate Estimation ◽  
Image Capture ◽  
Area Index ◽  
Modis Lai ◽  
Matlab Programming

Leaf area index (LAI) is one of the most important variables required for modelling growth and water use of forests. Functional–structural plant models use these models to represent physiological processes in 3-D tree representations. Accuracy of these models depends on accurate estimation of LAI at tree and stand scales for validation purposes. A recent method to estimate LAI from digital images (LAID) uses digital image capture and gap fraction analysis (Macfarlane et al. 2007b) of upward-looking digital photographs to capture canopy LAID (cover photography). After implementing this technique in Australian evergreen Eucalyptus woodland, we have improved the method of image analysis and replaced the time consuming manual technique with an automated procedure using a script written in MATLAB 7.4 (LAIM). Furthermore, we used this method to compare MODIS LAI values with LAID values for a range of woodlands in Australia to obtain LAI at the forest scale. Results showed that the MATLAB script developed was able to successfully automate gap analysis to obtain LAIM. Good relationships were achieved when comparing averaged LAID and LAIM (LAIM = 1.009 – 0.0066 LAID; R2 = 0.90) and at the forest scale, MODIS LAI compared well with LAID (MODIS LAI = 0.9591 LAID – 0.2371; R2 = 0.89). This comparison improved when correcting LAID with the clumping index to obtain effective LAI (MODIS LAI = 1.0296 LAIe + 0.3468; R2 = 0.91). Furthermore, the script developed incorporates a function to connect directly a digital camera, or high resolution webcam, from a laptop to obtain cover photographs and LAI analysis in real time. The later is a novel feature which is not available on commercial LAI analysis softwares for cover photography. This script is available for interested researchers.

Inter-comparison of remotely-sensed actual evapotranspiration products in the Zayandehrud river basin, Iran

2021 ◽  
Author(s):  
Neda Abbasi ◽  
Hamideh Nouri ◽  
Sattar Chavoshi Borujeni ◽  
Pamela Nagler ◽  
Christian Opp ◽  
...  
Keyword(s):  
Vegetation Index ◽  
Normalized Difference Vegetation Index ◽  
Field Measurements ◽  
Water Shortage ◽  
Remotely Sensed ◽  
Irrigation Scheduling ◽  
Accurate Estimation ◽  
Agricultural Areas ◽  
Eta Products

<p>Accurate estimation of evapotranspiration (ET) helps to create a better understanding of water allocation, irrigation scheduling, and crop management especially in arid and semiarid regions where agricultural areas are far more affected by water shortage and drought events. Remote sensing (RS) facilitates estimating the ET in regions where long-term field measurements are missed.  In this study, we compare the performance of free open-access remotely sensed actual ET products at eleven counties of the Zayandehrud basin. The Zayandehrud basin, one of the major watersheds of Iran, suffers from recurrent droughts and long-term impacts of aridity. The RS products used in this study are namely WaPOR (2009-2019), MOD16A2 (2003-2019), SSEBOp (2003-2019). We also merged the two products of SSEBOp and WaPOR and assessed its performance. To prepare the Merged ETa Product (MEP), WaPOR was resampled to the spatial resolution of SSEBOp. Then, the average pixel values of the resampled ETa product and SSEBOp were calculated. To compare ETa estimations over croplands in each county, maximum Normalized Difference Vegetation Index (NDVI) maps at annual scale (2003-2019) were prepared using LANDSAT 5, 7, and 8 images. Annual mean ETa estimations were then extracted over croplands by using annual maximum NDVI layers. We compared the RS-based ETa with reported long-term ETa values extracted from the local available literature. Our results showed a consistent underestimation of MOD16A2 in all counties. The MEP and WaPOR outperformed other products in the estimation of ETa in seven. Estimations of WaPOR and SSEBOp agreed in most of the counties. Our analysis displayed that, although MOD16A2 underestimated ETa values, it could together with SSEBOp capture the drought better than that of WaPOR and MEP in the lower reaches of the basin. Further study is needed to evaluate the monthly and seasonal performance of RS-based ETa products.</p>

Local Field Measurements in PrOs4Sb12 with Broken Time-Reversal Symmetry

2006 ◽  
Author(s):  
Shigeru Kasahara ◽  
Tsuyoshi Tamegai ◽  
Hitoshi Sugawara ◽  
Hideyuki Sato
Keyword(s):  
Local Field ◽  
Time Reversal ◽  
Field Measurements ◽  
Time Reversal Symmetry

scholarly journals A Modified Time Reversal Method for Guided Wave Detection of Bolt Loosening in Simulated Thermal Protection System Panels

Complexity ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Guan-nan Wu ◽  
Chao Xu ◽  
Fei Du ◽  
Wei-dong Zhu
Keyword(s):  
Time Reversal ◽  
Thermal Protection ◽  
Tone Burst ◽  
Guided Wave ◽  
Thermal Protection System ◽  
Protection System ◽  
Damage State ◽  
Wave Detection ◽  
Reconstructed Signal ◽  
Bolt Loosening

In this work, a modified time reversal method is proposed for guided wave detection and localizing loosened bolt in a complicated multibolt-jointed structure. Different from the traditional time reversal guided wave method, the response signal due to a tone burst input received at the healthy state is time reversed and recorded as a standard reemitting signal. In the detection process, this recorded standard signal is used for all damage cases to yield time reversal-focalized reconstruction signals. This largely improves the sensitivity of the focalized signal to damage state. In this paper, the peak amplitude of the focalized wave packet in the reconstructed signal is calculated and utilized as tightness index. By bonding PZT transducers at different joint locations inside the structure, multiple tightness indices, where each tightness index presents the correlation between the current joint condition to its healthy condition at the joint, can be obtained. To analyze a large number of tightness indices, a principle component analysis method is introduced, and a neural network-based loosening detection method is proposed. The proposed method is experimentally validated in a simulated double-layer bolt-jointed thermal protection system panel. Experimental results illustrate that the proposed method is effective to identify and localized the bolt loosening in complicated multibolt-jointed structure. The detection and identification of the location of multibolt loosening is realized.

scholarly journals Estimating Aboveground Biomass for Broadleaf Woody Plants and Young Conifers in Sierra Nevada, California, Forests

2010 ◽  
Vol 25 (4) ◽  
pp. 203-209 ◽  
Author(s):  
Thomas W. McGinnis ◽  
Christine D. Shook ◽  
Jon E. Keeley
Keyword(s):  
Sierra Nevada ◽  
Natural Resource ◽  
Aboveground Biomass ◽  
Plant Biomass ◽  
Field Measurements ◽  
Wildlife Habitat ◽  
Allometric Equations ◽  
Accurate Estimation ◽  
Regression Equations ◽  
Crown Diameter

Abstract Quantification of biomass is fundamental to a wide range of research and natural resource management goals. An accurate estimation of plant biomass is essential to predict potential fire behavior, calculate carbon sequestration for global climate change research, assess critical wildlife habitat, and so forth. Reliable allometric equations from simple field measurements are necessary for efficient evaluation of plant biomass. However, allometric equations are not available for many common woody plant taxa in the Sierra Nevada. In this report, we present more than 200 regression equations for the Sierra Nevada western slope that relate crown diameter, plant height, crown volume, stem diameter, and both crown diameter and height to the dry weight of foliage, branches, and entire aboveground biomass. Destructive sampling methods resulted in regression equations that accurately predict biomass from one or two simple, nondestructive field measurements. The tables presented here will allow researchers and natural resource managers to easily choose the best equations to fit their biomass assessment needs.

scholarly journals A coupled two-dimensional hydrodynamic and terrestrial input model to simulate CO<sub>2</sub> diffusive emissions from lake systems

2013 ◽  
Vol 6 (2) ◽  
pp. 3509-3556 ◽  
Author(s):  
H. Wu ◽  
C. Peng ◽  
M. Lucotte ◽  
N. Soumis ◽  
Y. Gélinas ◽  
...  
Keyword(s):  
Aquatic Ecosystems ◽  
Field Measurements ◽  
Terrestrial Ecosystems ◽  
Accurate Estimation ◽  
Diffusive Flux ◽  
Two Dimensional ◽  
Quality Model ◽  
Terrestrial Organic Matter ◽  
Carbon Dioxide Co2 ◽  
Lake Systems

Abstract. Most lakes worldwide are supersaturated with carbon dioxide (CO2) and consequently act as atmospheric net sources. Since CO2 is a major greenhouse gas (GHG), the accurate estimation of CO2 exchanges at air/water interfaces of aquatic ecosystems is vital in quantifying the carbon budget of aquatic ecosystems overall. To date, lacustrine CO2 emissions are poorly understood, and lake carbon source proportions remain controversial, largely due to a lack of integration between aquatic and terrestrial ecosystems. In this paper a new process-based model (TRIPLEX-Aquatic) is introduced incorporating both terrestrial inputs and aquatic biogeochemical processes to estimate diffusive emissions of CO2 from lake systems. The model was built from a two-dimensional hydrological and water quality model coupled with a new lacustrine CO2 diffusive flux model. For calibration and validation purposes, two years of data collected in the field from two small boreal oligotrophic lakes located in Québec (Canada) were used to parameterize and test the model by comparing simulations with observations for both hydrodynamic and carbon process accuracy. Model simulations were accordant with field measurements in both calibration and verification. Consequently, the TRIPLEX-Aquatic model was used to estimate the annual mean CO2 diffusive flux and predict terrestrial dissolved organic carbon (DOC) impacts on the CO2 budget for both lakes. Results show a significant fraction of the CO2 diffusive flux (~30–45%) from lakes was primarily attributable to the input and mineralization of terrestrial DOC, which indicated terrestrial organic matter was the key player in the diffusive flux of CO2 from oligotropical lake systems in Québec, Canada.

scholarly journals Transient elasticity imaging and time reversal

2011 ◽  
Vol 141 (6) ◽  
pp. 1121-1140 ◽  
Author(s):  
Habib Ammari ◽  
Lili Guadarrama Bustos ◽  
Hyeonbae Kang ◽  
Hyundae Lee
Keyword(s):  
Elastic Wave ◽  
Time Reversal ◽  
Stokes System ◽  
Quantitative Estimation ◽  
Field Measurements ◽  
Geometrical Parameters ◽  
Far Field ◽  
Layer Potential ◽  
Incompressible Elasticity ◽  
Wave Induced

We consider a purely quasi-incompressible elasticity model. We rigorously establish asymptotic expansions of near- and far-field measurements of the transient elastic wave induced by a small elastic anomaly. Our proof uses layer potential techniques for the modified Stokes system. Based on these formulae, we design asymptotic imaging methods leading to a quantitative estimation of elastic and geometrical parameters of the anomaly.

Time reversal imaging based on joint space–frequency and frequency–frequency data

2019 ◽  
Vol 11 (3) ◽  
pp. 207-214
Author(s):  
Tong Mu ◽  
Yaoliang Song
Keyword(s):  
Time Reversal ◽  
Joint Space ◽  
Data Matrix ◽  
Single Measurement ◽  
Practical Applications ◽  
Target Imaging ◽  
The Matrix ◽  
Space Frequency ◽  
Array Aperture ◽  
Value Decomposition

AbstractA new time reversal (TR) method for target imaging is proposed in this paper. Through single measurement by the antenna array, the received signals are utilized to form the space–frequency–frequency multistatic data matrix (MDM). Singular value decomposition is applied to the matrix to obtain the left singular vectors which span the signal subspace. The obtained vectors are divided into multiple subvectors by two different schemes and used to provide target signatures in the form of coarse frequency dependence and relative phase shifts that can be exploited to construct the imaging function. The performance of the proposed method is investigated through numerical simulations for both single and multiple targets, and the results are compared with the traditional TR method using the frequency–frequency MDM. It turned out that the proposed method is able to achieve high resolution with limited array aperture and shows satisfactory robustness in noise environment. Furthermore, experimental results are provided to show the availability of the method in practical applications.

scholarly journals On the Impact of Subaperture Sampling for Multispectral Scalar Field Measurements

Optics ◽  
2020 ◽  
Vol 1 (1) ◽  
pp. 136-154
Author(s):  
Christopher J. Clifford ◽  
Brian S. Thurow
Keyword(s):  
3D Imaging ◽  
Field Measurements ◽  
Scalar Fields ◽  
Reacting Flows ◽  
Spectral Information ◽  
The Novel ◽  
Reconstruction Quality ◽  
Plenoptic Camera ◽  
Jet Plumes ◽  
The Impact

The novel 3D imaging and reconstruction capabilities of plenoptic cameras are extended for use with continuous scalar fields relevant to reacting flows. This work leverages the abundance of perspective views in a plenoptic camera with the insertion of multiple filters at the aperture plane. The aperture is divided into seven regions using off-the-shelf components, enabling the simultaneous capture of up to seven different user-selected spectra with minimal detriment to reconstruction quality. Since the accuracy of reconstructed features is known to scale with the available angular information, several filter configurations are proposed to maintain the maximum parallax. Three phantoms inspired by jet plumes are simulated onto an array of plenoptic cameras and reconstructed using ASART+TV with a variety of filter configurations. Some systematic challenges related to the non-uniform distribution of views are observed and discussed. Increasing the number of simultaneously acquired spectra is shown to incur a small detriment to the accuracy of reconstruction, but the overall loss in quality is significantly less than the gain in spectral information.

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