Acoustical Imaging of near Surface Properties at the Rayleigh Critical Angle

1982 ◽  
pp. 157-174 ◽  
Author(s):  
G. L. Fitzpatrick ◽  
B. P. Hildebrand ◽  
A. J. Boland
Keyword(s):  
Surface Properties ◽  
Critical Angle ◽  
Near Surface ◽  
Acoustical Imaging

CREEPING SURFACE LONGITUDINAL ACOUSTIC WAVE: MAIN PROPERTIES AND APPLICATION POSSIBILITIES

2021 ◽  
pp. 4-12
Author(s):  
V. G. Shevaldykin
Keyword(s):  
Critical Angle ◽  
Flaw Detection ◽  
Ultrasonic Signal ◽  
Ultrasonic Waves ◽  
Concave Surface ◽  
Ultrasonic Tomography ◽  
Transverse Waves ◽  
Near Surface ◽  
The Third ◽  
Creeping Wave

Creeping ultrasonic waves have long been successfully used for flaw detection of near-surface and near-bottom zones of metal products. However, due to the fact that the creeping wave generates a lateral transverse wave directed into the metal volume at the third critical angle, it is also possible to test internal defects in principle. At known velocities of propagation of longitudinal and transverse waves in the metal, the third critical angle is easily calculated. Therefore, the time of propagation of the ultrasonic signal along any trajectory between points on the surface and in the volume of the metal can be calculated. Usually, creeping waves are used to test products of plane-parallel shape. There are no cases of their application on curved surfaces in the literature. It is possible that the creeping wave can also propagate over a concave surface. The aim of the article is to test experimentally new ways of using creeping waves. The propagation trajectories of the creeping and lateral transverse waves were studied on a steel plate. The time of passage of the ultrasonic signal along such trajectories of different lengths was measured, and the measurement results were compared with the calculated time values. The measured and calculated values coincided with accuracy sufficient for the coherent accumulation of echo signals that passed through the metal part of the path by the creeping wave and another part of the path by the lateral transverse wave.The propagation of the creeping wave over a concave surface was studied on a steel sample with cylindrical faces of different radii. As a result, it turned out that on a concave surface, the creeping wave propagates at the same speed of longitudinal waves as on a flat surface, but it decays much more strongly with distance. Studies have shown that creeping waves can be used in ultrasonic tomography, where a preliminary calculation of the propagation trajectories of ultrasonic signals is required. The propagation of creeping waves over concave surfaces extends the capabilities of the TOFD method to the area of intube testing

scholarly journals Near surface properties derived from Phobos transits with HP RAD³ on InSight, Mars

2021 ◽  
Author(s):  
Nils T Mueller ◽  
Sylvain Piqueux ◽  
Mark T Lemmon ◽  
Justin N. Maki ◽  
Ralph D. Lorenz ◽  
...  
Keyword(s):  
Surface Properties ◽  
Near Surface

CERES’ NEAR SURFACE PROPERTIES FROM LANDSLIDES

2017 ◽  
Author(s):  
Heather Chilton ◽  
◽  
Britney E. Schmidt ◽  
Ken L. Ferrier ◽  
Kayla Duarte ◽  
...  
Keyword(s):  
Surface Properties ◽  
Near Surface

scholarly journals Estimating Calibration Variability in Evapotranspiration Derived from a Satellite-Based Energy Balance Model

2018 ◽  
Vol 10 (11) ◽  
pp. 1695 ◽  
Author(s):  
Sulochan Dhungel ◽  
Michael Barber
Keyword(s):  
Energy Balance ◽  
Surface Temperature ◽  
Surface Properties ◽  
Vegetation Index ◽  
Selection Process ◽  
Random Noise ◽  
Sensible Heat Flux ◽  
Balance Model ◽  
Near Surface ◽  
Pixel Pair

Computing evapotranspiration (ET) with satellite-based energy balance models such as METRIC (Mapping EvapoTranspiration at high Resolution with Internalized Calibration) requires internal calibration of sensible heat flux using anchor pixels (“hot” and “cold” pixels). Despite the development of automated anchor pixel selection methods that classify a pool of candidate pixels using the amount of vegetation (normalized difference vegetation index, NDVI) and surface temperature (Ts), final pixel selection still relies heavily on operator experience. Yet, differences in final ET estimates resulting from subjectivity in selecting the final “hot” and “cold” pixel pair (from within the candidate pixel pool) have not yet been investigated. This is likely because surface properties of these candidate pixels, as quantified by NDVI and surface temperature, are generally assumed to have low variability that can be attributed to random noise. In this study, we test the assumption of low variability by first applying an automated calibration pixel selection process to 42 nearly cloud-free Landsat images of the San Joaquin area in California taken between 2013 and 2015. We then compute Ts (vertical near-surface temperature differences) vs. Ts relationships at all pixels that could potentially be used for model calibration in order to explore ET variance between the results from multiple calibration schemes where NDVI and Ts variability is intrinsically negligible. Our results show significant variability in ET (ranging from 5% to 20%) and a high—and statistically consistent—variability in dT values, indicating that there are additional surface properties affecting the calibration process not captured when using only NDVI and Ts. Our findings further highlight the potential for calibration improvements by showing that the dT vs. Ts calibration relationship between the cold anchor pixel (with lowest dT) and the hot anchor pixel (with highest dT) consistently provides the best daily ET estimates. This approach of quantifying ET variability based on candidate pixel selection and the accompanying results illustrate an approach to quantify the biases inadvertently introduced by user subjectivity and can be used to inform improvements on model usability and performance.

Shale Caprock/Acidic Brine Interaction in Underground CO2 Storage

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Abiola Olabode ◽  
Mileva Radonjic
Keyword(s):  
Surface Properties ◽  
Co2 Storage ◽  
Analytical Techniques ◽  
Elevated Pressure ◽  
Time Frame ◽  
Carbon Accounting ◽  
Pore Geometry ◽  
Fractional Flow ◽  
Near Surface ◽  
Carbon Dioxide Co2

Shale caprock integrity is critical in ensuring that subsurface injection and storage of anthropogenic carbon dioxide (CO2) is permanent. The interaction of clay-rich rock with aqueous CO2 under dynamic conditions requires characterization at the nanoscale level due to the low-reactivity of clay minerals. Geochemical mineral–fluid interaction can impact properties of shale rocks primarily through changes in pore geometry/connectivity. The experimental work reported in this paper applied specific analytical techniques in investigating changes in surface/near-surface properties of crushed shale rocks after exposure (by flooding) to CO2–brine for a time frame ranging between 30 days and 92 days at elevated pressure and fractional flow rate. The intrinsically low permeability in shale may be altered by changes in surface properties as the effective permeability of any porous medium is largely a function of its global pore geometry. Diffusive transport of CO2 as well as carbon accounting could be significantly affected over the long term. The estimation of permeability ratio indicated that petrophysical properties of shale caprock can be doubled.

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