scholarly journals Research on Resistor-Loaded Half-Ellipse Antenna System for GPR Application

2016 ◽  
Vol 2016 ◽  
pp. 1-6 ◽  
Author(s):  
Xueping Li ◽  
Jinjin Shao ◽  
Yu Zhang
Keyword(s):  
Ground Surface ◽  
Antenna System ◽  
The Other ◽  
Radiation Patterns ◽  
Resistive Loading

A resistor-loaded half-ellipse antenna system mounted on a vehicle as a candidate for the exploration of the lunar subsurface is investigated. The antenna system includes two identical half-ellipse antennas, one is used for transmission, and the other is for reception. A resistive loading technique for broadening the bandwidth and improving impulse radiation is introduced. The performance of the proposed antenna with different height above ground surface is studied, and the influence of the vehicle on the antenna is analyzed. Then the antenna is manufactured and mounted on a vehicle as some tests are done. The simulated and measured antenna VSWR and radiation patterns are compared together, and good agreements between them are achieved.

ON SHALLOW‐HOLE TEMPERATURE MEASUREMENTS—A TEST STUDY IN THE SALTON SEA GEOTHERMAL FIELD

Geophysics ◽  
1977 ◽  
Vol 42 (3) ◽  
pp. 572-583 ◽  
Author(s):  
Tien‐Chang Lee
Keyword(s):  
Numerical Methods ◽  
Ground Surface ◽  
Nonlinear Least Squares ◽  
Geothermal Gradient ◽  
Geothermal Field ◽  
The Other ◽  
Temperature Measurements ◽  
Salton Sea ◽  
Depth Interval ◽  
Average Value

Shallow‐hole (<13 m) temperature measurements made at various depths and/or times may yield reliable values of geothermal gradient and thermal diffusivity if the groundwater table is shallow (a few meters) such that the effect of time‐dependent moisture content and physical properties is negligible. Two numerical methods based on nonlinear least‐squares curve fitting are derived to remove the effect of annual temperature wave at the ground surface. One method can provide information on the gradient and diffusivity as a function of depth while the other gives average value over the depth interval measured. Experiments were carried in six test holes cased with 2 cm OD PVC pipes in the Salton Sea geothermal field. A set of 5 to 7 thermistors was permanently buried inside the individual pipes with dry sand. Consistent gradient determinations have been obtained with both numerical methods from six monthly observations. By linearly extrapolating the depths to the 100°C and 200°C isotherms from the calculated gradients and mean ground temperatures, we have found good agreement with the nearby deep‐well data for four holes. Discrepancy is found for two holes, one of which is located near the field of [Formula: see text] mud volcanoes and the other near the volcanic Red Hill, reflecting complicated local hydrologic conditions.

Theoretical and experimental examinations of the capacitively coupled resistivity (line antenna) method

Geophysics ◽  
2013 ◽  
Vol 78 (4) ◽  
pp. E189-E199 ◽  
Author(s):  
Qifei Niu ◽  
Yu-Hsing Wang
Keyword(s):  
Ground Surface ◽  
Antenna System ◽  
Geometric Factor ◽  
Gap Effect ◽  
Geometrical Factor ◽  
Measurement Bias ◽  
Current Frequency ◽  
Near Surface ◽  
Capacitively Coupled ◽  
Gap Height

The capacitively coupled (CC) resistivity method is an emerging geophysical technique for near-surface investigations. However, there are two major problems associated with using the CC resistivity (line antenna) system in ground investigations. These two problems are (1) the geometrical factor and (2) measurement biases. We first derive the geometric factor for the line-antenna array in a dipole-dipole configuration. The new expression of the geometric factor considers the separation between the two current (and the two potential) line antennas, thereby improving the accuracy of the measured apparent resistivity. Second, from the electroquasistatic point of view, a quadruline model that can describe the characteristics of the CC resistivity (line antenna) system is derived based on the previously published quadrupole model. The validity of the quadruline model is verified experimentally. Based on the quadruline model, it is found that the dielectric properties of the line-to-ground capacitor and the ground permittivity produce measurement bias at low and high current frequencies, respectively. If the operating current frequency is around the kHz range and the ground resistivity is relatively high, such as in permafrost areas, the ground permittivity can also create measurement bias to cause the actual value to be underestimated. The experimental results and the predictions by the quadruline model suggest that the measurement bias induced by the gap between the line antenna and the ground surface becomes significant and cannot be ignored as the gap height is large and the associated ground resistivity is low. In general, the CC resistivity (line antenna) measurements are not biased by the gap effect when the gap height is less than 0.01 m, which can easily be achieved for tests on flat ground.

scholarly journals Soil-Surface Straw Influences Micrometeorological Conditions Affecting Canola Mortality During Nighttime Frosts

2020 ◽  
Vol 12 (11) ◽  
pp. 246
Author(s):  
Samuel Kovaleski ◽  
Arno B. Heldwein ◽  
Genei A. Dalmago ◽  
Jorge A. de Gouvêa ◽  
Gilberto R. da Cunha ◽  
...  
Keyword(s):  
Heat Flux ◽  
Ground Surface ◽  
Soil Surface ◽  
Soil Heat Flux ◽  
Growth Cycle ◽  
The Other ◽  
Net Radiation ◽  
Plant Mortality ◽  
Seedling Mortality ◽  
Micrometeorological Conditions

Our objective was to measure alterations in the micrometeorological conditions surrounding canola seedlings during frost periods, and to quantify seedling mortality as a function of straw distribution on the ground surface. The data was acquired from 15 frosts in 2014. We used four treatments, comprising ground surface without straw (SWS), ground surface entirely straw-covered (SEC), sowing line without straw (SLW), and soil with preexisting surface straw (SES), over three experiments. Net radiation (NR), soil heat flux (G), air (Ta), leaf (Lf), rosette (Tr), and surface temperature (Ts), and plant mortality were evaluated. NR was higher in the SEC treatment and lower in the SLW treatment, whereas G was higher on straw-covered ground; Ts and Ta were lower in the SEC than in the other treatments during the most intense frosts. On 06/19, Tr in the SEC and SLW treatments was -0.66 &deg;C and 0.42 &deg;C, respectively; on 08/14, Lf was -3.62 &deg;C and -2.88 &deg;C in the SEC and SLW treatments, respectively. Plant mortality due to the frost on 06/19 was 30% in the SEC treatment, but 0% in the SLW treatment; the frost of 08/14 caused 33.8% mortality in the SEC treatment and 1.25% in the SLW treatment. This therefore showed that removing straw from the sowing line improved the microclimate around the plants, thus reducing canola mortality at the beginning of the growth cycle, which is when frost events most frequently occur.

Gravitational Stresses on Deep Tunnels

1952 ◽  
Vol 19 (4) ◽  
pp. 537-542
Author(s):  
Yi-Yuan Yu
Keyword(s):  
Complex Variable ◽  
Ground Surface ◽  
Finite Depth ◽  
The Other ◽  
Variable Method ◽  
Two Dimensional ◽  
Special Cases ◽  
Elasticity Problems ◽  
External Stresses ◽  
Rigid Lining

Abstract Gravitational stresses around a horizontal tunnel opening are determined by means of Muschelišvili’s complex variable method for solving two-dimensional elasticity problems. The tunnel is located at a large but finite depth underneath the horizontal ground surface. It has the shape of a general ovaloid, including the rounded-cornered square, the ellipse, and the circle as its special cases. The surrounding material is assumed to be elastic, isotropic, and homogeneous. Two problems are solved. In one problem an unlined tunnel is considered, which has a boundary free from external stresses. In the other the tunnel has a rigid lining, and a perfect bond is assumed to exist between the lining and the surrounding material so that the displacements at the boundary are zero.

Homogenization of Monthly Ground Surface Temperature in China during 1961–2016 and Performances of GLDAS Reanalysis Products

2019 ◽  
Vol 32 (4) ◽  
pp. 1121-1135 ◽  
Author(s):  
Wenhui Xu ◽  
Chenghu Sun ◽  
Jingqing Zuo ◽  
Zhuguo Ma ◽  
Weijing Li ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Land Surface ◽  
Southern China ◽  
Ground Surface ◽  
Warming Trend ◽  
Test Method ◽  
The Other ◽  
Central China ◽  
Surface Model ◽  
Ground Surface Temperature

Maps of observed ground surface temperature (GST) in China generally contain inhomogeneities due to relocation of the observation site, changes in observation method, transition to automatic instruments, and so on. By using the observations of collocated manual and automatic weather stations in China, bias in daily GST caused by the transition to automatic observation systems is corrected for the first time in the present work. Then, the inhomogeneities caused by nonclimatic factors (e.g., relocation of the station and change of observation time) in the historical records of monthly GST are further reduced by using the penalized maximal F-test method. Analysis based on this new homogenized dataset reveals that the trend of annual-mean GST in China is approximately 0.273°C decade−1 during 1961–2016. The warming trend is stronger in winter (0.321°C decade−1) and spring (0.312°C decade−1) and weakest in summer (0.173°C decade−1). Spatially, all the stations in China, except for a few stations in southern China, present warming trends in the annual mean and in spring, fall, and winter seasons. In summer, cooling trends are observed in central and southern China. Moreover, we assess the monthly GST from five reanalysis products of the Global Land Data Assimilation System (GLDAS) during 1980–2016. The warming trends of Noah and the Catchment Land Surface Model (CLSM) from GLDAS-V2.0 are the closest to those of the homogenized observation, while the linear trends in the other three products (Noah, CLM, and MOS) from GLDAS-V1 are obviously different from those of the homogenized observation. Also, it is found that the spatial distribution of the warming trend is substantially overestimated in central China but underestimated in the other regions of China in these five GLDAS reanalysis products.

XXIV.—The Scattering of Light

1914 ◽  
Vol 33 ◽  
pp. 264-281
Author(s):  
James Robert Milne
Keyword(s):  
Light Scattering ◽  
Systematic Study ◽  
Ground Surface ◽  
Single Layer ◽  
The Other ◽  
Total Emission ◽  
Special Apparatus ◽  
The Many ◽  
The One ◽  
Made In

SummaryThe present paper describes a number of experiments made in connection with Christiansen's experiment in which a beam of light is passed through a transparent insoluble powder immersed in a liquid, with the result that light of the particular colour for which the indices of powder and liquid are the same passes unaffected, while light of all other colours is scattered. In this communication only the simplest case of the above is dealt with, that, namely, in which a flat piece of glass, ground on one side, takes the place of the powder, the rugosities of the ground surface representing a single layer of grains, and air takes the place of the liquid. In such a case there is, of course, no colour of light for which the indices of solid and liquid are alike, and indeed it was found that the colour of the light made very little difference to the results. On the other hand, however, it soon became apparent that different ways of grinding the glass surface led to very different effects. Accordingly, as no previous work appears to have been done in this field, and as it seemed a promising one, it was decided to make a systematic study of the various cases. Each specimen of glass employed was photomicrographed, and had its polar light distribution measured by a photometer. Two methods of characterising the particular scattering power of a screen soon suggested themselves and have been formally defined—the one connected with the Angle of Maximum Total Emission, and the other with the Equivalent Cavity.It is hoped to continue the investigation not only on the above lines, but also in the direction of ascertaining the effect of a number of plates, i.e. of successive layers of light-scattering particles; and in investigating the polarisation effects, which some rough preliminary experiments have shown to be marked.I am glad of this opportunity of acknowledging the help I have received from the Trustees of the Carnegie Trust in the form of grants for the construction of the special apparatus necessary; and desire to tender my grateful thanks to Professor MacGregor for the many facilities for carrying on the work which he kindly placed at my disposal.

Photogrammetry of spherical shocks reflected from real and ideal surfaces

1977 ◽  
Vol 81 (4) ◽  
pp. 701-717 ◽  
Author(s):  
J. M. Dewey ◽  
D. J. Mcmillin ◽  
D. F. Classen
Keyword(s):  
Shock Waves ◽  
Energy Loss ◽  
Triple Point ◽  
Ground Surface ◽  
The Other ◽  
Computer Codes ◽  
Point Trajectories ◽  
Spherical Shock ◽  
The Ideal

A photogrammetrical technique has been used to study the interaction of two identical explosively produced spherical shock waves and to compare this interaction with the reflexion of one of the spherical shocks from the ground. It is postulated that there was no energy loss in the interaction of the two shock waves and that the interaction therefore simulated the reflexion of a spherical shock from an ideal non-energyabsorbing surface. The ‘ideal’ reflexions were compared with real reflexions from two types of ground surface: one smooth and the other rough. Experiments were carried out with the centres of the spherical shocks at two separations so that observations could be made of the interaction of shocks of different strength. Significant differences were shown to exist in both the strengths of the Mach shocks and in the triple-point trajectories over the different surfaces. The results are intended to aid in the evaluation of computer codes being developed to simulate spherical-shock reflexions from real surfaces.

Parametric analysis of the effects of stress relief on the performance and capacity of piles in nondilative soils

2011 ◽  
Vol 48 (9) ◽  
pp. 1354-1363 ◽  
Author(s):  
Gang Zheng ◽  
Yu Diao ◽  
C.W.W. Ng
Keyword(s):  
Ground Surface ◽  
Stress Relief ◽  
Load Test ◽  
The Other ◽  
Deep Excavation ◽  
Maximum Tension ◽  
Load Tests ◽  
Pile Load Test ◽  
Effects Of Stress ◽  
Pile Load Tests

To provide support to superstructure and substructure, piles are often installed beneath a deep basement prior to its excavation. However, the effects of stress relief on the performance and capacity of piles due to deep excavation are rarely reported in the literature. In this study, two different types of pile load tests were simulated with and without considering excavation effects by conducting parametric axisymmetric finite element analyses. The first test was a pile load test on a sleeved pile from the ground surface prior to deep excavation, and the other is a load test on an unsleeved pile at the final excavated level. It is found that an excavation could reduce the pile capacity by up to 45% and pile stiffness by up to 75%. The effects of stress relief due to an excavation increase with normalized excavation depth (H/L) and excavation radius (R/H). Moreover, the maximum tension induced in a pile by excavation varies with H/L, and it has a peak value when 1 < H/L < 1.25. The value of maximum tension increases with the pile–soil modulus ratio (Ep/Esm). When Ep/Esm = 100, peak tension develops at 0.5H. On the other hand, tension reaches a peak at 0.7H when Ep/Esm = 20.

EQUIVALENCE BETWEEN CONTINUOUS AND DISCRETE RADIATING ARRAYS

1961 ◽  
Vol 39 (2) ◽  
pp. 335-349 ◽  
Author(s):  
A. Ksienski
Keyword(s):  
The Other ◽  
Radiation Patterns ◽  
Continuous Excitation

The radiation patterns produced by continuous excitation distributions and discrete arrays are compared and the conditions are derived under which one type of source may be substituted for the other with negligible errors. It is shown that the aperture lengths in both cases should be the same but the element spacing is dependent on the type of pattern desired. Examples are computed to demonstrate these relations for both directive patterns and shaped beams.

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