Measurement of seismic attenuation from high‐resolution crosshole data

Geophysics ◽  
1996 ◽  
Vol 61 (4) ◽  
pp. 1175-1188 ◽  
Author(s):  
J. P. Neep ◽  
M. S. Sams ◽  
M. H. Worthington ◽  
K. A. O’Hara‐Dhand
Keyword(s):  
High Resolution ◽  
Velocity Structure ◽  
Spectral Ratio ◽  
Test Site ◽  
Compressional Wave ◽  
Seismic Attenuation ◽  
Frequency Content ◽  
Low Frequencies ◽  
Significant Difference ◽  
Q Values

High‐resolution crosshole seismic data have been acquired at the Imperial College borehole test site in Northumberland, England. Raypaths between source and receiver were horizontal and parallel to plane layered beds of sandstone, mudstone, and limestone. Shots were fired at 25 cm intervals between the depths of 50 and 72 m. Estimates of the total attenuation using the spectral ratio and centroid frequency shift methods show Q values that correlate well with the frequency content of the first arrivals. Synthetic modeling studies with and without intrinsic attenuation show that the contribution of scattering attenuation is significant and must be accounted for to recover the intrinsic Q values used in the modeling. At some depths, there appears to be an increase in the frequency content of the compressional wave with distance, implying a negative scattering Q. Snapshots of the wave as it travels across the velocity structure at this depth show that the high frequencies are preserved in the wavefield and the low frequencies are scattered to other depths. Intrinsic Q values of less than 20 were obtained at all depths. Within experimental error, there is no evidence to suggest any significant variation of attenuation with lithology. This is consistent with estimates of attenuation from core samples. However, there is a significant difference in the median of Q estimates from the crosshole and core data.

The effect of audio–visual expectancies on stereoacuity

2012 ◽  
Vol 25 (0) ◽  
pp. 160
Author(s):  
Marina Zannoli ◽  
Pascal Mamassian
Keyword(s):  
Visual System ◽  
Sound Source ◽  
Binocular Disparity ◽  
Frequency Content ◽  
High Pitch ◽  
Low Frequencies ◽  
High Frequencies ◽  
Depth Difference ◽  
Significant Difference ◽  
Do So

Because of greater attenuation of high frequencies, a distant sound carries more low frequencies. As the distance between the listener and a sound source increases, the sound is therefore perceived as having a lower pitch. In the present study, we investigated whether there pre-exists a relationship between depth, as it is perceived by the visual system, and pitch. To do so, we measured stereoacuity (the smallest detectable depth difference that can be seen from binocular disparity). Two lines were presented sequentially at a different depth. Each line was presented along with a beep that lasted as long as the presentation of the line. The two beeps could either have the same pitch or a different pitch associated with the two depths. When the pitch was different, the high pitch could either be associated with the near (congruent with the hypothesis) or the far (incongruent) line. Five participants were asked to determine which line was nearer and instructed not to pay attention to the sound. Results showed no significant difference between the congruent and incongruent sound conditions. However, sensitivity was much better in the two different-pitch conditions compared to the same-pitch condition. In addition, we found no difference between the same-pitch condition and a control condition in which no sound was presented. To conclude, our results suggest that a difference in pitch can improve stereacuity, independent of the frequency content of the sound.

scholarly journals Using GEDI Waveforms for Improved TanDEM-X Forest Height Mapping: A Combined SINC + Legendre Approach

2021 ◽  
Vol 13 (15) ◽  
pp. 2882
Author(s):  
Hao Chen ◽  
Shane R. Cloude ◽  
Joanne C. White
Keyword(s):  
High Resolution ◽  
Forest Canopy ◽  
Test Site ◽  
Convergent Series ◽  
Canopy Height ◽  
Ecosystem Dynamics ◽  
Sinc Function ◽  
Vertical Profiles ◽  
Legendre Series ◽  
Vertical Profiling

In this paper, we consider a new method for forest canopy height estimation using TanDEM-X single-pass radar interferometry. We exploit available information from sample-based, space-borne LiDAR systems, such as the Global Ecosystem Dynamics Investigation (GEDI) sensor, which offers high-resolution vertical profiling of forest canopies. To respond to this, we have developed a new extended Fourier-Legendre series approach for fusing high-resolution (but sparsely spatially sampled) GEDI LiDAR waveforms with TanDEM-X radar interferometric data to improve wide-area and wall-to-wall estimation of forest canopy height. Our key methodological development is a fusion of the standard uniform assumption for the vertical structure function (the SINC function) with LiDAR vertical profiles using a Fourier-Legendre approach, which produces a convergent series of approximations of the LiDAR profiles matched to the interferometric baseline. Our results showed that in our test site, the Petawawa Research Forest, the SINC function is more accurate in areas with shorter canopy heights (<~27 m). In taller forests, the SINC approach underestimates forest canopy height, whereas the Legendre approach avails upon simulated GEDI forest structural vertical profiles to overcome SINC underestimation issues. Overall, the SINC + Legendre approach improved canopy height estimates (RMSE = 1.29 m) compared to the SINC approach (RMSE = 4.1 m).

scholarly journals The Role of Transthoracic Ultrasound in the Study of Interstitial Lung Diseases: High-Resolution Computed Tomography Versus Ultrasound Patterns: Our Preliminary Experience

Diagnostics ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 439
Author(s):  
Donato Lacedonia ◽  
Giulia Scioscia ◽  
Angelamaria Giardinelli ◽  
Carla Maria Irene Quarato ◽  
Ennio Vincenzo Sassani ◽  
...  
Keyword(s):  
Computed Tomography ◽  
High Resolution ◽  
Lung Diseases ◽  
Interstitial Lung Diseases ◽  
High Resolution Computed Tomography ◽  
Pleural Line ◽  
Complementary Role ◽  
Number Of Patients ◽  
Significant Difference ◽  
Transthoracic Ultrasound

Transthoracic ultrasound (TUS) is a readily available imaging tool that can provide a quick real-time evaluation. The aim of this preliminary study was to establish a complementary role for this imaging method in the approach of interstitial lung diseases (ILDs). TUS examination was performed in 43 consecutive patients with pulmonary fibrosis and TUS findings were compared with the corresponding high-resolution computed tomography (HRCT) scans. All patients showed a thickened hyperechoic pleural line, despite no difference between dominant HRCT patterns (ground glass, honeycombing, mixed pattern) being recorded (p > 0.05). However, pleural lines’ thickening showed a significant difference between different HRCT degree of fibrosis (p < 0.001) and a negative correlation with functional parameters. The presence of >3 B-lines and subpleural nodules was also assessed in a large number of patients, although they did not demonstrate any particular association with a specific HRCT finding or fibrotic degree. Results allow us to suggest a complementary role for TUS in facilitating an early diagnosis of ILD or helping to detect a possible disease progression or eventual complications during routine clinical practice (with pleural line measurements and subpleural nodules), although HRCT remains the gold standard in the definition of ILD pattern, disease extent and follow-up.

scholarly journals Comparison and Evaluation of Different Pit-Filling Methods for Generating High Resolution Canopy Height Model Using UAV Laser Scanning Data

2021 ◽  
Vol 13 (12) ◽  
pp. 2239
Author(s):  
Ying Quan ◽  
Mingze Li ◽  
Yuanshuo Hao ◽  
Bin Wang
Keyword(s):  
High Resolution ◽  
Laser Scanning ◽  
Evaluation Framework ◽  
Canopy Height ◽  
Filter Method ◽  
Individual Tree ◽  
Significant Difference ◽  
Point Interpolation ◽  
Canopy Height Model ◽  
Height Model

As a common form of light detection and ranging (LiDAR) in forestry applications, the canopy height model (CHM) provides the elevation distribution of aboveground vegetation. A CHM is traditionally generated by interpolating all the first LiDAR echoes. However, the first echo cannot accurately represent the canopy surface, and the resulting large amount of noise (data pits) also reduce the CHM quality. Although previous studies concentrate on many pit-filling methods, the applicability of these methods in high-resolution unmanned aerial vehicle laser scanning (UAVLS)-derived CHMs has not been revealed. This study selected eight widely used, recently developed, representative pit-filling methods, namely first-echo interpolation, smooth filtering (mean, medium and Gaussian), highest point interpolation, pit-free algorithm, spike-free algorithm and graph-based progressive morphological filtering (GPMF). A comprehensive evaluation framework was implemented, including a quantitative evaluation using simulation data and an additional application evaluation using UAVLS data. The results indicated that the spike-free algorithm and GPMF had excellent visual performances and were closest to the real canopy surface (root mean square error (RMSE) of simulated data were 0.1578 m and 0.1093 m, respectively; RMSE of UAVLS data were 0.3179 m and 0.4379 m, respectively). Compared with the first-echo method, the accuracies of the spike-free algorithm and GPMF improved by approximately 23% and 22%, respectively. The pit-free algorithm and highest point interpolation method also have advantages in high-resolution CHM generation. The global smooth filter method based on the first-echo CHM reduced the average canopy height by approximately 7.73%. Coniferous forests require more pit-filling than broad-leaved forests and mixed forests. Although the results of individual tree applications indicated that there was no significant difference between these methods except the median filter method, pit-filling is still of great significance for generating high-resolution CHMs. This study provides guidance for using high-resolution UAVLS in forestry applications.

Least‐squares inversion of in‐situ sonic Q measurements: Stability and resolution

Geophysics ◽  
2004 ◽  
Vol 69 (2) ◽  
pp. 378-385 ◽  
Author(s):  
Aristotelis Dasios ◽  
Clive McCann ◽  
Timothy Astin
Keyword(s):  
High Resolution ◽  
Least Squares ◽  
Instantaneous Frequency ◽  
Spectral Ratio ◽  
Full Waveform ◽  
Multiple Measurements ◽  
Sandstone Reservoir ◽  
Gas Bearing

We minimize the effect of noise and increase both the reliability and the resolution of attenuation estimates obtained from multireceiver full‐waveform sonics. Multiple measurements of effective attenuation were generated from full‐waveform sonic data recorded by an eight‐receiver sonic tool in a gas‐bearing sandstone reservoir using two independent techniques: the logarithmic spectral ratio (LSR) and the instantaneous frequency (IF) method. After rejecting unstable estimates [receiver separation <2 ft (0.61 m)], least‐squares inversion was used to combine the multiple estimates into high‐resolution attenuation logs. The procedure was applied to raw attenuation data obtained with both the LSR and IF methods, and the resulting logs showed that the attenuation estimates obtained for the maximum receiver separation of 3.5 ft (1.07 m) provide a smoothed approximation of the high‐resolution measurements. The approximation is better for the IF method, with the normalized crosscorrelation factor between the low‐ and high‐resolution logs being 0.90 for the IF method and 0.88 for the LSR method.

Q estimation from vertical seismic profile data and anomalous variations in the central North Sea

Geophysics ◽  
1985 ◽  
Vol 50 (4) ◽  
pp. 615-626 ◽  
Author(s):  
S. D. Stainsby ◽  
M. H. Worthington
Keyword(s):  
North Sea ◽  
Pulse Width ◽  
Spectral Ratio ◽  
Seismic Profile ◽  
Seismic Attenuation ◽  
Recording Equipment ◽  
Vertical Seismic Profile ◽  
High Attenuation ◽  
Vsp Data ◽  
Central North Sea

Four different methods of estimating Q from vertical seismic profile (VSP) data based on measurements of spectral ratios, pulse amplitude, pulse width, and zeroth lag autocorrelation of the attenuated impulse are described. The last procedure is referred to as the pulse‐power method. Practical problems concerning nonlinearity in the estimating procedures, uncertainties in the gain setting of the recording equipment, and the influence of structure are considered in detail. VSP data recorded in a well in the central North Sea were processed to obtain estimates of seismic attenuation. These data revealed a zone of high attenuation from approximately 4 900 ft to [Formula: see text] ft with a value of [Formula: see text] Results of the spectral‐ratio analysis show that the data conform to a linear constant Q model. In addition, since the pulse‐width measurement is dependent upon the dispersive model adopted, it is shown that a nondispersive model cannot possibly provide a match to the real data. No unambiguous evidence is presented that explains the cause of this low Q zone. However, it is tentatively concluded that the seismic attenuation may be associated with the degree of compaction of the sediments and the presence of deabsorbed gases.

scholarly journals CNO abundances in giants of the peculiar globular cluster NGC 1851

2015 ◽  
Vol 11 (S317) ◽  
pp. 352-353
Author(s):  
G. Tautvaišienė ◽  
A. Drazdauskas ◽  
C. Lardo ◽  
S. L. Martell ◽  
E. Pancino ◽  
...  
Keyword(s):  
High Resolution ◽  
Globular Cluster ◽  
Mean Values ◽  
Significant Difference ◽  
The Mean ◽  
Cno Abundances

AbstractWe provide CNO and Fe abundance investigations for a sample of up to 45 NGC 1851 giants. High-resolution spectra were obtained with the VLT UVES spectrograph in the framework of the Gaia-ESO Survey. The stars in our sample can be separated into two groups with a difference of 0.1 dex in the mean metallicity, 0.3 dex in the mean C/N, and no significant difference in the mean values of C+N+O.

Comparison of seismic waves generated by different types of source

1963 ◽  
Vol 53 (5) ◽  
pp. 965-978 ◽  
Author(s):  
David E. Willis
Keyword(s):  
Seismic Waves ◽  
Nuclear Explosion ◽  
Test Site ◽  
Frequency Content ◽  
Nevada Test Site ◽  
Different Types ◽  
The Waves ◽  
Source Duration ◽  
Lower Frequencies

Abstract A comparison of the seismic waves generated by a nuclear explosion and an earthquake is discussed. The epicenter of the earthquake was located within the Nevada Test Site. Both events were recorded at the same station with the same type of equipment. The earthquake waves contained slightly lower frequency than the waves generated by the nuclear shot. The early P phases of the shot had larger amplitudes while the phases after Pg for the earthquake were larger. Seismic waves from collapses were generally found to be composed of lower frequencies than the waves from the original shot. Aftershocks of the Hebgen Lake earthquake were found to generate seismic waves whose frequency content was related to the magnitude of the aftershock. Spectral differences in quarry shot recordings that correlate with source duration times are also discussed.

Sign in / Sign up

Export Citation Format

Share Document