Sequential Parameter Estimation of Modal Dispersion Curves with an Adaptive Particle Filter in Shallow Water: Experimental Results

An adaptive particle filter method is presented for performing sequential geoacoustic estimation of a shallow water acoustic environment using the explosive sound sources. This approach treats environmental parameters and source–receiver distance as unknown random variables that evolve as the source moves. As a sequential estimation method, this approach reduces the expense of computation than genetic algorithm and yields results with the same accuracy. Comparing with standard Particle filter, proposed method can adjust control parameters to adapt to a rapidly changing environment. This approach is demonstrated on the shallow water sound propagation data which was collected during the ASIAEX 2001 experiment. The results indicate that the geoacoustic parameters are well estimated and source–receiver distance are also well determined.

Excitation of the global correlation wavefield by large earthquakes

SUMMARY Recorded globally, cross-correlated ground-motion time-series of the coda of large earthquakes enable the construction of a 2-D representation of correlation lapse time and inter-receiver distance—a global correlogram. A better understanding of how the features present in a correlogram are generated can revolutionize the characterization of planetary interiors. Here, we investigated correlograms based on individual large earthquakes and identified 12 events from the past decade with a multitude of prominent and some ‘exotic’ features in the first 3 hr following correlation origin. We found that the type of the source mechanism and energy-release dynamics are the key influencers responsible for individual correlograms equal in quality to a stack of hundreds of correlograms. A single event is sufficient in creating a correlogram resembling previous correlograms constructed from a large number of events, which reinforces the notion that the earthquake coda-correlation features are not ‘reconstructed’ body waves. Numerical simulations of the correlation wavefield can thus be based on exceptional-quality events, becoming more computationally affordable. Here, we explain more than 60 features of the global coda-correlogram, which presents the most extensive catalogue to date.

Steepest descent integration: A novel method for computing wavefields radiated from borehole sources

Borehole sources, including chemical explosives, air gun, water gun, and piezoelectric transducers in the borehole, generate seismic waves inside and outside the borehole. Modeling the wavefield is of key importance in acoustic logging, crosshole tomography, mining geophysics, and deep sounding seismic for interpretation of amplitude information of real data and prediction of energy-radiation patterns. Classic methods for modeling the wavefield inside a borehole, such as real-axis integration, are challenged by highly oscillatory integrals encountered when modeling the wavefield outside the borehole. We have developed a novel method, called steepest descent integration (SDI), which evaluates the oscillatory wavenumber integration by numerically integrating along the steepest descent path. The oscillation along the new integration path is significantly reduced. The contributions of poles and branch cuts are added if they are located between the steepest descent path and the real axis. The SDI is applicable to arbitrary frequency and source-receiver distance. Comparison with real-axis integration shows that the method can compute highly oscillatory integrals with better efficiency and accuracy. In addition, the SDI is more numerically robust because it generates no spurious arrivals, which are evident in the real-axis integration. Analysis of numerical examples at different source-receiver distance shows that SDI is more efficient when computing far-field seismograms. This SDI can also be used to compute highly oscillatory integral in other wave-propagation problems.

Reactive messengers for digital molecular communication with variable transmitter–receiver distance

The chemical reactivity of a molecular messenger has been employed to achieve effective information transfer in molecular communication with variable transmitter–receiver distances.

Relief geometric effects on frequency-domain electromagnetic data

A perpendicular transmitter-receiver coils arrangement used in the frequency-domain electromagnetic survey can have deviations in relation to its standard geometric definition due to the relief geometry of the surveyed area when combined with large transmitter-receiver distance and large transmitter loop size. This happens because the local relief characteristics along the transmitter loop wire laid on the ground can deviate the equivalent magnetic moment axis from the vertical, and the global characteristics locate the transmitter and receiver positions at different elevations. A study about that is carried on here substituting the rugged relief by an inclined plane. We have developed a new formulation for the [Formula: see text]-layered model that allowed us to investigate the relief geometry effects on FDEM data but restricting the analysis to the two-layer earth model, considering three cases of transmitter-receiver situations controlled by the relief conditions. The curves representing the Argand diagram and the apparent polarization parameter as a function of the apparent induction number were obtained for each relief model. Such procedures resulted to be very useful to demonstrate their behavior departing from those curves obtained for an inclined and a horizontal ground. These results show that small deviations in the verticality of the transmitter loop axis or in the horizontality of the surficial plane causes significant deviations, even for angles as small as 1°.

STUDY ON THE EFFECTS OF RECEIVER DISTANCE, HEIGHT AND MASS OF DROPPING STEEL BALLS ON SASW TEST RESULTS

A series of surface wave tests, namely the Spectral Analysis of Surface Wave (SASW) test, was done on asphalt pavement to study the effect of receiver distance, S; the height of dropping steel balls, H; and the mass of the source, m on the results of SASW evaluation. For each test, four steel balls with different masses, namely0.067kg, 0.228kg, 0.537kg, and 1.805kg, were used as sources, and the balls were dropped from varying heights, 0.25m and 0.50m. This test was conducted with two different configurations, in which the receivers were located 0.15m and 0.30m apart. This paper presents the results of the test in terms of maximum and minimum wavelength. The results proved that larger receiver distance yields large wavelength, and vice versa. The similar trend is observed when the mass of the dropping ball is increased. The height of the falling steel ball, however, did not have significant impact on the results of the SASW evaluation.