Transient Technologies LLC

Simulation of Subsurface Electromagnetic Wave Propagation and Scattering.

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A subsurface radar technique is used for a microwave non-invasive probing in opaque regions in soils, rocks, fresh water, brick, concrete etc. There is an inherent complexity of a subsurface radar survey some. Unavoidable features of a radar functioning, numerous wave propagation and scattering events complicate seriously a radar data processing and an interpretation [3]. Such electromagnetic events in subsurface radar involve:

  • dispersion effects caused namely by internal water in matter in a used microwave band [1].
  • various wave propagation phenomena like a multipath propagation [1]. lateral waves [1.4] etc..
  • strong diffraction events forced by comparability of magnitude of used wave-lengths and dimensions of subsurface finite-size objects should be detected by radar [3].
  • subsurface clutters and a statistical heterogeneity common for internal regions and a surface roughness,
  • inherent physical properties of a ultra-wide band (UWB) radiation and reception by transient antennas [2] as well as a
  • UWB scattering by finite-sized targets including the effect of near-field range.

A basic arrangement of subsurface radar is shown in Fig. la with the simulated characteristic waveforms SI...4(f) in Fig. lb for all specific points in a radar radio channel [2]. Two dipole antennas under a double passing excitation [2] form this radar radio channel. A waveform Sl(t) is an excitation signal for a transmitting (Tx) antenna that produced a signal S2(t), which is differ to Sl(t) and illuminates a subsurface target. Due to scattering this target generates an echo pulse signal S3(t) that reaches a receiving antenna (Rx). Signal S3(t) embodies the specific features of a target like additional ringing signal in its waveform. Finally the resulting signal in an antenna load has a waveform S4(t) that is quite different from an original waveform Sl(t). The presented data in Fig. lb obtained by simulation in time-domain (TD) illustrate an inherent complexity of signal transformation in subsurface radar especially due to influence of the near-filed effects. There are the two main research approaches in time-domain and in frequency-domain (FD that can be applied for investigation of the all effects on subsurface radar. Deterministic and statistical simulations should be employed for these goals also. This submission will present the applications of some TD and FD techniques developed for simulation of subsurface radar returns and making easy an interpretation of real field radar data.

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