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2 Acta Geophysica

2 2012

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The selection of artificial corner reflectors based on RCS analysis

Li C., Yin J., Zhao J., Zhang G., Shan X.

Acta Geophysica

2012

Vol. 60, no. 1

43-58

Artificial corner reflectors (ACRs) are widely applicable in monitoring terrain change via interferometric synthetic aperture radar (InSAR) remote sensing techniques. Many different types are available. The choice of the most appropriate ones has recently attracted scholarly attentions. Based on physical optics methods, via calculating the radar cross section (RCS) values (the higher the value, the better the detectability), the current study tested three ACRs, i.e., triangular pyramidal, rectangular pyramidal and square trihedral ACRs. Our calculation suggests that the square trihedral ACR produces the largest RCS but least tolerance towards incident radar ray’s deviation from optimal angle. The triangular pyramidal trihedral ACR is the most geometrically stable ACR, and has the highest tolerance towards incident radar ray’s deviation. Its RCS values, however, are the least of the three. Due to the high cost of deploying ACRs in the fields, the physical optics method seems to provide a viable way to choose appropriate ACRs.

Induced strains and defect continuum theory: Internal reorganization of load

Teisseyre R., Górski M.

Acta Geophysica

2012

Vol. 60, no. 1

24-42

Induced strains play an important role in mining regions and water dam areas. We consider a mechanism of reorganization of the applied stress load by some changes in rock-body defect distribution caused by human activity. A defect content increases with increasing stress load and related deformations; hence, a relationship could appear between seismic risk and deformation level. Recent progress in the Asymmetric Continuum Theory permits to consider some internal reorganization of the applied load due to internal defect content and distribution; in this paper we consider an increase of internal defect densities due to mining works and the appearance of reorganized internal stress distribution. A generalization of the Peach–Koehler forces acting on the defects makes it possible to define formation of induced strains; a character of resulting strains may essentially differ from the applied load. In the case of an axial load, this approach helps to understand formation of shear or rotational micro-fractures, usually recognized as fragmentation and slip motions.