A.Yu. Grinev, V.S. Temchenko, D.V. Bagno, A.E. Zaikin, E.V. Ilyin

Results of investigations in restoration of geometrical end electro-physical parameters restoration are presented for subsurface media and objects, their radio images forming. For this, ground penetrating radar with ultra wide-band short-pulse sounding signal is used. Methods and algorithms of restoration are based on relation of parameters of medium or object with its scattered electromagnetic field's signature. Method of computational diagnostics (MCD), a set of the direct problem solving techniques and global optimization algorithms are used for inverse problem solution. The MCD is based on smoothing functional minimization. This functional is the discrepancy function of measured space-time samples of scattered electromagnetic field and the direct problem solution results. This functional is non-convex and multi-extremal, and genetic algorithm is used for its minimization. Complementary methods were elaborated to include ultra wide-band transmit and receive antennas and electromagnetic wave propagation inside of underground medium into GPR model. These methods are: MCD - decomposition to plane waves; MCD - modelling with dipoles; MCD - virtual complex source. The methods are based on electromagnetic models of different levels of detailing and accuracy. To solve the direct problem, layered media' Green's function tensor is represented with limited number of plane E- and H-waves. Results of complex source's Geen's function approximation are presented. These results are used in modeling of ultra-wideband transmit-receive antenna of the GPR with equivalent complex sources. Basing on this approach, electrodynamic model of the GPR's antenna allows effectively solve the direct problem. Results of the GPR antenna simulation are presented, and a sources of single complex and paired complex dipoles are used for this. Algorithms of range migration and reverse projections are implemented for subsurface objects' radio images forming with multichannel GPR. Specifics of media (objects) parameters restoration, calibration procedures of GPR radio path, subsurface objects 3D images forming are discussed. Delivered methods and algorithms are integrated in multi-channel GPR software package. This provides effective restoration of subsurface media' and objects' geometry and electro-physical parameters, as well as forming of radio images of subsurface volume.