A visualization algorithm for a shallow subsurface object with electromagnetic pulsed wave in time domain is discussed. Scattered wave from a ground surface and underground object is obtained by using the FDTD method. A cost functional is defined with the difference between the scattered electromagnetic field components measured and simulated. Applying Particle Swarm Optimization (PSO) with a multi-stage optimization method to the optimization problem for minimizing the functional, a location, a dimension, and material parameters of the underground object are obtained. According to prescribed threshold values for cost functional, this multi-stage optimization reduces a estimated region for agents of PSO. For a dielectric scatterer and an air hole in a homogeneous lossy soil, numerical calculations are performed. From the results, the PSO based visualization algorithm with the multi-stage optimization method gives good reconstruction results.%都市部の道路工事では，埋設されているガス管及び水道管などの各種ライフラインの位置を事前に把握することは，配管の破損事故の防止や工期の短縮などの点において重要である．また，道路の陥没事故の発生原因としては空洞の存在や埋設物の老朽化による破損などが挙げられるが，突然発生することが多い陥没事故を未然に防ぐことは容易ではない．
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