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A differential preexcitation pulse technique in Brillouin optical time-domain analysis (DPEP-BOTDA) for decimeter spatial resolution is shown. This technique is based on the preexcitation of the stimulated Brillouin scattering and the subtraction of the Brillouin scattering due to an intensity dc level present in the optical pulse. The technique uses a pulse composed by a low intensity base with duration of tens of nanoseconds, which is followed by a shorter optical main pulse (e.g., 2 or 3 ns) with higher intensity. The technique is successfully checked in the laboratory. Two equal decimeter defects separated the same distance can be solved on a standard single-mode optical fiber of 2 km length.