Terahertz (THz) radiation suffers severe signal loss due to the high absorptivity of water vapor abundant in normal atmosphere, greatly limiting its potential in noninvasive material characterization. We propose a novel THz signal processing method that enables effective extraction of hidden sample information leading to accurate thickness determination. The thicknesses of multiple silicon wafers are measured using only a single THz pulse obtained in ambient atmosphere without any prior sample information. The results verify our proposed approach to achieve accurate and precise characterization of materials in a realistic environment.