Terahertz time-domain spectroscopy (THz-TDS) offers a range of unique imaging modalities due to the broad bandwidth, sub-picosecond duration, and phase-sensitive detection of the THz pulses. Previous research in the THz field primarily focused on improving the optoelectronics and on qualitative investigation of suitable applications. In this thesis, we use a quantitative approach to explore and extend the boundaries of the system. First, the possibility exists to combine spectroscopic characterization and/or identification with imaging because the THz radiation is broadband in nature. We describe a robust algorithm for extracting the optical constants and thickness, simultaneously and independently, from a sample. The technique extracts material parameters for both high and low index materials. Second, a fiber-coupled THz system provides an unparalleled opportunity to simulate seismic data collection. We demonstrate the homology between ultra-wideband seismic and THz imaging using multistatic reflective data acquisition. These results broaden the capabilities of THz imaging by borrowing from a mature imaging community. We investigate the resolution limits and show results from both simple and complex layered targets.