Modeling of Atmospheric Effects on Terahertz Imaging Systems

The terahertz (THz) electromagnetic frequency band is a potentially useful domain for remote sensing in military and Homeland Security applications. Sensors operating in this band gain some of the material penetrating abilities of radio waves, some of the image resolving capabilities of infrared (IR) devices, and an enhanced chemical discrimination capacity inherent to the THz band itself. Both passive (thermal) and active (maser) THz sensor operating modes have been contemplated, with the greatest emphasis on active sensors. Active sensors gain a particular advantage due to typical equivalent source brightness temperatures in the neighborhood of 1018 K. At these intensities, the significance of natural emission effects is negligible, but the influence of water vapor absorption can be significant at frequencies above 0.4 THz. For systems performance analysis we have developed simulation software to assess the limiting effects of the atmosphere on both passive and active terahertz imagers for various instrumental operating frequencies, bandwidths, sensor noise levels, integration times, and atmospheric conditions. We will show some of the early results of our modeling and simulation efforts, which illustrate the wide range of potential for atmospheric impacts on terahertz sensors. Presented at the ITEA Modeling and Simulation Conference held in Las Cruces, NM on 11-14 Dec 2006 and published in proceedings of the same. Sponsored in part by Defense Advanced Research Projects Agency and Army Communications-Electronics Command, Night Vision and Electronics Sensors Directorate (NVESD). The original document contains color images.