Measurements From an Open-Path Terahertz Transmissometer Designed for Deterministic and Stochastic Propagation Studies

The design of and attenuation measurements from an open-path terahertz transmissometer system operating near the 325-GHz water vapor absorption line is presented. This line-of-sight (LoS) transmissometer system uses a unidirectional transmitter and two phase-coherent receivers with the objective of validating and improving existing propagation models for use in THz remote sensing, radiolocation, communications, and related applications. The system is designed to measure attenuation and phase and amplitude statistics during continuous long-duration operations in diverse atmospheric conditions. The system has been configured for open-path measurements on an elevated link between the University of Colorado at Boulder (CU) and the National Telecommunications and Information Administration (NTIA) site in Boulder, Colorado, with a 1.925-km path length. Estimates of attenuation sensitivity to water vapor density obtained from data observed during an initial intensive observation period (IOP) are in good agreement with previous measurements and theory.