Development of an Open Path THz Transmissometer for Deterministic and Random Propagation Studies

The design of an open-path 320 GHz - 340 GHz coherent transmissometer for experimental measurements of amplitude scintillation, phase scintillation, angle-of-arrival (AoA) fluctuations, and transverse coherence near the 325.1529 GHz water absorption resonance is presented. The system uses a uni-directional transmitter and two phase-coherent receivers with adjustable transverse. The objective of the experiment is to verify and improve existing propagation models for use by designers of applied THz systems for remote sensing, radiolocation, or communications. System stability will be verified using a short range near-ground test path of several similar to 10's of meters length using a cable for locking the transmitter local oscillator (LO) to the receivers' LOs. This short range configuration, similar to tests conducted at Flatville, Illinois during the 1980s(1-3), permits characterization of system errors in all of the above parameters, thus yielding a baseline for the long range experiments. Characterization of the phase-coherent RF link will be studied vis-a-vis anticipated theoretical performance based on the Rytov approximation(4,5). The system will then be configured for long term open-path measurements on a 1.78 km elevated link between the University of Colorado at Boulder (CU) and the National Telecommunications and Information Administration (NTIA) Mesa site at the NOAA-NIST campus in Boulder, Colorado. The system will provide long range coherent THz propagation statistics during continuous long-duration study of turbulent atmospheric propagation effects over an extensive array of atmospheric conditions in a realistic operational environment.