Propagation modeling of moist air and suspended water/ice particles at frequencies below 1000 GHz

Propagation characteristics of the atmosphere are modeled for the frequency range from 1 to 1000 GHz (1 THz) by the modular millimeter-wave propagation model MPM. Refractivity spectra of the main natural absorbers (i.e., oxygen, water-vapor, suspended droplets and ice particles) are computed from known meteorological variables. The primary contributions of dry air come from 44 O2 lines. Results from extensive 60-GHz laboratory measurements of the pressure-broadened O3 spectrum were applied to update the line data base. The water-vapor module considers 34 local H2O lines plus continuum contributions from the H2O spectrum above 1 THz, which are formulated as wing response of a pseudo-line centered at 1.8 THz Cloud/fog effects are treated with the Rayleigh approximation employing revised formulations for the permittivities of water and ice. The influence of the Earth's magnetic field on O2 absorption line becomes noticeable at altitudes between 30 and 120 km. Anisotropic medium properties result, which are computed by the Zeema propagation model ZPM. Here the elements of a complex refractivity tensor are determined in the vicinity (plus or minus 10 MHz) of O2 line centers and their effect on the propagation of plane, polarized radiowaves is evaluated. A spherically stratified (0-130 km) atmosphere provides the input for the codes MPM and ZPM in order to analyze transmission and emission properties of radio paths. Height profiles of air and water vapor densities and of the geocoded magnetic field are specified. ZPM predicts polarization- and direction-dependent propagation through the mesosphere. Emission spectra of the 9+ line (61150 plus or minus 3 MHz) for paths with tangential heights ranging from 30 to 125 km are consistent with data measured by the shuttle-based millimeter-wave limb sounder MAS.