Dispersion by atmospheric water vapor at frequencies less than 1 THz

The refractivity of atmospheric water vapor at frequencies less than 1 THz is expressed as the sum of (1) the empirical radio refractivity, (2) a simple approximation to the line-by-line summation of dispersion contributions by resonances above 1 THz, and (3) a line-by-line summation over resonances below 1 THz. This simple approximation, which is valid in the temperature range -40°C to 40°C, reduces labor and computer time required to calculate dispersion. A similar approximation for absorption predicted by three different line shapes is also given. Measured and calculated radio refractivity data are compared, revealing discrepancies in temperature dependence. The three different dispersion line shapes are then compared and shown to be in good agreement with both