Comment on the Veracity of the ITU-R Recommendation for Atmospheric Attenuation at Terahertz Frequencies

The Radiocommunication Sector of the International Telecommunication Union (ITU-R) produces numerous global standards on the use and management of radiocommunication systems. Among these is Recommendation ITU-R P.676-11 (09/2016), which provides methods to estimate the attenuation by atmospheric gases for electromagnetic waves in the 1-1000 GHz frequency range. In this letter, we comment on the veracity of that recommendation in the 450-1000 GHz range. In particular, we compare ITU water vapor absorption estimates to the same data available from other sources: HITRAN and previously reported experimental measurements. We find that ITU estimates increasingly disagree with both sources as frequency and water vapor density increase, demanding a closer inspection as to the cause. This discrepancy is attributed to the method of inclusion of the summed contribution of resonance wings from absorption lines located in the >1 THz range, and the method to account for continuum absorption.