Feasibility analysis of optimal terahertz (THz) bands for passive limb sounding of middle and upper atmospheric wind

As of now, direct measurements of middle and upper atmospheric wind are still scarce, and the observation method is limited, especially for the upper stratosphere and lower mesosphere. This paper presents a study of band selection to derive line-of-sight wind from 30 km to more than 120 km using a high-spectral-resolution terahertz (THz) radiometer, which can fill the measurement gap between lidar and interferometer data. Simulations from 0.1-5 THz for evaluating the feasibility of the spaceborne THz limb sounder are described in this study. The results show that high-precision wind (better than 5 ms-1) can be obtained from 40 to 70 km by covering a cluster of strong O3 lines. By choosing strong O2 or H2O lines, the high-quality measurement can be extended to 105 km. The O atom (OI) lines can provide wind signals in the higher atmosphere. In addition, performance of different instrument parameters, including spectral resolution, bandwidth, and measurement noise, was analyzed, and, lastly, four different band combinations are suggested.