TeraHz Limb Sounder (TLS): A new instrument and remote sensing technique for Thermospheric Winds, Temperature, and Atomic Oxygen Density

TeraHz Limb Sounder (TLS) is a remote sensing radiometric instrument that collects light from Atmospheric Oxygen, O, emission lines that arise from transitions of the fine structure levels. The 2.06 THz OI emission (3P0->3P1) enables comprehensive remote sensing at altitudes between 100 and 250 km, while the 4.75 THz OI emission (3P1->3P2) extends the altitude range to >400km. The OI fine structure emission is present everywhere and is always in thermodynamic equilibrium with the ambient temperature at least up to 500 km altitude. As such, it is present at all local times and all latitudes and does not exhibit any space-time gradients over the terminators and within the aurora. Thereby, this is the only known thermospheric remote sensing technique that can measure the altitude profile of the thermospheric state at all local times and at all locations. The 2.06 THz implementation is proposed to fly on DYNAMIC as the DTLS instrument with 4 orthogonal look directions. We present its predicted performance, the derivation of vector winds, and the geophysical parameter inversion technique.