Simulation of a spaceborne metastable helium lidar

Abstract. Metastable helium (He*) lidar has extended atmospheric profiling into the thermosphere and lower exosphere in recent years. However, ground-based observations remain limited by weather conditions and geographic coverage. In this study, we propose a spaceborne He* lidar concept and assess its performance through numerical simulations. We use a global He* density model, compare its predictions with a representative ground-based observation, and specify the key instrument parameters. We then calculate the expected photon returns for an upward-looking lidar orbiting at approximately 400 km, accounting for saturation and measurement noise. Under the simulated conditions, He* density profiles can be retrieved up to 1000 km with a vertical resolution of 5 km and an integration time of 1 min. We also investigate temperature and line-of-sight velocity retrieval using three probing wavelengths with retrievals reported at 20 km altitude intervals between 500 and 700 km. The temperature retrieval captures the main features of the prescribed profile. These results highlight the potential of spaceborne He* lidar to extend localized ground-based observations towards global, altitude-resolved mapping of He*. Beyond density profiling, future temperature and line-of-sight velocity measurements could provide new observational constraints on the thermal structure and dynamics of the upper thermosphere, supporting investigations of helium variability and the evaluation of thermospheric models.