Advances in Space-borne Infrared Laser Occultation for Atmospheric Composition Profiles Detection

Accurately understanding the vertical distribution of major global atmospheric gases is a critical issue in climate change research and response. The  Low Earth Orbit-to-Low Earth Orbit (LEO-LEO) infrared laser occultation (LIO) detection technology enables three-dimensional, all-time, and high vertical-resolution simultaneous detection of multiple atmospheric composition (CO₂, CH₄, H₂O, O₃, N₂O, CO, etc.) and line-of-sight wind speed. This approach is expected to complement existing greenhouse gas column total measurement methods in the future. The LIO system consists of a transmitter and a receiver. It employs eleven carefully selected infrared laser signals within the shortwave infrared (SWIR) spectral region of 2–2.5 µm. Based on the differential absorption lidar (DIAL) principle, the system retrieves vertical profiles of greenhouse gases and further derives line-of-sight wind speed via spectral Doppler frequency shift. During an occultation event, the laser signal emitted by the transmitter is attenuated by the atmosphere before reaching the receiver. The transmitter realizes differential absorption atmospheric spectral detection through multiple laser channels. Each detection element adopts dual-channel detection, and the receiver performs high-sensitivity detection for each spectral channel. To ensure precise laser wavelength control, the LIO system adopts optical frequency comb stabilization technology. Additionally, a spatial heterodyne spectrometer is used to achieve extremely high spectral resolution within a narrow field of view. By scanning the Earth's atmosphere from top to bottom, the system allows for high-precision retrieval of trace gases profiles. Currently, no LEO-LEO occultation mission has been deployed in space. Research has been focused on frequency selection evaluation, inversion algorithm refinement, occultation orbit design, and detection performance simulations. The continued development of infrared laser occultation technology can provide essential vertical atmospheric datasets for future global climate change research.