Consultations on the WALES mission for profiling water vapor in the lower troposphere

This paper reviews the WALES mission by the European Space Agency (ESA) and the HALO missions conducted by Langley Research Center (LaRC) of NASA. It evaluates potential risks associated with spaceborne applications by examining factors such as single-pulse energy, pulse repetition frequency, optical frequency stability, efficiency, spectral purity, and reliability. The review also explores advancements in solid-state laser technology operating at 820 nm over the past two decades, as well as recent developments in diode-pumped Er:YAG lasers. Key innovations from these technologies have been incorporated into differential absorption lidar transmitters to enhance performance. Separating weather forecasting from climate-change research is recommended for spaceborne missions. The 935 nm spectral band is optimal for water vapor DIAL measurements in the upper troposphere and lower stratosphere (UTLS). In contrast, the 820 nm band is ideal for measurements in the lower troposphere.