[M-SD35] Future Missions of Satellite Earth Observation

[MSD35-P05] Technology demonstration of space-borne differential absorption lidar for global water vapor profiling - Ocean water vapor observations using integrated path differential absorption technique -

*Makoto Abo¹, Chikao Nagasawa¹, Yasukuni Shibata¹, Osamu Uchino², Tetsu Sakai³, Takashi Shibata⁴, Masaki Katsumata⁵ (1.Graduate School of System Design, Tokyo Metropolitan University, 2.National Institute for Environmental Studies, 3.Meteorological Research Institute, 4.Nagoya University, 5.Japan Agency for Marine-Earth Science and Technology)

Keywords:water vapor, lidar, heavy rain

Measurements of water vapor profiles are very important in the studies of atmospheric dynamics, clouds, aerosols, and radiation. Water vapor is the predominant greenhouse gas and its vertical distributions are important in the global climate system. Water vapor data would lead to benefits in numerical weather predictions, such as localized heavy rainfall events and typhoon forecasting. Passive remote sensing techniques from space provide global coverage of water vapor distribution lacking good vertical resolution, while lidar remote sensing techniques can provide water vapor distribution with high vertical resolution. The DIAL (Differential Absorption Lidar) technique is most available to perform high-resolution measurements of tropospheric water vapor distributions from space. Several researchers have proposed water vapor DIAL systems for spaceborne lidars, but have not been realized yet. We propose two-beam spaceborne water vapor DIAL with the OPA (Optical Parametric Amplifier) transmitter using the 1350-nm absorption band. OPA system using QPM (Quasi Phase Matching) device is one path amplifier, therefore OPA is advantageous for space use because it has less restrictions than conventional phase matching OPO. An error simulation is performed assuming that the platform altitude is 250km (super low altitude satellite), the receiver diameter is 0.8m, the laser energy is 20mJ, and the repetition rate of the laser shot pair (on-off) is 500Hz. It is shown that less than 10% water vapor profile measurement relative error is possible between 0-2km altitudes with spatial resolutions of 200m vertically and 20km horizontally in East Asia in summer.
We propose the spaceborne water vapor IPDA-DIAL, which is limited to low-altitude measurements using the IPDA method. Error simulations show that the IPDA-DIAL can measure water vapor from sea level to 300m altitude at night and from sea level to 500 m altitude during the daytime with an error of less than 10%, even though its specifications are lower than those of the previously proposed space-borne DIAL. Furthermore, it is shown that there is a possibility of snapshot observation of latent and sensible heat fluxes over the ocean by simultaneously measuring ocean wind velocity using scattered light from the sea surface.