9:15 AM - 9:30 AM
[MSD35-01] Technology demonstration of space-borne differential absorption lidar for global water vapor profiling - Simultaneous observations of sea surface wind speed -
Keywords:water vapor, lidar, sea surface wind speed
Measurements of water vapor profiles are very important in the studies of atmospheric dynamics, clouds, aerosols, and radiation. 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 proposed 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.
We also proposed 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.
Wind speeds along the ocean track were obtained using the attenuated backscatter coefficient at 1064 nm from the CALIPSO satellite. For validation, the wind speeds were compared with microwave radiometer data from AMSR-2 and observations by meteorological observation vessels. The figure shows that the microwave radiometer values are smaller than the wind speed obtained from CALPSO at locations with higher wind speeds. This is because the measurement area of the lidar is narrower than that of the microwave radiometer. On the other hand, in the relatively low wind speed region, both satellite data and ship's measurements are in good agreement, and the sea surface wind speed estimation from the sea surface scattering coefficient can be used.
We also proposed 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.
Wind speeds along the ocean track were obtained using the attenuated backscatter coefficient at 1064 nm from the CALIPSO satellite. For validation, the wind speeds were compared with microwave radiometer data from AMSR-2 and observations by meteorological observation vessels. The figure shows that the microwave radiometer values are smaller than the wind speed obtained from CALPSO at locations with higher wind speeds. This is because the measurement area of the lidar is narrower than that of the microwave radiometer. On the other hand, in the relatively low wind speed region, both satellite data and ship's measurements are in good agreement, and the sea surface wind speed estimation from the sea surface scattering coefficient can be used.