Abstract
We have studied a ground based coherent differential absorption LIDAR (DIAL) for vertical profiling of water vapor density using a 1.5μm laser wavelength. A coherent LIDAR has an advantage in daytime measurement compared with incoherent LIDAR because the influence of background light is greatly suppressed. In addition, the LIDAR can simultaneously measure wind speed and water vapor density. We had developed a wavelength locking circuit using the phase modulation technique and offset locking technique, and wavelength stabilities of 0.123 pm which corresponds to 16 MHz are realized. In this paper, we report the wavelength locking circuits for the 1.5 um wavelength.
Highlights
Water vapor in the atmosphere affects growing cumulonimbus which cause localized heavy rainfall, the measurement of water vapor density profile is required for the early prediction of this rainfall
In the band of optical amplifier, the strong line intensity is in shorter wavelength for 1520 nm - 1570 nm range, and the value is 3.066×10-24 at 1531.374 nm wavelength
One of the CW lasers is locked to the HCN R18 absorption line (1531.276 nm) by the phase modulation technique and the other CW laser is locked to the water vapor absorption line by the offset locking technique
Summary
Water vapor in the atmosphere affects growing cumulonimbus which cause localized heavy rainfall, the measurement of water vapor density profile is required for the early prediction of this rainfall. Height profiling of water vapor measurement using incoherent DIAL technique was reported in Ref. 1 and 2. Coherent DIAL technique can overcome this issue and was reported in Ref. 3 and 4. Good agreement result on water vapor density in comparison with that of radiosonde soundings was shown. Since late 1990s, we have been developing a wind sensing coherent Doppler LIDARs with 1.5 μm wavelength. The LIDAR with 1.5 μm wavelength has advantages such as its compactness and reliability by using telecom products. We consider to apply this technology to DIAL, and perform preliminary study on a ground based coherent DIAL for vertical profiling of water vapor density using a 1.53 μm laser wavelength. We discuss the concept, configuration, and simulation results of the LIDAR
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