A study on planetary atmosphere by the laser heterodyne spectroscopy

激光外差光谱技术具有光谱分辨率高、空间分辨率高、信噪比高等优点，是行星大气遥感中最有效的技术。本研究开发了一种用于行星大气观测的宽光谱范围可调谐半导体激光外差光谱仪。首先，研制了一台小型的可调谐半导体激光外差光谱仪，用于将行星大气的红外发射或吸收光谱转换到无线电波频率范围内。此外，还研制了一台声光射电光谱仪，以获得转换后的无线电频率范围内的光谱，然后，制作了一个光学系统，与空间和航天科学研究所的红外望远镜连接，用于观测金星大气层，以测试仪器。然而，由于红外望远镜的故障，原定1997年11月进行的观测未能进行。然后于1998年4月在国家天文台红外模拟器上进行了试验观测。最后，为了验证仪器的性能，进行了实验室测试和以太阳或月球为光源的地球大气观测。这些测试表明，光谱仪的信噪比是不够的，而月球观测表明，弱红外光谱可以用这种仪器测量。目前正在对该仪器进行改进，并将再次对行星大气层进行试验观测。

Laser heterodyne spectroscopy is the most powerful technique for remote sensing of planetary atmosphere because of its high spectral resolution, high spatial resolution, and high signal-to-noise ratio. In this study, a new tunable diode laser heterodyne spectrometer with a wide spectral range has been developed for planetary atmosphere observation.First, a small-sized laser heterodyne spectrometer with four tunable laser diodes was developed to covert the infrared emission or absorption spectra from planetary atmosphere into the radio wave frequency range. An acousto-optic radio spectrometer was also developed to obtain the spectra in the converted radio frequency range.Next, an optics for interface with the infrared telescope of the Institute of Space and Astronautical Science was made to observe the Venusian atmosphere for testing the instrument. However, observation scheduled in November 1997 was not carried out because of the trouble of the infrared telescope. Then the test observation was carried out with the infrared simulator of National Astronomical Observatory in April 1998. However, the infrared spectra of the Venusian atmosphere were not obtained because of bad weather.Finally, laboratory test and observations of the Earth's atmosphere using the sun or the moon as a light source were performed to check the performance of the developed instrument. These tests revealed that the signal-to-noise ratio of the spectrometer is not enough, while the moon observation demonstrated that weak infrared spectra can be measured with this instrument. The instrument is now under improvement and test observation of the planetary atmosphere will be performed again.