Spectrum characteristics of multichannel water Raman lidar signals and principal component analysis

Using a multichannel full Raman lidar, water Raman signals composed of 32 different Raman wavelengths were obtained, and the time and cloud-height dependences of each spectrum on clear and cloudy days were determined. Although the Raman signals of winter cloud have a higher intensity at short wavelengths than those of summer cloud, these two types of clouds have large overlapping regions in wavelength space. However, in eigenvector space, winter and summer clouds are located at different points and have no overlapping regions. We have suggested that, as a cloud Raman lidar, a multiple-wavelength Raman lidar must be used, and the principal component analysis (PCA) method should be applied to determine the relative amount of each water phase.