Eye safe lidar and passive EO sensing for cloud monitoring

摘要

This study has investigated the use of an eye safe lidar (1550 nm) with equivalent performance of an ordinary military laser range finder for cloud monitoring. The aim was to combine lidar data with camera images in the visible, short wave infrared (SWIR) and infrared (IR) to better estimate the cloud density and cloud coverage. The measurement was concentrated on low clouds, mostly of the cumulus type. We found that these clouds between 0-2 km often showed a layered structure and that they often indicated a limited optical density probably allowing for observation through the cloud. This information is hard to achieve from a passive EO sensor only. This was supported both from the simulation of the lidar response from thin clouds and from inverting the measured lidar waveform. The comparison between the camera image intensities and the integrated range corrected lidar signals showed both negative and positive correlations. The highest positive correlation was obtained from comparing the lidar signal with the cloud temperature as derived from the FLIR camera. However, there were many cases when one or two of the camera intensities correlated negatively with the lidar signal. We could for example observe that under certain conditions the cloud which was dark in the SWIR appeared as white in the visible camera and vice versa. Example of lidar and image data will be presented and analyzed.