Optical designs for improving performances of aerosol sensing micro-pulse lidars

This paper addresses current design improvement issues of aerosol sensing Micro-Pulse Lidars (MPL). MPLs are designed to adhere to eye-safety restrictions while achieving acceptable signal to noise ratios (SNR). This method is realized by reducing the per pulse energy of the laser and employing a narrow receiver field-of-view (FOV). Due to the narrow FOV requirement, only a partial return signal is measured until the laser beam propagates a distance where the receiver FOV fully overlaps the laser beam. This is called the full overlap distance and is usually 4 km or more for reasonable MPL parameters. Accurate MPL measurements are typically only possible beyond this distance. The fraction of laser beam energy that is within the receiver FOV versus range is called the overlap function. The causes of the overlap function are discussed. An overlap related problem with current MPL designs is that the majority of the atmospheric aerosols are located below a altitude of 4 km to 5 km, within the partial overlap region. Another problem is that the overlap function is not thermally constant. This introduces errors in the experimentally derived overlap function and system constant factor, ultimately leading to errors in the retrieved lidar signal.