Micro Pulse Lidar: Perfect Tool for Atmospheric Research
Micro pulse style lidars are active remote sensing tools proven to be highly useful in atmospheric research. This style of backscatter lidar has been around for decades; however, incremental improvements in photon counting, sensitivity, polarization, optical filters, coatings, and precision machining of each element support increasingly accurate analysis. Each iteration of the sensor provides a clearer “picture,” in much the same way that today’s ultra-high-definition televisions build on many years of technology development. The original analog CRT devices were severely limited in resolution, color and sharpness, compared to modern digital televisions that offer faster processes, extremely high resolution, and incredibly sharp images. Our technology is following a similar successful trajectory.
With our MPL and MiniMPL instruments we are currently gaining more attention in atmospheric research by focusing on particle type, size, transport and mass concentration at range. The detailed atmospheric feature information (such as Planetary Boundary Layer) is highly valuable as a means of improving the accuracy of emission flux estimates and refining atmospheric research models and forecasts.
Designed with the End Goal in Mind
The first generation of micro pulse lidar technology was designed by NASA for detecting high cirrus clouds. Our subsequent commercial “Micro Pulse LiDAR” generations (MPL and MiniMPL) have evolved with the goal of making the most cost-effective, robust, and sensitive backscatter lidar possible. This has been achieved by using quality lasers, rigid optics, and a narrow field of view (FOV), all of which contribute to stability, precision and accuracy.
Image of MiniMPL, in enclosure with 3D scanner, at Himalayan base camp
Our Micro Pulse LiDARs use photon-counting detectors with high quantum efficiency at the chosen wavelength, coupled with high pulse rate, lower energy per pulse lasers. When combined with extremely stable optics this efficient approach to photon management leads to much higher sensitivity than big pulse alternatives. In comparison, millipulse technologies use low pulse rate, high energy per pulse lasers. This often means higher instrument power requirements and larger physical units. Big lasers also tend to overheat and require more labor-intensive cooling systems. Required periods of time when units are switched off to cool make them undesirable as part of early warning systems.
Continuous collection of co-polarized and cross-polarized backscattered light is an important distinction of the MPL and MiniMPL systems. Because aerosol particle shapes interact with the polarization states differently the ratio of these interactions can be used to classify scatter from distinct classes of aerosols. This allows the instruments to distinguish Saharan dust from volcanic ash or pollen for example.
The choice of wavelength determines the day/night performance and minimum size of aerosols that can be detected. Today MPL and MiniMPL use a visible green wavelength of 532 nm, selected because of its superior ability to detect fine aerosols and penetrate through moisture.