If you are evaluating backscatter LiDAR sensors for measuring aerosols, cloud vertical structure, and planetary boundary layer (PBL) heights, what factors should you consider in your comparison? It really comes down to a choice between the traditional analog technology used in ceilometers and the more recent advanced technology found in Micro Pulse LiDAR (MPL) sensors.
To select the best tool for your needs, keep in mind the following differences between MPL and ceilometers.
- Sensitivity: The most important distinction is the massive gulf in sensitivity between MPL sensors and ceilometers. MPL sensors are hundreds of times more sensitive than ceilometers, resulting in a higher signal-to-noise ratio. This valuable feature means it can “see” further through the boundary layer, through more cloud layers, all the way up to high cirrus clouds.
- Mobility: The original Micro Pulse LiDAR technology was created to return accurate cloud and aerosol data used to meet the satellite ground truth verification needs of NASA. Today, there is a mini version of the sensor that utilizes the same technology and is built to the same standards – the Mini Micro Pulse LiDAR (MiniMPL). MiniMPL is a stand-alone mobile unit that can be used on vehicles, boats, and airplanes. It achieves the same goal as the original model ‒ detecting the size and type of aerosols in the atmosphere ‒ while offering the flexibility of a smaller unit. Data from the MiniMPL are highly effective for modeling cloud content, air quality and PBL measurements. A high pulse rate allows the instrument to accumulate data at a faster rate, which is required for mobile collection. In contrast, ceilometers are large, heavy and not as easily transportable, and are typically mounted on stationary platforms for stability.
- Polarization: MPL sensors return dual polarization backscatter measurements. These data allow researchers to discriminate between the occurrence of pure water clouds and mixed phase clouds, as well as to determine particulate concentration profiles, with measurements and analyses completed and reported in seconds. Ceilometers do not offer dual polarization so the backscatter measurements are less informative and less suitable for more complex decision making.
- Complete Data Picture: Sigma Space Corp. has manufactured sensors using Micro Pulse Lidar technology for NASA since 2004. MPL and MiniMPL sensors are the only LiDAR systems approved simultaneously by NASA for use in their global atmospheric monitoring network MPLNET and by the network of 31 European National Meteorological Services that make up EUMETNET. These systems are designed to measure PBL heights and aerosol and cloud vertical structure. Data collection is continuous, day and night, around the world. MPL and MiniMPL sensors are often co-located with other types of sensors, such as sun photometers and radiometers. The incorporation of compatible data from multiple sources creates a more accurate and complete picture of the atmosphere.
- Advanced Photon Counting: MPL sensors benefit from an advanced photon-counting technology deployed for the NASA Earth Observing System (EOS) program. The photon-counting detectors have high quantum efficiency at the chosen wavelength. This improved approach to photon management leads to higher sensitivity and better results. Ceilometers use an older analog technology that relies on less stable diode-pumped lasers, whose returns are converted into an aerosol signal via their calibration. Since MPL sensors directly count every photon and bin them all by time of flight, MPL data are inherently more accurate.
The lightweight and mobile capabilities of the MiniMPL, matched with its sensitivity, provides high-quality information across the board: hazard warnings in aviation, air quality monitoring and PBL measurements. The ceilometer is a reliable and trusted provider of cloud information for aviation applications; however, sensors built using Micro Pulse LiDAR technology do everything a ceilometer does and much more.