Micro Pulse LiDAR: A Critical Tool for Emission Source Detection
Micro Pulse LiDAR remote sensing data are used to calculate a highly accurate Planetary Boundary Layer (PBL) height to improve plume models that help assess emissions sources.
Poor air quality is a growing health issue that has a negative impact on the quality of life for millions of people. To help alleviate this serious problem, scientists at Bubbleology Research International (BRI) have developed an approach that combines data from multiple instruments to better understand pollution (gases and aerosols) sources and their movements in the atmosphere. In a recent emissions study, BRI used aerosol profile data in a plume inversion model to more accurately assess emissions related to oil production.
A key contributor to improvements in the plume inversion model is the Planetary Boundary Layer (PBL) height. The PBL acts like a cap, trapping pollutants in the atmospheric layer nearest the Earth’s surface. The PBL can grow to a height of thousands of meters during the day and collapse to 100 m or less at nighttime, varying spatially based on micro-climate. Real-time vertical profile data provides accurate PBL height, greatly improving the accuracy the plume model.
The Micro Pulse LiDAR (MPL) scanning system provides the most accurate information about the PBL by detecting and measuring the size and type of particles in the atmosphere in a vertical swath up to 15 kilometers high. By studying the movement of the emissions plume in relation to the PBL, wind direction and other factors, pollution sources are more easily identified.
“Observations show that plumes from a pipeline leak or other source diffuses vertically until it hits the PBL and reflects,” says Dr. Ira Leifer, chief scientist and CEO of BRI. “Without knowing where the PBL is, we can’t locate the leak precisely if we are too distant from the source. By improving the accuracy of the inversion plume calculations, we can better pinpoint the source and also improve exposure estimates for use in health effects studies.”
A MiniMPL sensor is one of 23 scientific instruments integrated into an innovative mobile platform called AMOG (AutoMObile trace Gas) Surveyor, built by BRI. BRI is a technology development and environmental consulting firm based in Southern California. AMOG is a passenger car modified with sensors that make a total of 31 measurements, including 13 trace gases, meteorology, solar spectra, and other parameters. All these data are collected while moving at normal driving speeds. BRI installed the portable MiniMPL system, weighing only 13 kg and using less than 100 W of energy, onto the mobile air quality lab’s roof, in its own special weatherproof housing.
“There is no other surface platform comparable to AMOG,” says Leifer. “Its many instruments provide a more complete picture of the atmosphere, and here in California, we can often conduct vertical atmospheric profiling with AMOG just by driving up a mountain – no airplane needed.”
In an emissions detection campaign in California focusing on natural gas leaks, BRI used local topography to validate the vertical structure revealed in the MiniMPL aerosol profile data. Finding the PBL height by mobile surface in situ measurements can be done if hills or mountains and roads are accessible nearby that rise above the PBL. BRI has conducted additional validation by comparing surface data collected on AMOG with a GRIMM aerosol size analyzer operated at the same time as the Mini-MPL, as well as comparing with concurrent airplane data.
BRI’s field tests demonstrate the ability of Hexagon’s MiniMPL sensor to provide accurate, real-time PBL height. “The MiniMPL has a better signal-to-noise ratio than other instruments, such as ceilometers, which improves our derivation of PBL height,” explained Leifer. By combining the PBL with a wide range of other measurements collected by sensors on AMOG, such as wind speed, wind direction and water vapor, researchers generate more accurate plume inversion models and thus have increased confidence in emission detection and quantification.
In addition to this mobile real-time solution, BRI and Hexagon recognize the need for semi-permanent/portable air quality stations at industrial sites, petroleum production and storage facilities, and mines to comply with increasingly stringent air quality regulations. By combining existing technology, a low maintenance, highly reliable solution is feasible in the future.