The goal of the project is to develop, test, and field demonstrate a remote sensing methane (CH₄) detector for use on aircraft and vehicles to detect leaks along midstream infrastructure of the natural gas supply chain.

Princeton University, Princeton, NJ 08544 
American Aerospace Technologies, Inc., Conshohocken, PA 19428

Fugitive CH₄ leaks from the natural gas supply chain to the atmosphere mitigate the climatic benefits of switching away from other fossil fuel sources, but large measurement challenges exist in identifying and quantifying CH₄ leak rates along the vast number and type of components in the natural gas supply chain. This is particularly true of the “midstream” components of gathering, processing, compression, transmission, and storage. In contrast to sampling well pads where spatial length scales are on the order of 10 m, the length scales of midstream components are immense. Nearly 500,000 km of transmission pipelines form a complex network across the U.S., and distributed at various points along these networks are another 700,000 km of gathering pipelines, 600 processing plants, 1,400 transmission compressor stations, and 400 underground storage units nationwide.

The large areal and linear extents of midstream infrastructure create sampling challenges. Mobile laboratories are limited to the road network and favorable (downstream) wind directions when, for example, sampling processing/compressor stations. Ground‐based measurements and tracer approaches also require favorable meteorological conditions. Because significant amounts of CH₄ are emitted into the compressor station exhaust, the warmer and more buoyant plumes often will not be captured by ground‐based techniques.

To address the plume lofting and large length scales for midstream sampling, this project will develop and deploy a novel remote sensing CH₄ sensor from either light aircraft or a mobile laboratory. This will involve sensor refinement, field testing, and algorithm development; validation experiments on a vehicle and then aircraft with controlled releases of CH₄; and flights along pipeline corridors in the Mid‐Atlantic and Marcellus Shale region to demonstrate commercial readiness.

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The key innovation is heterodyne enhanced chirp modulated chirped laser absorption spectroscopy (HE‐CM‐CLaDS), an approach that uses optical dispersion rather than absorption to detect atmospheric CH₄. Instead of detecting changes in light intensity as in an absorption-based measurement like all existing optical sensors, HE‐CM‐CLaDS detects the phase shift of laser light resulting from optical dispersion. One of the key advantages to this approach is its strong signal intensity, a feature that is critical for a backscattered approach where near‐infrared light is collected from a wide range of surfaces and ground cover. Remote standoff detection means the technique will be capable of deployment on a vehicle or aircraft for large area scanning such as an overflight of a pipeline corridor or around gathering or compressor stations. Finally, HE-CM-CLaDS provides a range‐resolved signal that allows for 3D tomographic images with appropriate sampling/scanning design.

Because the HE‐CM‐CLaDS sensor can be used to send trained personnel to a specific, targeted pipeline site to fix a given leak, the anticipated benefits are saved labor and travel costs, improved pipeline safety, and reduced pipeline explosions, which will result in fewer injuries/deaths and less property damage. This will benefit pipeline companies and operators by mitigating costs associated with fines, liability, and legal fees. In addition, industry will benefit from system-wide recovery of otherwise lost product. Finally, by providing a remote sensing leak detection technology for companies, leaks along the natural gas supply chain will be mitigated more efficiently and less CH₄ (and other associated hydrocarbons) will escape into the atmosphere, resulting in improved air quality and a reduced climatic footprint.

• The CLaDS sensor and drone tracking system were deployed with the laser directed out the back of a minivan. A cylinder of 99.9% methane was used for conducting controlled release experiments (10.0±0.6 standard cubic feet per minute, scfm), and the release point was located 19.5 m downwind of the CLaDS sensor. The field data collected using the full drone retroreflector tracking are being processed and will be presented in the Final Report.

  

• The CLaDS system was deployed in a van for two field measurements: 1) a controlled methane release at an emission rate well below (0.07 g CH₄ s-1) what is typically emitted from compressor stations (7 g CH₄ s-1) and 2) direct measurements of methane leaks from a local compressor station with a throughput (208 MMcf d-1) comparable to or below industry averages (700 MMcf d-1). In both cases, plumes of methane were readily detected by CLaDS, and the field leaks were verified with an in-situ methane monitor that made transects near the beam paths. Retroreflectors were used in both experiments to precisely define the optical beam path and ensure good signal-to-noise on the backscattered light. The field performance of the instrument in terms of sensitivity was consistent with project specifications.
• The Princeton team has implemented a lower frequency acoustic optical modulator (AOM) and real-time field-programmable gate array (FPGA) processing in the HE-CLaDS system, which allows for the demodulation of both HE-CLaDS signal and direct CLaDS signal using a single FPGA platform.
• Outdoor testing and validation of system performance has been conducted on the Princeton campus. By introducing calibrated flows of CH₄ along a 5-meter long, 12-inch diameter PVC pipe, sensitivity of the system has been validated. These tests demonstrate the linearity of the system, as well as the sensitivity of the measurement to the location of the leak along the laser path.
• A portable optical system for remote sensing of CH₄ has been developed and configured into a transportable system. The system can be easily switched between conventional CLaDS and HE-CLaDS operation mode. All the preliminary lab performance results confirm that the system is on trajectory to meet the desired specification requirements that include: sensitivity of <1 ppmv-m/Hz-1/2 CH₄ in atmospheric air, range-finding resolution of <0.1 m, and optical heterodyne enhancement of at least 10 dB when compared to direct optical detection.
• Design is underway of the collecting optics to maximize power collection and allow auto-refocusing and optimal reflected signal from a moving target on an unmanned autonomous vehicle. The lens design will be integrated with the collecting optics for conventional CLaDS and the HE-CLaDS systems.

• Implemented ranging capability using a FPGA, which will be used to integrate all functions of the CLaDS system in a single data acquisition and control system. Laboratory testing of the ranging capability has been initiated to test its compatibility with various CLaDS techniques. 

The project was terminated early per the request Princeton University. Task 8.0 – Airborne flight measurements which involved using the sensor with a small unmanned aerial system to detect CH4 leaks along petrochemical facilities such as a pipeline corridor, compressor station, or refinery did not occur. Submission of the final project report is pending.

$1,141,204

$285,299

NETL – Robert Vagnetti (robert.vagnetti@netl.doe.gov or 304-285-1334)
Princeton, University – Dr. Mark A. Zondlo (mzondlo@princeton.edu or 609-258-5037)