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High-Altitude, Aerial Natural Gas Leak Detection System
Project Number

The goal of this project is to develop a Remote Methane Leak Detector (RMLD) system for standoff sensing, from high altitudes, of natural gas distribution and transmission pipeline leaks.


Physical Sciences, Inc. (PSI) - Andover, MA

Heath Consultants, Inc. - Houston, TX


The U.S. natural gas transmission system consists of about 250,000 miles of pipeline, 1,700 transmission stations, and 17,000 compressors. Maintaining the security and integrity of this system is a continual process of searching for, locating, and repairing leaks. Performing leak surveys is very labor-intensive, in part because all currently used leak survey tools, including the traditional combustible gas indicators (CGI) and flame ionization detectors (FID), as well as the relatively new optical methane detection (OMD) tool, must be physically immersed within a leak plume to detect it. CGI and FID tools both draw gas into a combustion chamber and analyze the products of combustion to quantify local gas concentrations. The OMD projects an infrared beam across a short (~1 m) optical path open to the ambient air (“short-path”) and determines by spectroscopy the concentration of gas within the optical path. The short optical path must encompass the gas to detect it. Short-path Tunable Diode Laser Absorption Spectroscopy (TDLAS), configured optically like an OMD but with better sensitivity, has been utilized for leak detection.

These techniques can and have been used for airborne leak surveying. To perform these surveys, a light airplane or helicopter flies no higher than a few hundred feet above the pipeline. Significant leaks create a plume that is intercepted by the aircraft and detected by the on-board instrumentation.

Airborne natural gas sensor component schematic
Airborne natural gas sensor component schematic

The RMLD is a novel configuration of the highly sensitive and selective TDLAS. It projects onto a distant surface the infrared beam emitted by a telecommunications-style diode laser. An optical fiber cable connects the laser to the transceiver, which transmits the beam and receives scattered laser light. It senses the path-integrated concentration of methane between the transceiver and the illuminated surface. Because the RMLD is intended for use in walking leak surveys, it was designed to be handheld, lightweight, and power efficient. To accommodate these attributes, the sensor has a maximum range of about 100 feet, making it unsuitable for leak surveying from an aircraft. The current project will enhance the RMLD technology capability, extending its range to several thousand feet in a fashion that can be further extended to tens of thousands of feet, thereby enabling rapid airborne survey of large areas.


This leak detection technology will ultimately be capable of operating at heights of 50,000 feet and greater. High-altitude natural gas leak detection could provide an efficient and cost-effective means of continuously monitoring, in real time, fugitive gas emissions from the entire natural gas pipeline infrastructure.

Accomplishments (most recent listed first)

Project researchers have:

  • Completed and submitted the project Research Management Plan.
  • Completed and submitted the Technology Status Assessment.
  • Completed and submitted preliminary specification documentation.
  • Completed work to define the final specifications and design of the high-altitude leak detection sensor. The seed laser has been acquired and installed on the RMLD platform. A preliminary configuration for the airborne system design has been created.
  • Completed tasks for assembly and testing of the airborne sensors.
    • Spectral analysis, wavelength selection, and sensitivity estimate.
    • Amplifier selection and characterization.
    • Aircraft selection.
    • System specification.
    • Optical components selection.
    • Optical components configuration.
    • Seed laser testing.
    • DMD algorithm development.
    • Receipt of the optical fiber laser amplifier and characterization the amplifier performance.
    • Evaluation of methane detection limits of the amplified RMLD.
    • Assembly and alignment of the high-altitude optical transceiver.
    • Combination of the transceiver and amplified laser to form the complete sensor system.
  • Completion of outdoor system tests.
  • Completion of preparation for a system flight test, including coordination with a local transmission pipeline operator (however, the original pipeline operator pulled out of test, and a new operator could not be found).
  • Completion of an alternative test (simulating the flight test) using a methane-filled plastic bag mounted on a automobile driven through the methane sensor detection beam at speeds comparable to a slow-flying aerial survey aircraft.
  • Completion of verification of the capability for leak detection from an aircraft and demonstrate that altitude scaling expectations functioned as predicted.
Schematic of High-altitude Leak Detection System
Schematic of High-altitude Leak Detection System
air photo

Cessna 207 - Cabin with photographic equipment installed, and exterior view of camera port. The 207 has a factory-installed penetration of 22 inches in diameter, large enough to accommodate our initial transceiver design that incorporates a 10” diameter receiver and components to be mounted around the receiver.

Researchers utilized and extended the technology embedded within the handheld, battery-powered, laser-based RMLD product PSI developed to build and demonstrate a system for standoff sensing of natural gas distribution/transmission pipeline leaks. The solid-state, near-infrared lasers within RMLD were enhanced with scalable, high-power optical fiber amplifiers to provide a compact, power-efficient sensor designed for future application on an aerial platform. The project called for researchers to design, assemble, and flight test a prototype sensor intended to have an operational ceiling of 10,000 feet. Due to issues with the pull out of the gas company participating in the aerial flight leak test, a ground based test was used to test the system at conditions simulating low altitude aerial leak detection allowing evaluation of potential for scale up to high altitude capabilities. The system was designed and built to enable the RMLD to be used in the airborne platform as originally intended. In order to do so, three aspects of the system were modified: 1) the transmitted laser power was increased by use of an optical fiber amplifier, 2) the size of the optical receiver was increased, and 3) the laser wavelength was changed.

In conclusion PSI has designed and assembled a prototype airborne remote methane leak detector (aRMLD) sensor suitable for insertion and testing in a survey-capable aircraft. They have completed a study of the performance characteristics of the simultaneously enabling and limiting component of the sensor system, an erbium-doped fiber amplifier (EDFA) and its impact on the wavelength modulation spectroscopy (WMS) detection technique. While the EDFA performance was not as good as had been expected prior to this program, the knowledge gained from this work is very valuable for identifying characteristics that will enable future performance improvements. The contractor has performed an extensive set of ground-based measurements with the prototype system, both amplified and unamplified for characterization purposes and also in a simulation of a low-altitude leak survey scenario. PSI and their cost share partner, Heath Consultants, have received significant interest in a lowaltitude version of the airborne RMLD, one that surveys transmission pipelines from a helicopter flying at altitudes of ~500 ft AGL. This can be accomplished, as demonstrated, without the EDFA, but coupled with the large transceiver developed for the high-altitude RMLD. PSI and Heath are discussing means for addressing this opportunity.

Current Status

All research under this effort is complete. The final project report is available below under "Additional Information".

The project was funded under a 2004 DOE solicitation, announced in December 2004, that covered a broad range of oil and natural gas exploration and production technologies as well as those for natural gas delivery reliability.

Project Start
Project End
DOE Contribution


Performer Contribution


Contact Information

NETL – Richard Baker ( or 304-285-4714
Physical Sciences, Inc. (PSI) – David Green (, 978-738-8146)

Additional Information

Final Report [PDF-3.26MB] December, 2006

Pertinent Publications:
“Extending Optical Methane Leak Detection to Mobile Platforms”, B. D. Green, M. B. Frish, and M. C. Laderer, Physical Sciences Inc.; G. Midgley, Heath Consultants Inc., Proceedings of “Natural Gas Technologies 2005”, Orlando, FL, January 30 – February 2, 2005.