Natural gas leak mapper
Inventors
Reichardt, Thomas A. • Luong, Amy Khai • Kulp, Thomas J. • Devdas, Sanjay
Assignees
National Technology and Engineering Solutions of Sandia LLC • Sandia National Laboratories
Publication Number
US-7375814-B2
Publication Date
2008-05-20
Expiration Date
2025-03-11
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Abstract
A system is described that is suitable for use in determining the location of leaks of gases having a background concentration. The system is a point-wise backscatter absorption gas measurement system that measures absorption and distance to each point of an image. The absorption measurement provides an indication of the total amount of a gas of interest, and the distance provides an estimate of the background concentration of gas. The distance is measured from the time-of-flight of laser pulse that is generated along with the absorption measurement light. The measurements are formated into an image of the presence of gas in excess of the background. Alternatively, an image of the scene is superimosed on the image of the gas to aid in locating leaks. By further modeling excess gas as a plume having a known concentration profile, the present system provides an estimate of the maximum concentration of the gas of interest.
Core Innovation
The invention describes a backscatter absorption gas mapping system designed to detect the presence and location of gases that have a background concentration within an environment. The system achieves this by scanning a focused laser beam across a scene and measuring both the absorption of light by the gas and the distance to each point on the surface using time-of-flight measurements of laser pulses. This approach allows the system to differentiate excess gas concentrations from the background by combining absorption and distance data to form an image representing the gas presence above the ambient levels.
The system addresses the challenges associated with detecting gases like methane that are invisible and often occur at low concentrations alongside a natural background amount. Existing methods require manual, point-based detection that is labor-intensive and inefficient. The invention overcomes limitations of prior art backscatter absorption gas imaging (BAGI) systems such as signal noise from laser speckle, variations in backscatter surface properties, and the inability to correct for background gas concentration and varying distances between the sensor and backscatter surfaces.
By integrating an optical unit capable of producing tunable or multiple wavelengths of light, including at least one wavelength absorbed by the gas of interest, and a range measurement system that determines distance via round-trip time-of-flight of laser pulses, the system corrects absorption measurements for background concentration based on the path length. The processor constructs images that may include a superimposed view of the scene to visually locate gas leaks. Furthermore, modeling excess gas as a localized plume with a known concentration profile enhances the system's ability to estimate maximum concentrations of gases like methane in the environment.
Claims Coverage
The patent claims cover a system with multiple inventive features related to backscatter absorption gas measurement combined with range measurement for imaging gases with a background concentration. Three main inventive features can be identified from the independent claims.
Backscatter absorption gas measurement system with alternating multi-wavelength beams including distance measurement
An apparatus generates multiple light pulses in alternating sequences, where beams comprise a first wavelength absorbed by the gas of interest and second and third wavelengths used for absorption and range measurements. The range measurement is determined from the round-trip time-of-flight of light pulses at the first wavelength. A processor combines absorption and distance data to indicate gas presence in excess of background concentration, producing an image composed of pixels each sufficiently illuminated to allow absorption and distance determination.
Use of off-wavelength light to produce an image of the scene
The system includes measuring the intensity of backscattered light at a first wavelength that is not absorbed by the gas of interest. The processor uses this measured intensity to construct an image of the scene, which is then presented on a display, optionally formatted with distance information to enhance image quality.
Incorporation of optical parametric frequency converter for wavelength generation
The backscatter absorption gas measurement system incorporates an optical parametric frequency converter to generate the different required wavelengths of light used for absorption and range measurements, enabling precise wavelength selection tailored to the gas of interest.
Overall, the claims focus on combining multi-wavelength backscatter absorption measurement with range measurements via time-of-flight to correct for background gas concentration and varying distances, and on generating images of both gas presence and the scene. These inventive features allow accurate, robust detection and localization of gases with natural background concentrations, such as methane.
Stated Advantages
Provides portable, robust imaging of gas leaks above background concentrations remotely, reducing labor intensity compared to point measurement devices.
Corrects for variations in optical path length due to surface distance and background gas concentration enhancing measurement accuracy.
Reduces noise effects such as laser speckle and variations in laser intensity and surface reflectivity by scanning and normalizing measurements.
Enables superimposing of a scene image with gas presence image to aid in locating leaks effectively.
Allows estimation of maximum gas concentration in plumes using a known concentration profile model, improving quantitative assessment.
Documented Applications
Detection and mapping of natural gas leaks, particularly methane leaks, in distribution networks including buried piping where gas migrates through soil and fractures to the surface.
Rapid detection and tracking of hazardous gaseous leaks in atmospheric environments for public safety and health enhancement.
Remote real-time imaging of low concentration gases in the environment with a background concentration for leak location and extent assessment.
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