US 6,664,533 B1 · Apparatus and method of remote gas trace detection

Abstract

This specification discloses a method and apparatus for the mobile and remote detection of a gas, such as methane, in the atmosphere. The apparatus includes a TDL based Light Detection and Ranging (LIDAR) driven at carrier frequency lying within the absorption line of the gas. The apparatus also drives the TDL with a modulation frequency to generate upper and lower sidebands in the output of the TDL and with a low ramp frequency to sweep the output of the TDL across twice the width of the pressure-broadened absorption line of the gas, preferably the first overtone absorption line in the case of methane detection. The apparatus include reference and calibration cells or chambers, and includes a light collector and detectors to detect the quantity and modulation of the light that passes the reference or calibration cells and that is received by the apparatus after reflection back toward the apparatus from an uncooperative target. The apparatus further includes a signal processor that applies a derivative spectroscopy technique, such as frequency modulation spectroscopy or wavelength modulation spectroscopy, to determine the presence of the gas in the atmosphere.

Claims22

Dependent claims

A method of remotely detecting a particular gas dispersed in the atmosphere, the dispersed gas being of the type that absorbs light at frequencies within an absorption line range for the dispersed gas in the atmosphere, the method comprising the steps of:

driving a source of generally monochromatic light by a laser drive to provide a carrier output at a predetermined frequency;
frequency modulating the laser drive with a modulation frequency to generate at least one frequency modulated sideband signal in the output of the light source;
and
adding to the laser drive a ramp frequency to scan the light source and the sideband signal across a scan range including at least a portion of the absorption line range;
directing at least a test portion of the ramped and modulated light toward an uncooperative target;
collecting light reflected from the uncooperative target and directing it toward a first detector to generate at least one test signal based on the degree of attenuation of the sideband signal by the dispersed gas;
and
generating an output indicative of an amount of the dispersed gas in the atmosphere, if any, based on the at least one test signal.

5 more elements

A method of remotely detecting a particular gas dispersed in the atmosphere, the particular gas being of the type that absorbs light at frequencies within an absorption line range for the particular gas in the atmosphere, the method comprising the steps of:

A. applying direct current to a tunable diode laser in order to generate a source of generally monochromatic light driven to provide a carrier output frequency within the absorption line range;
B. frequency modulating the output of the laser drive with a modulation frequency to generate at least one upper sideband signal and one lower sideband signal;
and
C. adding to the laser drive a ramp frequency to scan the sideband signals across a scan range so that at least one of the sideband signals scans at least a portion of the absorption line range;
D. directing the ramped and modulated light toward an uncooperative target;
E. collecting the ramped and modulated light reflected from the uncooperative target toward a first detector to generate at least one test signal based on the degree of attenuation of at least the one sideband signal by the particular gas;
and
F. generating an output indicative of an amount of the particular gas in the atmosphere, if any, based on the at least one test signal.

5 more elements

Dependencies are inferred from the claim text.

Apparatus and method of remote gas trace detection

Life of this patent

Apparatus and method of remote gas trace detection

Life of this patent

Abstract

Claims22