Optical Remote Sensing of Fugitive Releases

• US 20110309248A1
• Filed: 06/20/2011
• Published: 12/22/2011
• Est. Priority Date: 06/21/2010
• Status: Active Grant

• Current Assignee: United States Environmental Protection Agency
• Original Assignee: The Agency, United States Environmental Protection Agency
• Inventors: Thoma, Eben Daniel, Secrest, Cary Doman, Mitchell, William A., Squier, William C.
• Granted Patent: US 8,445,850 B2
• Time in Patent Office: Days
• US Class Current: 250/339.06
• CPC Class Codes: G01J 1/0407 Optical elements not provided otherwise, e.g. manifolds, windows, holograms, gratings
• CPC Class Codes: G01J 1/0411 using focussing or collimating elements, i.e. lenses or mirrors; Aberration correction
• CPC Class Codes: G01J 1/4228 arrangements with two or more detectors, e.g. for sensitivity compensation
• CPC Class Codes: G01J 1/429 applied to measurement of ultraviolet light using counting tubes G01T

Abstract

Disclosed is an open-path optical sensor. Typically, the optical sensor directs UV radiation from a source assembly to a detector assembly along a monitoring path. The source assembly emits UV radiation corresponding to a signal channel and to a reference channel. The detector assembly detects UV radiation corresponding to the signal channel and to the reference channel. The detector assembly is in communication with a data acquisition system, which compares the intensity of the detected UV radiation corresponding to the signal channel to the intensity of the UV radiation corresponding to the reference channel.

Claims

1. An open-path optical sensor, comprising:

a source assembly, said source assembly emitting UV radiation corresponding to a signal channel; and

a detector assembly for receiving UV radiation emitting by said source assembly, said detector assembly comprising a first detector for detecting UV radiation corresponding to the signal channel;

wherein said first detector comprises a band-pass filter for rejecting UV radiation outside of the signal channel;

wherein the signal channel is a wavelength or range of wavelengths between about 170 nanometers and 230 nanometers.

2. An open-path optical sensor according to claim 1, wherein:

said source assembly emits UV radiation corresponding to the signal channel and a reference channel; and

said detector assembly comprises (i) a second detector for detecting UV radiation corresponding to the reference channel, and (ii) a data acquisition system in communication with said first detector and said second detector;

wherein said second detector comprises a band-pass filter for rejecting UV radiation outside of the reference channel;

wherein said data acquisition system calculates the ratio of (i) the intensity of the UV radiation corresponding to the signal channel to (ii) the intensity of the UV radiation corresponding to the reference channel;

wherein the reference channel is a wavelength or range of wavelengths between about 260 nanometers and 300 nanometers.

3. An open-path optical sensor according to claim 2, comprising a reflector for directing UV radiation emitted by said source assembly to said detector assembly.

4. An open-path optical sensor according to claim 3, wherein said source assembly and said detector assembly are positioned in a monostatic configuration.

5. An open-path optical sensor according to claim 4, comprising:

a plurality of reflectors for directing UV radiation emitted by said source assembly to said detector assembly, each of said reflectors being positioned at one end of a different monitoring path, said detector assembly being positioned at the other end of each monitoring path; and

a positioning device, said source assembly and said detector assembly being mounted on said positioning device, wherein said positioning device is capable of reorienting said source assembly and said detector assembly between the monitoring paths.

6. An open-path optical sensor according to claim 4, comprising:

a plurality of reflectors for directing UV radiation emitted by said source assembly to said detector assembly, each of said reflectors being positioned at one end of a different monitoring path, said detector assembly being positioned at the other end of each monitoring path; and

a gimbal mirror, said gimbal mirror being positioned to direct UV radiation from said source assembly to one of said reflectors and back to said detector assembly, wherein said gimbal mirror is capable of being reoriented between the monitoring paths.

7. An open-path optical sensor according to claim 2, wherein said source assembly and said detector assembly are positioned in a bistatic configuration.

8. An open-path optical sensor according to claim 7, comprising:

a plurality of source assemblies for emitting UV radiation toward said detector assembly, each of said source assemblies emitting UV radiation corresponding to the signal channel and the reference channel, wherein each of said source assemblies is positioned at one end of a different monitoring path, said detector assembly being positioned at the other end of each monitoring path; and

a positioning device, said detector assembly being mounted on said positioning device, wherein said positioning device is capable of reorienting said detector assembly between the monitoring paths.

9. An open-path optical sensor according to claim 2, wherein said source assembly emits collimated UV radiation.

10. An open-path optical sensor according to claim 2, wherein said source assembly emits UV radiation at a regular pulse frequency.

11. An open-path optical sensor according to claim 10, wherein said detector assembly comprises a lock-in amplifier for eliminating UV radiation not having the same regular pulse frequency as the UV radiation emitted by said source assembly.

12. An open-path optical sensor according to claim 2, wherein said detector assembly comprises a beam splitter for directing UV radiation to said first detector and to said second detector.

13. An open-path optical sensor according to claim 2, wherein said first detector is a photomultiplier tube and said second detector is a photomultiplier tube.

14. An open-path optical sensor according to claim 2, wherein:

the signal channel is a wavelength or range of wavelengths between about 200 nanometers and 210 nanometers; and

the reference channel is a wavelength or range of wavelengths between about 270 nanometers and 290 nanometers.

15. An open-path optical sensor according to claim 2, wherein:

the signal channel is a wavelength of about 205 nanometers; and

the reference channel is a wavelength of about 280 nanometers.

16. A pollution monitoring system, comprising:

a plurality of optical sensors according to claim 2; and

a controller in communication with said optical sensors, said controller analyzing data provided by said optical sensors to determine pollution characteristics.

17. A method of monitoring pollutant concentrations, comprising:

emitting UV radiation corresponding to a signal channel along a monitoring path, the signal channel being a wavelength or range of wavelengths between about 170 nanometers and 230 nanometers;

emitting UV radiation corresponding to a reference channel along the monitoring path, the reference channel being a wavelength or range of wavelengths between about 260 nanometers and 300 nanometers;

detecting the intensity of the UV radiation corresponding to the signal channel after the UV radiation has traversed the monitoring path;

detecting the intensity of the UV radiation corresponding to the reference channel after the UV radiation has traversed the monitoring path; and

calculating the ratio of the intensity of the UV radiation corresponding to the signal channel to the intensity of the UV radiation corresponding to the reference channel.

18. A method of monitoring pollutant concentrations according to claim 17, comprising:

emitting UV radiation corresponding to the signal channel along the monitoring path at a regular pulse frequency;

emitting UV radiation corresponding to the reference channel along the monitoring path at the regular pulse frequency;

filtering the UV radiation to eliminate UV radiation not having the same regular pulse frequency as the emitted UV radiation; and

filtering the UV radiation to eliminate UV radiation not corresponding to either the signal channel or the reference channel.

19. A method of monitoring pollutant concentrations according to claim 17, wherein:

the signal channel is a wavelength or range of wavelengths between about 200 nanometers and 210 nanometers; and

the reference channel is a wavelength or range of wavelengths between about 270 nanometers and 290 nanometers.

20. An open-path optical sensor, comprising:

a source assembly, said source assembly emitting infrared radiation corresponding to a signal channel and a reference channel; and

a detector assembly for receiving infrared radiation emitting by said source assembly, said detector assembly comprising (i) a first detector for detecting infrared radiation corresponding to the signal channel, (ii) a second detector for detecting infrared radiation corresponding to the reference channel, and (iii) a data acquisition system in communication with said first detector and said second detector;

wherein said data acquisition system calculates the ratio of the intensity of the infrared radiation corresponding to the signal channel to the intensity of the infrared radiation corresponding to the reference channel;

wherein the signal channel is a wavelength or range of wavelengths between about 2.9 microns and 3.2 microns;

wherein the reference channel is a wavelength or range of wavelengths (i) between about 2.8 microns and 2.9 microns or (ii) between about 3.2 microns and 3.3 microns.