Mapping air contaminants using path-integrated optical remote sensing with a non-overlapping variable path length beam geometry

• US 6,542,242 B1
• Filed: 05/10/2000
• Issued: 04/01/2003
• Est. Priority Date: 05/10/1999
• Status: Active Grant

• Current Assignee: University of Washington
• Original Assignee: University of Washington
• Inventors: Yost, Michael G., Hashmonay, Ram A.
• Primary Examiner(s): Turner, Samuel A.
• Application Number:
  US09/569,575
• Time in Patent Office: 1,056 Days
• Field of Search: 356/450, 356/451, 356/437, 356/438, 250/338.5, 250/339.8, 250/343, 250/344, 250/345
• US Class Current: 356/450
• CPC Class Codes: G01N 2021/1793 Remote sensing
• CPC Class Codes: G01N 2021/3513 Open path with an instrumental source
• CPC Class Codes: G01N 2021/3595 using FTIR
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

Path Integrated Optical Remote Sensing (PI-ORS) instruments are used to provide Path Integrated Concentration (PIC) data corresponding to a particulate concentration in region scanned by a sequence of optical beams. Prior art methods of developing spatial concentration maps using PIC data have required a relatively large number of intersecting beam paths. The present invention can produce spatial concentration maps using considerably fewer optical beams. Preferably, a non-overlapping radial beam geometry is used to produce PIC data that are processed to produce a spatial concentration map. The PIC data are indicative of the cumulative spatial concentration distribution of the contaminant in the sampling region. Once the PIC data are obtained, a specifically developed reconstruction algorithm is applied to the PIC data to create a map of concentration or contaminants or other constituents in the sampling region. Any of several different reconstruction algorithms can be employed. In general, a method for fitting or interpolating is used to estimate the cumulative distribution function of the contaminants or constituents of interest over the sampling region from the observed PIC data. Continuous or spline functions can be used in the reconstruction algorithm. Preferably, a smooth basis function minimization (SBFM) algorithm is used to fit a superposition of the integrated basis functions to the PIC data. The evaluation of the directional derivatives for the fitted integrated (cumulative) basis functions provides the desired map of concentration values over the sampling region. Using far fewer sources and detectors than the prior art, reasonably accurate concentration mappings can be achieved.

Claims

1. A method of mapping a property associated with a sampling region using path integrated data, comprising the steps of:

(a) defining a sampling region in which at least one property associated with said sampling region will be mapped;

(b) acquiring path integrated data for a plurality of paths within said sampling region;

(c) reiteratively generating a cumulative distribution function of said at least one property associated with said sampling region from said path integrated data; and

(d) using said cumulative distribution function to produce a map of said property for the sampling region.

2. The method claim 1, wherein the step of acquiring path integrated data for a plurality of paths comprises the step of directing energy along the plurality of paths, such that at least one path terminates within said sampling region, and at least one different path extends to at least a boundary of said sampling region.

3. The method of claim 1, wherein the step of acquiring path integrated data for a plurality of paths comprises the step of directing energy along the plurality of paths, such that said plurality of paths do not intersect.

4. The method of claim 1, wherein the step of acquiring path integrated data for a plurality of paths comprises the step of directing energy along the plurality of paths, such that said plurality of paths radiate from a substantially common origin.

5. The method of claim 1, wherein the step of acquiring path integrated data for a plurality of paths comprises the step of directing energy along at least three different paths.

6. The method of claim 1, wherein the step of acquiring path integrated data for a plurality of paths comprises the step of directing energy along at least three different paths;

and the step of reiteratively generating a cumulative distribution function comprises the step of combining a known parameter of said at least one property with the path integrated data to produce a cumulative distribution function.

7. The method of claim 6, wherein the property comprises a concentration of a constituent, and wherein the step of combining the known parameter of said at least one property with the path integrated data comprises the step of using one of a known concentration range of a constituent in said sampling region and a known disposition of said constituent in said sampling region.

8. The method of claim 1, wherein the step of acquiring path integrated data for a plurality of paths comprises the step maintaining a position of an energy source that emits energy along an axis, while varying a position of at least one energy detector along the axis, to provide a plurality of different length paths along the axis.

9. The method of claim 1, further comprising the step of emitting energy along the plurality of paths, and the step of acquiring path integrated data for the plurality of paths comprises the step of detecting the energy along each of a plurality of different length paths.

10. The method of claim 1, further comprising the step of emitting energy along the plurality of paths, and the step of acquiring path integrated data for the plurality of paths comprises the step of reflecting the energy back along each of a plurality of different length paths.

11. The method of claim 10, further comprising the step of sequentially emitting the energy in different directions, along each of the plurality of paths, wherein the step of acquiring path integrated data for the plurality of paths further comprises the step of detecting the energy that is reflected back along each of plurality of different length paths.

12. The method claim 11, further comprising the step of moving a source of the energy and an energy detector to sequentially emit the energy in different directions and to detect the energy that is reflected.

13. The method of claim 10, wherein the energy comprises one of light energy and acoustical energy.

14. The method of claim 1, wherein the sampling region is one of a gas, a liquid state, and a solid.

15. The method of claim 1, wherein the step of using said cumulative distribution function comprises the step of mapping a constituent concentration for the sampling region.

16. The method of claim 1, wherein the step of reiteratively generating said cumulative distribution function employs one of integrating over a discrete matrix of pixel values, a continuous function, a spline function matrix, and a smooth basis function minimization.

17. The method of claim 1, wherein the step of reiteratively generating said cumulative distribution function determines if an additional iteration is required as function of whether a predetermined limit has been achieved.

18. The method of claim 17, wherein the predetermined limit is a function of a level of noise associated with the step of acquiring the path integrated data.

19. A method of mapping contaminants within a sampling region using path integrated data, comprising the steps of:

(a) providing an instrument capable of generating path integrated concentration (PIC) data within said sampling region;

(b) using said instrument to acquire PIC data for a plurality of different paths within said sampling region;

(c) reiteratively generating a cumulative distribution function that fits the acquired PIC data; and

(d) using said cumulative distribution function to create a two-dimensional (2D) spatial map indicating levels of said contaminants within the sampling region.

20. The method of claim 19, wherein the step of providing an instrument comprises the step of providing an instrument that produces an illuminating signal that is one of an optical signal and an acoustic signal.

21. The method of claim 19, wherein the step of using said instrument to acquire PIC data comprises the steps of using said instrument to generate a first path having a first length, and then using said instrument to generate additional paths having different lengths.

22. The method of claim 21, wherein said instrument is used to generate at least three paths of different lengths.

23. The method of claim 19, wherein the step of using said instrument to acquire PIC data comprises the step of generating a plurality of non-intersecting paths.

24. The method of claim 19, wherein the step of using said instrument to acquire PIC data comprises the step of generating a plurality of paths that arrayed about a substantially common origin.

25. The method of claim 19, wherein the instrument comprises an illuminating unit and a detector, further comprising the step of providing a reflective unit that reflects a light signal emitted from said illuminating unit to said detector.

26. The method of claim 19, wherein the instrument comprises an illuminating unit and a detector, further comprising the step of providing a reflective unit for each of the plurality of paths that directs a signal emitted from said illuminating unit to said detector, the step of using said instrument to acquire PIC data comprising the step of varying an orientation of said instrument to determine directions of each of said plurality of different paths.

27. The method of claim 19, wherein the step of reiteratively generating the cumulative distribution function comprises the step of reiteratively generating a cumulative distribution function that is one of integrating over a discrete matrix of pixel values, a continuous function, a spline function matrix, and a smooth basis function minimization.

28. The method of claim 19, wherein the step of reiteratively generating the cumulative distribution function comprises the steps of determining if a level of improvement of a fit of the cumulative distribution function to the acquired PIC data between successive iterations exceeds a signal noise level associated with said instrument;

and, if so, then continuing the step of reiteratively generating the cumulative distribution function.

29. The method of claim 19, wherein the step of reiteratively generating the cumulative distribution function comprises the step of including known parameters for said contaminant within said cumulative distribution function such that fewer paths are required to acquired the PIC data.

30. The method of claim 29, wherein the step of including known parameters of said contaminant within said cumulative distribution function comprises the step of including at least one of a location of said contaminant within said sampling region and a concentration range of said contaminant within said sampling region.

31. A system for acquiring path integrated concentration (PIC) data from within a sampling region and generating a spatial concentration map based on said PIC data, comprising:

(a) an instrument that emits energy along a path;

(b) at least one detector disposed so as to detect the energy emitted by said instrument, said detector producing a signal indicative of the PIC data along said path;

(c) a memory in which a plurality of machine instructions are stored; and

(d) a processor that is coupled to said at least one detector, and to said memory, said processor executing said machine instructions stored in the memory, causing the processor to implement a plurality of functions, including;

(i) identifying a plurality of paths over which energy emitted by the instrument is directed and for which PIC data is obtained;

(ii) accumulating PIC data for each path defined by the user;

(iii) generating a cumulative distribution function that fits the accumulated PIC data; and

(iv) using the cumulative distribution function to generate a spatial concentration map.

32. The system of claim 31, wherein said instrument comprises one of a Differential Optical Absorption Spectroscopy device, a Tunable Diode Laser device, a Differential Absorption Lidar device, a backscatter Lidar device and an Open Path Fourier Transformation Infrared Spectroscopy device.

33. The system of claim 31, wherein said sampling region comprises a volume of fluid.

34. The system of claim 31, wherein said energy comprises light.

35. The system of claim 31, wherein the instrument sequentially emits energy along a plurality of different paths.

36. The system of claim 31, further comprising a reflector disposed on an axis of the path along which said energy is emitted, wherein said at least one detector is disposed adjacent said instrument, such that said reflector reflects said energy to said at least one detector.

37. The system of claim 36, wherein said at least one detector comprises a single detector, and said single detector is incorporated within said instrument.

38. The system of claim 31, further comprising a one of a plurality of detectors and a detector array disposed within said sampling region.

39. The system of claim 31, wherein said instrument comprises an interferometer.

40. A method of mapping a property associated with a sampling region using path integrated data, to enable the property to be evaluated at specific locations over the measurement path without utilizing path integrated data obtained from intersecting sampling paths, comprising the steps of:

(a) defining a sampling region in which at least one property associated with said sampling region will be mapped;

(b) acquiring path integrated data for a plurality of sampling paths within said sampling region, such that the plurality of sampling paths are not required to intersect in order to obtain path integrated data that can be used to evaluate the at least one property at specific locations over each of the plurality of sampling paths;

(c) reiteratively generating a cumulative distribution function of the at least one property associated with said sampling region from said path integrated data, said cumulative distribution function enabling the at least one property to be evaluated at specific locations over each of the plurality of sampling paths without evaluating an average of the at least one property over a length of each of the plurality of sampling paths; and

(d) using said cumulative distribution function to produce a map of the at least one property for the sampling region.

41. A method of mapping contaminants within a sampling region using path integrated data, comprising the steps of:

(a) providing an instrument capable of generating path integrated concentration (PIC) data within said sampling region;

(b) using said instrument to acquire PIC data for a plurality of different paths within said sampling region, such that none of the plurality of different paths are required to intersect in order to obtain the PIC data and so that said PIC data is usable to determine a contaminant concentration at specific locations over each of the plurality of sampling paths;

(c) reiteratively generating a cumulative distribution function that fits the acquired PIC data; and

(d) using said cumulative distribution function to create a map of said contaminants within the sampling region.

42. A method of evaluating at least one property associated with a plurality of sampling paths using path integrated data, to enable the at least one property to be evaluated at specific locations over each sampling path, comprising the steps of:

(a) defining a sampling region in which at least one property associated with said sampling region will be mapped;

(b) acquiring the path integrated data for a plurality of sampling paths within said sampling region; and

(c) reiteratively generating a cumulative distribution function of said at least one property associated with said sampling region from said path integrated data, said cumulative distribution function enabling the at least one property to be evaluated at specific locations over each of the plurality of sampling paths without evaluating an average of the at least one property over a length of each of the plurality of sampling paths.

43. A system for acquiring and evaluating at least one property associated with a plurality of sampling paths from within a sampling region using path integrated data, to enable the at least one property to be evaluated at specific locations over each sampling path, comprising:

(a) an instrument that emits energy along at least one path;

(b) at least one detector disposed so as to detect the energy emitted by said instrument, said detector producing a signal indicative of the path integrated data along said at least one path;

(c) a memory in which a plurality of machine instructions are stored; and

(d) a processor that is coupled to said at least one detector, and to said memory, said processor executing said machine instructions stored in the memory, causing the processor to implement a plurality of functions, including;

(i) identifying a plurality of paths over which energy emitted by the instrument is directed and for which path integrated data are obtained;

(ii) accumulating the path integrated data for each path identified by the user;

(iii) generating a cumulative distribution function that fits the accumulated path integrated data; and

(iv) using the cumulative distribution function to evaluate the at least one property at specific locations over each of the plurality of sampling paths.