Method and apparatus to simultaneously measure emissivities and thermodynamic temperatures of remote objects

• US 5,011,295 A
• Filed: 10/17/1989
• Issued: 04/30/1991
• Est. Priority Date: 10/17/1989
• Status: Expired due to Fees

• Current Assignee: Houston Advanced Research Center
• Original Assignee: Houston Advanced Research Center
• Inventors: Krishnan, Shankar, Margrave, John L., Hauge, Robert H., Hansen, George P., Rey, Charles A.
• Primary Examiner(s): Cuchlinksi, Jr., William A.
• Assistant Examiner(s): GUTIERREZ, DIEGO F
• Application Number:
  US07/422,644
• Time in Patent Office: 560 Days
• Field of Search: 374/126, 374/128, 374/9, 374/121, 374/124, 374/137, 356/43, 356/45
• US Class Current: 374/126
• CPC Class Codes: G01J 2005/0074 having separate detection of emissivity
• CPC Class Codes: G01J 2005/0077 Imaging
• CPC Class Codes: G01J 4/04 Polarimeters using electric detection means G01J4/02 takes precedence
• CPC Class Codes: G01J 5/0003 for sensing the radiant heat transfer of samples, e.g. emittance meter
• CPC Class Codes: G01J 5/0096 for measuring wires, electrical contacts or electronic systems
• CPC Class Codes: G01J 5/04 Casings
• CPC Class Codes: G01J 5/047 Mobile mounting; Scanning arrangements
• CPC Class Codes: G01J 5/08 Optical arrangements
• CPC Class Codes: G01J 5/0801 Means for wavelength selection or discrimination
• CPC Class Codes: G01J 5/0804 Shutters
• CPC Class Codes: G01J 5/0805 Means for chopping radiation
• CPC Class Codes: G01J 5/0808 Convex mirrors
• CPC Class Codes: G01J 5/0813 Planar mirrors; Parallel phase plates
• CPC Class Codes: G01J 5/0846 having multiple detectors for performing different types of detection, e.g. using radiometry and reflectometry channels
• CPC Class Codes: G01J 5/0896 using a light source, e.g. for illuminating a surface
• CPC Class Codes: G01J 5/58 using absorption; using extinction effect
• CPC Class Codes: G01J 5/59 using polarisation; Details thereof
• CPC Class Codes: G01J 5/80 Calibration using comparison with reference sources G01J5/52
• CPC Class Codes: G01N 2021/1793 Remote sensing
• CPC Class Codes: G01N 21/21 Polarisation-affecting properties G01N21/19 takes precedence
• CPC Class Codes: G01N 2201/0696 : Pulsed

Abstract

Method and apparatus for accurately and instantaneously determining the thermodynamic temperature of remote objects by continuous determination of the emissivity, the reflectivity, and optical constants, as well as the apparent or brightness temperature of the sample with a single instrument. The emissivity measurement is preferably made by a complex polarimeter including a laser that generates polarized light, which is reflected from the sample into a detector system. The detector system includes a beamsplitter, polarization analyzers, and four detectors to measure independently the four Stokes vectors of the reflected radiation. The same detectors, or a separate detector in the same instrument, is used to measure brightness temperature. Thus, the instrument is capable of measuring both the change in polarization upon reflection as well as the degree of depolarization and hence diffuseness. This enables correction for surface roughness of the sample and background radiation, which could otherwise introduce errors in temperature measurement.

Claims

1. Method for non-contact determination of the thermodynamic temperature of a remote object comprising the steps of:

a. directing a polarized light beam of a given wavelength toward said object to cause said light to be reflected from the surface of the object along a given plane of incidence,

b. measuring the amplitude and phase change of light reflected and transmitted from said object of said wavelength polarized both parallel and perpendicular to the plane of incidence to determine the spectral emissivity of the object.

c. interrupting said polarized light beam and concurrently measuring the self emission of the object exclusive of the reflected light to determine brightness temperature, and

d. combining the values obtained in b. and c. to determine the thermodynamic temperature of the object.

2. The method according to claim 1, wherein the measurement set forth in step b. is made by four separate detector means.

3. The method of claim 2, wherein the measurement set forth in step c. is made by an additional separate detector means, and the measurements in steps b. and c. are made simultaneously.

4. The method according to claim 1, wherein the light beam is interrupted repeatedly turning said light beam on and off.

5. The method according to claim 4, wherein the measurement in step b. is made when the light is on, and the measurement in step c. is made when the light is off.

6. The method of claim 1, wherein the measurements of steps b. and c. are at slightly different wavelengths.

7. The method of claim 1, wherein the measurement of step b. is made by a single detector means sequentially at four difference polarization states.

8. The method of claim 1 wherein the measurement in steps b, and c, and step d are at a single spot on a surface of said object.

9. The method of claim 1 wherein the measurement of steps b and c, and step d are made at a plurality of points defining an area of a surface of the object to determine the thermodynamic temperature at said plurality of points in order to provide a thermal image of said area.

10. The method of claim 1 further comprising the step of scanning a plurality of points in a surface of said object to determine the thermodynamic temperature at said plurality of points in order to provide a thermal image of said surface.

11. Apparatus for measurement of the thermodynamic temperature of a radiating object comprising

a light source means of given wavelength for reflecting a beam of light off the object at a given angle,

means for interrupting said beam of light,

detector means for receiving radiation from said object comprising both

the self-emitted radiation from the object when the light is off in order to determine the brightness temperature of the object and

combined reflected and transmitted radiation from the object when the light source means is on, in order to determine the emissivity of the object.

said detector means comprising means for amplitude splitting of the received radiation into two component beams,

means for dividing each of the two component beams into two beams each of polar components, and

means for measuring the intensities of the four resulting components, said intensities being related to the four Strokes vectors of the received radiation, and computing means for computing the brightness temperature and emissivity of the object and for combining said brightness temperature and said emissivity to determine the thermodynamic temperature of the object.

12. The apparatus of claim 11 further comprising filter means for discriminating between the self-emitted light and the reflected and transmitted light.

13. The apparatus of claim 11 further comprising means for making simultaneous measurements of the thermodynamic temperature at a plurality of points in a surface of said object in order to provide a thermal image of said surface.

14. The apparatus of claim 13 wherein said means for making simultaneous measurements of the thermodynamic temperature at a plurality of points in a surface of the object comprises means for subdividing the reflected, transmitted, and self-emitted radiation light from said plurality of points defining an area of the object surface.

15. The apparatus of claim 13 wherein the means for making simultaneous measurements of the thermodynamic temperature at a plurality of points in a surface of the object comprises means for scanning said surface.

16. Method for non-contact measurement of the thermodynamic temperature of a remote object, said method comprising the steps of

reflecting a beam of light of known frequency and polarization off the object at a given angle,

arranging a detector to receive radiation of said known frequency and at said given angle,

amplitude splitting of the radiation received by said detector followed by division of the split beam into four polarization components,

alternatively interrupting said beam of light while measuring the intensities of said four components to obtain four values for two states wherein one state comprises both transmitted and reflected radiation and the other state is self-emitted radiation;

and

irrespective of order, calculating the brightness temperature of the object from said self-emitted radiation intensities and emissivity of the object from said transmitted and reflected intensities, and combining these to determine the thermodynamic temperature of the object.

17. Method for non-contact determination of the thermodynamic temperature of a remote object, said method comprising the steps of directing a polarized light beam to the object causing said light to be reflected and transmitted from said object, measuring four polarization components of the light reflected and transmitted from the object to determine emissivity, interrupting said polarized light beam and simultaneously measuring the brightness temperature of the object from radiation self-emitted from the object, and combining the two measurements to determine the thermodynamic temperature.