Apparatus for measuring a characteristic of an object using an optical fiber and light pulses

• US 6,237,421 B1
• Filed: 06/17/1999
• Issued: 05/29/2001
• Est. Priority Date: 06/19/1998
• Status: Expired due to Fees

• Current Assignee: Kinzo Kishida
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Li, Xin zen, Miyazaki, Masayuki, Takada, Shiro
• Primary Examiner(s): NOORI, MAX H
• Application Number:
  US09/335,265
• Time in Patent Office: 712 Days
• Field of Search: 73/763, 73/766, 73/800
• US Class Current: 73/800
• CPC Class Codes: G01D 5/35348 using stimulated emission to detect the measured quantity
• CPC Class Codes: G01L 1/242 the material being an optical fibre
• CPC Class Codes: G01M 11/39 in which light is projected from both sides of the fiber or waveguide end-face

Abstract

A light intensity measurement unit can sample the light intensity of scattered light at time intervals of a certain length corresponding to two times the length of each of small equal length sections, into which a measurement area in an optical fiber is divided. A computation unit can then compute the strain and/or temperature of each of the small sections of the measurement area in the optical fiber, based on the light intensity of the scattered light measured by the light intensity measurement unit from the scattering gain coefficient of the scattered light associated with each of the small sections.

Claims

1. A measurement apparatus for measuring at least one of strain and temperature, of an object, said apparatus comprising:

an optical fiber secured to an object, said optical fiber having first and second ends;

pulsed pump light source means for injecting pulsed pump light into the first end of said optical fiber;

pulsed probe light source means for injecting pulsed probe light into the second end of said optical fiber;

control means operatively connected to said pulsed pump light source means and said pulsed probe light source means for setting the pulsed probe light to a frequency ν

s and for scanning the pulsed probe light over a range of frequencies;

light intensity measurement means for measuring intensity of output light emitted from the first end of said optical fiber;

filter means located in an optical path from the first end of said optical fiber to said light intensity measurement means, for selectively transmitting scattered light included in the output light; and

computation means operatively connected to said light intensity measurement means for computing at least one of strain and temperature of a zone of the object within a measurement area of said optical fiber from the scattered light reaching by said light intensity measurement means.

2. The measurement apparatus according to claim 1, wherein said computation means computes the variable Qs(i) in consideration of attenuation of the pulsed probe light in said optical fiber according to $\mathrm{Qs}$

(i)=ln

{Ps

(t,0)Ps

(t-LC,L)}+α

s

L

where Ps(t,0) is the light intensity of scattered light at the first end of said optical fiber measured at time t by said light intensity measurement means, Ps(t−

L/c,L) is the light intensity of the pulsed probe light at the second end of said optical fiber measured at time (t−

L/c), α

s is an attenuation coefficient of the pulsed probe light, L is the length of said optical fiber, and c is speed of the pulsed prone light in said optical fiber.

4. The measurement apparatus according to claim 1, wherein said computation means computes the contribution factor a(i,j) for each of the plurality of small sections according to $a$

(i,j)=Pk

(0)A



-ap

z·



z

where, assuming that the pulsed pump light is divided into n equal parts, Pk(0) is light intensity of a k-th small pump light part Pk numbered from a first end of the pulsed pump light when the pulsed pump light is incident on the first end of said optical fiber, A is cross-sectional area of a core of said optical fiber , α

_pis an attenuation coefficient of the pulsed pump light, z is distance from the first end of said optical fiber to a specified small section, and dz is the length of each of the plurality of small sections.

3. A measurement apparatus for measuring at least one of strain and temperature of an object, said apparatus comprising:

an optical fiber secured to an object, said optical fiber having first and second ends;

pulsed pump light source means for injecting pulsed pump light into the first end of said optical fiber;

pulsed probe light source means for injecting pulsed probe light into the second end of said optical fiber;

control means operatively connected to said pulsed pump light source means and said pulsed probe light source means for setting the pulsed probe light to a frequency ν

s and for scanning the pulsed probe light over a range of frequencies;

light intensity measurement means for measuring intensity of output light emitted from the first end of said optical fiber, said light intensity measurement means sampling light intensity of the scattered light at time intervals of a fixed length corresponding to two times the length of each of a plurality of small sections of equal lengths into which the measurement area in said optical fiber is divided;

filter means located in an optical path from the first end of said optical fiber to said light intensity measurement means, for selectively transmitting scattered light included in the output light; and

computation means operatively connected to said light intensity measurement means for computing at least one of strain and temperature of each of said plurality of small sections of said measurement area of said optical fiber from the intensity of the scattered light measured by said light intensity measurement means, and wherein said measurement area in said optical fiber is divided into m small equal sections, said pulsed pump light source means injects pulsed pump light with a time duration equal to n-times the length of each of the time intervals, which corresponds to two times the length of each of the plurality of small sections, into said optical fiber, and said computation means computes a scattering gain coefficient of scattered light associated with each of the plurality of small sections based on light intensity of scattered light having a frequency equal to the frequency ν

s of the pulsed probe light, the light intensity of the scattered light being sampled at the time intervals by said light intensity measurement means, according to equation (1), $\begin{array}{cc}\left(\begin{array}{cccccccccc}a<br><br>\left(1,1\right)& a<br><br>\left(1,2\right)& \mathrm{\cdots <br><br>}& a<br><br>\left(1,n\right)& 0& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& 0\\ 0& a<br><br>\left(2,2\right)& a<br><br>\left(2,3\right)& \mathrm{\cdots <br><br>}& a<br><br>\left(2,n+1\right)& 0& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& 0\\ \mathrm{⋮<br><br>}& \text{\hspace{1em}<br><br>}& \mathrm{⋰<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \mathrm{⋮<br><br>}\\ 0& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& a<br><br>\left(i,i\right)& a<br><br>\left(i,i+1\right)& \mathrm{\cdots <br><br>}& a<br><br>\left(i,i+n-1\right)& 0& \mathrm{\cdots <br><br>}& 0\\ \mathrm{⋮<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \mathrm{⋰<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \mathrm{⋮<br><br>}\\ 0& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& a<br><br>\left(m,m\right)& a<br><br>\left(m,m+1\right)& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& a<br><br>\left(m,m+n-1\right)\end{array}\right)<br><br>\left(\begin{array}{c}\mathrm{gs}<br><br>\left(1\right)\\ \mathrm{gs}<br><br>\left(2\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{gs}<br><br>\left(i\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{gs}<br><br>\left(m\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{gs}<br><br>\left(m+n-1\right)\end{array}\right)=\left(\begin{array}{c}\mathrm{Qs}<br><br>\left(1\right)\\ \mathrm{Qs}<br><br>\left(2\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{Qs}<br><br>\left(i\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{Qs}<br><br>\left(m\right)\end{array}\right)& \left(1\right)\end{array}$

where Qs(i)(i=i, . . . , m) is a variable determined by at least the light intensity of scattered light associated with i-th to (i+n−

1)-th small sections numbered from one at a first end of the measurement area, and the light intensity of the pulsed probe light incident on said optical fiber, gs(i) is the scattering gain coefficient of scattered light having a frequency equal to the frequency ν

s, associated with the i-th small section, and a(i,j) is a contribution factor representing a ratio of the light intensity of scattered light associated with a j-th small section to Qs(i), and wherein said computation means computes a frequency shift in the scattered light associated with each of the plurality of small sections based on scattering gain coefficients computed throughout the frequency range of the pulsed probe light, over which the frequency ν

s of the pulsed probe light has been scanned, to plurality of small sections based on the frequency shift computed, and/or light intensities of the scattered light associated with each of the plurality of small sections which have been obtained by scanning the frequency ν

s of the pulsed probe light.

5. The measurement apparatus according to claim 3, further comprising temperature measurement means for measuring temperature of a reference fiber portion associated with the scattering gain coefficients gs(m+1) to gs(m+n−

1) (or gs(1) to gs(n−

1)), which is a part of said optical fiber not secured to the object, wherein said computation means computes the scattering gain coefficients gs(m+1) to gs(M+n−

1) based on the temperature measured and computes the scattering gain coefficient associated with each of the plurality of small sections, according to the equation (1).

6. The measurement apparatus according to claim 3, wherein said optical fiber is partially secured to at least one object.

7. The measurement apparatus according to claim 3, wherein said computation means computes a strain change Δ

ε

that appears in each of the plurality of small sections, and the temperature Δ

T of each of the plurality of small sections, according to $\left(\begin{array}{c}\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>v\\ \frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{Ps}}{P_{\left(R\right)}}\end{array}\right)=\left(\begin{array}{cc}{C}_{\mathrm{\varepsilon <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>v}& C_{\mathrm{Tv}}\\ C_{\mathrm{\varepsilon <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>P}& C_{\mathrm{TP}}\end{array}\right)<br><br>\left(\begin{array}{c}\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\varepsilon <br><br>}\\ \mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>T\end{array}\right)$

where Δ

ν

is a frequency shift, Δ

P{dot over (s)} is a power shift in the light intensity of the scattered light measured or a variation in the scattering gain coefficient computed, P(R) is a light intensity of Rayleigh scattered light or the light intensity of the pulsed pump light, and C<sub>ε

ν</sub>

, C<sub>ε

p</sub>, C_tν

, and C_tp are constants of said optical fiber.

8. The measurement apparatus according to claim 7, wherein the light pulses included in each series of light pulses of the pulsed probe light have a constant pulse repetition rate.

9. The measurement apparatus according to claim 7, wherein the light pulses included in each series of light pulses of the pulsed probe light are a series of pulses that do not have a constant pulse repetition rate and correspond to a code.

11. The measurement apparatus according to claim 7, further comprising temperature measurement means for measuring temperature of a reference fiber portion associated with the scattering gain coefficients gs(m+1) to gs(M+n−

1) (or gs(1) to gs(n−

1)), which is a part of said optical fiber not secured to the object, wherein said computation means computes the scattering gain coefficients gs(m+1) to gs(M+n−

1) based on the temperature measured and computes the scattering gain coefficient associated with each of the plurality of small sections, according to the equation (5).

12. The measurement apparatus according to claim 7, wherein said computation means computes the contribution factor a(i,j) for each of the plurality of small sections according to $a$

(i,j)=Pk

(0)A



-ap

z·



z

where, assuming that the pulsed pump light is divided into n equal parts, Pk(0) is light intensity of a k-th small pump light part Pk numbered from a first end of the pulsed pump light when the pulsed pump light is incident on the first end of said optical fiber, A is cross-sectional area of a core of said optical fiber , α

_p is an attenuation coefficient of the pulsed pump light, z is distance from the first end of said optical fiber to a specified small section, and dz is the length of each of the plurality of small sections.

13. The measurement apparatus according to claim 7, wherein said computation means computes a strain change Δ

ε

that appears in each of the plurality of small sections, and the temperature Δ

T of each of the plurality of small sections, according to $\left(\begin{array}{c}\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>v\\ \frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{Ps}}{P_{\left(R\right)}}\end{array}\right)=\left(\begin{array}{cc}{C}_{\mathrm{\varepsilon <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>v}& C_{\mathrm{Tv}}\\ C_{\mathrm{\varepsilon <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>P}& C_{\mathrm{TP}}\end{array}\right)<br><br>\left(\begin{array}{c}\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\varepsilon <br><br>}\\ \mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>T\end{array}\right)$

where Δ

ν

is a frequency shift, Δ

Ps is a power shift in the light intensity of the scattered light measured or a variation in the scattering gain coefficient computed, P(R) is a light intensity of Rayleigh scattered light or the light intensity of the pulsed pump light, and C<sub>ε

ν</sub>

, C<sub>ε

p</sub>, C_tε

, and C_tp are constants of said optical fiber.

14. The measurement apparatus according to claim 7, wherein said optical fiber is partially secured to at least one object.

10. A measurement apparatus for measuring at least one of strain and temperature, of an object, said apparatus comprising:

an optical fiber secured to an object, said optical fiber having first and second ends, said optical fiber including a measurement area divided into m small equal length sections, each section having an identical length;

pulsed pump light source means for injecting pulsed pump light into the first end of said optical fiber;

pulsed probe light source means for injecting pulsed probe light into the second end of said optical fiber;

control means operatively connected to said pulsed pump light source means and said pulsed probe light source means for setting the pulsed probe light to a frequency ν

s and for scanning the frequency ν

s of the pulsed probe light over a range of frequencies;

light intensity measurement means for measuring intensity of output light emitted from the first end of said optical fiber;

filter means located in an optical path from the first end of said optical fiber to said light intensity measurement means, for selectively transmitting scattered light included in the output light; and

computation means for computing a distribution of at least one of strain and temperature of the object in said measurement area in said optical fiber,

said pulsed pump light source means injecting pulsed pump light with a time duration equal to n-times the length of a time period corresponding to two times the length of each of the m small sections into said optical fiber with respect to each pulse of the pulsed probe light incident on said optical fiber, under control of said control means,

said pulsed probe light source means successively injecting at least two series of light pulses of the pulsed probe light, each series being obtained by dividing discontinuous light with a certain time duration into units of the time period, under control of said control means, so that each pulse collides with corresponding pulsed pump light from said pump light source means at a certain position in said optical fiber, and

said computation means computing a scattered gain coefficient of scattered light associated with each of the m small sections based on the light intensity of scattered light having a frequency equal to the frequency ν

s of the pulsed probe light, measured by said light intensity measurement means, according to equation (5), $\begin{array}{cc}\left(\begin{array}{cccccccccc}a<br><br>\left(1,1\right)& a<br><br>\left(1,2\right)& \mathrm{\cdots <br><br>}& a<br><br>\left(1,n\right)& 0& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& 0\\ 0& a<br><br>\left(2,2\right)& a<br><br>\left(2,3\right)& \mathrm{\cdots <br><br>}& a<br><br>\left(2,n+1\right)& 0& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& 0\\ \mathrm{⋮<br><br>}& \text{\hspace{1em}<br><br>}& \mathrm{⋰<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \mathrm{⋮<br><br>}\\ 0& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& a<br><br>\left(i,i\right)& a<br><br>\left(i,i+1\right)& \mathrm{\cdots <br><br>}& a<br><br>\left(i,i+n-1\right)& 0& \mathrm{\cdots <br><br>}& 0\\ \mathrm{⋮<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \mathrm{⋰<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \mathrm{⋮<br><br>}\\ 0& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& a<br><br>\left(m,m\right)& a<br><br>\left(m,m+1\right)& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& a<br><br>\left(m,m+n-1\right)\end{array}\right)<br><br>\left(\begin{array}{c}\mathrm{gs}<br><br>\left(1\right)\\ \mathrm{gs}<br><br>\left(2\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{gs}<br><br>\left(i\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{gs}<br><br>\left(m\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{gs}<br><br>\left(m+n-1\right)\end{array}\right)=\left(\begin{array}{c}\mathrm{Qs}<br><br>\left(1\right)\\ \mathrm{Qs}<br><br>\left(2\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{Qs}<br><br>\left(i\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{Qs}<br><br>\left(m\right)\end{array}\right)& \left(5\right)\end{array}$

where Qs(i) (i=1, . . . m) is a variable determined by at least the light intensity of scattered light associated with i-th to (1+n−

1)-th small sections numbered from one at a first end of the measurement area, and the light intensity of the pulsed probe light incident on said optical fiber, gs(i) is the scattering gain coefficient of scattered light having a frequency equal to the frequency ν

s, associated with the i-th small section, and a(i,j) is a contribution factor representing a ratio of the light intensity of scattered light associated with a j-th small section to Qs(i), and wherein said computation means computes a frequency shift in the scattered light associated with each of the m small sections based on scattering gain coefficients computed throughout the frequency range of the pulsed probe light, over which the frequency ν

s of the pulsed probe light has been scanned, to compute at least one of the strain and the temperature of each of the m small sections based on the frequency shift computed, and/or light intensities of the scattered light associated with each of the m small sections which have been obtained by scanning the frequency ν

s of the pulsed probe light.

15. A measurement apparatus for measuring at least one of as strain and temperature, of an object, said apparatus comprising:

an optical fiber secured to an object, said optical fiber having first and second ends, said optical fiber including a measurement area divided into m small equal length sections, each section having an identical length;

pulsed pump light source means for injecting pulsed pump light into the first end of said optical fiber;

pulsed probe light source means for injecting pulsed probe light into the second end of said optical fiber;

control means operatively connected to said pulsed pump light source means and said pulsed probe light source means for setting the pulsed probe light to a frequency ν

s and for scanning the frequency ν

s of the pulsed probe light over a range of frequencies;

light intensity measurement means for measuring intensity of output light emitted from the first end of said optical fiber;

filter means located in an optical path from the first end of said optical fiber to said light intensity measurement means, for selectively transmitting scattered light included in the output light; and

computation means for computing a distribution of at least one of strain and temperature as of the object in said measurement area in said optical fiber,

said pulsed pump light source means injecting pulsed pump light with a time duration equal to n-times the length of a time period corresponding to two times the length of each of the m small sections into said optical fiber with respect to each pulse of the pulsed probe light incident on said optical fiber, under control of said control means,

said pulsed probe light source means injecting either pulsed probe light with the frequency ν

s, comprising a series of light pulses having a pulse repetition period equal to the time period, or at least two series of light pulses of the pulsed probe light with the frequency ν

s, in succession, each series of light pulses being obtained by dividing the pulsed probe light, under control of said control means, so that each pulse of the pulsed probe light collides with corresponding pulses of the pump light from said pump light source means at a certain position in said optical fiber, and

said computation means computing a scattered gain coefficient of scattered light associated with each of the m small sections based on the light intensity of scattered light having a frequency equal to the frequency ν

s of the pulsed probe light, measured by said light intensity measurement means, according to, $\left(\begin{array}{cccccccccc}a<br><br>\left(1,1\right)& a<br><br>\left(1,2\right)& \mathrm{\cdots <br><br>}& a<br><br>\left(1,n\right)& 0& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& 0\\ 0& a<br><br>\left(2,2\right)& a<br><br>\left(2,3\right)& \mathrm{\cdots <br><br>}& a<br><br>\left(2,n+1\right)& 0& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& 0\\ \mathrm{⋮<br><br>}& \text{\hspace{1em}<br><br>}& \mathrm{⋰<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \mathrm{⋮<br><br>}\\ 0& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& a<br><br>\left(i,i\right)& a<br><br>\left(i,i+1\right)& \mathrm{\cdots <br><br>}& a<br><br>\left(i,i+n-1\right)& 0& \mathrm{\cdots <br><br>}& 0\\ \mathrm{⋮<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \mathrm{⋰<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \mathrm{⋮<br><br>}\\ 0& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& a<br><br>\left(m,m\right)& a<br><br>\left(m,m+1\right)& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& a<br><br>\left(m,m+n-1\right)\end{array}\right)<br><br>\left(\begin{array}{c}\mathrm{gs}<br><br>\left(1\right)\\ \mathrm{gs}<br><br>\left(2\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{gs}<br><br>\left(i\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{gs}<br><br>\left(m\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{gs}<br><br>\left(m+n-1\right)\end{array}\right)=\left(\begin{array}{c}\mathrm{Qs}<br><br>\left(1\right)\\ \mathrm{Qs}<br><br>\left(2\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{Qs}<br><br>\left(i\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{Qs}<br><br>\left(m\right)\end{array}\right)$

where Qs(i) (i=1, . . . m) is a variable determined by at least the light intensity of scattered light associated with i-th to (1+n−

1)-th small sections numbered from one at a first end of the measurement area, and the light intensity of the pulsed probe light incident on said optical fiber, gs(i) is the scattering gain coefficient of scattered light having a frequency equal to the frequency ν

s, associated with the i-th small section, and a(i,j) is a contribution factor representing a ratio of the light intensity of scattered light associated with a j-th small section to Qs(i), and wherein said computation means computes a frequency shift in the scattered light associated with each of the m small sections based on scattering gain coefficients computed throughout the frequency range of the pulsed probe light, over which the frequency ν

s of the pulsed probe light has been scanned, to compute at least one of the strain and the temperature of each of the m small sections based on the frequency shift computed, and/or light intensities of the scattered light associated with each of the m small sections which have been obtained by scanning the frequency ν

s of the pulsed probe light.

16. The measurement apparatus according to claim 15, the light pulses included in each series of light pulses of the pulsed probe light are a series of pulses that do not have a constant pulse repetition rate and correspond to a code.

17. A measurement apparatus for measuring at least one of strain and temperature of an object, said apparatus comprising:

an optical fiber secured to an object, said optical fiber having first and second ends, said optical fiber including a measurement area divided into m small equal length sections, each section having an identical length;

reflection means arranged at the second end of said optical fiber;

pulsed pump light source means for injecting pulsed pump light into the first end of said optical fiber, the pulsed pump light being reflected by said reflection means;

pulsed probe light source means for injecting pulsed probe light into the first end of said optical fiber, the pulsed probe light being reflected by said reflection means;

control means operatively connected to said pulsed pump light source means and said pulsed probe light source means for setting the pulsed probe light to a frequency ν

s and for scanning the frequency ν

s of the pulsed probe light over a range of frequencies;

light intensity measurement means for measuring intensity of output light emitted from the first end of said optical fiber;

filter means located in an optical path from the first end of said optical fiber to said light intensity measurement means, for selectively transmitting scattered light included in the output light; and

computation means for computing a distribution of at least one of strain and temperature in said measurement area of the object in said optical fiber,

said pulsed pump light source means injecting pump light with a time duration equal to n-times the length of a time period corresponding to two times the length of each of the m small sections into said optical fiber with respect to each pulse of the pulsed probe light incident on said optical fiber, under control of said control means,

said pulsed probe light source means successively injecting at least two series of light pulses of the pulsed probe light, each series being obtained by dividing discontinuous light with a certain time duration into units of the time period, under control of said control means, so that each pulse collides with corresponding pulsed pump light from said pump light source means at a certain position in said optical fiber, and

said computation means computing a scattered gain coefficient of scattered light associated with each of the m small sections based on the light intensity of scattered light having a frequency equal to the frequency ν

s of the pulsed probe light, measured by said light intensity measurement means, according to $\left(\begin{array}{cccccccccc}a<br><br>\left(1,1\right)& a<br><br>\left(1,2\right)& \mathrm{\cdots <br><br>}& a<br><br>\left(1,n\right)& 0& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& 0\\ 0& a<br><br>\left(2,2\right)& a<br><br>\left(2,3\right)& \mathrm{\cdots <br><br>}& a<br><br>\left(2,n+1\right)& 0& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& 0\\ \mathrm{⋮<br><br>}& \text{\hspace{1em}<br><br>}& \mathrm{⋰<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \mathrm{⋮<br><br>}\\ 0& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& a<br><br>\left(i,i\right)& a<br><br>\left(i,i+1\right)& \mathrm{\cdots <br><br>}& a<br><br>\left(i,i+n-1\right)& 0& \mathrm{\cdots <br><br>}& 0\\ \mathrm{⋮<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \mathrm{⋰<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \text{\hspace{1em}<br><br>}& \mathrm{⋮<br><br>}\\ 0& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& a<br><br>\left(m,m\right)& a<br><br>\left(m,m+1\right)& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& a<br><br>\left(m,m+n-1\right)\end{array}\right)<br><br>\left(\begin{array}{c}\mathrm{gs}<br><br>\left(1\right)\\ \mathrm{gs}<br><br>\left(2\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{gs}<br><br>\left(i\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{gs}<br><br>\left(m\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{gs}<br><br>\left(m+n-1\right)\end{array}\right)=\left(\begin{array}{c}\mathrm{Qs}<br><br>\left(1\right)\\ \mathrm{Qs}<br><br>\left(2\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{Qs}<br><br>\left(i\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{Qs}<br><br>\left(m\right)\end{array}\right)$

where Qs(i) (i=1, . . . m) is a variable determined by at least the light intensity of scattered light associated with i-th to (1+n−

1)-th small sections numbered from one at a first end of the measurement area, and the light intensity of the pulsed probe light incident on said optical fiber, gs(i) is the scattering gain coefficient of scattered light having a frequency equal to the frequency ν

s, associated with the i-th small section, and a(i,j) is a contribution factor representing a ratio of the light intensity of scattered light associated with a j-th small section to Qs(i), and wherein said computation means computes a frequency shift in the scattered light associated with each of the m small sections based on scattering gain coefficients computed throughout the frequency range of the pulsed probe light, over which the frequency ν

s of the pulsed probe light has been scanned, to compute at least one of the strain and the temperature of each of the m small sections based on the frequency shift computed, and/or light intensities of the scattered light associated with each of the m small sections which have been obtained by scanning the frequency ν

s of the pulsed probe light.