Abstract: A shape measurement system and method for a three-dimensional shape of a linear object over a long distance with high resolution. The shape measurement system comprises: a multicore optical fiber having a center core positioned in the center of the cross section thereof and three or more outer peripheral cores positioned at equal intervals concentrically with respect to and outside of the center core; a measurement device for measuring the backward Brillouin scattered light distribution in the propagation direction of each core of the multicore optical fiber; and an analysis device for calculating position coordinates, in three-dimensional space, of a linear structure having an unknown three-dimensional shape from the backward Brillouin scattered light distributions of a multicore optical fiber positioned along the linear structure having an unknown three-dimensional shape and a multicore optical fiber positioned along a linear structure having a known three-dimensional shape.

Abstract: The present application pertains to two-dimensional ultrasound transducers and systems, methods of making such transducers and systems, and methods for using such transducers and systems including processing of data acquired with such devices and systems.

Abstract: Provided are a vibration object monitoring method and apparatus, a computer device, and a storage medium. The method includes: in response to detecting that a vibration object exists in a monitoring video picture for a target monitoring region, a vibration object region in the monitoring video picture is determined, where the vibration object region is a region where the vibration object is located in the monitoring video picture; displacement information of a key point of the vibration object in the vibration object region is recorded; vibration information of the vibration object in the monitoring video picture is determined based on the displacement information; and a vibration object monitoring result for the target monitoring region is generated according to the vibration information. The abnormal vibration monitoring can be performed on the vibration object in the target monitoring region in time according to this method.

Abstract: A temperature sensor including a sapphire optical fiber and a nanoporous cladding layer covering at least a portion of the sapphire optical fiber.

Abstract: A method and system for detecting a tunnel block falling disease based on visual and mechanical perception includes: capturing tunnel inner wall images, and preliminarily identifying a block falling disease using a trained first neural network model; constructing a circle based on a center which is the center position of the suspected disease determined in the preliminary identification process, dividing the circle equally through a plurality of diameters, pressing against the center of the suspected block falling disease in a pose perpendicular to the inner wall of the tunnel, moving in the diameter directions within the range of the suspected block falling disease, recording the displacement, and acquiring force and torque at the suspected block falling disease position during the movement; and determining the suspected tunnel block falling disease based on the acquired displacement, force and torque, using a second neural network model, and determining the tunnel block falling disease.

Abstract: A method and apparatus are provided for determining movement of a fluid into or out of a subsurface wellbore, to thereby enable accurate allocation of fluids being produced by or injected into each of several zones of the wellbore. A temperature change is effected in the fluid in a semi-continuous or pulsed manner at one or more locations in the wellbore. A temperature of the fluid is measured at one or more sensing locations downstream of the location of the temperature change. A time of flight model is used to determine, for a plurality of points of interest, a fluid flow direction, bulk flow rate and/or a cumulative flow rate contribution.

Abstract: An optical device for the contactless measurement of a liquid level contained in a storage device by an optical signal, the optical device including an optical unit fixedly positioned above the storage device and an electronic control unit capable of emitting an optical signal, dissociated from the optical unit and positioned at a distance from the optical unit. The optical unit includes a single channel for the emission and the reception of the optical signal. The optical unit is connected to the electronic control unit through an optical fibre capable of transmitting the optical signal emitted by the electronic control unit and an optical signal reflected by the liquid. The optical fibre has first and second optical cores that juxtapose each other such that at least a part of the optical signal emitted in the first optical core of the optical fibre is backscattered in the second optical core.

Abstract: Described herein are methods for treating a subterranean formation penetrated by a wellbore with a retarded acidizing fluid containing an acid and an acid retarding agent, the concentrations of which are adjusted based on measured parameter values of the formation. Also described is a method for treating a subterranean formation by introducing an acid to the formation following the introduction of an acid retarding agent to the formation. Also described is a method for acid fracturing a subterranean formation including reducing the concentration of an acid retarding agent contained in a retarded acidizing fluid over the course of the acid fracturing operation.

Abstract: Disclosed are a temperature control method of an optical modulator and an apparatus therefore. The temperature control apparatus of an optical modulator according to an exemplary embodiment of the present disclosure is to provide a temperature control method of an optical modulator which performs a calibration mode to select a heater control voltage with a maximum optical modulation amplitude (OMA) while adjusting a heater control voltage which drives a heater of the optical modulator, stores a reference temperature measurement code based on a measured temperature value of the optical modulator while driving the heater at a selected heater control voltage, and performs a lock mode which controls a temperature of the optical modulator by changing the heater control voltage using the reference temperature measurement code after stopping the optical modulation amplitude detecting operation and an apparatus therefor.

Abstract: A method of mounting a rail monitoring member/element at a mounting location of a rail for rail traffic, in particular on a railway track, is disclosed. The rail monitoring member includes a strain sensor member with a carrier on which a strain gauge, being an optical fiber with a fiber Bragg grating, is fixed. The method steps include: determination of the temperature of the rail and/or rail monitoring member at the mounting location; checking whether the determined temperature is within a predefined temperature interval; providing heating or cooling application to the rail and/or rail monitoring member at the mounting location, if the determined temperature is not within the predefined temperature interval; positioning and adhesively fixing of the carrier of the rail monitoring member at the mounting location. The method can be carried out easily and allows reliable and accurate monitoring of the rail using a strain sensor member.

Abstract: A dynamic Brillouin fiber sensor that is immune to fluctuations in the power, frequency, or polarizing state of the pump and probe beams is described herein. A new measurand that combines information from the complex Stokes and anti-Stokes interactions is provided to extract the absolute Brillouin frequency shift while rejecting the majority of noise sources that may limit the performance of current slope-assisted Brillouin optical time domain analysis systems.

Abstract: The present invention discloses a distributed pulsed light amplifier based on optical fiber parametric amplification, comprising a pump pulsed light source, a sensing pulsed light source, a synchronization device, a two-in-one optical coupler, an optical circulator, a parametric amplification optical fiber, a first optical filter, a photoelectric detector and a signal acquisition device. According to the distributed pulsed light amplifier, high-power pulsed light is used as pump light to generate an optical fiber parametric amplification effect near a zero-dispersion wavelength of an optical fiber, thereby amplifying a power of another sensing pulsed light. Meanwhile, due to the fact that effective optical fiber parametric amplification cannot be achieved through low-power light leakage outside a duration interval of the pump pulsed light, leaked light from the sensing pulsed light cannot be amplified, and the effect of amplifying a pulse extinction ratio can be achieved at the same time.

Abstract: A method is described for enabling Raman Based Distributed Temperature Sensing (DTS) systems to operate over larger environmental temperature ranges than any systems available today.

Abstract: An integrated detection and suppression system includes a fiber harness having at least one fiber optic cable for transmitting light defining at least one node arranged to measure one or more conditions. A light source is operably connected to the fiber harness to transmit light along the fiber harness to the at least one node. A control system is operably coupled to the fiber harness such that scattered light associated with the node is transmitted to the control system, wherein the control system analyzes the scattered light to determine at least one of a presence and magnitude of the one or more conditions. At least one suppressant outlet is associated with at least one node and is operably connected to the control system configured to initiate a response for the delivery of a volume of suppressant through a suppressant outlet associated with a particular node.

Abstract: A disclosed optical waveguide element includes a cladding portion formed on a substrate; an optical waveguide which is formed inside the cladding portion and has a refractive index higher than that of the cladding portion; an optical filter which is inserted into a slit formed in the cladding portion to divide the optical waveguide into a first optical waveguide and a second optical waveguide; and a first thin film element which is inserted into the slit along with the optical filter and is provided with a first thin film lens, wherein the first thin film lens provided in the first thin film element converges light that has propagated through the first optical waveguide and outputs into the slit into the second optical waveguide.

Abstract: The present invention is a temperature sensor for cryogenic systems using a fiber optic interrogation system that is capable of a large number of temperature readings across the cryogenic environment at high resolutions. The invention also includes a method of using such a system to measure temperatures in a cryogenic environment and a method of making such a system.

Abstract: An apparatus for monitoring vibration of a downhole component includes an optical fiber sensor including at least one optical fiber operably connected to an interrogation unit. The at least one optical fiber has a resonant segment that is fixedly attached to the component via attachment points on the component, the resonant segment between the attachment points being separate from the component and having a resonant frequency based at least on the length of the resonant segment.

Abstract: According to an embodiment there is provided a distributed optical sensing apparatus for determining of a primary quantity along a waveguide, the distributed optical sensing apparatus comprising: an electromagnetic radiation source adapted for coupling electromagnetic radiation into the waveguide to thereby generate in the waveguide (e.g. by interaction with the waveguide) a first response radiation and a different second response radiation; a detector device adapted for providing a first measurement signal indicative of the first response radiation and a second measurement signal indicative of the second response radiation; an evaluation unit adapted for deriving a secondary quantity (e.g. a loss) based on the first measurement signal and the second measurement signal; the evaluation unit being further adapted for deriving the primary quantity based on the secondary quantity and at least one of the first measurement signal and the second measurement signal.

Abstract: A temperature distribution measurement system includes an optical fiber, a laser light source optically connected to the optical fiber, a photodetector configured to detect light backscattered in the optical fiber, and a temperature distribution measurement unit configured to perform correction calculation using a transfer function on a measured temperature distribution obtained from an output from the photodetector. The temperature distribution measurement unit acquires an actual temperature distribution in a location where the optical fiber is laid and determines appropriateness of the transfer function by computing a difference between the measured temperature distribution after the correction and the actual temperature distribution.

Abstract: The present invention discloses distributed optical fiber temperature sensor based on optical fiber delay technology, including a tunable optical transmitter module, an optical receiver module, a signal processing and controlling module and multiple distributed sensing modules connected in series via transmission fibers. The multiple wavelengths optical signals transmitted from the tunable optical transmitter module respectively are transmitted into the first sensing module, and then transmitted out from the last sensing module. The output multiple wavelengths optical signals arrive at the optical receiver module. The optical receiver module converts optical signals of all wavelengths into electrical signals and transmits them into the signal processing and controlling module.

Abstract: A dynamic fiber temperature sensing package is provided herein. The sensing package includes a support structure, a holder coupled to the support structure, a sheath coupled to the support structure via the holder, and a fiber optic temperature sensor positioned within the sheath. The holder includes a material having a first thermal conductivity and the sheath includes a material having a second thermal conductivity, wherein the second thermal conductivity is greater than the first thermal conductivity.

Abstract: Automated systems and methods for testing the efficacy and reliability of distributed temperature sensing (DTS) system. The DTS system has a fibre optic sensing cable laid out on a structure to be monitored, and a DTS unit for sensing temperature along a sensing line at locations thereof. The DTS unit is optically coupled to the sensing cable. The sensing cable is optically coupled to a test cable to form the sensing line. Also provided, is a cooling device for cooling the test cable. A controller periodically actuates the cooling device to thereby test the efficacy and reliability of the DTS system. A relay configured for communication with the DTS unit and the controller is operable to trigger an alarm condition in response to a signal received from the DTS unit indicative that a temperature drop in the sensing line at a location thereof has been detected.

Abstract: An apparatus and method for suppressing stimulated Raman scattering (SRS) in fiber optic distributed temperature sensing systems by use of a combination of a pump and seed lasers with chosen frequency differences.

Abstract: The present invention discloses distributed optical fiber temperature sensor based on optical fiber delay technology, including a tunable optical transmitter module, an optical receiver module, a signal processing and controlling module and multiple distributed sensing modules connected in series via transmission fibers. The multiple wavelengths optical signals transmitted from the tunable optical transmitter module respectively are transmitted into the first sensing module, and then transmitted out from the last sensing module. The output multiple wavelengths optical signals arrive at the optical receiver module. The optical receiver module converts optical signals of all wavelengths into electrical signals and transmits them into the signal processing and controlling module.

Abstract: The present apparatus includes: an intensity ratio calculation unit configured to calculate a first and a second intensity ratios which are ratios of Stokes light intensity to anti-Stokes light intensity obtained when a light pulse is output to a first end and a second end of an optical fiber, respectively; a temperature calculation unit configured to calculate a temperature distribution along the optical fiber based on a reference temperature, the first and the second intensity ratios, and a total length loss ratio, which is a loss ratio of Stokes light to anti-Stokes light with regard to a total length of the optical fiber; and a total length loss ratio calculation unit configured to calculate the total length loss ratio based on the first and the second intensity ratios with regard to a location in a predetermined section close to both ends of the optical fiber whose temperature is kept constant.

Abstract: An optical fiber sensing apparatus includes: a substrate configured to deform in response to an environmental parameter; an optical fiber sensor including a core having at least one measurement location disposed therein and a protective coating surrounding the optical fiber sensor, the protective coating made from a polyimide material; and an adhesive configured to adhere the optical fiber sensor to the substrate, the adhesive made from the polyimide material.

Abstract: A temperature sensor includes a photon source, a fluorescent element and a photodetector. The fluorescent element includes a temperature-insensitive first fluorophore and a temperature-sensitive second fluorophore. The photodetector includes a first photosensor exhibiting a first spectral responsivity and a second photosensor exhibiting a second spectral responsivity. The first fluorophore may be selected to optimize the first spectral responsivity and the second fluorophore may be selected to optimize the second spectral responsivity. To measure a temperature of a surface, the fluorescent element may be placed adjacent to the surface and irradiated with a photon beam. First photons emitted from the first fluorophore and second photons emitted from the second fluorophore are collected.

Abstract: A dispersion and loss spectrum auto-correction distributed optical fiber Raman temperature sensor has a dual fiber pulsed laser module with dual Raman wavelength shifts. The laser module is composed of a power supply (11), an electronic switch (12), a primary laser (13) and a secondary laser (14), a first combiner (15), a bidirectional coupler (16), a multimode fiber (17), an integrated optical fiber wavelength division multiplexer (18), a second combiner (19), a direct detection system (20), a signal collection and processing system (21) and a display (22). The sensor uses two light sources that have two Raman wavelength shifts, wherein the central wavelength of backward anti-Stokes Raman scattering peak of the primary light source coincides with that of the backward Stokes scattering peak centre wavelength of the secondary light source, and the time domain reflection signal of the one-way optical fiber Rayleigh scattering is deducted.

Abstract: A component sensing system for monitoring the condition of ceramic tiles in a combustion chamber of a gas turbine engine. The sensing system includes an optical fiber that is mounted to the component being monitored, for example, the ceramic tiles in the gas turbine combustion chamber. The optical fiber can be formed in any suitable orientation or configuration, such as a meandering or serpentine orientation. The fiber is optically coupled to a Brillouin signal analyzer that provides an optical pulse to the sensing section of the fiber and detects Brillouin backscattering from the fiber as the pulse travels along the fiber. The frequency of the Brillouin backscattering signal is monitored relative to the distance along the sensing section of the fiber. A rise in temperature at a location of the fiber shows up in the analyzer as an increase in frequency of the backscattered signal.

Abstract: Optical sensors and sensing methods are provided. A particular method includes applying light to a first end of an optical fiber. Light reflected by at least one of a first photonic crystal sensor coupled to a second end of the optical fiber and a second photonic crystal sensor coupled to the second end of the optical fiber is detected. The first photonic crystal sensor exhibits a first reflection spectrum that changes responsive a first sensed parameter and the second photonic crystal sensor exhibits a second reflection spectrum that changes responsive a second sensed parameter. A parameter value of at least one of the first sensed parameter and the second sensed parameter is determined based on the detected light.

Abstract: An optical fiber is provided with a first measurement portion and a second measurement portion provided with covering layers different at least in any one of heat capacity and heat conductivity. Then, the first measurement portion and the second measurement portion are located in the same measurement position and light is inputted from a temperature measurement device into the optical fiber. Thereafter, the temperature measurement device receives backscattered light generated inside the optical fiber to measure temperature distribution in a longitudinal direction of the optical fiber. An analyzer analyzes a variation over time of the temperature distribution outputted from the temperature measurement device to calculate a temperature and a wind velocity in a measurement position where the first measurement portion and the second measurement portion are located.

Abstract: A Brillouin analysis sensor system comprising: a Brillouin analysis sensor; a polarization beam splitter/combiner, operably connected to the Brillouin analysis sensor between the sensor and the sensing fibre, for receiving polarized lightwaves from the sensor, combining the lightwaves and launching combined lightwaves waves in the sensing fibre a first direction, and a phase conjugate mirror at a free end of the sensing fibre for receiving combined lightwaves from the polarization beam splitter/combiner, rotating the polarization of the combined lightwaves and launching the rotated combined lightwaves in the sensing fibre in an opposing direction to the first direction.

Abstract: The present invention relates to a measuring method and a controlling method of measuring the physical quantity such as a fluid temperature distribution and the like by using an optical fiber sensing technique of BOCDA system. In the measuring method, an optical fiber that functions as a BOCDA-type optical fiber sensor is disposed along a flow direction of a fluid that flows though a pipe line and in the pipe line. Since the optical fiber directly contacts with the fluid that flows though the pipe line, it is possible to rapidly measure the fluid temperature distribution. Also, based on this measurement result, the controlling method adjusts each temperature of one or more heating/cooling means provided along the longitudinal direction of a pipe line, thereby controlling at high accuracy the fluid temperature distribution in the pipe line.

Abstract: A temperature measuring apparatus and a temperature measuring method that may simultaneously measure temperatures of objects in processing chambers. The temperature measuring apparatus includes a first light separating unit which divides light from the light source into measurement lights; second light separating units which divide the measurement lights from the first light separating unit into measurement lights and reference lights; third light separating units which further divide the measurement lights into first to n-th measurement lights; a reference light reflecting unit which reflects the reference lights; an light path length changing unit which changes light path lengths of the reference lights reflected by the reference light reflecting unit; and photodetectors which measure interference between the first to n-th measurement lights reflected by the objects to be measured and the reference lights reflected by the reference light reflecting unit.

Abstract: A plasma processing apparatus and a temperature measuring method that may measure a temperature of an object in a processing chamber by a low-coherence interferometer without forming a hole in a holding stage or an upper electrode of the plasma processing apparatus, thereby performing a plasma process of a substrate with high precision and uniformity. The plasma processing apparatus is implemented by disposing a light source collimator outside of a light source window, disposing a light-receiving collimator outside of a light-receiving window, allowing a measurement light emitted from the light source collimator to pass through the light source window to be obliquely emitted to a surface of the object to be measured, and allowing the reflected measurement light to pass through the light-receiving window to be incident on the light-receiving collimator. The temperature of the object in the processing chamber may be measured by the low-coherence interferometer.

Abstract: Apparatus for spatially resolved temperature measurement, comprising at least one optical fibre (4) for spatially resolved temperature measurement, at least one laser light source (1), the light (11) from which can be coupled into the optical fibre (4), wherein those components (12, 12a, 12b) of the light (11) produced by the laser light source (1) which are scattered back in the optical fibre (4) can be coupled out of the optical fibre (4) and detected, modulator means (2) permitting the modulation of the light (11) that is to be coupled into the optical fibre (4), and also demodulator means (5, 6) which permit a demodulation of those components (12, 12a, 12b) of the light (11) which are coupled out of the optical fibre (4), wherein the demodulator means (5, 6) are designed as optical demodulator means (5, 6) and/or wherein the modulator means (2) are designed as optical modulator means (2).

Abstract: A fiber optic splice housing and integral dry mate connector system. In a described embodiment, a fiber optic connection system includes optical fiber sections in respective conduit sections. Each of the conduit sections is received in the housing assembly. An optical connection between the optical fiber sections is positioned within the housing assembly.

Abstract: A temperature sensor that has an elongated sensing element having a length of at least 10 m, measured at a temperature of 20° C. The elongated sensing element includes an elongated jacket and an optical fiber mounted in the jacket and having an EFL of at least 0.35%, wherein the elongated sensing element has an average temperature error of less than 2° C.

Abstract: A fiber optic splice housing and integral dry mate connector system. In a described embodiment, a fiber optic connection system includes optical fiber sections in respective conduit sections. Each of the conduit sections is received in the housing assembly. An optical connection between the optical fiber sections is positioned within the housing assembly.

Abstract: A measuring device including at least one optical fiber which contains a series of Bragg gratings distributed between first and second ends of the fiber. A light source is arranged to emit a luminous flux at multiple wavelengths incident on the first end of the fiber, and an instrument connected to the second end of the fiber measures the power of the light transmitted at each emitted wavelength, enabling implementation of the method. In the method the power of the light transmitted by the optical fiber in a spectrum including wavelengths is measured.

Abstract: An apparatus for measuring environmental parameters includes: an optical fiber sensor configured to be disposed along a path in an environment to be measured, the path of the optical fiber sensor defining a longitudinal axis; and at least one section of the optical fiber sensor configured so that an entire length of the at least one section is exposed to an at least substantially homogeneous environmental parameter, at least part of the at least one section extending in a direction having a radial component relative to the longitudinal axis.

Abstract: A temperature sensor that has an elongated sensing element having a length of at least 10 m, measured at a temperature of 20° C. The elongated sensing element includes an elongated jacket and an optical fiber mounted in the jacket and having an EFL of at least 0.35%, wherein the elongated sensing element has an average temperature error of less than 2° C.

Abstract: The invention relates to a method for integrating an optical waveguide (3) of a temperature sensor and/or strain sensor into a temperature and/or strain measuring component (1) made of a base material (2), onto which a coating (5) is applied. The optical waveguide (3) is arranged on a predetermined measurement plane, whereupon a coating (5) is applied. The aim of the invention is to allow an optical waveguide (3) to be accurately integrated into and tightly joined to the body of a temperature and/or strain measuring component (1).

Abstract: The polarization-maintaining fiber of the invention includes a core (1) made of germanium doped silica glass; a stress-applying part (3) made of boron doped silica glass; a cladding (2) made of pure silica glass; and a polyimide coating layer (4) with a thickness of 10 ?m or less that surrounds the outer periphery of the cladding (2).

Abstract: A fiber-optic temperature sensor assembly comprises a cap with an inner cavity. A sensor substance is received loosely in the inner cavity of the cap, the sensor substance having light-emitting properties adapted to change with specific temperature variations. An optical fiber has a first end received in the inner cavity of the cap and fusion spliced thereto, and a second end of the optical fiber being adapted to be connected to a processing unit for transmitting light signals from the sensor substance to the processing unit when the fiber-optic temperature sensor assembly is subjected to specific temperatures. A method for manufacturing the fiber-optic temperature sensor assembly is defined.

Abstract: A sensing cable has a sensing fiber assembly, which includes a pair of sensing fibers joined by a turnaround section with a modal filter, at a terminating end of the sensing fibers. The sensing cable also includes an inner sleeve that surrounds the sensing fiber assembly and an armored casing that caps the terminating end of the inner sleeve. The sensing cable has a low profile and its components are each made of high temperature and hydrogen tolerant materials and are capable of prolonged operation at high temperatures, such as up to 300° C., in hydrogen environments over long lengths of fiber. A distributed thermal sensing (DTS) interrogator is connected to the sensing cable and performs DTS measuring according to protocols and algorithms that leverage the modal filter of the turnaround section to calculate temperature readings along the sensing fiber assembly.

Abstract: A method for calculating a temperature along a length of a sensing fiber of a distributed thermal sensing (DTS) system. The sensing fiber, which has two ends, is heat resistant for operation up to 300° C. The DTS system includes a two-channel DTS interrogator that is attached to each of the two ends of the sensing fiber. The DTS interrogator interrogates the sensing fiber from both ends, calculates a temperature difference between co-located positions along the length of the sensing fiber for each end, and determines an error associated with the temperature difference. Based on the determined error, a corrected temperature value along the length of the sensing fiber is calculated and outputted.

Abstract: A multi-mode optical waveguide fiber including a central core region having an outer radius surrounded by an inner cladding region having an outer radius, the inner cladding region having a lower index of refraction than the central core region, wherein both the central core and inner cladding regions are doped with fluorine, wherein the refractive index profile of the central core region is of the gradient index type and the central core region in the range of r?[0-ra] comprises germanium at a maximum concentration within the range of 0.5 percent by weight to 4.0 percent by weight taken at a given radius, wherein said fiber has an Overfilled Modal Bandwidth >500 MHz·km at a wavelength of 850 nm and 1300 nm, according to IEC 60793-2-10.

Abstract: For a temperature measurement in areas having electromagnetic fields, shielding devices must be provided. According to the proposed technique, at least one temperature sensor is designed as a fiber-optic sensor having Bragg gratings (FBG), wherein the sensor is arranged in a non-metallic housing that precludes or minimizes expansion effects for the individual FBG sensors. For example, the proposed technique can be used advantageously to measure the temperature distribution in oil sand deposits, for which purpose a suitable measuring arrangement is required.

Abstract: A temperature measurement system includes: a laser light source; an optical fiber; and a temperature measurement unit configured to acquire a measured temperature distribution of a temperature of a temperature measurement area along an installation path of the optical fiber by detecting backscattered light of the incident laser light in the optical fiber, wherein the temperature measurement unit sequentially makes a correction for the measured temperature distribution a plurality of times so as to make a square error between a convolution of a transfer function of the optical fiber along the installation path and the corrected temperature distribution and the measured temperature distribution smaller in each of the corrections, and the temperature measurement unit also replaces a corrected temperature at a specific point of the installation path with an estimated temperature at the specific point in each of the corrections.