CN102353474A - Seawater temperature profile BOTDA measuring method based on optical fiber Brillouin scattering principle - Google Patents
Seawater temperature profile BOTDA measuring method based on optical fiber Brillouin scattering principle Download PDFInfo
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Abstract
A seawater temperature profile BOTDA measuring method based on an optical fiber Brillouin scattering principle is disclosed. In the invention, a sensitive optical cable is formed by combining a pressure sensing fiber which directly contacts with the seawater and a temperature sensing fiber which shields seawater pressure. A measuring part of a measuring system based on a BOTDA principle comprises: a narrow linewidth laser, an optical coupler, a pulse generator, a first light modulator, a light amplifier, a sweeping-frequency electrooptic modulator, a circulator, a grating filter, an optical isolator, a polarization scrambler, an optical filter, an optical switch and a Brillouin frequency shift detection unit. The sensitive optical cable used in the invention has a small volume, is convenient to be used and possesses good seawater corrosion resistance. The measuring system has high reliability and sensitivity, can provide continuous temperature field distribution of the seawater profile and is suitable for real-timely measuring the seawater temperature profile continuously.
Description
Technical field
The present invention relates to a kind of method, belong to field of measuring technique along depth direction measurement ocean temperature distribution situation.
Background technology
Ocean temperature is the important content in oceanographic survey, the monitoring, is indispensable technical parameter in marine hydrology, meteorological observation and the investigation.The measurement of ocean temperature section has crucial Practical significance to research Marine Sciences, marine environmental monitoring, seasonal climate prediction and sea fishery etc.So-called seawater temperature profile measurement is meant along depth direction measures the ocean temperature distribution situation.Need provide the temperature information of the depth of water and respective depth, long-time real-time monitored also need provide observation time.
The major equipment that is used for seawater temperature profile measurement both at home and abroad is ocean, a thermohaline deep-sea visualizer (CTD), and instrument mainly is equipped with the electronic surveying circuit by temperature, salinity and three kinds of sensors of pressure and constitutes.It with electronic part encapsulations such as data acquisition unit, data transmission unit and power supplys in high-intensity pressure vessel.CTD thermometric degree of accuracy can reach 0.001 ℃ of grade, and it patrols thermometric degree, salinity and the degree of depth through hanging in the different depth pointwise, and shortcoming is to realize the variation of real-time and long-time simultaneous observation temperature profile.
Chinese patent " seawater temperature sensor chain " has proposed the quasi-distributed sensor chain structure of a kind of many linear transducer arrays type, and its structure comprises temperature sensor, pressure transducer, float, wirerope, hangs steel column, load-bearing steel column and shielded cable.Wherein, the encapsulation type thermistor temperature sensor is embedded on the float, and float is configured on the wirerope with 5cm to 100cm spacing, and the two ends of wirerope are locked in the steel bowl of hanging steel column and load-bearing steel column with wirerope steel bushing and wire fixture respectively.Pressure transducer is fixed on the top of the load-bearing steel column of thermistor chain lower end, and the shielded cable of a branch of 33 each 50m length is passed by the center pit of float, as transmission cable.
In addition; The SEAGUARD sensor chain system of Norway AANDERAA company adopts the quasi-distributed sensor chain structure of many linear transducer arrays type; Can be used for measuring ocean environment parameters such as dissolved oxygen DO, conductivity, temperature, electric current, pressure and morning and evening tides, the basic element of character comprises sensor chain and registering instrument.This system can adopt the self-tolerant working method, and each back opening entry measurement data of throwing in after measurement after a while, is salvaged the water surface, and the storage data of extracting in the registering instrument are carried out analyzing and processing.If apolegamy is gathered in real time and the communications accessory also can be realized real-time measurement.This system can establish 25 measurement points, adopts sensor chain stationary fixture fixation of sensor at each measurement point, can fix 2 sensors in each anchor clamps.300 meters of sensor chain length overall Ke Da, system adopts the encapsulation type thermistor temperature sensor.
Though more than two kinds of quasi-distributed sensor chain structures overcome CTD and can only pointwise patrol the shortcoming of surveying and can not measuring in real time, temperature chain volume is huge, is inconvenient to use the winch folding and unfolding; The measured node quantity of total system is limited by power supply capacity, is difficult to satisfy spatial resolution height (observer nodes is intensive) and the big application requirements of the scope that fathoms; Anti-interference and shielding problem in electrical isolation in the needs consideration seawater and the electric signal transmission course; Can only measure fixing spatial point position temperature and depth information, can not implementation space continuous distribution formula truly measure.
Distribution type fiber-optic Brillouin sensing technology is a kind of novel measuring technique, and only having needs one-shot measurement can obtain along particular advantages such as continuous distribution information, measuring accuracy height, accurate positioning, the distance sensing of tested of whole optical fiber are far away.Adopt distribution type fiber-optic Brillouin sensing technology to realize that seawater temperature profile measurement need use special optical cable, specific (special) requirements such as this optical cable should be able to satisfy the tolerance marine corrosion, have good tension and compressive property, volume is little, in light weight, be easy to lay; In addition, owing to the influence of ocean current, optical cable can not keep desirable perpendicular attitude, and its length is also inconsistent with the actual depth of water, so require seawater temperature profile measurement with optical cable ability while sense temperature and corresponding Water Depth Information.But existing optical cable can not satisfy above application demand.
Summary of the invention
The object of the present invention is to provide a kind of ocean temperature section BOTDA measuring method based on the optical fiber Brillouin scattering principle; It can be in real time and simultaneous observation temperature profile dynamic change for a long time; And can the continuous coverage of implementation space point, needn't consider advantages such as electrical isolation and anti-interference problem.
The alleged problem of the present invention realizes with following technical proposals:
Brillouin scattering based on the principle of optical water temperature measurement section BOTDA, it will directly contact with the seawater pressure sensor fiber and the shielding of the water temperature of the pressure sensor fiber combined together to form a sensing fiber, by narrow line width of the laser, optical coupler, a pulse generator, the optical modulator, grating filter, an optical amplifier, a polarization controller, circulators, optical switches, optical detectors, and the Brillouin frequency shift detection units based on a Brillouin optical time Domain reflection principle of measuring part measuring system when measuring the sensor cable into the sea, narrow linewidth laser optical signal emitted by the optical coupler into two signals, one output optical signal as the LO light, the a second polarization controller controls the polarization state of the optical signal LO; other light signal by a first polarization controller controlling a polarization state of the optical signal, the pulse generator and the first optical modulator modulating a pulse light, pulsed light through the first an optical amplifier, filtered by the first grating filter introduced the first optical amplifier noise radiated from the heat, and then the circulator and the light switch into the sensing fiber in a sensing fiber, the sensing fiber produced since the release Brillouin backscattered light through the circulator and the second optical amplifier and a second grating filter, the photodetector with the outside of the LO light achieve optical heterodyne detection, and finally by the Brillouin frequency shift detection unit from the microwave sweep method the photodetector output signal is demodulated and strike the sensing fiber optic cable along the length distribution of the scatterers Brillouin frequency shift information, and then based on the Brillouin frequency shift and temperature, water depth corresponding to different function of the static pressure relationship, obtained along the sensing fiber length distribution and the temperature distribution of water depth, water temperature profiles to achieve the distributed measurement.
Above-mentioned ocean temperature section BOTDA measuring method based on the optical fiber Brillouin scattering principle; Said Brillouin shift detecting unit is by microwave local oscillator; Frequency mixer; Amplifier; Low-pass filter; Data collecting card and computing machine are formed; During detection; Thereby the frequency of regulating microwave local oscillator by certain frequency interval one by one travels through given frequency range; The brillouin frequency shifting signal of the microwave signal of microwave local oscillator output and photoelectric detector output carries out mixing in frequency mixer; Output signal after the mixing amplifies and low-pass filter filtering through amplifier; By the data collecting card image data and be transferred to computing machine and handle; For each scattering point that distributes along fiber lengths; All data that computing machine will obtain in a microwave frequency sweep cycle are carried out the Lorentz match; Obtain Brillouin's spectral distribution curve, the frequency that the amplitude maximum point is corresponding in the curve is the Brillouin shift of this scattering point.
The alleged problem of the present invention can also adopt another technical scheme to realize:
A kind of ocean temperature section BOTDA measuring method based on the optical fiber Brillouin scattering principle; It constitutes sensing optic cable with pressure sensing optical fiber direct and contact with sea water with the temperature sensing optical fiber combination that has shielded seawater pressure together, and forms a measure portion based on the measuring system of Brillouin optical time domain analysis principle by narrow linewidth laser, photo-coupler, pulse producer, first photomodulator, image intensifer, frequency sweep electrooptic modulator, circulator, grating filter, optoisolator, scrambler, optical filter, photoswitch, Brillouin shift detecting unit; Said frequency sweep electrooptic modulator comprises second Polarization Controller, sweep generator, second photomodulator; Sensing optic cable is put into seawater during measurement; The light signal that narrow linewidth laser produces is divided into two-way through photo-coupler; One road light signal is through the polarization state of first Polarization Controller control light signal; Become burst pulse light by pulse producer, first light modulator modulates; Through the spontaneous emission noise that first image intensifer amplifies, the first grating filter filtering, first image intensifer produces, get into a sensor fibre in the sensing optic cable through first optoisolator, circulator, photoswitch again; Another road optical signals frequency sweep electrooptic modulator produces the continuous light signal of about 11 GHz frequency displacements, chooses the upper side band of modulated signal through optical filter, gets into another sensor fibre in the sensing optic cable through second optoisolator, scrambler, photoswitch; Article two, optical fiber constitutes loop through the joints of optical fibre under water; When the two-way light frequency difference of transmission was consistent with the Brillouin shift of certain scattering point in the optical fiber in opposite directions in the Fiber In The Loop FITE, the stimulated Brillouin scattering signal that produces at this scattering point in the optical fiber was the strongest; The stimulated Brillouin scattering signal gets into the Brillouin shift detecting unit through photoswitch, circulator; Adopt electric light frequency sweep method to ask for by the Brillouin shift detecting unit along the Brillouin shift information of each scattering point of sensing optic cable fiber lengths distribution; And then according to the funtcional relationship of Brillouin shift and temperature, corresponding different sea water advanced static pressures; Obtain sea water advanced and Temperature Distribution, realize the distributed measurement of ocean temperature section along the sensor fibre length distribution.
Above-mentioned ocean temperature section BOTDA measuring method based on the optical fiber Brillouin scattering principle; Said Brillouin shift detecting unit is by photoelectric detector; Amplifier; Low-pass filter; Data collecting card and computing machine are formed; Photoelectric detector is an electric signal with the stimulated Brillouin scattering light conversion of signals; Amplify and low-pass filter filtering through amplifier; By the data collecting card image data and be transferred to computing machine and handle; For each scattering point that distributes along fiber lengths; All data that computing machine will obtain in a microwave frequency sweep cycle are carried out the Lorentz match; Obtain Brillouin's spectral distribution curve, the frequency that the amplitude maximum point is corresponding in the curve is the Brillouin shift of this scattering point.
The method of confirming the scattering point position in above-mentioned two kinds of technical schemes is identical: send light pulse from an end of optical fiber constantly at t=0; Begin to receive a series of scattered signal from t=0, measure the corresponding scattered signal of certain scattering point and the time interval between the input optical pulse at the transmitting terminal of pulsed light
t, according to formula
L=
Ct/(2
n) confirm the fiber lengths between this scattering point and the pulse light incident side
L, in the formula
cBe the light velocity in the vacuum,
nRefractive index for optical fiber.
The sensing optic cable that uses in above-mentioned two kinds of technical schemes is identical; By two button stainless steel flexible hoses and sub-optical cable of temperature inside sensing and the sub-optical cable composition of pressure sensing; The sub-optical cable of said temperature sensing by temperature sensing optical fiber be sleeved on its outside stainless steel sleeve pipe and form; The sub-optical cable of said pressure sensing is by pressure sensing optical fiber and be sleeved on its outside bourdon tube successively and the stainless steel wire mesh grid is formed, and said pressure sensing optical fiber surface is coated with polyurethane pressure sensitive material layer.
Above-mentioned ocean temperature section BOTDA measuring method based on the optical fiber Brillouin scattering principle, the temperature sensing optical fiber in the sub-optical cable of said temperature sensing is provided with 2～4; The sub-optical cable of said pressure sensing is provided with two.
The beneficial effect of sensing optic cable that the present invention designs is: two button stainless steel flexible hoses have good tension and lateral pressure resistant performance, are used for load-bearing so that optical cable is rendered to projected depth; Adopt the stainless steel sleeve pipe to have the anti-simultaneously seawater pressure of good temperature-sensitive performance, entry terminal water-tight during use makes temperature sensing optical fiber not affected by force, improves thermometric precision; The polyurethane pressure sensitive material has higher pressure sensitivity, can improve spatial resolution when being used for bathymetric survey, proofreaies and correct optical cable and tilts for the influence of section temperature-measuring results because of ocean current.Bourdon tube and stainless steel wire mesh grid are used to strengthen the physical strength of optical fiber, are easy to dry, and be anticorrosive.
The present invention will be applied to the real-time monitoring of ocean temperature section based on the measuring technique of optical fiber Brillouin scattering principle; The problem that existing measurement temperature chain volume is huge, can not realize continuous monitoring can be solved well, and the continuous temperature field distribution of seawater section can be provided.
Description of drawings
Below in conjunction with accompanying drawing the present invention is made further detailed description.
Fig. 1 is the sectional view of sensing optic cable proposed by the invention;
Fig. 2 is the BOTDR optical fiber sensing system;
Fig. 3 is the BOTDA optical fiber sensing system;
Fig. 4 composes distribution example along the Brillouin on the fiber lengths.
Each label is among the figure: 1, two button stainless steel flexible hoses; 2, temperature sensing optical fiber; 3, stainless steel sleeve pipe; 4, stainless steel wire mesh grid; 5, bourdon tube; 6, pressure sensing optical fiber; 7, polyurethane pressure sensitive material layer; EOM1, first photomodulator; EOM2, second photomodulator; EDFA1, first image intensifer; EDFA2, second image intensifer; PC1, first Polarization Controller; PC2, second Polarization Controller; OF, optical filter; PS, scrambler; GX, sensor fibre.
Used symbol in the literary composition:
T,Ocean temperature;
P, seawater pressure;
, the sub-optical cable of temperature is in temperature
TThe time corresponding Brillouin shift;
T r ,Reference temperature;
, the corresponding Brillouin shift of the sub-optical cable of temperature when reference temperature;
, the sub-optical cable of pressure is in temperature
TCorresponding Brillouin shift during with pressure P;
P r , reference pressure;
, the corresponding Brillouin shift of the sub-optical cable of pressure when reference temperature and reference pressure;
, be the temperature sensing coefficient of the sub-optical cable of temperature;
, the sub-optical cable of pressure the temperature sensing coefficient;
, the sub-optical cable of pressure the pressure sensing coefficient; BOTDR, Brillouin light Time Domain Reflectometry; BOTDA, Brillouin optical time domain analysis.
Embodiment
BOTDR and BOTDA system realize distributed measurement by the method that detects Brillouin shift; Measuring method of the present invention is: during measurement measuring instrument is installed in oceanographic buoy, boats and ships or offshore oil platform; Sensing optic cable is vertically put into seawater; Send light pulse from an end of optical fiber; In fiber medium, produce Brillouin scattering; Temperature and pressure can cause that all the frequency displacement of Brillouin scattering changes; Fig. 4 is a kind of embodiment (is stairstepping along the Temperature Distribution of fiber lengths by 5 intervals and changes, have nothing in common with each other corresponding to the Brillouin shift of each interval peak light strength).As can be seen from Figure 4, the brillouin spectrum along the 150m sensor fibre shows the temperature variant obvious skew of centre frequency (Brillouin shift) that Brillouin composes when temperature variation.The degree of depth of seawater is embodied by the hydrostatic pressing measured value of seawater, is obtained by the sub-optical cable of pressure sensing in the present embodiment.The temperature of seawater is obtained by the sub-optical cable of temperature sensing.Utilize the Brillouin shift detecting unit to measure the frequency displacement numerical value of each sub-optical cable along each scattering point of fiber length.Measure equation is:
Wherein,
T, PDifference representation temperature, pressure;
T r , P r Be respectively reference temperature, reference pressure;
With
Be respectively the sub-optical cable of temperature in temperature
TWith
T r The time corresponding Brillouin shift; For the sub-optical cable of temperature sensing because the strain that brings of seawater pressure of having adopted the stainless steel sleeve tube shield, Brillouin shift only and temperature correlation,
Temperature sensing coefficient for the sub-optical cable of temperature;
With
Be respectively the sub-optical cable of pressure in temperature
T, the corresponding Brillouin shift when pressure P and reference temperature, reference pressure;
,
Be respectively the temperature and pressure transduction factor of the sub-optical cable of pressure.Through laboratory calibration of the system (see the back of the specific process step of measuring part) to determine the coefficients
,
,
.
During actual measurement; Adopt the Brillouin shift detecting instrument to measure the Brillouin shift
of the sub- optical cable of TEMP along each scattering point signal of fiber lengths distribution; Demarcate temperature coefficient
by the laboratory, can find the solution Temperature Distribution along fiber lengths according to formula (1).For the sub-optical cable of pressure sensing, its Brillouin shift comprises two parts: the frequency displacement that frequency displacement that temperature variation is introduced and hydrostatic pressing are introduced.The Temperature Distribution numerical value that the sub-optical cable of temperature sensing is recorded, adopt the Brillouin shift of each scattering point signal that the sub-optical cable of pressure sensing that the Brillouin shift detecting instrument measures distributes along fiber lengths along cable length
, the laboratory calibration coefficient
With
Substitution formula (2) is found the solution the hydrostatic force distribution along fiber lengths, according to the force value of seawater
PTry to achieve the sea water advanced of correspondence
H:
, wherein,
Proportion for seawater.And then obtain sea water advanced information along fiber lengths, finally draw out temperature-depth curve by above measured value.
Utilize the attitude of optical cable of the present invention can also provide the ocean current distribution situation of coastal water depth direction, the relation that the sub-optical cable of fiber lengths and pressure is measured between sea water advanced promptly reflects the attitude of optical cable.
Referring to Fig. 1, optical cable provided by the invention comprises: two stainless steel flexible hose 1, the sub-optical cable of temperature sensing and two sub-optical cables of pressure sensing buckled.The sub-optical cable of temperature sensing is made up of temperature sensing optical fiber 2 and stainless steel sleeve pipe 3 thereof.The sub-optical cable of pressure sensing comprises pressure sensing optical fiber 6, bourdon tube 5 and stainless steel wire mesh grid 4, and pressure sensing optical fiber 6 surfaces coated are covered with polyurethane pressure sensitive material layer 7.
The main making step of optical cable comprises among the present invention:
1, temperature sensing optical fiber 2 coated with thermally conductive ointment (when improving temperature control, reducing the optical fiber wearing and tearing) coat stainless steel sleeve pipe 3 then, process the sub-optical cable of temperature sensing;
2, with pressure sensing optical fiber 6 coated with polyurethane pressure sensitive material layers 7, outsourcing bourdon tube 5 and stainless steel wire mesh grid 4 are processed the sub-optical cable of pressure sensing (two) then;
3, three strip optical cables are twisted the coiled one so that improve counter-bending ability, the two button of outsourcing stainless steel flexible hoses 1 are processed this optical cable then.Attention: earlier with the slight strand of the sub-optical cable of temperature sensing around, windings of again two sub-optical cables of pressure sensing being taken advantage of a situation, defence damage polyurethane pressure sensitive material layer 7.
This cable outer diameter is 10～12mm, and the resistance to tension maximum can reach 3000 newton, 350 meters of cable lengths.Two button stainless steel flexible hoses 1 are that the steel band of 0.2～0.3mm is processed by thickness.The about 3mm of stainless steel sleeve pipe 3 overall diameters of the sub-optical cable of temperature sensing, thick 0.2mm.The pressure sensitive material that the sub-optical cable of pressure sensing applies requires low Young modulus and higher Poisson ratio (to be respectively 8*10 in the present embodiment
7Pa and 0.4).Naked fine 2～3 one magnitude that improve of the remolding sensitivity of the sub-optical cable of pressure sensing.Stainless steel wire mesh grid 4 adopts the STAINLESS STEEL WIRE braiding of diameter 0.2mm to form; Close the turning to of stainless steel wire that lateral pressure resistant bourdon tube 5 adopts diameter 1mm.
During practical implementation, the temperature sensing optical fiber 2 in the sub-optical cable of temperature sensing is bonding by certain spaced points and stainless steel sleeve pipe 3 inwalls in the whole length range of optical fiber along axis direction, guarantee that the optical fiber between the adhesive spots is in the state that freely relaxes.Each parts of the sub-optical cable of pressure also select spaced points bonding, the deadweight of being born sub-optical cable by stainless steel wire mesh grid 4.
Referring to Figure 2, the optical fiber sensing system BOTDR, the narrow linewidth laser light emitted by the optical coupler outputs, light as the polarized light, a second polarization controller (PC2) for controlling the polarization state of the optical signal LO ; other light via a first polarization controller (PC1) controls the polarization state of the optical signal through the first electro-optic modulator (EOM1) is modulated into pulse light, via the first optical amplifier (EDFA1) amplified, filtered by the first grating filter out the first optical amplifier from the heat emission (ASE) noise, the optical signal by the circulator into the sensing fiber and the optical switch in an optical fiber, the fiber produced by the Brillouin backscattered light and a second optical circulator Amplifier (EDFA2) and a second grating filter, the photodetector with the outside of the LO light achieve optical heterodyne detection, and microwave frequency sweep method outputs an electrical signal from the photodetector is demodulated Brillouin frequency shift information, adjustment the center frequency of the local oscillator of microwave, microwave local oscillator signal and the Brillouin mixing, the output signal by a low-pass filter, by the data acquisition card and transfer data to the computer for Lorentz fitting, maximum point amplitude spectrum The frequency corresponding to the scattering point is the Brillouin frequency shift.
Referring to Fig. 3; In the BOTDA optical fiber sensing system; Narrow linewidth laser is divided into two-way through photo-coupler with light signal; One road optical signals, first photomodulator (EOM1) is modulated into burst pulse light; First Erbium-Doped Fiber Amplifier (EDFA) (EDFA1) amplifying optical signals; Spontaneous radiation (ASE) noise that the first grating filter filtering, first Erbium-Doped Fiber Amplifier (EDFA) (EDFA1) produces; The direction of propagation of optoisolator restriction light, last optical signals photoswitch gets into an end of a certain optical fiber in the sensing optic cable; Another road optical signals second photomodulator (EOM2) produces the continuous light signal of about 11 GHz frequency displacements; Second Polarization Controller (PC2) and scrambler (PS) carry out the control of polarization state; Optical filter OF chooses the upper side band of modulated signal, and last light signal gets into an end of another optical fiber of sensing optic cable through photoswitch; Article two, optical fiber constitutes loop through the joints of optical fibre under water.When the two-way light frequency difference of transmission was consistent with the Brillouin shift of optical fiber point in opposite directions in the Fiber In The Loop FITE, optical fiber was the strongest at the stimulated Brillouin scattering signal that this point produces.The stimulated Brillouin scattering signal gets into the Brillouin shift detecting unit through circulator, is accomplished functions such as opto-electronic conversion, data filtering, Lorentz match, data management and demonstration by the Brillouin shift detecting unit.
Device name that adopts in the Brillouin system in the present embodiment and model are:
Narrow linewidth laser adopts TL-2020-C-102-A; Photo-coupler, splitting ratio are 50:50; Photomodulator (EOM) adopts 10 Gb/s lithium niobate light intensity modulator MOD22212; Pulse producer adopts 81110A; Image intensifer (EDFA) adopts EDFA-PA-1-X-FC type Erbium-Doped Fiber Amplifier (EDFA); Circulator adopts 3 mouthfuls of circulators; Grating filter adopts parameter 1550nm ± 40nm grating; Polarization Controller (PC) adopts PCD-M02; Photoelectric detector adopts UltraFast-200SM; Microwave local oscillator adopts HWFS46-10K; Frequency mixer adopts HWMY82C; Low noise amplifier adopts NLNA00201L30; Low-pass filter adopts LPF100; Data collecting card adopts ZT410-2X; Sweep generator (frequency synthesizer) adopts HWFS46-10K; Optical filter (OF) adopts 1550.0336nm ± 0.08nm grating; Optoisolator, PIIS1-121122; Scrambler (PS) adopts PCD-003, and photoswitch adopts PRMS-12T1L1222 and PRMS-14M1L1222..
Measuring process of the present invention is:
1. laboratory temperature is demarcated: get sensing optic cable sample (being no less than 15 meters in the present embodiment) and put into attemperating unit and carry out temperature value calibration normal pressure (reference pressure) under, at first regulate attemperating unit to 35 ℃, successively decrease with the temperature interval of setting then, up to-2 ℃.The demarcation of temperature is confirmed according to actual measurement requirement at interval, according to the temperature gradient distribution rule of 300 meters seawater, sets series and demarcates temperature value in the present embodiment: 35 ℃, and 25 ℃, 15 ℃, 5 ℃ ,-2 ℃.Here getting reference temperature is 25 ℃.Adopt the Brillouin shift detecting instrument to measure corresponding each temperature spot
TThe Brillouin shift of following temperature sensing optical fiber
Thereby, same temperature spot measure down repeatedly to nominal data (
) repeatedly measured value average to obtain better repeatability and precision, with each temperature value
TAnd corresponding Brillouin shift
Mean value carries out linear fit according to formula (1) and finds the solution coefficient
Because normal pressure is measured down, in the formula (2)
P-P r =0, adopt the Brillouin shift detecting instrument to measure corresponding each temperature spot
TThe Brillouin shift of downforce sensor fibre
, same temperature spot is measured repeatedly down, thus to nominal data (
,
T) repeatedly measured value average to obtain better repeatability and precision, with each temperature value
TAnd corresponding Brillouin shift
Mean value carries out linear fit according to formula (2) and finds the solution coefficient
..
2. laboratory pressure calibration: get sensing optic cable sample (being no less than 15 meters in the present embodiment) and put into pressure and regulate container and carry out the calibration of normal temperature (reference temperature) downforce value; At first regulating force value is 0MPa; Increase progressively with the pressure intervals of setting then, up to 3MPa.Demarcate at interval and confirm, set serial calibration value: 0MPa, 0.5MPa, 1MPa, 1.5MPa, 2MPa, 2.5MPa, 3MPa in the present embodiment according to actual measurement requirement.Because normal temperature is measured down, in the formula (2)
T-T r =0, adopt the Brillouin shift detecting instrument to measure corresponding each pressure
PThe Brillouin shift of some downforce sensor fibre
, same spot pressure measure repeatedly down in case to nominal data (
,
P) repeatedly measured value average, thereby obtain better repeatability and precision, with each force value
PAnd corresponding Brillouin shift
Mean value carries out linear fit according to formula (2) and finds the solution coefficient
..
3. before measuring in real time, connect each unit of system earlier, whether check system is in proper working order.
4. guarantee that system lays sensing optic cable along depth direction through optical cable laying under the good situation of system performance.
5. optical cable laying finishes and then can formally begin the real-time measurement of ocean temperature section.The control photoswitch with laser pulse generator cut-in temperature sensor fibre 2, is received the brillouin frequency shifting signal that causes along the temperature in the fiber lengths scope by the Brillouin shift detecting unit earlier.Control photoswitch again after accomplishing temperature survey,, receive the brillouin frequency shifting signal that causes along the temperature and pressure acting in conjunction in the fiber lengths scope by the Brillouin shift detecting unit laser pulse generator cut-in pressure sensor fibre 6.
6. Brillouin shift detecting unit data that 5. step is obtained by formula the calibrating parameters that 1. 2. provides of (1), formula (2) and step carry out demodulation, finally calculate along temperature in the fiber lengths scope and depth value.
7. realize functions such as printing reports (describing ocean temperature-depth relationship), data transmission with curve and form by the management software of installing in the Brillouin shift detecting unit.
During practical implementation; If receive the restriction of demarcating container; Can adopt the method for demarcating the back stranding; That is: demarcate earlier temperature-sensitive optical fiber 2 and the pressure sensing optical fiber 6 of coated with polyurethane pressure sensitive material layer 7 in the sensing optic cable; The detailed process of demarcating is 1. 2. identical with step; And then the making stranding, but note trying not to introduce stress in the stranding process.
Claims (4)
1. ocean temperature section BOTDA measuring method based on the optical fiber Brillouin scattering principle; It is characterized in that; It constitutes sensing optic cable with pressure sensing optical fiber direct and contact with sea water with the temperature sensing optical fiber combination that has shielded seawater pressure together, and by narrow linewidth laser; Photo-coupler; Pulse producer; First photomodulator; Image intensifer; The frequency sweep electrooptic modulator; Circulator; Grating filter; Optoisolator; Scrambler; Optical filter; Photoswitch; The Brillouin shift detecting unit is formed the measuring system based on the Brillouin optical time domain analysis principle; Said frequency sweep electrooptic modulator comprises second Polarization Controller, sweep generator, second photomodulator; Sensing optic cable is put into seawater during measurement; The light signal that narrow linewidth laser produces is divided into two-way through photo-coupler; One road light signal is through the polarization state of first Polarization Controller control light signal; Become burst pulse light by pulse producer, first light modulator modulates; Through the spontaneous emission noise that first image intensifer amplifies, the first grating filter filtering, first image intensifer produces, get into a sensor fibre in the sensing optic cable through first optoisolator, circulator, photoswitch again; Another road optical signals frequency sweep electrooptic modulator produces the continuous light signal of about 11 GHz frequency displacements, chooses the upper side band of modulated signal through optical filter, gets into another sensor fibre in the sensing optic cable through second optoisolator, scrambler, photoswitch; Article two, optical fiber constitutes loop through the joints of optical fibre under water; When the two-way light frequency difference of transmission was consistent with the Brillouin shift of certain scattering point in the optical fiber in opposite directions in the Fiber In The Loop FITE, the stimulated Brillouin scattering signal that produces at this scattering point in the optical fiber was the strongest; The stimulated Brillouin scattering signal gets into the Brillouin shift detecting unit through photoswitch, circulator; Adopt electric light frequency sweep method to ask for by the Brillouin shift detecting unit along the Brillouin shift information of each scattering point of sensing optic cable fiber lengths distribution; And then according to the funtcional relationship of Brillouin shift and temperature, corresponding different sea water advanced static pressures; Obtain sea water advanced and temperature information, realize the distributed measurement of ocean temperature section along the sensor fibre length distribution.
2. according to the said ocean temperature section BOTDA measuring method of claim 1 based on the optical fiber Brillouin scattering principle; It is characterized in that; Said Brillouin shift detecting unit is by photoelectric detector; Amplifier; Low-pass filter; Data collecting card and computing machine are formed; Photoelectric detector is an electric signal with the stimulated Brillouin scattering light conversion of signals; Amplify and low-pass filter filtering through amplifier; By the data collecting card image data and be transferred to computing machine and handle; For each scattering point that distributes along fiber lengths; All data that computing machine will obtain in a microwave frequency sweep cycle are carried out the Lorentz match; Obtain Brillouin's spectral distribution curve, the frequency that the amplitude maximum point is corresponding in the curve is the Brillouin shift of this scattering point.
3. according to the said ocean temperature section BOTDA measuring method of claim 2 based on the optical fiber Brillouin scattering principle; It is characterized in that; Said sensing optic cable is made up of two button stainless steel flexible hoses (1) and the sub- optical cable of temperature inside sensing thereof and the sub- optical cable of pressure sensing; The sub- optical cable of said TEMP is by TEMP optical fiber (2) and be sleeved on its outside stainless steel sleeve pipe (3) and form; The sub- optical cable of said pressure sensing is by pressure sensing optical fiber (6) and be sleeved on its outside bourdon tube (5) successively and stainless steel wire mesh grid (4) is formed, and said pressure sensing optical fiber (6) surfaces coated is covered with polyurethane pressure sensitive material layer (7).
4. according to the said ocean temperature section BOTDA measuring method of claim 3, it is characterized in that the temperature sensing optical fiber (2) in the sub-optical cable of said temperature sensing is provided with 2～4 based on the optical fiber Brillouin scattering principle; The sub-optical cable of said pressure sensing is provided with two.
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