Background
The atmospheric wind field information is an important parameter of the atmosphere and plays an important role in the fields of civil aviation, meteorology and wind power. Wind field detection facilitates the study of weather events, climate change and environmental issues. The wind measurement laser radar mainly uses the aerosol backscattering signal and the local oscillator light of the radar as beat frequency through the Doppler effect to obtain the Doppler frequency shift of the scattering signal, so that the wind speed information is obtained.
The inversion of the three-dimensional wind field requires radial wind speed measurement values in at least three directions, and the laser radar realizes measurement in multiple directions through light beam scanning. For flat terrain, the wind field is uniformly distributed, and low-speed scanning is beneficial to pulse accumulation and improves the detection range; for complex terrain, the wind field changes rapidly, and in order to achieve measurements of transient gusts and turbulence, the beam scanning speed is required to be as fast as possible. In addition, when the radar is applied to a moving platform, such as a vehicle and a buoy, the change of the attitude also puts a dynamic change requirement on the scanning speed of the light beam.
The existing laser radar system has two light beam scanning modes: optical switch switching mode and mechanical scanning mode.
The optical switch switching modes can be divided into two types: 1. magneto-optical switch, 2.MEMS switch. The magneto-optical switch has high requirements on the environment, and the MEMS switch has fussy control and low reliability.
The mechanical scanning mode has the problems of large volume, complex installation, low reliability and the like, and a controller needs to be additionally installed independently.
Neither of the above two methods can meet the requirement of adaptive switching scanning rate. According to the influence of various complex terrains of the use environment or the factors of the motion state of an object, the radar detection is required to change the detection rate at any time, and the three optical switches cannot be realized.
Disclosure of Invention
The technical scheme is as follows: in order to solve the technical problem, the invention provides a self-adaptive multi-channel wind-finding laser radar system, in particular to a system
The device comprises a tunable semiconductor laser, an acousto-optic modulator, an EYDFA amplifier, an optical fiber circulator, a DWDM wavelength division multiplexer, a photoelectric detector, a signal processing module and an attitude sensing module; the tunable semiconductor laser outputs continuous signals to the acousto-optic modulator; the acousto-optic modulator is used for carrying out optical pulse modulation processing and transmitting a signal to the EYDFA amplifier; the EYDFA amplifier is used for amplifying light energy of signals and transmitting the signals to the optical fiber circulator, the optical fiber circulator is of a multi-port structure, signals of the EYDFA amplifier enter the optical fiber circulator through a port 1, and signals of a port 2 enter the DWDM through a port 2; the DWDM wavelength division multiplexer sends out echo signals which enter from a port 2 of the optical fiber circulator and exit from a port 3 of the optical fiber circulator and are transmitted to the photoelectric detector; the photoelectric detector is used for performing beat frequency processing on the echo signal and local oscillation light of the tunable semiconductor laser, transmitting the processed signal to the signal processing module for processing, and the attitude sensing module is used for outputting a signal of the final object with the motion state change.
As an improvement, the wind parameter reconstruction module is further included; the wind parameter reconstruction module is used for outputting various parameters of wind and loading the parameters in the signal processing module.
The system comprises a tunable semiconductor laser, an attitude sensing module, a signal processing module and a frequency changer, wherein the tunable semiconductor laser is used for converting wind into turbulent wind or transient gust, and the attitude sensing module is used for sensing the wind speed and the wind speed of the wind turbine.
As an improvement, the tunable semiconductor laser comprises two spaced sets of sampled gratings, a gain section and a phase section, wherein the gain section and the phase section are disposed between the two sets of sampled light.
As an improvement, the acousto-optic modulator is provided with at least one group, which comprises an acousto-optic device, an optical fiber coupling system and a driver, and is used for modulating the driving electric signal according to different extinction ratios, so that the on-off control of the optical signal can be realized.
As an improvement, the wind parameter reconstruction module is used for outputting wind state parameters including but not limited to wind direction, wind speed and turbulence, wherein the radial wind speed is expressed as
f
0The frequency shift amount of the
device 2, f is the receptionScattered return light to the light source.
As an improvement, when scanning for two-channel anemometry, setting a wind vector
According to the geometrical relationship:
the plane wind speed and the plane wind direction of the light beam are respectively as follows:
the turbulence is:
wherein T is the length of the time sliding window,
the mean value of radial wind speed in T time, los is 1,2 is the beam number, sigma
TTo sum the data at time T.
As an improvement, the frequency changer sets the threshold value of each area according to the feedback information of signal processing, when the threshold value is reached, the frequency changer starts to act, and the change frequency directly feeds back the uITLA for adjusting the conversion rate.
As an improvement, the attitude sensing module performs corresponding monitoring according to the motion frequency of an object mounted on the radar, and performs corresponding compensation processing for the frequency of the synchronous radar, wherein during specific compensation, when V is equal to Z and is equal to 0, the default object is stationary, and when V is greater than Z, a corresponding frequency is output to perform compensation processing on the frequency of the utila. Wherein, the uotla refers to a tunable semiconductor laser; v refers to the frequency of motion of the mounted radar object; z refers to radar frequency.
Has the advantages that: the radar system provided by the invention can automatically adjust the channel switching rate by combining real-time wind condition and attitude sensing, thereby maximally utilizing system resources and realizing high-precision wind measurement as required. The adjustable laser adopted by the system is simple to control, high in switching frequency, long in service life and good in reliability; the DWDM technology is mature, the cost is low, external signal control is not needed, and signals are output in multiple paths; the signal processing module processes needed data in time and distributes the data to a lower level; the wind parameter reconstruction module can clearly know the current wind state; attitude sensing and frequency change can change corresponding parameters according to the real-time wind speed state, so that the effect of improving the performance of the radar is achieved.
Detailed Description
The following examples are given to further illustrate the embodiments of the present invention. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
Referring to fig. 1, in the adaptive multi-channel wind lidar system of the present invention, a tunable semiconductor laser 1 outputs continuous signal light after wavelength adjustment, is connected with an acousto-optic modulator 2 for optical pulse modulation, is connected with an EYDFA amplifier 3 for optical energy amplification, passes through an optical fiber circulator 4, enters from a port 1 into a port 2, enters into a DWDM wavelength division multiplexer 5 for light splitting, so that laser with different wavelengths enters into a telescope through different channels to emit to the atmosphere, echo signals scattered by the atmosphere are received through the same emitting port, and enter into a photodetector 6 after passing through the ports 4 and 3 of the optical fiber circulator 4 and 2, the echo signals and local oscillation light of the tunable semiconductor laser 1 carry out beat frequency, the signals after beat frequency enter into a device 7 for data processing, various parameters of the air output by an air parameter reconstruction module 8, a frequency changer 9 finds turbulence or transient air matrix state after data processing of the signal processing module 7, the speed needs to be adjusted, the speed is fed back to the device 1 to change the frequency, and the attitude sensing module 10 feeds back the change of the motion state of the mounted object to the tunable semiconductor laser 1 to change the frequency.
The components of the radar system of the present invention are further described and illustrated in detail below.
The tunable semiconductor laser 1, as shown in fig. 2, adopts a tunable seed source and has the working principle: the laser has a sampling grating as a reflection grating at each of two ends of the resonant cavity. The grating spacing of the two sampled gratings is designed to be slightly different. The resulting spectra will have different mode spacing. Resonant amplification of the light is only possible if the modes are at the same time on both fiber reflection peaks. The reflection spectrum of one of the gratings is shifted by changing the injected current, so that the coincidence position of the reflection peaks is changed, and output light with different frequencies is obtained. Similarly, a first-stage phase region is arranged in the middle and also serves as a fine adjustment region, quasi-continuous wavelength adjustment is realized by changing oscillation positions of modes through the fine adjustment region, the range can reach hundreds of nanometers, and the selected wavelength is finer.
Sampling grating section: injection current IDER1,2Changing the reflection peak, coarse tuning the wavelength
Phase section: injection current Ip, shifted longitudinal mode spectrum, fine wavelength tuning
A gain section: injecting a current I to provide a gain
The wind speed precision is influenced by the wavelength precision due to the correlation of the wind speed and the wavelength in the wind speed inversion.
The acousto-optic modulator 2 is used for modulating waveform, and the invention adopts a fiber acousto-optic modulator which mainly comprises an acousto-optic device, a fiber coupling system and a driver. In the system, a single or multiple acousto-optic modulators can be used for modulation, and switching control of optical signals can be realized by modulating driving electric signals according to different system extinction ratios in a matching manner as shown in fig. 3.
The EYDFA amplifier 3 is based on a double-cladding optical fiber pumping MOPA amplification technology, after pumping light and signals enter a double-cladding gain optical fiber at the same time, low-level particles rise to a high level and finally return to a ground state stably, the original signal light is amplified by reversing the number of the particles, and a multi-stage amplification structure can be realized.
The optical fibre circulator 4 enables bidirectional signal transmission over a single optical fibre, the direction of signal transmission of the circulator being irreversible, and optical signals being directed from one port to another port only in one direction at a time, the optical signals being re-directable but having to pass through the ports in sequence in one direction. A three-port, i.e., three-port, circulator optical signal in the present invention must travel from port 1 to port 2 and then to port 3.
As shown in fig. 4, the DWDM wavelength division multiplexer 5 is actually integrated like a plurality of WDM devices. After passing through DWDM, multiple wavelengths pass through multimode fiber, and laser with different wavelengths is separated by the WDM. Coupling a plurality of wavelength composite lasers modulated by the DBR tunable seed source laser to a DWDM optical device through optical fibers, refracting the light into each optical fiber array through a prism, placing a filter of a dielectric film at the front end of each optical fiber array, and transmitting the light into the optical fibers through the filter only if the wavelength of the light is within the filtering range; if not, the filter plate which can not pass through the wavelength can be reflected back by the filter plate, at the moment, a layer of reflection film is plated on the edge of the module, the light reflected back by the first filter plate is reflected to the port of the next optical fiber array again, and the filter plates with different wavelengths are placed at the next port. The method is used for realizing the optical switching by sequentially and repeatedly acting, finding out the proper wavelength through the back-and-forth reflection of different filters and reflectors, and then enabling the light to enter the corresponding port of the optical fiber array, so that most wavelengths in the multimode optical fiber are decomposed into a single wavelength and output from different wavelength channels. Because the optical switch module in the radar system needs low insertion loss, high return loss, high withstand power and high reliability, the DWDM key parameters can well meet the requirements.
The photodetector 6 converts the received optical signal into an electrical signal, and outputs the electrical signal after internal amplification.
The signal processing module 7 is used for carrying out algorithm processing on the received electric signals and connecting the electric signals to an upper computer in a communication mode.
As shown in fig. 5, the wind parameter reconstruction module 8 converts the processed signal according to the doppler shift principle and the trigonometric geometric relationship, and outputs the wind state, such as wind direction, wind speed, and turbulence.
The radial wind velocity is expressed as:
f
0the amount of frequency shift, f, of the
device 2 is the received scattered return light.
When the two-channel wind measurement scanning is carried out, the return light is received, the processing calculation is carried out, and the wind vector is set
According to the geometrical relationship:
the plane wind speed and the plane wind direction of the light beam are respectively as follows:
the turbulence is:
wherein T is the length of the time sliding window,
the mean value of radial wind speed in T time, los is 1,2 is the beam number, sigma
TTo sum the data at time T.
The working principle of the frequency changer 9 is as follows: according to the feedback information of signal processing, threshold values of all areas are set, when the threshold values reach a certain threshold value, the threshold values start to act, and the change frequency is directly fed back to the uITLA to adjust the conversion rate.
When Ti is presentlosWhen the frequency is less than or equal to P, measuring at a conventional frequency; when Ti is presentlosWhen the gradient is larger than or equal to P, the frequency is changed along with the change of the gradient. As shown in FIG. 6, after data processing, TilosWhen the threshold value is not less than A, B, C.
The working principle of the posture sensing module 10 is as follows: the processing method is as shown in fig. 7, when V ═ Z ═ 0, the default object is still, and when V > Z, a corresponding frequency is output to compensate the frequency of the utila. Where uotla refers to a tunable semiconductor laser; v refers to the frequency of motion of the mounted radar object; z refers to radar frequency.
The self-adaptive multi-channel wind lidar disclosed by the invention can automatically adjust the channel switching rate by combining real-time wind condition and attitude sensing, thereby maximally utilizing system resources and realizing high-precision wind measurement as required. The adjustable laser adopted by the system is simple to control, high in switching frequency, long in service life and good in reliability; the DWDM technology is mature, the cost is low, external signal control is not needed, and signals are output in multiple paths; the signal processing module processes needed data in time and distributes the data to a lower level; the wind parameter reconstruction module can clearly know the current wind state; attitude sensing and frequency change can change corresponding parameters according to the real-time wind speed state, so that the effect of improving the performance of the radar is achieved.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.