CN112929082A - Visibility analysis method and analyzer based on dual-wavelength detection - Google Patents
Visibility analysis method and analyzer based on dual-wavelength detection Download PDFInfo
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Abstract
The invention discloses a visibility analysis method based on dual-wavelength detection, which adopts two free space optical lasers with the wavelengths of 1640nm and 1550nm respectively to carry out mutual communication of two paths of optical signals, calculates corresponding error rates through received signals, analyzes the error rates of two paths of different optical signals, and respectively calculates the proportion of atmospheric turbulence and cluster fog which affect the visibility.
Description
Technical Field
The invention relates to a visibility detection technology, in particular to a visibility detection method based on dual-wavelength detection.
Background
Since the 21 st century, the science and technology of China has rapidly developed, and particularly in the aspect of sea, land and air traffic, the technology is more brand new. The developed traffic promotes resource interaction and accelerates life rhythm on one hand, and brings many potential safety hazards on the other hand. Traffic accidents caused by weather factors such as haze and rainfall are frequent, and the traffic accidents are all caused by insufficient visibility in high-speed driving. Under the condition of low visibility, the occurrence rate and the severity of traffic accidents are far greater than those of normal weather, so that the visibility of a traffic system is accurately monitored in real time, and early warning is timely performed on vehicles, flights and the like in driving, the method is an effective means for avoiding the occurrence of traffic accidents, and has important significance in the aspect of traffic safety guarantee. Meanwhile, the atmospheric stability can be analyzed through the visibility, so that the visibility is also an important element of meteorological observation.
At present, three methods, namely a visual method, an instrumental method and a video monitoring method, are commonly used for monitoring visibility. As the name suggests, the visual measurement method is to judge the visibility of the environment by observing the farthest visible target with human eyes, and only can estimate the visibility and has a high subjectivity, so the visual measurement method has a great limitation in the use of modern society with high requirements for data accuracy. The measurement method is to use a visibility monitor to replace an observer in the visual measurement method. Common methods used in the instrumental methods include aerosol sampling, optical methods, photographic methods, and the like. Among them, the transmission type visibility instruments are used more commonly, and the visibility is calculated by measuring the atmospheric transmittance. The method has a relatively accurate monitoring effect, but the monitoring has relatively large deviation under the conditions of extreme weather such as sand dust, large haze and the like. At present, video monitoring methods do not have mature technology at an application level and are still in a research stage. Furthermore, the observation objects of these methods are often an integral whole of all factors affecting visibility, and cannot refine factors such as atmospheric turbulence or fog which affect visibility. In real life, the effects of different factors are different, for example, air traffic is affected much more by atmospheric turbulence than by land traffic.
Disclosure of Invention
The invention aims to solve the defects in the prior art and provide an analysis method which can effectively distinguish the influence of atmospheric turbulence and fog on visibility and accurately monitor the visibility in real time.
In order to achieve the purpose, the invention provides a visibility analysis method based on dual-wavelength detection, which adopts two free space optical lasers with the wavelengths of 1640nm and 1550nm to carry out two-path optical signal mutual communication, calculates the corresponding error rate through received signals, analyzes the error rates of two paths of different optical signals, and respectively calculates the proportion of atmospheric turbulence and mass fog which affect the visibility.
The visibility analysis method of the invention adopts the error rate of the optical signal of the 1640nm wavelength laser to calculate the channel fading coefficient caused by the atmospheric turbulence, and adopts the error rate of the optical signal of the 1550nm wavelength laser to calculate the channel fading coefficient caused by the combination of the atmospheric turbulence and the mist, thereby calculating the channel fading coefficient caused by the mist; then, a visibility measuring environment is established through experiments, the visibility of the experimental environment is manually set, the relation between the channel fading coefficient and the visibility is fitted, and a visibility-channel fading coefficient model is established.
In some embodiments, it is preferable that the transmission signal of the free space optical laser is modulated by a phase shift keying orthogonal frequency division multiplexing technique.
The visibility analysis method calculates each channel fading coefficient through the error rate of two paths of light signals, and the calculation method comprises the following steps:
(1) calculating the signal-to-noise ratio mu according to the formula:
wherein, Ber is the calculated error rate of the corresponding optical signal; pe(mu) is a conditional bit error rate,
a and b are shape parameters, η is a scale parameter, and I is light intensity;
(2) according to the signal-to-noise ratio mu, calculating a corresponding fading coefficient h:
wherein R is the corresponding coefficient of the free space optical laser, P is the average power, N0Is gaussian white noise.
The fading coefficient h obtained by calculating the error rate of the optical signal of the 1640nm wavelength laser is the channel fading coefficient h caused by the atmospheric turbulenceflow(ii) a And (3) calculating the optical signal error rate of the 1550nm wavelength laser to obtain a fading coefficient h: h is hflow+hfog，hfogIs the channel fading coefficient caused by the cloud.
The construction method of the visibility-channel fading coefficient model comprises the following steps:
setting a model: k ═ fflow(hflow)+ffog(hfog)
Wherein f (-) corresponds to the relationship between the fading coefficient and visibility as a function of position;
the method comprises the following steps of establishing a visibility measuring environment through a laboratory, fitting the relation between a fading coefficient and visibility through manually setting the visibility of the experimental environment, and establishing an equation set:
by changing K, hflow，hfogAnd obtaining a relation model of the data.
The invention also provides a visibility analyzer adopting the analysis method, which comprises a 1640nm free space optical laser, a 1550nm free space optical laser, two-path signal processing modules and a visibility analysis module; 1640nm free space optical laser and 1550nm free space optical laser are used for modulating transmission signals by phase shift keying orthogonal frequency division multiplexing technology; 1640nm free space optical laser and 1550nm free space optical laser carry out signal transmission each other to transmit the signal received to corresponding signal processing module respectively and carry out photoelectric conversion after, send to visibility analysis module and carry out data processing and calculation.
Compared with the prior art, the invention has the following advantages:
1. the invention analyzes two factors of atmospheric turbulence and mist which affect visibility by utilizing different influences of atmospheric turbulence and mist on communication quality received by free space optical communication, thereby analyzing the influence of the two factors of atmospheric turbulence and mist on visibility based on double-wave optical signal fading: channel fading of the wavelength 1640nm caused by the cloud is very small and negligible, so that the fading coefficient of the atmospheric turbulence is calculated through the error rate of the optical signal of the wavelength 1640nm, the fading coefficients of the cloud and the atmospheric turbulence are calculated by combining the error rate of the optical signal of the wavelength 1550nm, and the specific gravity of the influence of the two factors on visibility is calculated.
2. The invention can effectively realize real-time and accurate monitoring of visibility by establishing a relation model between the fading coefficients of the foggy group and the atmospheric turbulence and the visibility.
3. The invention analyzes the monitoring signal by the signal processing technology in free space optical communication, replaces the traditional measuring method, is not influenced by extreme weather, can effectively distinguish the cluster fog from the atmospheric turbulence, and has higher accuracy and stability.
Drawings
FIG. 1 is a visibility analyzer of the present invention;
fig. 2 is a transmission process of an optical signal of the dual-wavelength free-space optical communication system in fig. 1;
fig. 3 is a flow chart of signal data processing of the visibility analysis method of the present invention.
In the figure, a 1-1550nm free space optical laser, a 2-1640nm free space optical laser, a 3-signal processing module I, a 4-signal processing module II, a 5-visibility analysis module are arranged.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings.
As shown in fig. 1, the present patent is a visibility analysis system based on dual-wavelength detection, and the core points are a dual-wavelength free space optical communication system and a visibility analysis module based on signal processing.
The flow of the whole system is as follows: in the free space optical communication module, two free space optical lasers are used for communication, and lasers of 1640nm and 1550nm (1550nm free space optical laser 1 and 1640nm free space optical laser 2) are respectively adopted. The received optical signals are subjected to signal processing (the signal processing module I3 and the signal processing module II 4 respectively convert the received optical signals into electric signals), corresponding information is decoded, the error rate is calculated, and finally, the visibility is analyzed by using the error code of the information. And the proportion of factors influencing visibility is analyzed by the difference of the error rates of two paths of different optical signals.
At the transmitting end, the signal is mainly modulated onto an optical carrier and transmitted through the atmosphere. Research at present finds that Orthogonal Frequency Division Multiplexing (OFDM) technology is a modulation method capable of effectively suppressing atmospheric turbulence. This patent therefore employs phase shift keying orthogonal frequency division multiplexing (PSK-OFDM) to modulate the transmission signal. A model of atmospheric turbulence and cluster fog influence on an optical signal in the transmission process is obtained by analyzing the transmission characteristics of a spatial optical channel based on PSK-OFDM modulation, so that detailed visibility information is further obtained in real time.
In the system, the signals transmitted at both ends are the same, and let the OFDM-modulated signal be x (t), which can be expressed as
Wherein XiFor symbol information on the k sub-carrier, fkIs the frequency of the k-th subcarrier. After transmission through the channel, the signal is affected by noise due to turbulence, cloud, etc. Let the noise due to turbulence be n (t) and the noise due to cloud be m (t), and the signals obtained at the receiving end can be respectively represented as x (t) + n (t) and x (t) + m (t) + n (t) due to the different penetration abilities of the light with different wavelengths, as shown in fig. 2. The channel fading model of the system and the fading model caused by the cloud are analyzed separately below.
The specific calculation method is shown in fig. 3. After the optical signal is transmitted through the atmosphere, the optical signal received by the detector can be represented as an electrical signal after photoelectric conversion:
y(t)＝Rhx(t) (2)
where R is the response coefficient of the optical detector, h represents the channel fading coefficient of the combination of turbulence and cloud, which can be expressed as:
h＝hflow+hfog (3)
wherein h isflowIs the channel fading coefficient caused by atmospheric turbulence, and hfogIs the fading coefficient caused by the cloud. The channel fading model can be represented by a weber distribution:
where a and b are shape parameters, η is a scale parameter, and I is light intensity. The cloud fading coefficient can be expressed by a Kruse model:
where V denotes the visibility range, λ is the actual transmission wavelength, λ0For the converted standard wavelength, 1550nm was set. q is the size distribution of the scattering coefficient.
The cloud fading coefficient can be expressed as:
hfog＝exp(-σfogL) (6)
where L is the transmission distance. The signal-to-noise ratio of the optical signal received by the receiving end can be expressed as:
where P is the average power, N0Is gaussian white noise. According to the existing research, the average bit error rate expression of the PSK system can be written:
wherein P ise(μ) is the error rate of PSK-OFDM, expressed as:
where K is a K-ary PSK code and Q is a Gaussian Q function:
according to f (I) and Pe(μ), and formula (8), the following formula can be obtained:
after the Ber in the formula is measured, the signal-to-noise ratio mu can be calculated according to various parameters;
again from the equation 7, the data is,
wherein R, P, are known, N0Is a fixed value, thus writing out
the fading coefficient h can be obtained.
For two channels of different wavelengths, h can be separately determined due to different signal-to-noise ratiosflow，hfog。
Fig. 3 shows a flow of the visibility analysis module, which first demodulates spatial optical signals with different wavelengths, calculates an error rate after signal processing, and then derives a signal-to-noise ratio through the formula described above, so as to further obtain a joint channel fading coefficient (1550nm) and an atmospheric turbulence fading coefficient (1640nm), and by cooperative calculation of the two, a cloud fading coefficient and a turbulence fading coefficient can be obtained respectively. According to multiple experiments and training, a relation model of a fading coefficient and visibility can be established, and assuming that the visibility is K, the relation model can be expressed as follows:
K＝fflow(hflow)+ffog(hfog) (9)
wherein f (-) corresponds to the relation between the fading coefficient and the visibility, and is a position function, here we construct the visibility measuring environment through the laboratory, and can fit the relation between the fading coefficient and the visibility through artificially setting the visibility of the experimental environment, and construct an equation set:
by changing K, hflow，hfogAnd obtaining a relation model of the data.
Claims (7)
1. A visibility analysis method based on dual-wavelength detection is characterized in that two free space optical lasers with wavelengths of 1640nm and 1550nm are used for mutual communication of two paths of optical signals, corresponding error rates are calculated through received signals, error rates of two paths of different optical signals are analyzed, and the proportion of atmospheric turbulence and cluster fog which affect visibility is calculated respectively.
2. The visibility analysis method according to claim 1, wherein the visibility analysis method calculates the channel fading coefficient caused by atmospheric turbulence by using the error rate of the optical signal of the laser with the wavelength of 1640nm, and calculates the channel fading coefficient caused by the combination of atmospheric turbulence and mist cloud by using the error rate of the optical signal of the laser with the wavelength of 1550nm, thereby calculating the channel fading coefficient caused by mist cloud; then, a visibility measuring environment is established through experiments, the visibility of the experimental environment is manually set, the relation between the channel fading coefficient and the visibility is fitted, and a visibility-channel fading coefficient model is established.
3. The visibility analysis method according to claim 2, wherein the visibility analysis method modulates a transmission signal of the free space optical laser by a phase shift keying orthogonal frequency division multiplexing technique.
4. The visibility analysis method according to claim 3, wherein the visibility analysis method calculates each channel fading coefficient by the error rate of two paths of light-sharing signals, and the calculation method is as follows:
(1) calculating the signal-to-noise ratio mu according to the formula:
wherein, Ber is the calculated error rate of the corresponding optical signal; pe(mu) is a conditional bit error rate,
channel fading model
a and b are shape parameters, η is a scale parameter, and I is light intensity;
(2) according to the signal-to-noise ratio mu, calculating a corresponding fading coefficient h:
wherein R is the corresponding coefficient of the free space optical laser, P is the average power, N0Is gaussian white noise.
5. The visibility analysis method according to claim 4, wherein the fading coefficient h calculated from the error rate of the optical signal of the laser with the wavelength of 1640nm is a channel fading coefficient h caused by atmospheric turbulenceflow(ii) a And the attenuation coefficient h obtained by calculating the error rate of the optical signal of the 1550nm wavelength laser is as follows: h is hflow+hfog，hfogIs the channel fading coefficient caused by the cloud.
6. The visibility analysis method according to claim 5, wherein the visibility-channel fading coefficient model is constructed as follows:
setting a model: k ═ fflow(hflow)+ffog(hfog)
Wherein f (-) corresponds to the relationship between the fading coefficient and visibility as a function of position;
the method comprises the following steps of establishing a visibility measuring environment through a laboratory, fitting the relation between a fading coefficient and visibility through manually setting the visibility of the experimental environment, and establishing an equation set:
by changing K, hflow，hfogAnd obtaining a relation model of the data.
7. A visibility analyzer adopting the analysis method of any one of claims 1 to 6, wherein the visibility analyzer comprises a 1640nm free space optical laser, a 1550nm free space optical laser, a two-way signal processing module, and a visibility analysis module; the 1640nm free space optical laser and the 1550nm free space optical laser carry out transmission signal modulation by a phase shift keying orthogonal frequency division multiplexing technology; the 1640nm free space optical laser and the 1550nm free space optical laser perform signal transmission mutually, transmit received signals to corresponding signal processing modules respectively for photoelectric conversion, and then transmit the signals to a visibility analysis module for data processing and calculation.
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| US20090180781A1 (en) * | 2008-01-11 | 2009-07-16 | Battelle Memorial Institute | Systems and methods for free space optical communication |
| CN106685523A (en) * | 2016-12-12 | 2017-05-17 | 西安电子科技大学 | Index Weber and APD based error rate calculating method of PPM wireless optical communication system |
| CN111769880A (en) * | 2020-07-03 | 2020-10-13 | 中国计量大学 | Serial relay OFDM free space optical communication system and method applying wavelength diversity |
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| US20090180781A1 (en) * | 2008-01-11 | 2009-07-16 | Battelle Memorial Institute | Systems and methods for free space optical communication |
| CN106685523A (en) * | 2016-12-12 | 2017-05-17 | 西安电子科技大学 | Index Weber and APD based error rate calculating method of PPM wireless optical communication system |
| CN111769880A (en) * | 2020-07-03 | 2020-10-13 | 中国计量大学 | Serial relay OFDM free space optical communication system and method applying wavelength diversity |
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