CN108897059A - A kind of Infrared Targets imaging detectivity analysis method - Google Patents
A kind of Infrared Targets imaging detectivity analysis method Download PDFInfo
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Abstract
The present invention relates to a kind of Infrared Targets, and detectivity analysis method is imaged, and constructs a set of infrared imaging detection Performance Evaluation Model.Based on overall system performance parametric mathematical model, it will affect three factors of Infrared Targets imaging system detection performance：Infrared imaging system hardware parameter, atmospheric environment and scene characteristics connect, and the detectivity of Infrared Targets imaging is predicted using particular probe criterion.The present invention is good to the performance of Infrared Targets imaging detectivity analysis, and operation is succinct, and confidence level is high.Detectivity prediction technique of the invention can also be used to select infrared imaging system appropriate according to target type and image-forming range.
Description
Technical field
The present invention relates to a kind of Infrared Targets, and detectivity analysis method is imaged, and specifically Infrared Targets imaging can be visited
Period analysis method is surveyed, infrared detection technique field is belonged to.
Background technique
In natural environment, all temperature are higher than the object of absolute zero all in ceaselessly outwardly emitting infrared radiation.By
In the characteristic information that this radiation includes object itself, thus we using the spontaneous radiation of this object, developed at
Ripe infrared imagery technique.This technology has been widely used in the every field such as military affairs, industry, scientific research.With two generations
Focal plane arrays (FPA) infrared imagery technique be constantly progressive and it is more and more widely used, how could accurately and effectively comment
Valence infrared imaging system becomes the infra-red detectable of specific objective a current research hotspot.
In order to solve this problem, it would be desirable to the Infrared Targets imaging detection performance evaluation system an of standard is established,
According to the performance parameter of system, goes to predict the probability that certain detection system identifies target in a specific environment, avoid setting
The detection system counted out is not able to satisfy given requirements, and causes greatly to lose.This infra-red detectable analysis model is theoretical
On need the infra-red radiation in conjunction with the performance parameter of infrared detector itself, current characteristics of atmospheric transmission and target and background
Characteristic is modeled and is calculated, and the probability that target is detected in specific environment is predicted with certain detection criterion.And
By simulating the parameters such as the atmospheric transmittance under different time and atmospheric condition, it is easiest to be visited so as to calculate target
The when and where of survey.
The appraisal procedure of current most of country is still based on mathematical model before, is carried out a large amount of field experiment and is taken
It obtains experimental data and instructs the design and optimization of imaging system to predict the detection identification probability at different role distance.This biography
The prediction technique of system needs a large amount of field trial, can expend a large amount of manpower and material resources, but also the big compression ring in outfield must be taken into consideration
The influence to modeling of various typical physical effects and background clutter in border, detector, when testing MRTD curve, there is also many
The stability for the interference caused by subjective factors experimental result that human eye distinguishes, so that traditional prediction technique spends the time longer, and effect
It is poor.
Summary of the invention
It is an object of the invention to overcome the deficiencies of the prior art and provide a kind of Infrared Targets, and detectivity analysis side is imaged
Method, this method performance is good, operation is succinct and confidence level is high.
The object of the invention is achieved by following technical solution：
A kind of Infrared Targets imaging detectivity analysis method is provided, is included the following steps：
S1. the temperature for calculating the corresponding geographical coordinate points of each pixel in target scene image, obtains the temperature of target scene
Spend field；
S2. it calculates in target scene image, the temperature difference for the target and background that user specifies and the spatial frequency f of target；
S3. according to the spatial frequency f of target, periodicity N can be solved by calculating maximum；
S4. periodicity N50 when 50% detection probability of differential thermal calculation of target and background is utilized；
S5. N/N50 ratio is utilized, detection probability Pinf is calculated.
A kind of method according to target selection infrared imaging system is provided simultaneously, is included the following steps：
S1. the temperature for calculating the corresponding geographical coordinate points of each pixel in target scene image, obtains the temperature of target scene
Spend field；
S2. it calculates in target scene image, the temperature difference for the target and background that user specifies and the spatial frequency f of target；
S3. according to the spatial frequency f of target, periodicity N can be solved by calculating maximum；
S4. periodicity N50 when 50% detection probability of differential thermal calculation of target and background is utilized；
S5. N/N50 ratio is utilized, detection probability Pinf is calculated；
S6. if infrared imaging system detection probability Pinf is less than given threshold, it is higher infrared to replace detection performance
Imaging system, return step S2；If infrared detection system detection probability Pinf is more than or equal to given threshold, it is determined that this is infrared
Imaging system.
Preferably, according to the spatial frequency f of target in step S3, calculating the maximum specific method that can solve periodicity N is：
Wherein Mag is the magnifying power of infrared system, and R is target with a distance from optical system；Cd is the characteristic dimension of target,AwTarget region area is specified for user.
Preferably, the tool of periodicity N50 when in step S4 using 50% detection probability of differential thermal calculation of target and background
Body method is：
ΔTRSSFor the temperature difference of target and background, C is that background clutter is horizontal.
Preferably, the specific method of calculating detection probability Pinf is in step S5：
Ratio=N/N50E=2.7+0.7*Ratio。
Preferably, the temperature that the corresponding geographical coordinate points of each pixel in target scene image are calculated in step S1, obtains
The specific method in the temperature field of target scene is：
S11. the material image for receiving the target scene of user's input, is compiled according to the material in the material image of target scene
Number, the emissivity ε and reflectivity α of every kind of material are extracted from Materials Library；
S12. the radiation energy of each pixel in target scene is calculated；
S13. the equation of heat balance for establishing target scene solves the material surface temperature of the corresponding geographical coordinate points of each pixel
Spend ti,j, and then obtain the temperature field of target scene.
Preferably, the specific method of the radiation energy of each pixel is in calculating target scene in step S12：
1) the solar radiant energy Q that receives is calculated each pixelsun；
2) the long _ wave radiation energy Q that receives is calculated each pixelsky；
3) the radiation energy Q of material surface is calculated each pixelrad；
4) dominant heat exchange energy Q is calculated to each pixelCV；
5) latent property heat exchange energy Q is calculated to each pixelLE。
Preferably, the equation of heat balance that target scene is established in step S13 is：
Qsun+Qsky=Qrad+Qcv+Qle。
Preferably, it calculates in target scene image, the specific method of the temperature difference for the target and background that user specifies is：
S21. the target in the specified material image of user is obtained, remaining is background area；
S22. the temperature difference T of target region and background area is calculatedRSS：
In formula：ti,jThe material surface temperature at target area pixel (i, j) is represented, POT is that target pixel points are always a
Number, μbkgFor environmental background temperature, by taking mean value to obtain each pixel temperature in background area.
Preferably, the specific method for calculating the spatial frequency f of target is：
(1) transmission function of infrared imaging system is calculated；
(2) calculation display transmission function；
(3) Modulation Transfer Function of Human Visual System is calculated；
(4) transmission function of infrared imaging system, display transmission function and Modulation Transfer Function of Human Visual System are multiplied, are obtained
To the transmission function MTF in the horizontal and vertical direction of infrared imaging systemxs(f), MTFys(f)；
(5) the minimum detectable temperature difference function MRTD (f) of infrared imaging system is calculated,
Wherein Δ fnInfrared imaging system is noise equivalent bandwidth, SNRDTThe threshold value vision of lines can be differentiated for observer
Signal-to-noise ratio, NETD are the noise equivalent temperature difference of infrared system, and α is horizontal instantaneous field of view, and β is vertical instantaneous field of view, τdFor scanning
Residence time, fpFor frame frequency；MTFs(f) fetch water the delivery function MTF that flates pass respectivelyxs(f), the MTF of vertical directionys(f), calculate or
The MRTD (f) in horizontal and vertical direction；
(6) MRTD (f) in horizontal and vertical direction is enabled to be respectively equal to target background temperature difference TRSS, solve target x, the side y
Upward corresponding spatial frequency fx、fy, then the spatial frequency of target be
Preferably, the method for calculating the transmission function of infrared imaging system is：
Infrared light enters detector by optical system, and after being converted to electric signal, entering signal processing circuit is handled；
Calculating optical system transter Hopt(fx,fy)；The horizontal and vertical direction transmission function of calculating detector；Calculate signal processing
Circuit transfer function MTFe；Calculate separately the transmitting letter of the transmission function and vertical direction that obtain infrared imaging system horizontal direction
Number.
Preferably, signal processing circuit transmission function MTF is calculatedeSpecific method be：Calculate the biography of low-pass filter circuit
Delivery function MTFe1；Calculate the transmission function MTF of high-pass filtering circuite2；Calculate the transmission function MTF that high frequency recommends circuite3；Meter
Calculate signal processing circuit transmission function be：
MTFe=MTFe1MTFe2MTFe3。
Preferably, it is as follows to calculate method for display transmission function：
For cathode-ray tube display transmission function MTFmCalculation method is as follows：
MTFm=exp (- 2 π2δ2f2)
δ is the standard deviation of display luminous point distribution in formula；Direction transmission function horizontal and vertical for light-emitting diode display
MTFmx、MTFmyCalculation method is as follows：
MTFmx=sinc (π xfx)
MTFmy=sinc (π yfy)
X, y are respectively subtended angle of the LED in normalization space in formula.
Preferably, Modulation Transfer Function of Human Visual System calculation method is as follows：
M is infrared imaging system angular magnification in formula；K is parameter related with brightness of display screen L,
K=1.272081-0.300182lgL+0.04261 (lgL)2+0.00197(lgL)3。
The present invention has the following advantages that compared with prior art：
(1) present invention by infrared imaging Performance Evaluation Model by the hardware parameter of infrared imaging system, atmospheric environment and
Target background characteristic three parts combine, and using the comprehensive performance parameter mathematical model of system, will affect infrared detection system
Each factor of performance connects, and comes in advance in conjunction with the characteristic and atmospheric attenuation of infrared target background, and using particular probe criterion
Survey the field performance of infrared detection system and the detectivity of target, property of the present invention to Infrared Targets imaging detectivity analysis
Can be good, operation is succinct, and confidence level is high.
(2) present invention determines the detectable probability of target, compared with field trial, more by way of numerical calculation
It is objective, more efficient, cost of implementation is low.
(3) Infrared Targets detection property analysis method of the invention be suitable for all kinds of infrared system detection performances assessment and
The assessment of the detectable probability of target, versatility is good, high reliablity.
(4) Infrared Targets detectivity analysis method of the invention can accurate evaluation infrared system detection performance, for
The improvement of infrared system detection performance provides theoretical direction foundation.For specific objective, by general to different distance condition detection
The calculating of rate, it is determined whether need replacing infrared system, infrared system appropriate is selected to be detected, guarantee acquisition probability
And detection accuracy.
Detailed description of the invention
Fig. 1 is flow diagram of the invention；
Fig. 2 is Objective extraction figure of the invention；
Fig. 3 is detectivity line chart at times of the invention.
Specific embodiment
Below in conjunction with the drawings and specific embodiments, the present invention is described in further detail, but the embodiment should not be understood
For limitation of the present invention.
Detectable period analysis method is imaged in Infrared Targets, and in conjunction with Fig. 1, its step are as follows：
S1. the temperature for calculating the corresponding geographical coordinate points of each pixel in target scene image, obtains the temperature of target scene
Spend field：
S11. receive the material image of the target scene of user's input and ensure data, according to the material image of target scene
In material number, the emissivity ε and reflectivity α of every kind of material are extracted from Materials Library；；
S12. the radiation energy of each pixel in target scene is calculated, specific step is as follows：
1) calculating each pixel the solar radiant energy direct sunlight received can be calculated as follows：
Qsund=rIscPm cosi
In formula, r for day correction factor；IscFor solar constant；P is the atmospheric transparency of target scene region, is led to
It crosses meteorological data to obtain, extraordinary fine day P takes 0.85, preferable fine day P to take 0.8, and P takes 0.65 when medium fine day, poor
Fine day P take 0.532.M is the air quality of target scene region, and i is the angle of incidence of sunlight that the material corresponds to atural object,
It is determined according to the normal vector for ensureing the pixel in data.
The specific calculation formula of sun scattering energy is as follows：
In formula, IscFor solar constant, h is solar elevation, and β is the inclination angle that the pixel corresponds to atural object, according to guarantee
The normal vector of the pixel determines in data.P is the atmospheric transparency of target scene region.
The solar radiation that the pixel receives can be expressed as：
Qsun=(1- α) (Qsund+Qsuns)
In formula, α is the reflectivity of the material of the pixel, QsundFor direct sunlight energy, QsunsFor solar scattered radiation energy
Amount.
2) the long _ wave radiation energy that receives is calculated each pixel
Long _ wave radiation is general related with some meteorological conditions, and long _ wave radiation is under the conditions of cloudless sky：
In formula, a, b are empirical, and a takes 0.61, b to take 0.05；ε is material emissivity；σ is Stefan-Boltzmann
Constant, σ=5.67 × 10-8W·m-2·K-4；eαFor the vapour pressure near the ground of target scene region, unit is kPa, eα's
Calculation formula is as follows：
In formula, rh is the relative humidity of the atmosphere of target scene region, TαIt is the atmosphere of target scene region
Temperature.
3) itself radiation energy is calculated to each pixel
The object that any temperature is higher than absolute zero all can convert heat into radiation constantly to space radiated electromagnetic wave
Energy.It can be by object as grey body processing, according to Stefan-Boltzmann law, the radiation value calculation formula of grey body in engineering
For：
In formula, ε indicates the emissivity of heat source surface material, and σ is Boltzmann constant, ti,jMaterial is corresponded to for the pixel
The corresponding geographical coordinate points material surface temperature of the temperature on surface, i.e. pixel, for amount to be asked.QradIt is then the pixel material table
Face amount of infrared radiation.
4) dominant heat exchange energy is calculated to each pixel
When object and the environment of surrounding are there are when temperature difference, just having an exchange of heat, direction is from high temp objects to low
Warm object, and the temperature difference is bigger, heat exchange is also bigger.The heat between object and ambient atmosphere is related generally in Simulations of Infrared Image
Exchange, referred to as dominant heat exchange.It can be expressed as：
QCV=h (tI, j-Tα)
In formula, h is parameter related with wind speed, it is assumed that wind speed v, unit are metre per second (m/s)s, close to the actual effect of body surface
Wind speed is V.For windward side, V is equal to 0.25v, and for leeward, V is equal to 0.3+0.05v.The heat-exchange system of body surface
For h=3.5+5.6V.
5) latent property heat exchange
For some materials containing moisture, due to the evaporation of water, it will take away the heat of a part from material.
The heat exchange due to caused by moisture loss is known as latent property heat exchange in this way, can be calculated with following formula：
QLE=ρaLCDvWs(qa-qc)(7-8)
In formula, ρaFor the atmospheric density of target scene region；L is the latent heat of vaporization of water；CDFor the drag coefficient of wind,
Take 0.002；V is the wind speed of target scene region；WsMaterial surface water content is corresponded to for the pixel；qaFor target scene
Ratio in the air of region is wet；qcFor the saturation specific humidity of the air under the environment temperature of target scene region.
S13. amount of radiation is brought into equation of heat balance, every kind pixel of target scene is calculated by Newton iteration method
The material surface temperature t of the corresponding geographical coordinate points of pointi,j, equation of heat balance is as follows
Qsun+Qsky=Qrad+Qcv+Qle
According to the temperature of each pixel, the temperature field of target scene is obtained.
S2. spatial frequency is calculated：
S21. the target in the specified material image of user is obtained, remaining is background area；
S22. the temperature difference of target area and background area is calculated, this model uses Δ TRSSThe temperature difference is counted, calculation method is such as
Under：
In formula：ti,jThe material surface temperature at target area pixel (i, j) is represented, POT is that target pixel points are always a
Number, μbkgFor environmental background temperature, mean value is taken to obtain each pixel temperature in background area.This method more comprehensively considers
The variation of target temperature has been arrived, the true target background temperature difference is relatively accurately reflected.
S23. parameter detector emulates
Infrared imaging system imaging, infrared light enters detector by optical system, after being converted to electric signal, entering signal
Processing circuit is handled, and is shown by display.The space transmission characteristic of infrared imaging system mainly includes：Optical system
Transmission function, the transmission function of detector, the transmission function of signal processing circuit, the transmission function of display.These physics effect
It should be considered as linear transmission effects to be simulated using the modulation transfer function (MTF) of each comprising modules, therefore total system passes
Delivery function can be multiplied to obtain by the transmission function of modules.
1) transfer function H of optical systemopt(fx,fy) calculate：
The MTF of optical system depends on wavelength, focal length and the shape in aperture.In imaging systems, the diffraction of optical system
Limit, geometrical aberration also have a great impact to its optical system transfer function.Usual diffraction limits corresponding transmission function in low frequency
Decline is very fast, trails in high frequency longer；And transmission function corresponding to geometrical aberration drop at low frequency it is relatively slow, drop in high frequency compared with
Fast and hangover is shorter.
By linear theory it is found that geometrical aberration and diffraction limit aberration are unrelated, therefore optical system overall transfer function Hopt(fx,fy)
The product of aberration function is limited for geometrical aberration and diffraction：
Hopt(fx,fy)≈Hdiff(fx,fy)Haber(fx,fy)
The transmission function of the optical system of diffraction limit depends on the shape of wavelength and aperture, fx,fyRespectively target water
Flat, vertical direction spatial frequency.
For circular aperture fx=fy=f：
fc=D0/λ0For the spatial-cut-off frequency (cycle/mrad) of incoherent optical processor；D0It is the effective of optical system
Aperture (mm)；λ0For the central wavelength (μm) of incoherent light, average operation wavelength (λ can use1+λ2)/2；[λ1, λ2] it is operation wavelength
Range；F is spatial frequency.
For square aperture fx=fy=f:
fc=D0/λ0For spatial-cut-off frequency (cycle/mrad)；D0It is the effective aperture (mm) of optical system.
In non-diffraction limit optical system, the Energy distribution of the disc of confusion as caused by aberration is Gaussian, has circle symmetric figure
Formula, standard deviation σc(mm), the form of transmission function is
Haber(f)=exp (- 2 π2σ2f2)
σ is the standard variance for the optical system measured with angle, σ=σc/ f, σ unit are cycle/mrad, it and disperse
The percentage of shared energy has direct relationship in circle.It is assumed that all energy all concentrate in disc of confusion, then standard variance
σcIt is equal to the 1/4 of disperse circular diameter.This hypothesis can approximate disc of confusion well shape, and it is easily controllable.Wherein more
The diameter of speckle can be determined by following formula：
2) the horizontal and vertical direction transmission function of detector calculates：
The type of detector mainly has the multiple types such as unit, polynary (series, parallel, series-parallel) and sprite detector
Type, different types of detector transmission function are also had any different.Wherein, unit, multiunit detector horizontal direction space transmit letter
Number is
In formula：α is the space subtended angle of rectangular detector horizontal direction.
For sprite detector, the transmission function of horizontal direction is influenced by two factors, one is reading section length
The influence of generation, transmission function caused by read-out area influences are MTFl：
MTFl=sinc (π lfx)
In formula：L is to read the corresponding angular distance (mrad) of section length.
Second, being influence caused by diffusion and scanning speed imbalance.In the area Sao Ji of sprite detector, diffusion and scanning
Transmission function MTF caused by speed mismatchdvFor
MTFdv={ (D τ K2+1)2+[(μaE-vs)τK]2}-1/2
In formula：D is carrier diffusion coefficient (cm2·s-1), it is the performance parameter of detector；τ is carrier lifetime (s),
For the performance parameter of detector；K=2 π fx/ f ', f ' are the focal length (cm) of detector；μaFor ambipolar mobility (cm2·V-1·s-1)；E is bias field (Vcm-1), it is the performance parameter of detector；vsFor scanning speed (cms-1), it is the property of detector
It can parameter.
In practical debugging process, we can be by finely tuning the operating voltage of each band, while observing its output
As a result, so that it is determined that optimum operating voltage.In this case, the influence of speed mismatch item can be ignored, it is only necessary to calculate diffusion
Caused by influence factor, at this point, transmission function can be reduced to：
It can be obtained from above, the horizontal direction transmission function MTF of sprite detectordxFor the product of above-mentioned two function, i.e.,
MTFdx=MTFlMTFdv
Meanwhile detector also can be equivalent to a RC low-pass first order filter, transmission function is
In formula：f0For the 3dB frequency (c/mrad) of spatial frequency domain.
Usually as basic parameter provide be temporal frequency domain 3dB frequency ft0It (Hz), can be by the 3dB of temporal frequency domain
Frequency conversion.Sometimes ft0It does not provide, but provides carrier lifetime τ, then can convert f in the following wayt0：
ft0=1/2 π τ
MTFdtAs time filtering, horizontal direction is acted only on.
Therefore the horizontal direction transmission function of detector should also be with MTFdtIt is multiplied, obtains the final transmitting letter of horizontal direction
Number MTFdx·MTFdt。
In vertical direction, detector is to complete what spatial sampling was imaged by discrete scan line, therefore have phase
As property.Strictly, vertical direction is unsatisfactory for linear and space-invariance, but when spatial frequency is less than scanning sampling
When Nyquist frequency, still available delivery function is described.
Vertical direction transmission function form is as follows：
In formula：fyFor vertical direction spatial frequency (c/mrad)；fNyFor Nyquist frequency.
3) signal processing circuit transmission function MTFeCalculating：
Signal processing circuit includes that the low-pass filter circuit, high-pass filtering circuit and high frequency being sequentially connected in series extract circuit.
The transmission function of low-pass filter circuit is MTFe1：
Low-pass filter is in the transmission function of temporal frequency domain
MTF=[1+ (ft/ft0)2]-1/2
In formula：ftFor the spatial frequency (Hz) of target；ft0For the 3dB frequency (Hz) of low-pass filter, ft0=1/2 π RC, R,
C is respectively the resistance and capacitor of low-pass filter.
In thermal imaging system, electronic circuit receives the temporal frequency f of signalt(Hz) and the spatial frequency f (c/ of target
Mrad) be it is relevant, conversion formula is
ω is the angular scanning speed of infrared system, τdFor the scanning residence time of infrared system, α is horizontal instantaneous field of view.
Temporal frequency is converted into spatial frequency, then the transmission function that can obtain spatial frequency domain is
MTFe1=[1+ (f/f0)2]-1/2
The MTF of high-pass filtering circuite2：
The link for completing similar differential process in circuit is high pass R1C1Filter, characteristic frequency is (i.e. on high-pass filter
Rise 3dB frequency) ft0For
ft0=1/2 π R1C1
It is obtained with the method similar with low-pass filter：
In formula：f0For high-pass filter spatial frequency domain 3dB frequency.
High frequency recommends the MTF of circuite3：
It is a kind of MTF enhancing circuit that high frequency, which recommends circuit, and mtf value can be greater than 1, and it is f that maximum, which recommends Frequency point,max, recommend
Amplitude is K (>=1), and transmission function is represented by
Calculating the total transmission function of signal processing circuit is MTFe=MTFe1MTFe2MTFe3。
4) calculating of display transmission function
The display used in thermal imaging system is cathode-ray tube (CRT) or light emitting diode (LED) array.
For the MTF of cathode-ray tubem：
It has been generally acknowledged that point brilliance distribution is Gaussian Profile on CRT, so transmission function is
MTFm=exp (- 2 π2δ2f2)
In formula：δ is the standard deviation (mrad) of display luminous point distribution, if the standard deviation in the direction display x and y is not
Together, then the σ in the direction x and y is substituted into respectivelyxAnd δyCalculate the direction x and y MTFm。
For the MTF of LEDm：
The luminous distribution for often assuming that LED is rectangular box shape function, therefore, the horizontal and vertical direction transmission function of LED
Respectively
MTFmx=sinc (π xfx)
MTFmy=sinc (π yfy)
In formula：X, y is respectively subtended angle (mrad) of the LED in normalization space.
5) Modulation Transfer Function of Human Visual System
The infrared radiation images of thermal imaging system detection need to export over the display, finally by eye-observation and by human brain
Corresponding judgement and decision are made, therefore thermal imaging system, human eye, brain are an organic combinations, must be examined in performance model
Consider the transmission characteristic of human eye.
Human eye transmission function is：
In formula：M is infrared system angular magnification, is the system parameter of infrared system：K is related with brightness of display screen L
Parameter, as L cd/m2When expression, it is represented by
K=1.272081-0.300182lgL+0.04261 (lgL)2+0.00197(lgL)3
S24. the calculated each section MTF function of S23 step is multiplied, obtain system it is total be adjusted to transmission function MTFs
(f), the transmission function MTF in horizontal and vertical direction is respectively includedxs(f), MTFys(f)。
According to MTFs(f) MRTD (f) is calculated, obtains the MRTD curve of infrared system, calculation formula is：
In formula：MTFs(f) MTF is replaced with respectively for horizontal and vertical direction for the modulation transfer function of systemxs(f),
MTFys(f), it can be obtained by the MTF curve multiplication of modules；ΔfnInfrared system is noise equivalent bandwidth, SNRDTFor observer
The threshold value visual signal to noise ratio that lines can be differentiated, generally taking 2.25, f is object space frequency, and NETD is the noise etc. of infrared system
The temperature difference is imitated, α is horizontal instantaneous field of view (mrad), and β is vertical instantaneous field of view (mrad), τdTo scan residence time (s), fpFor frame
Frequently (s-1)。
After the MRTD curve for solving the direction x, y respectively, the MRTD (f) in the direction x and y is respectively equal to target background temperature difference
TRSS, solve corresponding spatial frequency f on target x, y directionx、fy, then the final spatial frequency of target be
S3. periodicity N can be solved by calculating maximum：
Decomposable periodicity N represents the probability size that target is detected.One very high N value represents very high
Detection probability, definition are as follows：
The decomposable periodicity of N-target (cycles/mrad)
F-spatial frequency (cycles/mrad)
Mag-infrared system magnifying power
Cd-target characteristic dimension (m)
R-target (km) with a distance from optical system
Characteristic size is the target area area A in the specified material image of userw(m2) radical sign is opened to be calculated：
S4. it calculates N50 (detectable probability be 50% solve periodicity)：
The formula for calculating N50 is as follows：
Periodicity when N50-50% detection probability
ΔTRSSFor target/background temperature difference
C-background clutter is horizontal, and rule of thumb artificial specified, 1.0 is low, and 1.5 is slightly lower, and 2.0 is general, and 2.7 is high.
S5. detection probability is calculated：
Next need to calculate N/N50 ratio, to solve in next step：
Ratio=N/N50
The ratio of Ratio-N and N50
N-object solving periodicity
Periodicity when N50-50% detection probability
Pinf is acquisition probability, is calculated by an empirical destination probability transfer function：
Pinf-acquisition probability
E-2.7+0.7*Ratio
The ratio of Ratio-N and N50.
Threshold value can be manually set, if Pinf is more than or equal to threshold value, show that the infrared target is detectable, if being lower than threshold
Value shows that the infrared target is not detectable.If being lower than threshold value, the replaceable higher infrared imaging system of detection performance is visited
It surveys, until the Pinf of infrared detection system is more than or equal to threshold value.
It is illustrated in figure 2 Objective extraction figure of the invention；Fig. 3 show detectivity line chart at times of the invention,
The material image that the present invention is inputted by user calculates target temperature field using equation of heat balance, extracts from temperature field
Target, and detector performance and target property are modeled, calculate the detectivity of target.Invention has the advantages of high efficiency, error is small
And execution degree is high.
The above, optimal specific embodiment only of the invention, but scope of protection of the present invention is not limited thereto,
In the technical scope disclosed by the present invention, any changes or substitutions that can be easily thought of by anyone skilled in the art,
It should be covered by the protection scope of the present invention.
The content being not described in detail in this specification belongs to the prior art well known to those skilled in the art.
Claims (14)
1. detectivity analysis method is imaged in a kind of Infrared Targets, which is characterized in that include the following steps：
S1. the temperature for calculating the corresponding geographical coordinate points of each pixel in target scene image, obtains the temperature field of target scene；
S2. it calculates in target scene image, the temperature difference for the target and background that user specifies and the spatial frequency f of target；
S3. according to the spatial frequency f of target, periodicity N can be solved by calculating maximum；
S4. periodicity N50 when 50% detection probability of differential thermal calculation of target and background is utilized；
S5. N/N50 ratio is utilized, detection probability Pinf is calculated.
2. a kind of method according to target selection infrared imaging system, which is characterized in that include the following steps：
S1. the temperature for calculating the corresponding geographical coordinate points of each pixel in target scene image, obtains the temperature field of target scene；
S2. it calculates in target scene image, the temperature difference for the target and background that user specifies and the spatial frequency f of target；
S3. according to the spatial frequency f of target, periodicity N can be solved by calculating maximum；
S4. periodicity N50 when 50% detection probability of differential thermal calculation of target and background is utilized；
S5. N/N50 ratio is utilized, detection probability Pinf is calculated；
S6. if infrared imaging system detection probability Pinf is less than given threshold, the higher infrared imaging of detection performance is replaced
System, return step S2；If infrared detection system detection probability Pinf is more than or equal to given threshold, it is determined that the infrared imaging
System.
3. Infrared Targets as described in claim 1 imaging detectivity analysis method and as claimed in claim 2 according to mesh
The method of mark selection infrared imaging system, which is characterized in that according to the spatial frequency f of target in step S3, calculating maximum can be solved
The specific method of periodicity N is：
Wherein Mag is the magnifying power of infrared system, and R is target with a distance from optical system；Cd is the characteristic dimension of target,AwTarget region area is specified for user.
4. method as claimed in claim 3, which is characterized in that detected in step S4 using the differential thermal calculation 50% of target and background
The specific method of periodicity N50 when probability is：
ΔTRSSFor the temperature difference of target and background, C is that background clutter is horizontal.
5. method as claimed in claim 3, which is characterized in that the specific method of calculating detection probability Pinf is in step S5：
Ratio=N/N50E=2.7+0.7*Ratio.
6. method as claimed in claim 3, which is characterized in that calculate each pixel pair in target scene image in step S1
The temperature for answering geographical coordinate point, the specific method for obtaining the temperature field of target scene are：
S11. the material image for receiving the target scene of user's input, is numbered according to the material in the material image of target scene,
The emissivity ε and reflectivity α of every kind of material are extracted from Materials Library；
S12. the radiation energy of each pixel in target scene is calculated；
S13. the equation of heat balance for establishing target scene solves the material surface temperature of the corresponding geographical coordinate points of each pixel
ti,j, and then obtain the temperature field of target scene.
7. method as claimed in claim 6, which is characterized in that calculate the spoke of each pixel in target scene in step S12
Penetrate can specific method be：
1) the solar radiant energy Q that receives is calculated each pixelsun；
2) the long _ wave radiation energy Q that receives is calculated each pixelsky；
3) the radiation energy Q of material surface is calculated each pixelrad；
4) dominant heat exchange energy Q is calculated to each pixelCV；
5) latent property heat exchange energy Q is calculated to each pixelLE。
8. the method for claim 7, which is characterized in that the equation of heat balance for establishing target scene in step S13 is：
Qsun+Qsky=Qrad+Qcv+Qle。
9. method as claimed in claim 3, which is characterized in that calculate in target scene image, target and back that user specifies
The specific method of the temperature difference of scape is：
S21. the target in the specified material image of user is obtained, remaining is background area；
S22. the temperature difference T of target region and background area is calculatedRSS：
In formula：ti,jThe material surface temperature at target area pixel (i, j) is represented, POT is target pixel points total number, μbkg
For environmental background temperature, by taking mean value to obtain each pixel temperature in background area.
10. method as claimed in claim 3, which is characterized in that the specific method for calculating the spatial frequency f of target is：
(1) transmission function of infrared imaging system is calculated；
(2) calculation display transmission function；
(3) Modulation Transfer Function of Human Visual System is calculated；
(4) transmission function of infrared imaging system, display transmission function and Modulation Transfer Function of Human Visual System are multiplied, are obtained red
The transmission function MTF in the outer horizontal and vertical direction of imaging systemxs(f), MTFys(f)；
(5) the minimum detectable temperature difference function MRTD (f) of infrared imaging system is calculated,
Wherein Δ fnInfrared imaging system is noise equivalent bandwidth, SNRDTThe threshold value vision noise of lines can be differentiated for observer
Than NETD is the noise equivalent temperature difference of infrared system, and α is horizontal instantaneous field of view, and β is vertical instantaneous field of view, τdIt is resident to scan
Time, fpFor frame frequency；MTFs(f) fetch water the delivery function MTF that flates pass respectivelyxs(f), the MTF of vertical directionys(f), calculate or level
With the MRTD (f) of vertical direction；
(6) MRTD (f) in horizontal and vertical direction is enabled to be respectively equal to target background temperature difference TRSS, solve on target x, y direction
Corresponding spatial frequency fx、fy, then the spatial frequency of target be
11. method as claimed in claim 10, which is characterized in that the method for calculating the transmission function of infrared imaging system is：
Infrared light enters detector by optical system, and after being converted to electric signal, entering signal processing circuit is handled；It calculates
The transfer function H of optical systemopt(fx,fy)；The horizontal and vertical direction transmission function of calculating detector；Calculate signal processing circuit
Transmission function MTFe；Calculate separately the transmission function of the transmission function and vertical direction that obtain infrared imaging system horizontal direction.
12. method as claimed in claim 11, which is characterized in that calculate signal processing circuit transmission function MTFeSpecific side
Method is：Calculate the transmission function MTF of low-pass filter circuite1；Calculate the transmission function MTF of high-pass filtering circuite2；Calculate high frequency
Recommend the transmission function MTF of circuite3；Calculate signal processing circuit transmission function be：
MTFe=MTFe1MTFe2MTFe3。
13. method as claimed in claim 10, which is characterized in that it is as follows that display transmission function calculates method：
For cathode-ray tube display transmission function MTFmCalculation method is as follows：
MTFm=exp (- 2 π2δ2f2)
δ is the standard deviation of display luminous point distribution in formula；Direction transmission function MTF horizontal and vertical for light-emitting diode displaymx、
MTFmyCalculation method is as follows：
MTFmx=sinc (π xfx)
MTFmy=sinc (π yfy)
X, y are respectively subtended angle of the LED in normalization space in formula.
14. method as claimed in claim 10, which is characterized in that Modulation Transfer Function of Human Visual System calculation method is as follows：
M is infrared imaging system angular magnification in formula；K is parameter related with brightness of display screen L,
K=1.272081-0.300182lgL+0.04261 (lgL)2+0.00197(lgL)3。
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