2013 Vol. 42, No. 2
2013, 42(2): 285-289.
To study the characteristic of aerodynamic heating on common aviation vehicle(CAV) from near continuous flow region to rare transitional flow one, the surface aerodynamic heat flux distribution on CAV was measured in the ground test with infrared thermographic technique under the typical orbital parameter conditions. The function and parameter of hypersonic low density wind tunnel and infrared camera as well as the shape characteristic of the CAV were given in this paper firstly. Three simulation means such as viscous interaction parameter, enthalpy difference between total enthalpy and wall enthalpy and Knudsen number parameter adopted in the hypersonic low density wind tunnel were presented. At the test conditions M=7, =0, 12 and M=12, =24, heat transfer distributions on the whole model surface, typical flow field schlieren pictures and infrared mappings were obtained. The heat transfer results at the model windward centerline, windward wing forward edge and theoretical computation were compared at different Mach number and different attack angle. Test result shows that heat flux distributions on windward wing forward edge possesses of shape as saddle, that the influence of the variety of attack angle on aerodynamic heating is distinct.
2013, 42(2): 290-293.
During the high speed flight of a missile, its dome was subject not only to high temperature, but also to load caused by pneumatic calefaction. In this work, the deform of both the planar window and the spherical dome made of ZnS material were ANSYS-based calculated at a temperature of 500℃ and at the pneumatic pressure of 4 atm. Furthermore, the effect of deform on IR imaging system quality were analyzed by ZEMAX optical design software. As to the IR long wavelength imaging system with optical parameters, field of view of 13, focal length of 70 mm, and F number of 1, effect of pneumatic calefaction on imaging system quality was discussed. It has been demonstrated that the modulation transfer function (MTF) (16 lp/mm) in all field of view is insensitive to deform of IR planar window. However, deform of spherical dome could cause MTF declined by maximum 2.56%.
2013, 42(2): 294-299.
Predigesting geometrical model of a certain aircraft was established, and its flight path was set. Aerodynamic heating and radiation from sun, ground and atmosphere were considered comprehensively, then physical models of heat conduction were founded against three shielding coatings with different emissivity and physical characteristic of stealth aircraft skin. Based on one dimensional heat conduction equation, temperature distributions of skins with different emissivity were calculated between 12:00 pm and 12:45 pm. Finally, influence of environment radiation was considered, the infrared radiant intensity distributions of skins with different emissivity were calculated numerically in 3-5 m and 8-14 m. The result improves that with skin emissivity reducing the infrared radiant intensity of skin diminishes at a certain extent, but due to influence of environment radiation, the effect of aircraft infrared stealth is not ideal only by skin emissivity decreasing.
2013, 42(2): 300-304.
An infrared radiation model of decoys was built to indicate the characteristics of infrared decoys based on its spatial and temporal distribution characteristics. Then the interaction between infrared decoys and environmental targets was analyzed, and the mathematical model on the reflection characteristics of environmental objectives was established based on bidirectional reflectance distribution function(BRDF), which was used to calculate the radiance reflected by the surface of environmental targets from the infrared decoys irradiance in the observe direction. Finally, a 3D real-time simulation of the ground environment was performed before and after decoys launch. The simulation result showed the effect of decoys radiation on ground environment at different time after decoys launch, which was of great significance for infrared decoys research.
2013, 42(2): 305-310.
It was a difficult problem in infrared target tracking field that how to effectively exclude the interference of infrared decoy, especially for that infrared decoy technique had developed more and more advanced as a common measure to interfer infrared tracking capability. Based on discussing characteristic difference of infrared targets and decoys, a multi-target tracking strategy to track excluding the infrared decoy was firstly proposed. And an improved joint probabilistic data association(JPDA) algorithm with fusion of multiple features was established. Finally, the process of tracking with excluding infrared decoy was simulated. Simulation results showed that the proposed algoritllIn can track target at real-time, which has higher accuracy for resolving the problem of the infrared target recognition that infrared decoys form false targets and the target block.
2013, 42(2): 311-316.
For mastering the dynamic infrared radiation characteristics on the surface of terminal-sensitive projectile when it was projected from cabin of the carrier shell, according to the structure characteristics, combining with the dynamic model of the deceleration and despinning stage, the physical model of temperature field and radiation characteristics were established under the comprehensive effect of aerodynamic heating, internal heat source and the heat exchange with environment. Based on the coupled solution of thermal balance equations and trajectory model, the distribution law of surface temperature field and radiance were obtained. Finally, the infrared radiation intensity of different spectral bands varying with flying time were calculated and analyzed in different initial conditions. The results provide valuable reference for the infrared detection and recognition of terminal-sensitive projectile.
2013, 42(2): 317-323.
In order to overcome the difficulty of nonlinearity and ill-posedness of the defect quantitative identification with the single-side infrared inspection, a new algorithm(Chaos-LM hybrid algorithm),which combined the chaos algorithm with the Levenberg-Marquardt method,was introduced in this paper. And a new concept of relative sensitivity coefficient was also brought forward to analyze the defect inspectability. Through analyzing the relative sensitivity coefficient, it was found that the inspectability of different parameters describing the size and position of the defect was different, and the inspection carried out at the time with maximum surface temperature difference was more desirable than that in steady heat transfer state. Both of the transient and steady inspections were tested by a series of numerical experiments, and the experimental results are consistent with the analysis of relative sensitivity coefficient. Besides, the numerical experiments have certified the effectiveness of the Chaos-LM hybrid algorithm, and show that the identification results are stable and globally optimal.
2013, 42(2): 324-328.
A kind of pyroelectric infrared temperature measurement system was designed, which core was the ATmage32 SCM. It was a non-contact and voice prompt temperature measurement system by using pyroelectric infrared sensor. It used the pyroelectric infrared sensor to extrat the temperature of the human body and the DS18B20 to measure the environmental temperature, which could achieve the temperature compensation to reduce the measurement error. It could be controlled to realize the temperature convertion and processing, and sent the temperature value to the LCD to display and the voice prompt by the AVR SCM. Simultaneously, it was added the clock function and overtemperature alarm function to make the design more practical. The temperature measurement range was from 35-42℃. The measurement time was less than 1s. The temperature measurement system had the advantages of handy use, good flexibility, high reliability, and had a promotional value.
2013, 42(2): 392-397.
Focusing is one of the key technologies to improve the imaging quality in multispectral CCD camera. The design, realization, and performance of a focusing system for multispectral CCD camera were presented in detail, featuring wide field of view and wide swath wide with TMA optical system, based on earth observation satellite. First, the focusing precision required was calculated according to the shortest spectrum wave in the optical system. Compared with other focusing methods, the method of direct adjusting CCD focal plane was proposed, which was suitable for this CCD camera optical system. Second, a focusing system was developed, the hardware system including stepper motor, worm couple, pair of gears, precision screw ball, linear bearing, and encoder was constructed. And its theoretical focusing sensitivity was calculated to be 0.12 m, The proposed focusing system has the advantages of lower constructional complexity, easier hardware implementation and high focusing sensitivity. Finally, experimental setup was constructed to evaluate the focusing precision performance of the focusing system. The result of the experiment indicated the 3.62 m(3) precision of focusing in a range of 2.2 mm. And after mechanical vibration test and thermal vacuum test, the focusing precision was 3.64 m(3) precision of focusing in a range of 2.2 mm. The experimental result shows that the proposed focusing system is remarkable, reasonable, and reliability, as well as stable, which meet the focusing precision requirements for multispectral CCD camera.
2013, 42(2): 398-402.
For medium wave cool 640512 detector with staring focal plane array, a MWIR continuous zoom optical system with large zoom range was designed. The optical system imaged thrice. The operating wavelength range was 3.7-4.8 m, F number was 4 and the zoom ratio was 30:1. The optical system could realize 23-701 mm continuous zoom and meet 100% cold shield efficiency with smooth zoom locus. Three infrared materials of Si, Ge and ZnSe were used in the optical system. The system could correct the off axis aberration and higher order aberration by leading the aspheric surface and the diffractive surface. The MTF was above 0.15 within the whole focal range at the spatial frequency of 30 lp/mm and it approached the diffraction limit. The results show that the MWIR continuous zoom optical system has large zoom ratio, high resolution, small volume and excellent image quality.
2013, 42(2): 403-407.
Hybrid refractive-diffractive design offers a new approach for athermalization design in wide temperature range. In this paper, working wavelength is in 3-5 m. For cool 320240 infrared detector, pixel size 30 m30 m, this system can realize 400 mm and 800 mm dual filed-of-view and the F-number of 2/4 respectively. Two systems both can obtain the cold shield efficiency of 100% though controlling machine structure. A diffractive surface was introduced in the shared part of two different focal length position. It achieve the athermal design using only one diffractive surface. The evolution of the system was given in the temperature range -40-60℃. The results show that at the spatial frequency of 18 lp/mm the MTF approach to the diffractive limitation.
2013, 42(2): 408-412.
In the ion beam figuring technique, to improve the solution precision of the dwell time algorithm on the edge of the component, the initial surface of the error should be extended smoothly and limited. A curve surface extending algorithm was proposed which is based on the Gaussian curve. The character of smooth, limitary and parameter continuity were used. When the curve surface extending method was used in the dwell time solving process of a surface error with high frequency noise, the residual error of the dwell time algorithm on the edge was controlled. The ratio of the surface error constringency in the whole caliber reached 97% by RMS. The results show that the surface extending algorithm which based on the Gaussian curve can extend the surface error of optics smoothly. And it has good ability to oppose the noise disturbance. It improved the solution precision of the dwell time algorithm.
2013, 42(2): 413-417.
With the rapid economic development, the ambient air quality has been on the slide. Gas emission sources monitoring was an important research in the field of environment science. The high temperature reference spectral line model method and standard gas measurement method were put forward and realized, by which the synthetic calibration spectrum was corrected and the high temperature gas concentration retrieval accuracy was improved based on the nonlinear least square algorithm of numerical calculation. The concentrations of the standard gas CO were inversed under different temperatures by the experiment measured transmittance spectra. As a result, the accuracy has been improved greatly, comparing to concentration inversion results with no temperature correction calibration spectrum. The results in the paper were important for high temperature gas spectral features, perfecting quantitative analysis algorithm, accurately monitoring gas emissions concentration not at the room temperature, infrared guidance and so on.
2013, 42(2): 418-422.
SiO2 films were deposited on fused silica substrates by ion beam sputtering(IBS) technology, and the effects of thermal treatment on structural characteristic were researched. The effects of annealing temperature on surface roughness of IBS-SiO2 films were very large, low annealing temperature could reduce the surface roughness, but high annealing temperature could increase the surface roughness, the proper annealing temperature had almost no impact on surface roughness. Amorphous structures of IBS-SiO2 films were researched by XRD technology. When the annealing temperature was 550 ℃, the largest short range order and the shortest average distance were obtained, the results were the same as the fused silica substrate, and the structure was stable. Expermental results show that structural characteristic of IBS-SiO2 films can be improved by the proper thermal treatment.
2013, 42(2): 423-427.
For the endoscope with imaging fiber bundle, either the configuration or the imaging quality of its objective lens should satisfy some new requirements. Firstly, the fundamental of the objective lens design was analyzed, and the retrofocus objective lens was chosen as an initial structure for this design. Then an objective lens for the fiber-optic endoscope was designed with the software Zemax. The operation wavelength, focal length, FOV(field of view) and relative aperture of the designed lens are 0.38-0.78 m, 0.921 mm, 100 and 1/4 respectively. Its total length is 10.32 mm. It's telecentric in image space. The MTF value of the lens is greater than 0.85 at the spatial frequency of 38 lp/mm. Furthermore, a model of the designed lens combined with the imaging fiber bundle was established in the software Tracepro. The coupling efficiency of the simulated system is about 96% and the illumination of output end is uniform. All the results show that the designed lens has the peculiarity of wide FOV, short focal length, logical configuration, high coupling efficiency and uniformity illumination at image plane. It is suitable for the fiber-optic endoscope.
2013, 42(2): 428-432.
Using the 4-D code for laser propagation in the atmosphere, uplink for the relay mirror system was simulated. Under H-V5/7 turbulence model, the relationship between launching power and power coupling efficiency between the receiver at the relay platform and the transmitting telescope on the ground, received power and peak power density of far-field at the relay platform was investigated. The result shows that the received power at the relay platform in creased with the increase of coupling efficiency and beam quality of the received laser. A critical distortion number NDc, which when the distortion number exceeded the peak power of the far-field would descend, also existed. The critical value with different turbulence strength for uplink propagation of relay mirror system was further studied, and a fitting result was obtained and could be expressed as NDc=22.36e-0.26(D/r0)+36.87.
2013, 42(2): 459-464.
Position sensing detector (PSD) is an optics sensor that can detect the center of the incident light. It has the advantages of fast response, high position resolution and simple circuit, these characteristics make it a wide range of application in precision measurement such as angle and position detection. A optical experiment on a optic bench A823 was chose for data acquisition under the DOS operating system and Borland C++ builder, C program was written for a real-time transformation between analog voltage and digital voltage, then position coordinate was calculated and the error was analyzed. 2L10_SU65_SPC02 PSD used in this experiment is from Sitek corporation in Sweden, through the error analysis the main conclusions include fringe effect of PSD, the main influence about the position error are natural daylight and fluorescent light. If eliminate influence factor precision will improve a lot.
2013, 42(2): 465-469.
In order to overcome the deficiency of single uniform fiber grating Sagnac loop, which has poor channel isolation, the comb filter with a cascade of Sagnac loop was proposed. Also, the frequency spectrum characteristic of the single uniform fiber grating Sagnac loop, two and three order Sagnac loop were analyzed with Jones matrix theory. For the case of three order Sagnac loop, a comb filter which has 0.8 mm spacing and 0.1 nm FWHM was got. Furtermore, in the same channel spacing, this comb filter's FWHM was only 1/4 that of the single uniform fiber grating Sagnac loop's. The results show that the system channel isolation degree is improved effectively, and a comb filter which has uniform passband interval, high channel isolation, narrow FWHM characteristics was proposed, this kinds of filter can meet the WDM requirement better.
2013, 42(2): 470-475.
Random perturbations exist in the working environment of submarine optic fiber cable, so using traditional single-pulse TDR to detect the fault of submarine optic fiber cable sheath can not get ideal waveform due to the interference of random noise, and fault detecting effect is unsatisfactory. To solve this problem, an equivalent circuit model of submarine optic fiber cable sheath was proposed based on the structural characteristics of submarine optic fiber cable sheath, which is equal to a lossy-nonuniform transmission line with random perturbations. And a fault-detecting method was put forward, which adopted unipolar coding pulse as detecting signal. Through theoretical analysis and experimental studies, this program can effectively reduce the nosie of system without reducing the spatial resolution and improve the system gain compared with single-pulse TDR. So the detecting result can be improved, and meet the requirements of submarine optic fiber cable sheath fault-detecting engineering.
2013, 42(2): 476-481.
Improving the precision of fiber optic gyroscope (FOG) in vibration environment is important in the application of FOG. Current research on reducing FOG vibration error are mainly concentrate on improving FOG mechanical structure and reinforcing fiber coil. However, fiber tail length asymmetry also has been demonstrated an important reason which can affect the vibration error of FOG. Firstly, the basic theory of phase shift of FOG caused by elastic-optic effect due to vibration was introduced. Then the length of fiber tail on the left and right asymmetry was shown to be the reason of nonreciprocal phase shift in the condition of vibration. Theoretical formula between the length difference of fiber tail in two directions and the output error of gyroscope was derived. Finally, simulations were performed to show the relationship between fiber tail length asymmetry and FOG output error.
2013, 42(2): 482-488.
A dual-tone modulation intersatellite microwave photonics link model was presented including optical source, Mach-Zehnder modulator, erbium-doped fiber amplifier and photodiode. An exact analytical solution for any harmonic and intermodulation components at the output of the detector was deduced with the method of bessel expansion, fourier transform/inverse fourier transform and graf addition theory, thus, the expression of SNDR was derived considering the effects of third-order intermodulation distortion (IM3). The SNDR, fundamental and IM3 power varies with the radio frequency (RF) input power under different modulation modes was analyzed. Numerical results indicate that the SNDR, fundamental and IM3 power increases and decreases as the increase of RF input power, there is an optimum RF input power that maximize the SNDR. The SNDR of double sideband modulation is larger than single sideband modulation under the same RF input power and it is suitable for the application of intersatellite microwave photonics link.
2013, 42(2): 489-494.
In order to investigate the stabilization of optical axis of semi-strapdown seeker, the factors that influence the stabilization were analyzed. The essence of semi-strapdown stabilization was proposed by comparing with the traditional gyro stabilization method. The expression of the inertia-space velocity of optical axis was showed, and the main factors that influence the semi-strapdown stabilization were analyzed. The matched filter and disturbance obverse were used to improve the precision of semi-strapdown stabilization against missile disturbance and disturbance torque. The numerical simulation result shows that the matched filter rises 38 dB of the coupling precision at 1 Hz; the influence to stabilization caused by disturbance torque is greatly reduced by disturbance observer; and the stabilization error caused by velocity measurement is improved by using high precision and low noise sensor. The integrated simulation result shows that the stabilization error is declined nearly 94 percent after compensating for the three main factors.
2013, 42(2): 495-498.
Luminance gain, which was directly affect the image quality of night vision system in low light level condition, was an important technological index to evaluate the ability to amply image light intensity. In order to improve the repetitive characteristic of image intensifier's luminance gain, changing process of light source color temperature, light source output luminance and screen luminance had been studied respectively, theory of light source color temperature, light source output luminance and screen luminance impacting on luminance gain had been analyzed. The conclusion with warming-up of light source should not be less than 15 minutes and work time for image intensifier should not be less than 1 minute had been established. Test result showed that repetitive characteristic of image intensifier was better than 3% when light source had been warmed-up sufficiently and image intensifier's work time was controlled strictly.
2013, 42(2): 499-502.
The noise factor, which is the main factor affecting the noise performance of image intensifier and can accurately reflect the noise characteristics of the microchannel plate, is the ratio of the input signal to noise ratio and the output signal to noise. According to definition of noise factor of microchannel plate and test principle, filmed MCP test system was established in order to study the technical way to reduce noise factor of MCP. The input surface of the MCP was covered with ion feedback film, which had a great impact on the noise factor of the MCP. Hence, noise factor of filmed MCP and un-filmed MCP were measured respectively, and the noise factor with different material, different channel pore, different incident electrons and MCP voltage were measured too. Relationships between noise factor and incident electron, noise factor and MCP voltage was obtained. That was valuable to reduce the noise of filmed MCP.
2013, 42(2): 503-506.
Hadamard transform imaging spectrometer is a multi-channel detection digital transform spectrometer detection technology. The spectromter used this technology to achieving spectral imaging. Based on the digital micromirror array device of the Hadamard transform spectrometer working principles and the instrument, a series of precision laboratory calibration methods were researched and employed for the Hadamard transform imaging spectrometer. A point light source in long distance was used for the pixel response nonuniformity correction of the CMOS detector. The uncertainty of the relative calibration was 4.6%. Solar simulator and spectral radiometer were used in absolute radiation calibration of the whole system, and the uncertainty of the absolute radiation calibration was 8.92%. Both of the uncertainty of relative calibration and the uncertainty of the absolute radiation calibration met the requirements of the projection. By actual objects imaging, the laboratory calibration methods of the Hadamard transform imaging spectrometer are proved accurate.
2013, 42(2): 507-512.
In order to meet the demand of measuring the projectile-curtain parameter of multibarrel volleyed weapons, a method basing on the divided six-light-screen array was put forward. When projectiles from multibarrel volleyed weapons past through the divided screens, each small screen sensor would put out signals. The multi-channels data acquisition device captured these signals and then calculated the times of between different signals. The time sequence for a projectile past through six screens can be identified according to the principle that the flying time between the symmetry screens was the same and the flying time in different position in one screen was different. Finally the flying parameters for every projectile can be worked out. The efficiency of the algorithm has been verified by emulation tests. Besides, the implementation scheme for the light screen was given, and has been verified by the high rate firing tests.
2013, 42(2): 513-518.
Line segment feature is widely used in the field of image analysis and processing, and line segment extraction is an important step in pattern recognition and image matching which are feature-based. The pros and cons of the line segment extraction method directly affects the complexity and the processing effects of high-level image processing. However, there were some problems in most of the current line segments extraction methods. For instance, the endpoints of the extracted line segment were not accurate enough and the extracted line segments were always discontinuous. A HOG-feature-based approach was represented to overcome the above two problems. In order to extract line segments efficiently, in this method, the integration on rows and columns of a matrix was used to realize the projection of line segments with particular direction in the original image. And then with the application of the property of the rectangular function's first derivative, the line-segment endpoints positions were determined via the column vector's derivative. Theoretical analysis and the results of experiments verified that this method can not only extract straight segments accurately, but also solve the straight segment fracture and endpoints inaccurate problems existing in the classic methods to some extent.
2013, 42(2): 519-523.
To improve optical micro scanning device position calibration precision of the micro thermal imaging system, a Fourier transform micro displacement detection method based on histogram statistical tension was proposed. It can improve image contrast and enhance image details according to histogram features of micro thermal imaging. And with the images enhanced by histogram statistical tension can increase displacement detection accuracy by Fourier transform. So it also can improve the scanning calibration position precision. The construct experiment of before and after images enhance were done. The experiment results show that with the method of histogram statistical tension the position calibration is more precise, the reconstructed image has higher quality and more abundant details.
2013, 42(2): 524-527.
Compared with the nearby undisturbed seawater the temperature difference in the ship wake is tiny and the ship wake presents obscure configuration. These induce the low contrast of the infrared ship wake image and the borders of the wake images are difficult to be extracted. According to the characters of ship wake and infrared wake image, a border detecting method by dynamic texture and mathematical morphology was proposed. Firstly, the infrared wake image sequence was pre-segmented by dynamic texture method, and then the edges in the wake area were extracted by Canny operator. The extracted edges were dilated, labeled and selected by the mathematical morphology and the true wake borders were extracted. The experimental results show that processing the wake images by the methods mentioned above can effectively extract the borders of the ship wake and get better results.
2013, 42(2): 528-532.
In order to build the general and objective fusion image quality assessment method, the key technique of fusion image quality subjective assessment were presented such as assessment object, assessment condition, assessment index and data processing based on the analysis to image quality subjective assessment method. Two subjective assessment indexes were provided including target detectable ability and details resolvable ability according to two typical vision tasks of target detection and scene understanding. Furthermore, the correlation was investigated between the whole perceptual quality with target detectable ability and details resolvable ability respectively. Experiments were performed for 189 fusion images generated by 9 kinds of fusion algorithms fusing visible and infrared images under 3 kind different scenes. Statistical result showed that the high correlation between the whole perceptual quality with details resolvable ability compared with the low correlation to target detectable ability. However, the index of target detectable ability was still effective and could be used in the actually vision task.
2013, 42(2): 533-536.
Low sampling frequency and echo broadening are the main reasons for low peak detection accuracy in digital pulsed laser ranging. The traditional inverse distance weighted interpolation algorithm (IDW) for peak detection can only solve the problem of low sampling frequency. Aim at the problem, an improved inverse distance weighted interpolation algorithm(ⅡDW) was proposed. The sampling peak value is firstly located, then sampling spots within the researching radius of the rising edge and falling edge were assigned with different weight according to the different distance to the peak value separately, finally the peak time was corrected by weighted average. This algorithm reduces peak detection errors caused by restriction of sampling frequency and echo broadening effectively and improves the detection precision of digital pulsed laser ranging.
2013, 42(2): 537-542.
The guided filter is an edge preserving filter proposed in recent years, which can be broadly used in many image processing applications such as smoothing, detail enhancing, dehazing, etc. A high performance VLSI (Very Large Scale Integration) architecture of guided filter for single image was proposed. The architecture of the guided filter was fully pipelined, which can process images at the speed of nearly one pixel/cycle, without any off-chip memory. Moreover, a method which enable the size of the filtering window to be flexibly changed at run time was achieved. The architecture was implemented on FPGA of Altera's Cyclone Ⅲ and synthesis result shows that the requirement of logic elements and memory is acceptable for low-end FPGAs. Additional experimental results show that the proposed architecture is capable of processing video with dimension of 1 024 by 1 024 at the frame rate of 100 FPS. The architecture can be used as accelerator card for PC or front end of embedded systems for different kinds of real-time image processing tasks.
2013, 42(2): 543-548.
A multi-kernel tracking algorithm based on projection histogram matching and topology constraint was proposed in the mean shift framework, in order to overcome problems caused by partial occlusions and location deviation in the forward looking infrared(FLIR) target tracking. Firstly, target location was predicted by matching the spatio-intensity 2D projection histograms of consecutive frames. Secondly, multiple independent kernel-based trackers were built utilizing the target foreground and background information, which could improve the discrimination of the target model. Finally, topology constraint was used to optimize multiple tracking results, and those trackers with better performance were chosen to generate the final tracking result. Experimental results demonstrate that the proposed algorithm can track target accurately and robustly, and especially in the cases of partial occlusions or location deviation, the average tracking error of the proposed algorithm is much less than that of the traditional algorithm. Therefore, the algorithm has high practicality and feasibility in the FLIR imaging guidance.
2013, 42(2): 329-333.
A kind of narrow line-width fiber laser using F-P fiber ring filter was proposed and experimentally demonstrated, which has a ring cavity. A F-P fiber ring filter consisted of two optical couplers of 30:70 and a length of 2 m unpumped Erbium-doped fiber. The comb spectrum produced by F-P fiber ring filter can magnify the free spectral range of the laser mode, eliminate mode hopping and increase the stability of the mode in a certain extent. The research shows that the fineness of F-P fiber filter can be improved through the optimization of Erbium-doped fiber and the selection of couplers. Unpumped Erbium-doped in the F-P fiber ring acts as saturated absorber, which can compress the linewidth of output laser effectively. Polarization-maintaining fiber grating(PM-FBG) and F-P fiber ring filter are both applied into Erbium-doped laser, the output of narrow linewidth and dual-wavelength laser is obtained, and the 3 dB linewidth of dual-wavelength laser are both less than 0.07 nm(spectrometer minimum resolution). The fiber laser had a stable output whose maximal peak power fluctuation was less than 0.4 dB within observation time of 2 h.
2013, 42(2): 334-338.
In order to study the Energy Pooling process of the rubidium vapor laser, this paper established a rate equation model which took Energy Pooling effect into consideration. Through calculating it was found that when the magnitude of the pump intensity was, the influence of Energy Pooling process on laser photon emission rate was not remarkable. The influencing degree was related to the excited population density and the rate coefficient. With the increasing of pump intensity and excited population density, the Energy Pooling process reduced laser photon emission rate. However, under the conditions of lower pump intensity and lower excited population density, Energy Pooling significantly reduced the spontaneous radiation so that the laser photon emission rate was increased.
2013, 42(2): 339-343.
In order to reduce the influence of backscattering on the ring laser gyro, backscattering properties in the passive ring cavity was investigated. First, stable solutions of forward and backscattering light intensity and their temporal evolutions for quick turn-on and turn-off of incident light were obtained. Second, full width at half maximum of forward and backscattering light in the ring cavity as a function of incident laser frequency was derived. In the end, variation of forward and backscattering light as a function of incident laser frequency with different frequency scanning speed was discussed. It is found that the whole backscattering intensity is much larger than the single round backscattering intensity and full width at half maximum of backscattering light intensity is 0.64 times of forward light intensity. These findings are of some help to the measurement of backscattering as well as measurement of cavity loss using laser frequency scanning.
2013, 42(2): 344-348.
A diode-pumped injection-seeded Tm,Ho:YAP laser was reported. The output single-frequency pulse energy of 2.8 mJ at pulse repetition frequency of 100 Hz with a pulse width of 289 ns was obtained. Using the injection-seeded Tm, Ho:YAP as the emission source, a laser Doppler velocity measurement experiment by means of heterodyne coherent detection was demonstrated. The detecting target was an air fan with diameter of 10 cm and the maximum linear velocity of 20.4 m/s. The Doppler frequency shift, carrying the velocity information of the air fan, was achieved from heterodyne signal between the local oscillator and the scattering light from the air fan. Under various velocity conditions, the linear velocity of the air fan was achieved from the experimental data. Compared with the actual speed of the air fan, the measurement error of experiment was less than 1 m/s.
2013, 42(2): 349-354.
LIDAR data filtering is to obtain high-precision digital elevation model of improved hierarchical moving curved fitting algorithm, removed the rough points and most of the buildings side points, by gridding points, data index were calculated, used the least squares fitting surface, the adjacent surfaces maintained a certain overlap degree, automatically set the threshold for processing the raw data. Finally, used the multi-scale weighted interpolation method to generate digital elevation model. Adopt test data provided by international photogrammetry and remote sensing society(ISPRS).Results show that the algorithm reduced three types error possibility, total error of filtering in first study area decreases from 8.39% to 7.40%, and the total error in the second study area decrease from 6.39% to 5.86%, the generated digital elevation model to meet the precision requirements, algorithm can be popularized.
2013, 42(2): 355-360.
Three different manners of environmental factors' effects on the light intensity and bias of four-frequency laser gyro were summarized. Since both light variation and null drift were the laser gyro's response to environmental factors' effects, light intensity can reflect the environmental factors' effects on laser gyro's bias well. As a result, a novel approach of light intensity compensation of four-frequency laser gyro's bias based on BP neural network was presented. A BP neural network of laser gyro's bias was set up. Then the light intensity compensation experiments for three different mechanisms of generating null drift, including startup null drift, mode hopping, and high-low temperature process, were carried out. It can be concluded that the approach can distinguish above three different mechanisms and compensate for their effects. The approach is meaningful to enhancing the laser gyro's performance under the complex environment.
2013, 42(2): 361-365.
The development of a high brightness fiber coupled laser diode module for pumping Ytterbium-doped large-core double cladding fiber lasers was reported. This module was based on high power broad area single emitters which were free space combined in a step arrange manner. The fast axis and slow axis of each diode laser were collimated by micro-lens, and the output beam of diode lasers was combined in the fast axis direction. Then the combined beam was focused using two groups of cylinder lens in the fast and slow axis direction respectively in order to eliminate the spherical aberration. Finally, the combined beam was coupled into an optical fiber. In this experiment, six 976 nm LDs with power of 6 Watts per diode were coupled in a 105 m, 0.15 NA optical fiber. The output power of the fiber coupled module was 29.0 W at operating current of 6.2 A. The coupling efficiency reached 80.1%, and the brightness exceeded 4.74 MW/cm2-str.
2013, 42(2): 366-371.
Dynamic control error of precise two-dimensional mirror was the important influencing error factor on simulation precision of the laser guided weapon countermeasure simulation system, the accurate error model was the foundation for precision analysis of the simulation system. At present classical frequency method was adopted to analyze the control error by setting up the transfer function of the servo system, the modeling process was complex and accurate model was not easy to build. Then the paper gave the principle of the identification method, the design approach of input LFM signal, the ranks and parameters of the equivalent control error model which was built by using RWLS method. The proposed model was verified by simulative test by inputting the sine signal according to the performance index of the mirror. The result showed that the estimate output was consistent with the simulation output: the estimate average error and maximum error were 0and 13 respectively, which explained the accuracy of the control error model and provided the support for modeling the dynamical control error of other simulation equipment in the simulation system.
2013, 42(2): 372-375.
Based on ray tracing method, the laser transmission model of typical tapered multimode fiber was established. Integrating the peculiarity of jamming laser beam from the laser jammers, the coupling efficiency and transmission modes of laser spot throughout the tapered multimode fiber were calculated. Experiments were designed and conducted to verify the simulation. The results indicate that the output laser spot behaves circular when a laser spot with Gauss distribution incidences the tapered multimode fiber; the coupling efficiency decreases when the incident angle increases, and the decrement rate decreases as the incident angle increases. In order to solve the circular laser spot distribution, a new method of a small angle bending of the connected cylindrical fiber was introduced, and the output laser spot was improved to two-dimensional normal distribution, the theoretical coupling efficiency was about 80%. This provides a theoretical and experimental support for jamming laser intervening into the laser guided weapon countermeasure hardware-in-loop system.
2013, 42(2): 376-380.
With rapid development of space rocket technology, a key problem needs to be solved. How is small size defect (less than 8 mm) in grain with large coating thickness (greater than 4 mm) detected The holographic maps of solid grains with different thickness were gained by using laser holographic interferometry. The effects of coating thickness and defect size on the deformation of grain were investigated. When coating thickness was fixed at 6 mm, the available detected threshold limit size of defect was about 2 mm. If the sizes of defect were less than 2 mm, distinct interference fringes were not obtained. The actual sizes of defects located between coating with thickness 2-6 mm and grain were calculated by experimental data. Verified by experiment, the average values of the error were less than 5%. Final results indicate that the nondestructive laser holographic interferometry is a kind of valid and accurate method for measuring unbonded defect (less than 8 mm) between coating and grain with coating thickness above 4 mm.
2013, 42(2): 381-386.
For the purpose of fabricating high-quality mesh in a deep concave spherical substrate by laser direct writing technique, the constant exposure dose control must be realized during the whole scanning process. Firstly, the principle of the equipment for fabricating mesh in a deep concave spherical substrate via laser direct writing technique was introduced. Then scanning motion states for writing arbitrary line of latitude were analyzed, and the formulas that expresses the mathematical relationships between the dimensions of the substrate, parameters of mesh and the scanning velocity were deduced. The mathematical model of scanning with constant exposure dose was built, and the servo control system including software and hardware was developed according to the mathematical model. The servo control system could tune the scanning angular velocity precisely according to the latitude of lines to maintain the linear velocity invariantly, so as to keep the exposure dose constant and improve the quality of lines. So far, constant exposure dose control was realized finally. Mesh with 500 m gridding period was fabricated in a deep concave spherical substrate with a rise-span ratio of 0.31. Lines on the substrate have good uniformity, steep and straight side walls parallel to each other after development, and errors of line width and gridding period are within 1% and 5%, respectively.
2013, 42(2): 387-391.
A new solid-state calorimeter for intense lasers was presented. A numerical calculation model was setup to study the laser absorbed procedure. An energy absorbing cavity, constructed with several segments that were nearly heat insulating from each other, was designed, which had characteristics of high threshold on laser induced damage, fast thermal balancing and higher energy absorbed ratio. A detector array was designed for temperatures measurements. According to the temperatures response characteristics of the segmented cavity, a calculating method, based on energy deposition, was developed to obtain the accurate laser energy, which had good adaptability on irregular laser energy intensity distributions. The results of validating experiments show that the calorimeter has good repetition and accuracy within the range of hundreds of kilo-joules.
2013, 42(2): 433-437.
ICP (Inductively Couple Plasma) etching in InAs/GaSb type Ⅱ superlattice infrared detector material with Cl2/Ar and SiCl4/Ar were studied. The results show that the etching depth is linear with etching time for both etching gases. The etching rate is 100 nm/min at a set of conditions: RF power of 50 W, SiCl4 flow for 3 sccm, Ar to 9 sccm, the standard operating pressure is 2 mTorr. The etching rate did not depend on the doping concentration. The Ar flow fluctuation has no significant effect on etching rate when using SiCl4/Ar as the etch gases. But this condition exists in Cl2/Ar, especially when the flow of Ar under 3 sccm, and the etching rate droped with the reduction of Ar flow.
2013, 42(2): 438-442.
PbS nanocrystals with different precursor molar of [S2-]/[Pb2+] were prepared in alcohols medium from water-solubility precursors. The crystal structure, average particle size, morphology and luminescence properties of as-synthesized products were characterized by X-ray diffraction (XRD) spectra, transmission electron microscope (TEM) images, ultraviolet-visible (UV-VIS) absorption spectra and photoluminescence (PL) spectra. The XRD patterns show that the average particle size of the samples is calculated to be increased from 3.9 nm to 5.9 nm with the [S2-]/[Pb2+] molar ratio enhanced. The PL emission peak position is red-shifted from 1 009 nm to 1 486 nm. The influence of different [S2-]/[Pb2+] molar ratios on growth rate of PbS nanocrystals was discussed and the growth mechanism was thought to be the diffusion-controlled growth model via Ostwald ripening.
2013, 42(2): 443-448.
To improve image quality of subpixel imaging further, quantitative evaluation of image quality of subpixel imaging system based on MTF was proposed. The MTF of two main modes of CCD subpixel imaging was derived. Taking minimum contrast ratio of human eye 0.05 as threshold, analysis showed that theoretical limiting resolution of interlaced sampling mode and four-point sampling mode were improved to 1.4 times and 1.86 times respectively, and MTF values at Nyquist frequency of two modes were increased by 0.110 6(27%) and 0.167 9(41%), respectively. Evaluation of MTFA in(0, 0.5) illustrates that two CCD subpixel imaging modes both have better image quality than CCD common imaging mode, and the image quality of four-point mode is the best. A mathematical model for simulating CCD subpixel imaging using Matlab was established, the results of simulation of bar-target verify the correctness of the analysis based on MTF.
2013, 42(2): 449-453.
According to the requirement of stealth performance for the precision guided weapon, infrared and ultraviolet (IR/UV) characteristic signal of the HTPB composite propellant was measured based on a simplified rocket motor, and the IR/UV extinction ability of ferrocene was compared. It was analyzed that the nozzle temperature of motor is influenced by the ferrocene. The results show that the ferrocene is converted rapidly from its solid state to its gaseous state by primary power of a pyrotechnical composite based on nitrate of potash, sulphur, and phenolic resin, and a sheet of aerosol film is formed. The aerosol film can absorb infrared and ultraviolet from the flame of propellants, and the attenuation ratio may exceed 50% in 710-3 500 cm-1 waveband when the content of ferrocene is 30%. But it will increase the infrared radiation intensity of flame of the HTPB composite propellant when the content of ferrocene exceeds 50%.
2013, 42(2): 454-458.
The effect of electron radiation on LED was studied. Making use of the electron beam from electron accelerator to simulate the space electron irradiation, test the energy electron was at 1.0 MeV and the maximal total dose at 1106 rad(Si). The optical, electrical and annealing properties were measured after radiation. The results showed that with the increase of radiation dose, LED's light power degenerated linearly, while its voltage increased, and the degenerate extent was diverse in different experimental conditions. In addition, after a period of annealing time, LED's capability recovered to some extent and kept stable. The experimental result was analyzed and discussed through the mechanism of electron radiation.
