2019 Vol. 48, No. 3
column
- Invited column-“Hyperspectral remote sensing applications”
- Infrared technology and application
- Laser technology and application
- Laser radar technology
- Photoelectric device and microsystem
- Optical communication and optical sensing
- Photoelectric measurement
- Optical design and simulation
- Information acquisition and identification
- Atmospheric optics
2019, 48(3): 303001.
doi: 10.3788/IRLA201948.0303001
With the rapid development of hyperspectral imaging technology, space hyperspectral remote sensing data have been successfully applied to various fields in recent years. The development of space hyperspectral imaging technology at home and abroad was reviewed, the technical standards of representative space hyperspectral imagers were introduced. The latest applications of hyperspectral data in land resources, agriculture and forestry, ocean and lake remote sensing, urban environment, disaster monitoring and other fields in the past five years were systematically summarized and analysed. The outlook of future hyperspectral remote sensing was provided including hyperspectral information extraction and application based on AI technology, the multi-source data fusion and applications, and the analysis and application of hyperspectral data for deep space exploration. Further developments of space hyperspectral imager technology driven by applications will promote the innovated use of hyperspectral data in a wider range of fields.
2019, 48(3): 303002.
doi: 10.3788/IRLA201948.0303002
GF-5 satellite was successfully launched on May 9, 2018. It is the first hyperspectral observation satellite in China. The Greenhouse gas Monitoring Instrument is one of the payloads. It is the first satellite -borne greenhouse gas remote sensing equipment in the world to use spatial heterodyne spectroscopy technology for hyperspectral spectroscopy. The basic working principle of the payload was described, including the principle of light splitting, working mode and band setting. The optical system of the payload consisted of five parts. The core unit was a bonded interferometer. In order to avoid spectral aliasing, the parameters of narrowband filters were required to be high. In order to improve the on-orbit data quantification level, a calibration device based on diffuse reflector system was designed, which can meet the requirements of spectral and radiation calibration. Finally, the basic process of payload data processing was sorted out, and the first batch of observed data was restored by spectrum. The first-level data products are successfully obtained, which lays a foundation for the next application of greenhouse gas inversion.
2019, 48(3): 303003.
doi: 10.3788/IRLA201948.0303003
Compared with traditional multispectral load, the space hyperspectral load has a great improvement in spectral resolution. With the development of quantitative remote sensing, space-based detection can not only collect geometric information of ground targets, but also detect the material composition of atmosphere, land resources, battlefield environment and marine resources by using hyperspectral data. With the continuous development of space hyperspectral technology, it has become possible to monitor global climate, natural resources and hydrographic landforms with high temporal resolution. According to different imaging principles, hyperspectral detection can be divided into interference spectrometer, diffraction spectrometer and filter spectrometer. In this paper, grating diffraction spectrometer, time Fourier transform spectrometer, space Fourier transform spectrometer, AOTF spectrometer, LCTF spectrometer and hyperspectral filter spectrometer were introduced, and the advantages and limitations of each spectrometer were analyzed.
2019, 48(3): 303004.
doi: 10.3788/IRLA201948.0303004
Plateau lakes were of great significance in reflecting changes of regional natural environment under the background of global climate change. Based on the new homemade remote sensing data source, Tiangong-2 multi-spectral data, an automatic extraction algorithm for frozen lake was proposed by used object oriented method combined with water index and elevation information. The algorithm took full account of the characteristics of different forms of water, which can simultaneously extract frozen and unfrozen lakes, and exclude the influence of glaciers and rivers. For the selected 7 typical regions, automatic extraction algorithm was used to carry out lake extraction test and accuracy verification. The overall accuracy of lake extraction is 99.10% and F-score is 0.982. The results show that Tiangong-2 multi-spectral data has a significant application potential in the extraction of plateau lakes. As an effective data source, it can be applied to the study of lake extraction and change in the Tibetan Plateau, and provides data support for the study of regional climate change.
2019, 48(3): 303005.
doi: 10.3788/IRLA201948.0303005
In order to obtain a wide field of view(FOV) and high spatial resolution hyperspectral image while the scanning mirror swinging, the channel separation, FOV and mechanical splicing are required for the geostationary full spectrum hyperspectral imager. If the sub-FOV images are directly spliced, the spectral information of the feature will be distorted because of the different geometric deformation between the sub-FOVs. It was assumed that the difference of the corresponding image points' coordinates between the sub-FOVs was caused by the changes of each sub-FOVs' internal parameters in the paper. A block adjustment method based on the panoramic distortion tangent correction formula was proposed to achieve FOV stitching in the image side coordinate system. The FOV stitching experiment was completed on the basis of four sub-FOVs simulation images in the visible to near-infrared channel, and the stitching accuracy of 0.72 pixels was achieved. The splicing accuracy of the proposed method is close to the block adjustment method's based on the collinear conditional equation. The algorithm is simpler and suitable for primary image production without the assistance of control points and DEM.
2019, 48(3): 303006.
doi: 10.3788/IRLA201948.0303006
The wavelength drift and performance decay of hyper-spectral imager are the main problems that must be solved for long-term operation in orbit. The Fraunhofer absorption line, which is unique in the solar radiation spectrum and the atmospheric backscattering radiation spectrum, can be used as the benchmark for the wavelength calibration. According to the requirement for wavelength calibration precision of instrument, the high precision solar reference spectrum was optimized, then 87 Fraunhofer absorption lines were selected by the convolution of instrument slit function. The system error caused by the line asymmetric and the random error caused by the instrument detection capabilities were analyzed.Based on maximum deviation and RMS, the exact positions for available 76 solar Fraunhofer lines were determined under the condition that the calibration accuracy was better than 0.01 nm. This study lays the foundation for high precision wavelength calibration of hyper-spectral imaging on- orbit.
2019, 48(3): 304001.
doi: 10.3788/IRLA201948.0304001
Thermistor type infrared detector is the key element of the infrared earth sensor, which plays an important role in measuring precision of satellite attitude． The manufacturing process of the thermistor type infrared detector is complex, and the technical difficulties are great. Owing to the failure of these devices is mainly caused by noise, it is necessary to study new noise testing method to eliminate the failure devices. According to the structural characteristics of infrared detector based on thermistor of ternary Mn-Ni-Co oxide, the noise models were discussed in detail, and the noise test method based on infrared detector in different bias voltage was studied, then the corresponding testing system was designed. Test results show that the local noise and test accuracy of the system meet the requirements. The system will provide an experimental platform for the research of noise screening in different bias voltages, and lay a foundation for further analysis and research on the mechanism of noise variation in different bias voltages.
According to the false alarm problem in infrared early warning satellite, the space radiation environment of the geosynchronous orbit infrared early warning satellite was studied. Based on the analysis of satellite's background radiation characteristics in the detection spectrum and as a benchmark, the radiation sources in space environment that may cause false alarms of infrared early warning satellite were analyzed. The radiation characteristics of various sources in the 2.63-2.83 m short-wave detection spectrum and the 4.18-4.50 m medium-wave detection spectrum of infrared early warning satellite were discussed and calculated individually. The results show that the irradiance of direct solar radiation on the satellite detector is much larger than the background radiation intensity of the satellite, so evasive measures should be taken. The main false alarm sources of infrared early warning satellite are lunar radiation and low-Earth orbit spacecraft radiation. The influence of lunar radiation is mainly due to the focusing factor of lens. The influence of near-Earth orbit spacecraft radiation occurs in the mid-wave detection spectrum of infrared early warning satellite. The research results can provide reference for the study of corresponding background suppression and false alarm sources identification technology.
2019, 48(3): 304003.
doi: 10.3788/IRLA201948.0304003
The measurement method based on infrared pyroelectric principle has the advantages of convenient measurement, long life, low power consumption, etc. Therefore, gas measurement, based on infrared pyroelectric has been widely used in the gas measurement monitoring system of urban pipe network, environmental monitoring and other occasions. However, in the infrared pyroeletric gas measurement, there will be multi-frequency interference signal mixed in output signal, which directly leads to low measurement accuracy. To solve this problem, infrared pyroelectric gas measurement method based on Goertzel algorithm was proposed, and the signal acquired by the AD was processed by digital filtering. Simulation analysis and comparison of filtering effect between Goertzel algorithm and moving average algorithm was finished. The simulation results show that Goertzel algorithm has filtering error of only 0.166 7%, variation size of the measurement result is only 0.058%, and its accuracy and stability are 51 and 18.4 times better than the moving average algorithm, respectively. Finally, an experiment system was built, and the measured results show that Goertzel filter algorithm can effectively improve measurement accuracy and stability of the gas concentration, and the measurement accuracy can reach 4 ppm.
The interaction between laser induced plasma hot core and shock wave was a basic physical phenomenon in the scientific problem of laser induced drag reduction. An experimental platform based on shock tube and laser energy deposition was established, and the high-precision schlieren system was used to capture the flow structure characteristics of laser induced plasma hot core under the normal shock. The experimental results show that the interface of laser induced plasma hot core deforms and bends and finally forms a double vortex ring structure, the width rapidly increases and then decreases and gradually stabilizes at about 7.7 mm, the length decreases first and then linearly increases at a rate of 114.3 m/s after the shock leaves the hot core. The mechanism of laser induced drag reduction was further revealed from the microscopic level, which has good reference value for the related research of plasma induced flow control.
2019, 48(3): 306002.
doi: 10.3788/IRLA201948.0306002
Irradiation experiments with a 1 064 nm pulse laser were conducted to investigate the image interrupt effect of pulse laser irradiating CMOS camera with rolling shutter. Image interrupt effects were observed in the experimental results with bright area and dark area in the vertical direction. Calculation results show that the number of dark area rows is a constant. According to the integrating mode and scanning mode of CMOS image sensor, the formation mechanism of image interrupt effect is the storage asynchronism of CMOS with rolling shutter. Theoretical calculation value fit well with the experimental result. The reason of the existing of image without dark area was also theoretically explained. Method based on stitching several interrupted images was proposed to obtain a full image without interruption, which was very similar to the experimental imaging results.
2019, 48(3): 306003.
doi: 10.3788/IRLA201948.0306003
As non-metallic materials have strong absorption of long-wave infrared laser, the CO2 laser is often used to prepare PMMA micro-channels. Due to the Gaussian distribution of the laser light intensity, the cross-section of the micro-channels prepared by the conventional method is triangular. This can't meet the practical application requirements in the microfluidic chip. In this paper, a CO2 laser multi-path translational method was proposed, which used the HAZ formed by the first etching as a boundary multi-pass lateral overlap translation etching, so that high quality micro-channels with ideal trapezoid cross section can be quickly prepared. In addition, the micro-channel fabricated in this way is smoother and more practical compared with the static multi-pass method in cross-section, HAZ, surface roughness.
2019, 48(3): 306004.
doi: 10.3788/IRLA201948.0306004
2D distribution measurement on temperature and concentration of combustion flow field can be obtained by tunable diode laser absorption tomography technique. A new method using multiple absorption lines to reconstruct 2D temperature distribution was developed. In the method, different lines were combined based on the property of temperature sensitivity. And the area interested were reconstructed by the line pairs which were optimal for the temperature. In this paper, four H2O lines were selected to reconstruct the temperature distribution using Gauss and random models in a range of 300-1 500 K. The simulation results show that the new method improves the reconstruction quality with reconstructed error of 0.039 6 comparing with two-line thermometry of 0.095 2. In engineering application, the multiple absorption lines combination optimization method can effectively improve the reconstruction quality when the temperature range of the area of interest can be predicted.
2019, 48(3): 306005.
doi: 10.3788/IRLA201948.0306005
The cladding surface of the substrate was fixed at an upward angle which was greater than 90 in relative with the horizontal surface, where the single cladding tracks were formed by the laser inside powder feeding technology. The relationship among the tilted angle of the powder feeding nozzle, the pressure of the protection air and the powder spot diameter at the working plane were studied based on the experimental data. The effect of laser power and scanning velocity on the height and width of the tracks was analyzed, while the powder feeding rate and defocus amount kept unchanged. The liquid molten pool tended to drop by the drag force of its gravity, and the height peak offset was also studied. With the increase of the titled upward angle, the powder spot size at the working plane became larger, while the pressure of the protection air did the other way. For upward cladding, the effect of process parameters on the width and height shows a good accordance with the horizontal cladding. However, the height of the cladding layer was dramatically affected by the laser power, scanning speed and the tilted angle. The peak height offset of the molten pool got smaller with the decrease of the power and increase of the scanning speed and tilted angle. By using the optimized process parameters and the proper protection air pressure, a 3D part with the maximum titled angle of 150 was formed which also had the good feature accuracy and fine microstructure.
2019, 48(3): 306006.
doi: 10.3788/IRLA201948.0306006
Spectral beam combining of a broad area diode laser is a promising technique for direct diode laser applications. Grating external cavity spectral beam combination bases on wavelength selection characteristics of the grating and external cavity diode laser technology to achieve the lock of the single emitter spectrum and the combination of all the sub beam combining elements into one output. The beam quality of the output is equivalent to a single beam combining element, and the brightness and power are greatly improved, simultaneously. Based on the coupler free grating external cavity structure, spectral beam combination of a single diode laser short array stripe was realized. The characteristics of spectrum, power and beam quality of the output beam were analyzed. At the pump current of 70 A, a continuous output power of 40.8 W was obtained. The fast and slow axis beam quality were 0.41 mmmrad and 9.16 mmmrad (including 95% energy) respectively, the corresponding electro -optic conversion efficiency was 38.4% and the brightness was up to 67.90 MW/(cm2sr).
2019, 48(3): 306007.
doi: 10.3788/IRLA201948.0306007
In recent years, with the rapid development of technology in the fields of microelectromechanical systems, micromedical treatment and tissue engineering, micro-operation technology has attracted extensive attention from scientific research and industry, it plays a vital role in the miniaturization, functionalization and manufacture of integrated devices for future micro-nano technologies. Microstructures are fabricated using femtosecond laser two-photon polymerization, whose size is at the microscopic scale, the texture is brittle, the adhesion is large and the scale effect is significant, the surface force of the microstructure gradually replaces gravity to dominate. These factors further increase the difficulty of micro-operations. Therefore, a microoperating device based on capillary action of glass capillary tube was proposed, which used the capillary force to pick up and move the microstructure, and then assembled the different microstructures together. The method can assemble not only micro-originals, but also micro-devices with different materials and different characteristics to form a complex mixed microstructure.
2019, 48(3): 330001.
doi: 10.3788/IRLA201948.0330001
Fine imaging of long distance targets can be achieved by the synthetic aperture lidar (SAL). Due to the principle of range Doppler for SAL imaging, loss of altitude information is caused by the mapping for ground scenes to the imaging plane. A 3D reconstruction method of range scanning SAL was proposed in the paper. Multi synthetic aperture images in a certain scanning angle range were obtained by the range scanning SAL. Then, the 3D reconstruction was conducted through the overlap imaging of adjacent strip images for targets. On the basis of results simulated by TerraSAR, the 3D reconstruction for targets was realized using the range scanning SAL.
2019, 48(3): 330002.
doi: 10.3788/IRLA201948.0330002
In order to improve identification probability of terminal sensitive sub-ammunition under complex battle circumstances, the method of extracting the armor target based on the linear array LiDAR was proposed. Combined with stable scanning theory, 3D point cloud imaging on the scanning area was realized. Firstly, the height and gradient combination threshold segmentation algorithm was proposed by analyzing the height data in the point cloud; Then the coordinate transformation was used to adjust the slope ground, and the seed were automatically acquired through the geometric size of the typical armored targets for regional growth segmentation; finally, the extraction of armored targets was achieved through the geometric features of the target. The simulation shows that linear array LiDAR can accurately extract the armor target at the height of 50-120 m in battlefield, which provides technical support for the target detection of new terminal sensitive sub-ammunition.
2019, 48(3): 330003.
doi: 10.3788/IRLA201948.0330003
Multibeam LIDAR has been widely applied in the fields of unmanned ground vehicle, mobile measurement and robots because of its low cost, small size and capability of acquiring 3-dimensional distance of objects in the scene. To reduce occlusion and improve the density and coverage of point cloud, two or more LIDAR devices are integrated together to complement each other. As the installation position and attitude of the LIDAR are different, relative position calibration is a key step before fusing different laser data. In order to calibrate the relative spatial position relationship, a method based on coplanar constraints was proposed. Different LIDARs captured the range data of the same plane simultaneously. Although the range data had different coordinate systems, they represented the same plane. Relative positions between LIADR were initially obtained by fitting the common plane of multiple range data of different coordinate systems, and then optimized by L-M algorithm to enhance the calibration accuracy. This method is simple, accurate, and suitable for most LIDAR configurations in practical applications.
2019, 48(3): 320001.
doi: 10.3788/IRLA201948.0320001
To verify the sensitivity of the single event transient effects of SiGe BiCMOS linear devices, a typical operational amplifier THS4304 and a voltage regulator TPS760 were selected to study the single event effects with pulsed laser. In the experiments, a method was proposed to determine the laser threshold energy of single event transient by gradual changing energy. And the sensitive region of single event effects within the device was analyzed by point-by-step scanning method. On this basis, the interaction between the pulse laser energy and the single event transient was analyzed, and the single event effects cross section was obtained, which provided a reference for the selection and application of the SiGe BiCMOS devices in the satellite electronic system and the design of the radiation hardening.
2019, 48(3): 320002.
doi: 10.3788/IRLA201948.0320002
In order to obtain high diffraction efficiency, high extinction ratio, wide spectrum, and large angle tolerance grating structure, a polarizing beam splitter with inverted trapezoidal double layer metal grating structure working in the near-infrared wavelength region was proposed. The PBS structure included a high refractive index dielectric layer and cut the photoresist of the grating region into an inverted trapezoidal structure, which increased the transmission efficiency and extinction ratio of the grating. Rigorous coupled-wave analysis method was used to simulate and optimize the polarization beam splitter parameters. The results show that more than 97% transmission efficiency of the transverse magnetic wave and over 95% reflection efficiency of the transverse electric wave can be achieved in the wavelength range from 1 290 to 1 840 nm. The corresponding maximum extinction ratios for the transmittance and reflectance are 33 dB and 53 dB, respectively. The proposed grating has an extinction ratios over 22 dB in the 1 550 nm wavelength and a large angle from -40 to 40, which meets the requirements for the high-performance polarizing beam splitters. Compared with the commonly used double layer metal rectangular gratings, the proposed inverted trapezoidal double layer structure exhibits higher transmittance and reflectance, which has greater design flexibility.
2019, 48(3): 320003.
doi: 10.3788/IRLA201948.0320003
The laser feedback technique had the advantage of high sensitivity, which could fulfill the displacement and deformation measurement of targets with black and rough surfaces without the need of cooperative target mirrors. In this paper, in order to eliminate the influences of environment (including air pressure, base vibration, drift in temperature, etc.) on measurement accuracy, steady orthogonally polarized microchip laser was designed and assembled. The orthogonally polarized laser feedback system was built with optical components and electric circuits. The system had capability to achieve long-distance measurement and work in steady state. The system could effectively reduce the influences of environment and improve the accuracy of the laser feedback interferometer.
2019, 48(3): 320004.
doi: 10.3788/IRLA201948.0302004
Based on the rigorous vectorial diffraction theory, the mechanism that the subwavelength gratings convert circular polarized light into linear polarized light was analyzed. Based on the analysis results, a design method of controlling polarization state of output beam with grating spatial distribution was proposed. Using this method, several subwavelength grating polarizers with annular gratings areas were designed. By changing the number of the annular gratings areas, different type of cylindrical vector beams can be obtained. Using the Richards-Wolf vectorial diffraction method, the amplitude and intensity distributions of the different components in the vicinity of focus were calculated on high numerical aperture condition. Most of the intensity distributions in the vicinity of focus were flattop distributions. The full width at half maxima of intensity is 1.541 in radial direction. Compared with other type of beams such as linearly polarized beam, radially polarized beam and azimuthally polarized beam, the optical performances of the output beams from the polarizers designed in this research are distinctly particular.
2019, 48(3): 322001.
doi: 10.3788/IRLA201948.0322001
A kind of optical fiber laser displacement sensor with multi longitudinal mode beat frequency was proposed and designed. The sensor could be realized by using the beat frequency signal between different modes in the resonator to monitor the small displacement of the object. The sensor used a strain sensing substrate structure to effectively protect the optical fiber and buffer the deformation caused by stretching and compression, and increase the sensitivity of the sensor. At the same time, the original multi longitudinal mode beat fiber laser was improved, which made the system get higher signal-to-noise ratio. The measuring principle of multi longitudinal mode beat sensor was described, and strain gage was designed and built. In the experiment, four different beat frequency signals were selected as sensing signals. The experimental data show that the frequency shift is basically linear in the range of 0 to 30 mm, and the highest linear fitting degree can reach 0.999 4, which is in agreement with the theoretical results. Because the precision of the stretching platform is limited, the measuring accuracy of the sensor is 110-3 mm. Repeated experiments show that the sensor has good stability.
2019, 48(3): 322002.
doi: 10.3788/IRLA201948.0322002
The space-time block coding (STBC) has the property of diversity gain in the visible light multiple-input multiple-output (MIMO) communications. However, its validity is low. And the spectrum efficiency is improved in the spatial modulation (SM) coding while the reliability was poor. Therefore, based on the advantages of STBC and SM coding, a STBC-SM concatenated coding was investigated in the visible light MIMO communications. A visible light indoor transmission channel model was established as Lambertian light attenuated. The validity and reliability of the system was verified. Simulation results indicate that the reliability of the STBC-SM concatenated coding is 5-8 dB more than SM under the precondition of ensuring the original validity and the same error rate, and on the premise of ensuring the original reliability, the efficiency of STBC-SM concatenated coding is higher than that of STBC. It shows that the concatenaed codes designed in this paper can effectively settle the contradiction between validity and reliability in the communication system, and has a good theoretical significance for researching indoor visible MIMO communication.
2019, 48(3): 322003.
doi: 10.3788/IRLA201948.0322003
To realise the on-site, rapid and high sensitivity detection of trace polycyclic aromatic hydrocarbons (PAHs) in coastal water, a portable high-sensitive surface-enhanced Raman scattering sensor was developed, and a high-efficiency outside optical path of spectrometer assembled with inverted telescope structure was applied, which optimized the collection efficiency around 3.7 times better than a commercial optical probe, and the optical path was about 120 mm long. A high sensitive surface-enhanced Raman scattering (SERS) sensor was also established with 350 mm300 mm180 mm, 15 kg quality and 30 W power consumption, which can satisfy the portable requirements in on-site detection. PAHs in coastal sea water were detected on-site using this sensor, and signals of naphthalene, acenaphthylene, phenanthrene, chrysene, benzo (k) fluoranthene, benzo (b) fluoranthene, benzo (a) pyrene and so on were recognized. Meanwhile, the results were confirmed by the gas chromatography (GC). Besides, volatile naphthalene was discriminated by SERS but wasn't recognized by GC. SERS detection of Shilaoren and Maidao area of Qingdao coastal area showed that in Shilaoren coastal area, with the increase of offshore distance, the contents and concentration of PAHs were similar, but in Maidao coastal area, the contents and concentration of PAHs reduced significantly. The results indicate that SERS sensor is portable, convenient and with high sensitivity, and can provide data for PAHs monitoring in the high pollution area.
2019, 48(3): 317001.
doi: 10.3788/IRLA201948.0317001
In order to better realize non-invasive, real-time and dynamic skin tomographic imaging and improve the imaging signal-to-noise ratio (SNR), the performance of the reflective laser confocal system was evaluated comprehensively. Structure function as variable metric for wave front was introduced, and the basic mathematical properties was analyzed. The wave aberration of different scales in the structure function was analyzed emphatically. After that, the numerical simulation for low order aberration presented by Zernike polynomials was investigated. The ability of structure function to characterize low order aberrations was verified. Because confocal microscopy was required to pass through the skin, it was important to think about the effects of human tissue in the pre-test process and analyze its effects on the system's SNR; Finally, the wavefront of the actual skin lens system was analyzed, and a SNR of 95.7 dB was obtained after system calibration, and the correctness and feasibility of the method were verified. By means of the variable scale evaluation method, the non-invasive imaging system can be evaluated more comprehensively and it can effectively guide the detection and adjustment of similar equipment.
2019, 48(3): 317002.
doi: 10.3788/IRLA201948.0317002
Sinusoidal phase-shifting interferometry (SinPSI) suffered from modulation error. To cope with this problem, an arbitrary sinusoidal modulation SinPSI (ASM-SinPSI) method was proposed, which extracted wavefront phase from Fourier spectrum of the interferometric signal. In ASM-SinPSI, firstly the modulation amplitude was determined from the strength ratio of the first and third spectrum peaks. To avoid being divided by zero in calculating the ratio, a spatially random sampling strategy was adopted. Then the absolute values and signs of sine and cosine of wavefront phase were determined from the first three spectrum peaks, and the phase was calculated with arctangent. Simulations demonstrated that the wavefront phase retrieval error is 0.016 rad without prior knowledge of the modulation. In experiments with modulation amplitudes of 1.6, 2, 2.5 and 3 rad, wavefront phases were accurately measured with ASM-SinPSI, and the maximum deviation from the exact phase was 0.058 7 rad. ASM-SinPSI, having the benefit of extracting wavefront phase with arbitrary unknown modulation amplitude between 1.5-3.5 rad, relaxed the demanding requirement on the phase shifter of interferometers.
2019, 48(3): 317003.
doi: 10.3788/IRLA201948.0317003
In order to acquire spectral polarization information of the image under single-frame imaging conditions, an encoding aperture measurement method based on intensity modulation was proposed. The method used the spectral polarization intensity modulation module composed of an achromatic 1/4 wave plate, a multistage phase retarder and an analyzer, and modulated the spectrum of each element of the Stokes parameters of the incident light to different frequencies. And the modulated spectrum was compressed and coded by a spectral imaging system composed of coded aperture and dispersive prism, and was detected by CCD. The modulated spectral information was reconstructed using the TwIST algorithm, and then the spectrum of Stokes elements can be reconstructed by further separating the spectrum channels. Taking a single pixel as an example, the modulation of incident light intensity modulation, spectral reconstruction, and demodulation of Stokes parameters were simulated numerically.The results show that this method can achieve the acquisition of spectral polarization information of sparse images. This process requires only one measurement of the image and therefore has a high-speed acquisition capability.
2019, 48(3): 317004.
doi: 10.3788/IRLA201948.0317004
In the process of approaching a non-cooperative target, it would result in a large amount of calculation using the extracted feature points directly for relative navigation due to the excessive number of feature points. In order to reduce the amount of computation for relative navigation, a subset should be selected from the extracted feature points. Assuming that the extracted feature points were in the same plane of the non-cooperative target, the selection of feature points for non-cooperative target could be transformed as the selection of feature points on the image plane. At the same time, this paper also studied dilution of precision (DOP) for vision-based system and proposed the method that the convex hull of the feature points on the image could be selected as the subset for relative navigation based on the fact that the DOP was inversely proportional to the area of the subset. The simulation shows that the convex hull of feature points can provide high accuracy for relative navigation and reduce the number of feature points effectively. It also shows that the computation time of calculation convex hull is far less than searching the subset with optimal PDOP.
2019, 48(3): 317005.
doi: 10.3788/IRLA201948.0317005
A strategy for improving the precision of material removal model based on deep neural networks was proposed. A deep learning algorithm with ability of feature selecting was proposed. A series of simulation samples composed of a material removal rate and corresponding polishing parameters were generated based on the model of material removal rate for robot polishing. The deep learning algorithm learned both the simulation samples and practical samples and then a deep learning model was established. The error between material removal depth of the test samples and material removal depth estimated by polishing parameters by using proposed deep learning model was calculated and compared. The results show that the improved model can achieve higher accuracy than the traditional models.
2019, 48(3): 318001.
doi: 10.3788/IRLA201948.0318001
In order to better analyze the integrated installation of ground-based large telescopes' Coude optics system, the error analysis was carried out on three levels, and the Brownian Bridge walk was used to establish the Coude optics system error model. Firstly, based on the equation of light path, the optical fuzzy the Coude optics system under the influence of atmosphere disturbed was analyzed. Secondly, the optical blur caused by dynamic error and the accumulation printing through effect of gravity were analyzed. Finally, using the Brownian Bridge walk, the error model of the focus position of the Coude optics system was established under the full consideration of error chain closure. The results show that even in the temperature gradient of 0.4 ℃/m, atmospheric disturbances can also cause the deviation of about 0.2, equaling to the atmospheric coherent length of 2.3 mm. On the other hand, because the symbols of the refractive compensation were consistent, the effects of atmospheric disturbances cannot be compensated by averaging. According to the improved error model, focus position error of the Coude optics system reduce about 20% compared to the results obtained based on the assumption of independent distribution, that is, the error closure was considered more fully.
2019, 48(3): 318002.
doi: 10.3788/IRLA201948.0318002
A combined non-tracking concentrated optical (CNTCO) system composed of line Fresnel lens (LFL), reflection-type secondary optical element(R-SOE) and total internal reflection prism (TIRP) was proposed due to the high failure rate and high cost of the automatic solar tracking system. Moreover, the principle and design method of each component were discussed. The structure of the system was optimized and simulated in optical design software Zemax. The results show that the average concentration efficiency of the system reaches up to 24.1%, an 18.7% increasement compared with a combined system consisted of LFL and R-SOE (FRS), on the condition that the pitch angle is up to 16. The non-tracking concentrated photovoltaic module based on CNTCO system was integrated and preliminarily tested. The test results indicate that the photoelectric transformation efficiency of the module could be optimized up to 19.6% on non-tracking condition, even still up to 5.9% after 4 hours.
2019, 48(3): 318003.
doi: 10.3788/IRLA201948.0318003
The influence of the position of the sparse aperture mirror hard spot and the layout of the edge sensor on the precision of the relative pose control was studied. Using the geometry characteristic of sparse aperture, a primary mirror model composed of seven circular apertures was established and the control matrix of relative pose among apertures was derived. The generalized least squares method was used to solve this problem, considering the large condition number of control matrix, ridge regression was introduced and the intrinsic bound on the error function of the control matrix was also given. The possible 128 location strategies between edge sensors and hard spots and the effect of geometric distance on the condition number of control matrix were analyzed. The results show that the layout of the hard points and edge sensors is intrinsically linked to the coefficient matrix, the sparse aperture is serious Multi-Collinearity with respect to the coefficient matrix of pose control, and the normal matrix appears seriously ill-conditioned. The condition number of normal matrix are reduced significantly when the distances between the adjacent two edge sensors while the layout is fixed. For the ill-conditioned problem of the normal matrix, the ridge regression is used to effectively suppress the ill-conditioned characteristic by choosing appropriate ridge parameters. Using this method, the redundant edge sensor structure can be effectively used to realize data fusion and ensure the stability and reliability of the measurement system.
In order to solve the evaluation problem of optical system under partially polarized light conditions caused by single ray tracing method, a full-field, full-pupil ray tracing method based on Stokes notation was proposed. The refractive and reflection Mueller matrix expressions were improved. The analytical relationship among the degrees of polarization(DOP) of the incident light, the ray angle and the DOP of the emitting light was analyzed. The analysis results show that when the difference value between the incident angle and the emergence angle was less than 5.7, the influence of the system on the DOP of the light can be reduced effectively. According to the space target polarization imaging requirements, a polarization imaging optical system with micro-polarizer array(MPA) was designed. The resolution was 0.5 m at the distance of 500 km. Dynamic data exchange(DDE) was used to trace the full-field and full-pupil rays for the optimized optical system. Four Stokes vectors and full-field polarization distributions were both calculated and displayed. Due to the DOP of any field of view can be calibrated, the polarization detecting accuracy of the optical system was improved. Therefore, the target can be recognized by matching the DOP of the incident light and the DOP of any field of view.
2019, 48(3): 326001.
doi: 10.3788/IRLA201948.0326001
A new method of bubble recognition using optical underwater imaging was presented by employing Zernike moments and gray gradient, to differentiate bubbles from solid particles. This method included 3 parts: image division, image pre-processing and feature extraction for bubble recognition. Firstly, images of the suspended particles were obtained from underwater particle database, in which a particular bubble was divided and selected manually from the whole. Secondly, image pre-processing was employed to enhance single bubble images, to extract and represent bubble silhouette and gray level. Thus, the database of bubble features were selected and formed. Finally, the shape descriptor, Zernike moments, was utilized to measure the similarity with features of other suspended particles to differentiate circle particles from the irregular ones. Subsequently, the center of circle particle and the trend of gray gradient were computed, so as to distinguish the bubbles from solid particles. The experimental results show that, the accuracy of bubble recognition is up to 94%. It is concluded that this method not only recognizes bubbles from irregular suspensions, but also improves gray gradients calculation for enhanced results. By extracting and distinguishing object features through the prospects of both shape and gray, this method enhances the accuracy of bubble recognition, with higher precision and broader suitability.
2019, 48(3): 326002.
doi: 10.3788/IRLA201948.0326002
In order to solve the problem of infrared dim and small target detection under the complex background of infrared, a detection algorithm for dim and small targets in complex background based on background adaptive multi feature fusion was proposed. Firstly, the isolated noise points are removed by spatial filtering of infrared images, and the constant false alarm rate was used to eliminate large area stationary background and obtain a suspected target set. And then most of the false targets in the suspected target were eliminated by combining the background information of the infrared image, the gray feature of the dim and small moving target and the direction gradient feature of the target and the surrounding pixels. Finally, the detection of infrared dim and small targets in complex background was realized. The experiment shows that the algorithm can realize fast infrared dim and small target detection with low signal to noise ratio under complex background, which has the characteristics of high detection probability, fast speed and good robustness.
2019, 48(3): 326003.
doi: 10.3788/IRLA201948.0326003
Object tracking is a challenging research topic, which is widely used in infrared imaging search, infrared precision guidance, intelligent surveillance, motion recognition and other fields. In this paper, a robust template patches-based target tracking method with sparse representation was proposed. Firstly, the adaptive template patches selection mechanism was proposed using the discriminative information to capture the target. Then, the sparse representation was introduced to describe the patches to deal with the shortcoming of histogram's sensitivity to light, which expanded the application of the algorithm. Thirdly, the target location was voted and fused by constructing a voting map. Finally, a dynamic updating scheme of patches was proposed to address appearance variations. The simulation experiments of test image sequences demonstrate the robustness of the proposed tracker, which is able to deal with many challenges, such as deformation, changes of illumination, partial and total occlusions, false target jamming and background interference.
2019, 48(3): 311001.
doi: 10.3788/IRLA201948.0311001
Based on the stellar broad-spectrum imaging signal intensities measured by observational stars day and night, firstly, the calibration error of atmospheric transmittance by Langley method were studied using MODTRAN software. The system parameters and the spectral characteristics of stellar spectra were taken into account during this process. Wide spectral transmittance of the whole atmosphere was obtained by calibrating the intensity of the star imaging. Then, the relationship between the atmospheric transmittance of wide spectrum and the atmospheric transmittance of the laser band was studied by using the atmospheric model, and the atmospheric transmittance of 532 nm and 1 064 nm were obtained. Finally, the atmospheric transmittance measured by stellar observation during the daytime was compared with the solar transmittance measured by the solar radiometer. The results show that the atmospheric transmittance obtained by the two methods has the same trend and the similar size. On this basis, the continuous observation of total atmospheric transmittance is carried out, the diurnal continuous data of total atmospheric transmittance is obtained, especially the data of total atmospheric transmittance at weak turbulence moment of dawn and dusk. The work enriches the measurement of total atmospheric transmittance and promoted the research and application of ground-based laser engineering.
According to laser statistical scattering properties of ice crystal particles with rarefied random distribution, differential scattering section(DSS) of ice spheres with exponential distribution, lognormal distribution, Gamma distribution changed with scattering angles were calculated numerically and analyzed at 0.65, 1.31 and 1.55 m, respectively. The results show the change of incident laser wavelength has a certain effect on DSS of ice-crystal layer. And DSS of ice spheres with exponential distribution is the largest, which is several orders of magnitude larger than the other two distributions. So different laser wavelength and size distribution models of ice particles have great influence on laser scattering properties of rarefied random distributed ice crystal particles. The works in this paper are based on the foundation for further study development of the effect of ice-crystals cloud on the laser propagation properties in the ground-air links.
