Laser radar technology
2019, 48(6): 630001.
doi: 10.3788/IRLA201948.0630001
The range image reconstruction algorithm of Geiger-mode APD laser radar system was studied, and a reconstruction algorithm based on pixel neighborhood kernel density estimation was designed. Starting from the system principle, the theoretical basis of the reconstruction algorithm of range image was studied with the detection probability model. According to the characteristics of the system, an improved algorithm based on pixel neighborhood kernel density estimation was proposed and its principle was analyzed. The histogram algorithm and the neighborhood kernel density estimation algorithm were verified by simulation data, and the range reconstruction accuracy rate curve was used for quantitative evaluation and comparison. The algorithm was further applied to real Geiger mode APD lidar data to reconstruct range image. The experimental results show that the reconstruction algorithm based on the statistical neighborhood kernel density estimation can effectively improve the reconstruction effect of the range image at low frame counts.
2019, 48(6): 630002.
doi: 10.3788/IRLA201948.0630002
Aiming at the problem that the current mobile robots have low accuracy for the construction of environmental maps, the calibration methods of ranging and angle measurement of LiDAR were proposed respectively. The error propagation law was used to analyze the ranging error factor of the LiDAR. It can be seen that the LiDAR ranging error was mainly caused by the echo intensity and the measuring distance, and the ranging error correction model was derived. By analyzing the error factors of LiDAR angle measurement, a triangulation calibration method was proposed for the error caused by the eccentricity of the mechanical scanning axis and the geometric rotation center, and the angle error correction model was established. The mobile robot coordinate conversion system was modified according to the LiDAR ranging and the angle correction model. The experimental results show that the standardization of the distance measurement increases the standard deviation of the longitudinal coordinate difference of the plane obstacle data by 30%-60%, which is close to the real geometric feature of the object. The angle measurement method improves the coincidence effect of the obstacle data by 30%. The accuracy of map construction of mobile robots is improved using the calibration method.
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.
2018, 47(9): 930001.
doi: 10.3788/IRLA201847.0930001
Aiming at the mapping requirements of forestry, architecture, offshore, island reef and beach, the Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, has developed a prototype of airborne dual-frequency laser radar. It can simultaneously carry out mapping of terrain and submarine terrain. The prototype has been tested in Wuzizhou Island of Sanya with a maximum detection depth of 30 m, equivalent to 50 m under class A water quality conditions, the minimum detection depth of 0.22 m. Depth data and single-beam sonar data comparison error is 0.108 m, ranging data and field-measured data comparison error is 0.18 m. The results are in accordance with the design expectations.
2018, 47(9): 930002.
doi: 10.3788/IRLA201847.0930002
Simultaneous wind measurements in stratosphere with high-spatial resolution for gravity waves study are scare. In recent years, lots of gravity waves cases were observed by mobile Rayleigh Doppler lidar of University of Science and Technology of China benefiting from the system with excellent performance. In this paper, a brief introduction of the Rayleigh Dopplar lidar system was made. The wind field gravity waves cases in the altitude region 15-60 km were also performed, which were carried out for 2 months started from October 7th, 2015 in Jiuquan(39.741N, 98.495E), China. After the 2-D fast Fourier transform of those mesoscale fluctuations of the horizontal wind velocity, the two dimensional spectra analysis and band-pass filter results of these fluctuations exhibited the presence of dominant oscillatory modes with wavelength of 4-15 km and period of around 10 hours in several cases. The observed cases demonstrate the Rayleigh Doppler lidar's capacity in measuring and studying gravity waves.
2018, 47(9): 930003.
doi: 10.3788/IRLA201847.0930003
Because of the requirement of autonomous navigation, an integrated lidar of ranging and communication based on pseudorandom code modulation was proposed. The system had the advantages of low power consumption, small volume and multi-function. Adopting pseudorandom code, the lidar system realized the integration of ranging and communication. Adopting silicon photomultiplier (SiPM) to achieve photon counting realized the miniaturization of lidar system. The design principle, component, simulation, and the experiment result of the system were introduced in detail. The result shows that the maximum detection range can reach 1 km for the target with 0.1 reflectivity under daylight, and the range resolution is less than 1 m. The maximum communication range can reach 3.7 km with 10 kbps code rate and error rate less than 10-5.
2018, 47(8): 830001.
doi: 10.3788/IRLA201847.0830001
In order to solve the problem that LIDAR data segmentation algorithm cannot adapt to the environmental characteristics and determine the threshold continuously and accurately, an adaptive LIDAR data segmentation algorithm based on environmental features was proposed. According to the data characteristics of the two-dimensional lidar and the geometric characteristics of the indoor environment, the virtual environment line was fitted with the adjacent point of the laser radar data. The intersection of the virtual environment line and the adjacent laser scanning ray was taken as the reference point to determine the adaptive threshold pre-segmentation of radar data. In view of the defects in the data pre segmentation results completed by the above method, a method for judging pseudo breakpoints after data pre segmentation was proposed, and the algorithm was optimized. The algorithm was compared and analyzed with piecewise threshold segmentation algorithm and linear equation threshold segmentation algorithm. The LIDAR data segmentation algorithm adapting to environmental characteristics achieves a successful segmentation rate of 98% for the experimental data, and has better environment adaptability and higher segmentation accuracy.
2018, 47(8): 830002.
doi: 10.3788/IRLA201847.0830002
The main function of powered lower limb prosthesis is to help the amputees to achieve independent and comfortable walking. In order to make the powered lower limb prosthesis coordinate with the user, it is necessary to recognize the motion intention of the user. By knowing the environment information in front of the user, and taking it as a prior knowledge of motion intention recognition, the recognition accuracy of motion intention will be improved. In order to provide environment information in advance for the powered lower limb prosthesis, a wearable terrain recognition system was designed. The 2D lidar installed in the waist were used to collect the terrain data in front, then extract linear feature of the collected data using agglomerative hierarchical clustering algorithm, finally the terrain was recognized using finite automaton. In the experiment, four terrains were tested, including level ground to up/down stair and up/down slope. Results show that the recognition accuracy of the system to four terrains reaches to 95.8%, and it can obtain the information of terrain parameter including angle of slope, number of steps, stair height and stair depth which can't be obtained from the traditional motion intention recognition methods. It proves that the system is effective and feasible for powered lower limb prosthesis.
2018, 47(8): 830003.
doi: 10.3788/IRLA201847.0830003
Application of 2 m laser in lidar systems, remote sensing, requires more accurate wavelength. Based on the analysis of the quasi-three-level side pumped Tm:YAG laser system, the oscillating conditions of this laser were predicted from the point of pump threshold with taking into account reabsorption loss. The model accurately predictes that the laser central wavelength is switchable in the range of 2.0-2.1 m by means of different laser parameters, such as crystal temperature, the crystal length, the transmission of the output coupler.
2018, 47(8): 830004.
doi: 10.3788/IRLA201847.0830004
The emitted laser is a single frequency source in the traditional coherent detection, and this system can be used in the field of objects measuring and tracking. But in the typical ladar system abroad, it can be used in Range-Doppler(R-D) imaging through the mode-locked pulse burst combined with coherent receiving method. Therefore, the numerical simulation of R-D imaging based on the mode-locked laser pulse burst was analyzed. Firstly, the numerical model of the mode-locked pulse burst was built up. Secondly, the unfolded frequency spectral of the laser pulse was given and the matched filter of the echo signal was designed through the spinned-target model. At last, the FFT and IFFT were adopted in the processing while the R-D image can be obtained with different rotating angular speed. On the other hand, the SNR can be enhanced with many frame accumulations based on the R-D image output. From the simulation analysis of R-D imaging, the fingerprint image of the spinned-target with a macro-pulse(including many micro pulses) was obtained, it is very important in the target discrimination of the ballistic missile defense.
2018, 47(2): 230001.
doi: 10.3788/IRLA201847.0230001
Doppler wind lidar with its high resolution, high precision, large detection range, the ability to provide three-dimensional wind field information, has attracted the attention of multinational scholars, and put a lot of manpower and material resources to carry out research. The Doppler wind lidar was designed to obtain single longitudinal mode, narrow linewidth and high power laser output by seed injection. The slow drift of the center frequency of the laser, ambient noise, laser rod temperature change or the vibration disturbance may cause the failure of seed injection. Then the laser spectrum was transformed from a single longitudinal mode output to a multiple longitudinal mode output. The linewidth of single longitudinal mode laser output was about 200 MHz. However, the multi-longitudinal mode laser output had a wide linewidth,which led to widened Rayleigh backscattering spectrum and then great speed errors in the speed inversion condition. The pulse screening circuit was developed to filter the multi longitudinal mode pulse during the data acquisition, which can effectively reduce the error of wind speed inversion and improve the precision of wind speed measurement.
2018, 47(2): 230002.
doi: 10.3788/IRLA201847.0230002
The precision of wind filed retrieved from coherent wind lidar scanning measurement mode using VAD method could be substantially low without quality control. By investigating error sources in the scanning measurement mode, based on least square VAD fitting algorithm, a stepwise regression procedure for quality control of the data involved in wind regression was presented. The statistical parameters adopted for the quality control process included SNR, data residual, scanning interval effective data and the data efficiency. Based on the technique proposed, the quality control strategy was designed and verified by comparing the Lidar retrieved 2 955 pair of 10-minuts averaged wind data with those derived from the wind cup data. The result shows that the root mean square deviation (RMSD) of the wind speed has been reduced for approximately 44% from 0.97 m/s to 0.54 m/s, while the RMSD of wind direction has been reduced for approximately 26% from 7.47 to 5.55.
2018, 47(2): 230003.
doi: 10.3788/IRLA201847.0230003
The staring imaging lidar, whose indexes selection influences the load of spacecrafts seriously, is an important method for the pose measurement of non-cooperation target in space. Selecting the indexes of lidar reasonable is significant, opposite to the traditional method by experience, making it not only satisfy the demands of space mission, but also effectively reduce the load of spacecrafts and energy consumption. Macro model for compatibility between indexes of on-orbit lidar and attribute of target was proposed to provide a theoretical basis for indexes selection of lidar. Four indexes included lidar output power, lidar resolution, lidar field angle and lidar ranging precision. The processes were as follows. The initial values of the lidar resolution and field angle can be calculated by the scale of the target and distance between lidar and target. The transmitting power can be acquisited by iterating the maximum measurement distance. The reasonable resolution and field angle can be measured by iterating the second order parameters of the target surface depth co-occurrence matrix. The ranging precision of the lidar can be acquired by iterating the result of the point clouds registration algorithm. The experimental result of lidar indexes selection shows that proposed model can satisfy the requirement for the lidar parameters optimal selection.
2018, 47(2): 230004.
doi: 10.3788/IRLA201847.0230004
Streak array detecting lidar has advantages of high ranging accuracy, long detecting distance, wide ranging gate and high data acquiring rate, which is widely used in topographic mapping, coastal zone monitoring, urban 3D remodeling, forest ecological research etc. The traditional method on signal discrimination has some limitations in the depth extraction of echo signal, which affects the capability of depth distinguish and target recognition of streak array detecting lidar. For this problem, an iteratively weighted centroid algorithm was introduced while dealing the streak images and the unique advantages on centroid location of the algorithm were discussed. The key parameters of the algorithm were determined according to signal distribution character of streak array detecting lidar. By using this algorithm, the range image with clear boundary feature of a target was obtained at the distance of 1.4 km. The boundary blurring effect was effectively suppressed in the depth extraction process and the resolution ability of the system was improved. Compared with traditional centroid algorithm, the ranging accuracy was improved by 17%.
2018, 47(12): 1230001.
doi: 10.3788/IRLA201847.1230001
With high accuracy, high spatial-temporal resolution, large scale coverage, coherent Doppler lidar has been widely applied in the detection of wind shear, aircraft vortex, wind power generation, atmosphere turbulence and so on. For lidar signal processing, the key issue is how to extract weak Doppler frequency shift in the weak backscatter signal. Based on the atmospheric slices model, the simulated echo signal of coherent Doppler lidar was processed by different time-frequency methods. Simulation results show that the adaptive optimal-kernel time frequency representation outperforms the others, having the advantages of lower computation cost, suppressing cross terms efficiently and higher resolution in both time and frequency domains. Then the adaptive optimal-kernel time frequency representation was applied to the field experiment data derived from a 1.5m Coherent Doppler lidar in Hefei, Anhui Province in March, 2017. The retrieved wind velocity results were compared with that derived from the fast Fourier transform algorithm. Experimental results show that the range resolution is 1.2 meter within 3 kilometers, and maintains the continuity of wind speed retrieved form weak signal using a 50-points window in the far field over 3 kilometers. Furthermore it can track the wind details better and enhance the detection range to 6 kilometers as the temporal resolution is set to 1 second.
2018, 47(12): 1230002.
doi: 10.3788/IRLA201847.1230002
Based on the CALIPSO satellite observations from June 2006 to December 2016, the aerosol spatiotemporal distribution characteristics above the East China Seas (the Bohai Sea, the Yellow Sea and the East China Sea) were analyzed. The results indicate that:(1) Aerosols in the three seas are mainly Clean Marine, Dust and Polluted Dust, and the sum of the three percentages is nearly 90%. The predominant aerosol type is different in different seas; (2) Aerosols above each sea tend to exponentially decay as the height increases. The aerosol type changes significantly in the space below 4 km, but there exists only Dust, Polluted Dust and Smoke above 4 km; (3) Temporal distribution characteristics show that almost all aerosol types vary with months and seasons. In spring, the three seas are Dust aerosols accounted for the largest proportion. In summer, Clean Marine aerosols obviously have the greatest impact for the East China Sea. In autumn and winter, the Bohai Sea and the Yellow Sea are mainly composed of Dust aerosol, while the East China Sea is Clean Marine aerosol as main component.
2018, 47(12): 1230003.
doi: 10.3788/IRLA201847.1230003
Using a tunable fiber laser of 1 550 nm wavelength, a high resolution imaging differential synthetic aperture ladar(DSAL) was set up in the laboratory. DSAL imaging experiments were carried out using a cooperative target at distance of 1.85 m. The phase history data (PHD) of the target returns were reconstructed and high resolution synthetic aperture images were generated by straightforwardly following standard DSAL image formation theory. High resolution DSAL images at various azimuth moving conditions were given in detail. Experimental data show that using the reconstructed PHD by DSAL technique, much better focused images can be produced, which demonstrates that the DSAL technique can robustly remove the common phase errors in the PHD. Moreover, DSAL images with various azimuth moving conditions show that even if the azimuth speed is 30% longer or shorter than its ideal value, the DSAL images are all well or at least acceptably focused, which means that a DSAL system is possibly well adaptive to the variation of its azimuth speed.
2018, 47(12): 1230004.
doi: 10.3788/IRLA201847.1230004
The calibration of water vapor mixing ratio is an important issue for Raman lidar. A dual wavelength lidar was developed and tested for the self-calibration of water vapor mixing ratio based on the two YAG laser, which emitted laser pulses at the wavelengths of 532.1 nm and 659.7 nm. From the analysis of the lidar measurements, it indicates that the capability of lidar satisfies with the requirements of water vapor mixing ratio self-calibration completely. In the altitude range, in which the measured aerosol liar scattering ratio was about 1.01, the calibration constant of nitrogen mixing ratio was determined to be 0.5450.031 from the lidar measurements, and the relative uncertainty was about 5.7%. The determination of the nitrogen mixing ratio calibration constant was the key step in the water vapor mixing ratio self-calibration, which lays a foundation for the self-calibration could and the water vapor mixing ratio.
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