As a signal processing theory, compressive sensing (CS) breaks through the limitations of the traditional Nyquist sampling theorem and provides the possibility to solve the high sampling rate, large data volume, and real-time processing difficulties of traditional high-resolution radar. Based on the theory of single-pixel cameras, an array detection imaging system is built, and main structural parameters are analyzed. The simulation experiment of a simple target is organized to show that the number of measurements can be reduced by achieving the parallel operation through increasing the number of detectors. When the target changes, it is found that the sparsity problem has a great influence on the number of measurements. Therefore, an improved method is proposed using the structure flexibility of fiber array and detectors, which can reduce the number of measurements simultaneously while decreasing the number of detectors, which is superior to the original method.
Although the streak tube imaging lidar(STIL) is widely applied in target recognition and imaging, combining the compressive sensing(CS) theory with it has only just begun. To the best of our knowledge, most studies on this combination theory are about ultra-fast imaging. We harness the advantages of streak tube and CS to provide a novel idea in three-dimensional imaging. The imaging system model is built, and mainly structures are introduced such as fiber array and digital micromirror device(DMD). Simulation experiments are organized. In the process of reconstructing the intensity image and range image of the target, the extraction methods of measurement matrix required by the CS algorithm are given respectively.
Streak tube imaging lidar has been widely applied in target recognition and imaging because of its high accuracy and frame rate. Compressed ultrafast photography technique employs a digital micromirror device (DMD) and a streak camera. It is developed to satisfy the requirements of imaging of ultrafast processes. The concept of structure provides a new direction for three-dimensional (3-D) imaging. This paper studies the streak tube 3-D imaging system based on compressive sensing (CS) from the perspective of imaging system construction and image reconstruction algorithms. The system model is built, and mainly structures are introduced such as the fiber array and DMD. Two simulation experiments are organized. First, the stripe images of a simple target are obtained. In the process of reconstructing the intensity image and range image, the extraction methods of the measurement matrix required by the CS algorithm are given, respectively. The resulting images and variance curve show that the image quality increases with the number of measurements. The second experiment with a complex target is carried out. Two levels of distance interval are used to analyze the imaging effect in the simulation. It is found that the image resolution is directly related to the distance interval selection.
Three-dimensional imaging is increasingly becoming important in a number of applications that observe and analyze real-world environments. Range sensors, such as flash imaging Lidar and Time-of-flight camera, which can deliver high accuracy range measurement images, but are limited by the low resolution. To overcome this limitation, this paper shows the benefit of multimodal sensor system, combining a low-resolution range sensor with a high-resolution optical sensor, in order to provide a high-resolution, low-noise range image of the scene. First, an extrinsic calibration algorithm is used to align the range map with optical image. Then, an image-guided algorithm is proposed to solve the super-resolution optimization problem. This algorithm using the Markov Random Field framework. It defines an energy function that combines a standard quadratic data term and a regularizing term with the weighting factors that relate optical image edges to range map edges. Experiments on synthetic and real data are provided and analyzed to validate this method. The result confirms that the quality of the estimated high-resolution range map is improved. This work can be extended for video super-resolution with the consideration of temporal coherence.
Nowadays, there are two main methods to realize three-dimensional non-scanning laser imaging detection, which are detection method based on APD and detection method based on Streak Tube. However, the detection method based on APD possesses some disadvantages, such as small number of pixels, big pixel interval and complex supporting circuit. The detection method based on Streak Tube possesses some disadvantages, such as big volume, bad reliability and high cost. In order to resolve the above questions, this paper proposes an improved three-dimensional non-scanning laser imaging system based on Digital Micromirror Device. In this imaging system, accurate control of laser beams and compact design of imaging structure are realized by several quarter-wave plates and a polarizing beam splitter. The remapping fiber optics is used to sample the image plane of receiving optical lens, and transform the image into line light resource, which can realize the non-scanning imaging principle. The Digital Micromirror Device is used to convert laser pulses from temporal domain to spatial domain. The CCD with strong sensitivity is used to detect the final reflected laser pulses. In this paper, we also use an algorithm which is used to simulate this improved laser imaging system. In the last, the simulated imaging experiment demonstrates that this improved laser imaging system can realize three-dimensional non-scanning laser imaging detection.
The four-quadrant detector is a photoelectric position sensor based on the photovoltaic effect. It is widely used in many fields such as target azimuth measurement, end-guided weapon and so on. The selection of the spot and the calculation of the center position are one of the main factors that affect the accuracy of the position measurement of the fourquadrant detector. In order to improve the positioning accuracy of the four-quadrant detector, the method of determining the best spot size is obtained from the theoretical research. The output signal of the four-quadrant detector is a weak narrow pulse signal, which needs to be magnified and widened at high magnitudes. The signal preprocessing method is simulated and experimentally studied. Detecting the spot and the signal processing is realized by the four-quadrant detector, which is important for the use of quadrant detectors for high-precision position measurements.
Compared with traditional 3-D shape data, ladar range images possess properties of strong noise, shape degeneracy, and sparsity, which make feature extraction and representation difficult. The slice image is an effective feature descriptor to resolve this problem. We propose four improved algorithms on target recognition of ladar range images using slice image. In order to improve resolution invariance of the slice image, mean value detection instead of maximum value detection is applied in these four improved algorithms. In order to improve rotation invariance of the slice image, three new improved feature descriptors—which are feature slice image, slice-Zernike moments, and slice-Fourier moments—are applied to the last three improved algorithms, respectively. Backpropagation neural networks are used as feature classifiers in the last two improved algorithms. The performance of these four improved recognition systems is analyzed comprehensively in the aspects of the three invariances, recognition rate, and execution time. The final experiment results show that the improvements for these four algorithms reach the desired effect, the three invariances of feature descriptors are not directly related to the final recognition performance of recognition systems, and these four improved recognition systems have different performances under different conditions.
In order to study the influence of nonlinear sweep voltage on the range accuracy of streak tube imaging lidar, a nonlinear distance model of streak tube is proposed. The model of the parallel-plate deflection system is studied, and the mathematical relation between the sweep voltage and the position of the image point on the screen is obtained based on the movement rule of phoelectron. And the mathematical model of the sweep voltage is established on the basis of its principle. The simulation of streak image is carried out for the selected staircase target, the range image of the target can be reconstructed by extremum method. Comparing reconstruction result and actual target, the range accuracy caused by the nonlinear sweep voltage is obtained. The curve of the errors varying with target ranges is also obtained. And the range accuracy of the system is analyzed by the means of changing the parameter relate to sweep time.
A shape descriptor and a complete shape-based recognition system using slice images as geometric feature descriptor for ladar range images are introduced. A slice image is a two-dimensional image generated by three-dimensional Hough transform and the corresponding mathematical transformation. The system consists of two processes, the model library construction and recognition. In the model library construction process, a series of range images are obtained after the model object is sampled at preset attitude angles. Then, all the range images are converted into slice images. The number of slice images is reduced by clustering analysis and finding a representation to reduce the size of the model library. In the recognition process, the slice image of the scene is compared with the slice image in the model library. The recognition results depend on the comparison. Simulated ladar range images are used to analyze the recognition and misjudgment rates, and comparison between the slice image representation method and moment invariants representation method is performed. The experimental results show that whether in conditions without noise or with ladar noise, the system has a high recognition rate and low misjudgment rate. The comparison experiment demonstrates that the slice image has better representation ability than moment invariants.
The article introduced the system structure and imaging principle of no three-dimensional imaging laser radar. This paper used the XC7K325T XILINX chip of KINTEX 7 series and used temporal interpolation method to measure distance. Rough side used PLL multiplier 400MHZ, which reached 2.5ns time accuracy. This method used a thin chip delay chains carry resources to reach 50ps accuracy and greatly improved the accuracy of the timing of imaging. <p> </p>Application technique used a delay line in APD array imaging system, such that each channel distance accuracy greatly improved. Echo signal by photoelectric conversion is completed by APD array detector, and designed by the impedance amplifier and other analog signal processing circuit. FPGA signal processing circuit is to complete the back-end processing, which is the timing function. FPGA array timer clock is to achieve coarse portion through timing, and delay line technique for measuring the length of time a non-integer multiple of the period of the laser pulse emission and the moment of reception, each stage of the delay units delay accuracy of sub ns magnitude, so as to achieve precision measuring part timers. With the above device was close imaging experiments, obtaining the 5 × 5 pixel imaging test results, presented to further improve system accuracy improved method.
This paper focuses on the study of Signal Receiving Circuit of Lidar. A signal receiving circuit for a pulsed time-of-flight (TOF) Lidar has been designed. This paper introduces the theories of Lidar and high speed photoelectric detection. The circuit consists of APD array, transimpedance amplifier and differential received amplifier. In the circuit, we use an APD as a photoelectric transformer, AD8015 is used in the circuit because it’s wide bandwidth, and single supply transimpedance. The AD8130 is a differential-to-single-ended amplifier with extremely high CMRR at high frequency, therefore it is used to converting differential signals to single-ended signals. In this paper, the laser pulse signal of 905nm wavelength, 20ns pulse width is used to detect experimentally verified. It is tested that the performance of the receiving circuit of Lidar satisfies the request of the principle system.
Proc. SPIE. 9618, 2015 International Conference on Optical Instruments and Technology: Optical Systems and Modern Optoelectronic Instruments
KEYWORDS: LIDAR, Data acquisition, Telecommunications, Control systems, LabVIEW, Field programmable gate arrays, Data communications, Avalanche photodetectors, Analog electronics, Optical communications
Lidar has been widely used in areas of ranging and imaging. To be able to perform real-time control of the entire system, this article designed a lidar data acquisition system based on LabVIEW and the PC system allows real-time display for data acquired by lidar system. Through the serial port, the PC system can adjust part of the laser radar system parameters, such as frequency, APD (Avalanche Photo Diode) bias, the echo threshold, etc in real-time. In this way, we achieve the instruction communication between the PC system and the lidar. In addition, the PC system can also acquire data from the lidar through the Ethernet. Through the practical test, the PC system can successfully acquire and display the echo signal measured by lidar system in real-time, and function of parameter adjustment is also very sensitive.
This paper presents a foreign fiber detecting system based on multi-spectral technique. The absorption rate and the reflectivity of foreign fibers differently under different wavelengths of light so that the characteristics of the image has difference in the different light irradiation. Contrast pyramid image fusion algorithm and adaptive enhancement is improved to extracted the foreign fiber from the cotton background. The experimental results show that the single light source can detect 6 kinds of foreign fiber in cotton and multi-spectral detection can detect eight kinds.
Compared to scanner imaging ladar, non-scanning LADAR plays a more prominent role in the militarily imaging
scenarios. Non-scanning LADAR has many advantages, such as structure simplicity, high reliability, imaging efficiency
and etc. However the range accuracy is low. This paper proposes a technique to use a designed delay line module in the
APD array LADAR systems, which could significantly improve the range accuracy in all channels. A semiconductor
laser is used as light source. A 5×5 APD array detector is adopted as the sensitive unit. A 25 channel parallel amplifier
circuit is designed to process the signal with bandwidth 240 MHz . Field Programmable Gate Array (FPGA) is used to
process these 25 signals paralleled, with a delay line module designed, to significant improve the ranging accuracy .The
clock frequency of FPGA is 400MHz with accuracy 2.5ns. The delay lines module are used to measure part of pulse
flying time, which is shorter than the clock cycle and could not be directly measured by the clock, and that is the cause of
the ranging accuracy. Every delay cell is 46picoseconds , total timing accuracy is less than 500picoseconds. By using
above technique, a short distance imaging experiment is presented and get the 5 ×5 pixels range image. The result is
analyzed together with the factors, which influence the accuracy of ranging image, it shows the ranging accuracy of each
pixel is 10cm. And some advanced methods are proposed to improve the accuracy of the system in the future.
Active multi-spectral detection technology is used to acquire the information of the targets，such as spectrum, distance,
intensity, and location and so on. So the active multi-spectral detection technology becomes one of the main trends of
development of detection system in the future. Based on the analyzing the theory of streak tube lidar active multi-spectral
detection system, we design a wavelength conversion circuit which can be applied to implement wavelength conversion
in the streak tube lidar in the active multi-spectral detection. Through the O-E-O conversion mode, the wavelength of
laser echo signal which contains the target information is transformed into another wavelength which represents the
spectral peak response wavelength of the stripe tube photocathode. The simulation results show that when the input laser
echo signal wavelength is 1.55um, and the after-converted wavelength is 0.85um , the photon conversion efficiency can
reach 2.2×106 ,the signal to noise ratio can reach 19.3dB. And when the target distance or the signal bandwidth
increases, the signal to noise ratio(SNR) will decrease accordingly.
Three dimensional flash imaging lidar technology is widely used in the field of military and national economic construction. The preliminary simulation research is an indispensable aspect in the design of the new lidar. In order to establish a simulation model most close to the real scene, the spatial effect of the simulation system during the laser roundtrip transmission process must be considered. This paper describes the physical mechanism of the formation of atmospheric turbulence, the power spectral density function of the distribution of atmospheric refractive index and the phase distortion due to atmospheric disturbances during light propagation in space. Then the phase-screen distribution of atmospheric turbulence is derived using power spectrum retrieval and time-dependent wavefront tilt parameter. In addition, numerical simulation is conducted using statistical methods. A three dimensional target range imaging simulation model containing laser characteristics, target characteristics, receiver characteristics and laser speckle is established. And the phase screen is introduced into the calculation model to simulate the results in turbulent atmosphere. The major contribution of this paper is transforming the influence of beam spreading and drifting caused by laser propagation in turbulent flow to the influence of target range imaging, which better reveals the diffusion and position drift of imaging on detection surface caused by turbulence. Results show that larger values of refractive index structure parameters and lidar target distance produce blurry and drifting imagery.
In the system based on the streak tube imaging lidar (STIL), the streak image on the salt screen captured by the CCD
camera not only includes the range information, but also provides the material attribute, the angle information of the
target and so on, that is the intensity information. It is generally assumed that the image brightness on the salt screen
reflect the laser intensity of the target. However, the brightness not only relates to the density of the electron beam, but
also relates to the accelerating voltage. The relative intensity of the streak image will be distorted for reasons of the
different accelerating voltage resulted by the different coming time. An amended method that there is a weighted
processing for the intensity information based on the range information was proposed, a research on the reconstruction of
the intensity image was processed, and some effects were achieved.
The technology of three-dimensional laser imaging is applied widely in the field of military use and civilian use etc.
There are mainly two methods for three-dimensional laser imaging. One of them is based on APD arrays, and the other is
based on streak tube. The latter represents relatively mature technology for providing high-resolution 3D laser radar
images. In both of them, the realization of intensity image and range image is the foundation and key of
three-dimensional laser imaging. It presents the method for three-dimensional laser imaging using multiple-slit streak
tube to get clear, exact intensity image and range image. The multiple-slit streak tube imaging lidar (MS-STIL) approach
uses several slits instead of the usual single slit to provide a number of additional capabilities over conventional laser
radar systems. And it researches into the algorithm for the realization of intensity image and range image and processes
the simulative streak tube image with it via the analysis of multiple-slit streak tube's imaging theory, and finally carries
through the simulation of intensity image and range image.
Based on the theory of lidar system,a model of lidar system was established. We focus on the math model of the
noise and the simulation of NEP and SNR, and designed relative programmes for it. In case of different existing
models on transmitting system, air condition and detecting system, simulation for lidar system can be realized.
Rational and effective design of imaging laser radar systems is the key of imaging laser radar system research.
Design must fully consider the interrelationship between various parameters. According to the parameters, choose
suitable laser, detector and other components. To use of mathematical modeling and computer simulation is an effective
imaging laser radar system design methods. This paper based on the distance equation, using the detection statistical
methods, from the laser radar range coverage, detection probability, false-alarm rate, SNR to build the laser radar system
mathematical models. In the process of setting up the mathematical models to fully consider the laser, atmosphere,
detector and other factors on the performance that is to make the models be able to respond accurately the real situation.
Based on this using C# and Matlab designed a simulation software.
The fiber optic gyroscope plays an important role in the family of inertia devices. But in the dynamic condition,
Because of the nonlinear output and the nonlinear graduation factor and zero-bias by temperature, the open-loop FOG
can't apply in some fields. Therefore, how to reduce the bad affection by temperature is urgent. This article proposed a
new method to digitize the open-loop FOG and compensate the temperature error and nonlinear graduation factor. This
detection circuit for FOG is mainly based upon C8051F350 MCU. There are 24 bit A/D converter and temperature
sensor. What is more important, its area is only 5×5 mm<sup>2</sup>, which is propitious for minimizing and engineering. By
analyzing and researching a great of experience data, we build the model of zero-bias temperature character,
graduation factor temperature nonlinear character and output nonlinear character. Then we compensate the character
mentioned above. Test result shows that the system reaches the expected performance. It is meaningful for
engineering, minimizing and application.