Long Period Fiber Gratings(LPFGs) were inscribed by using a 800 nm femtosecond laser and their high-temperature properties were verified in this paper. Firstly, an inscription system for the laser into fiber cores was designed using a camera and an electric moving platform. With controlling a pulse laser of 1.3 mW, a LPFG was inscribed in a non-hydrogen-loaded bare fiber using point by point technique, and the resonant peak of the LPFG is about -17 dB in the 1 200~1 700 nm band. Then, high temperature sensing experiments were performed on the LPFG by a high temperature box, obtained results show that the linearity of the resonance peak changes is about 0.992 and temperature sensitivity is 0.056 nm/℃ at 300-800 ℃. It demonstrates that the inscription technology for LPFGs by using the 800 nm femtosecond laser is feasible and obtained LPFGs have good response characteristics and stability, and are suitable for the high-temperature measurement.

To enlarge the transmission scale and improve the transmission precision of an azimuth transmission system based on sine wave magneto-optic modulation, a new method of transmitting the azimuth in a large-scale and high-precision was established. The principle of the current azimuth transmission system was analyzed, and a double-angle formula was introduced to enlarge the transmission scale. A model to measure the azimuth was established according to analyzing the relationship between the azimuth and the extremum of the modulated light, and the measurement model was expatiated by comparing the extremums. A integrated method combined the approximation in little-scale with the looking-up table in large-scale was presented to calculate the arc tangent function in the model. Simulation results indicate that the theoretic transmission scale is widened obviously and the precision is improved. Experiment results show that the actual transmission scale is -64-64° and the transmission error is under 10″, which is better than those of the current methods. The method provides a new way to transmit the spatial azimuth in large-scales and high-precision.

An optimized method was proposed to improve the processing efficiency of Selective Laser Melting (SLM) for multi-parts. First, the time consuming of the SLM process was analyzed and the 2.5D nesting rules for the optimization were established to reduce the time consuming. Then, the 2.5D automatic nesting was studied. A simplified method which uses the 3D projection to convert the 2.5D nesting to the 2D nesting and an algorithm for generating the projection from slice data were presented. Finally,by taking a operation model for an example, an experiment was performed on the virtual SLM system developed with OpenGL and VC++ to simulate the motion of real system and to validate the feasibility of the method. The result shows that the processing times are reduced from 4 to 3, the recoating times are from 3 892 to 2 231 and the expected processing time has been from 91 276 s to 69 918 s at a scanning speed of 600 mm/s, slicing thickness of 0.035 mm and track space of 0.08 mm.The time consuming has been significantly reduced as compared with that before optimization.

A small-aberration retrieval method based on spot images was introduced and an analytic formula to computer the point spread function for a small aberration optical system was derived according to the scalar diffraction theory and Bessel series. With this formula, the objective function and its gradient were given for the small-aberration retrieval method. Then, the optimized method was used to solve this problem. The effectiveness of this method was demonstrated by using the numerical simulation under ideal and noisy conditions，respectively, and the influence of the size of spot object on the retrieval results was also analyzed. This method uses aberration's Zernike coefficients as optimization variants and computes the objective function and its gradient with analytic expressions to avoid Fourier transform or numerical integral needed in common aberration retrieval methods. Therefore, it improves the speed of aberration retrieval greatly.

A real-time monitoring system of composite impact loads was constructed by a Fiber Bragg Grating(FBG) sensor network, and the wavelet packet feature extraction and a Support Vector Regression(SVR) were used to identify the impact location. For the impact response signals at the same position measured by different FBG sensors, the wavelet packet energy spectrum analysis shows that some specifically frequency bands of sensor signals are sensitive to the impact. The relation between impact location and wavelet energy was studied and the sixth decomposition level wavelet packet energy was chosen as the characteristic vector of the impact location. The SVR whose tuning parameters have been optimized was used to established the sample regression model and predict the impact location. The result shows that network testing error of the SVR is 4.81％. The research provides a practical reference for the impact performance evaluation of the structures from carbon fiber reinforced plastics.

A Computer Numerical Control (CNC) non-contact super-smooth polishing method for optical components was proposed. Polishing fluid was provided through a center hole of the polishing tool for the optical surface and it interacted with the surfaces of optical components drived by a rotated polishing tool to remove the materials on the optical components minutely. The motion trajectory of the polishing tool could be controlled by the computer. According to the proposed principle, a prototype of CNC non-contact super-smooth polishing machine for the optical components was designed and developed, and its minimum feed rate and positioning accuracy for the linear motion axis are 0.000 1 m/s and 0.008 mm,respectively; the minimum rotate speed and positioning accuracy for the swing shaft are 0.002 8 r/min and 15′,respectively. The performance of the prototype could meet the requirements of spherical/aspherical optical components with diameters less than 200 mm for super-smooth polishing. To verify the prototype, an experiment was performed on a fused silica component. After super-smooth polishing for 20 min, the surface roughness of two points on the optical component is improved from 1.03 nm and 0.92 nm to 0.48 nm and 0.44 nm, which shows the polishing accuracy has been optimized greatly.

Measurement point distribution in contact measuring large aspheric optical surface was researched. By the radial and uniform measurement points with different density distributions, various surface deviations represented by different Zernike polynomials were sampled respectively. Then, the maximum PV and RMS errors were calculated and analyzed. Measurement results of a 1.8 m parabolic mirror were taken as examples, and it indicates that the low density radial measurement point distribution can meet the measurement needs at the forming and coarse grinding stages because the surface deviations show large rotate-symmetrical forms. Moreover, the uniform distribution of measurement points is an effective way to improve measurement accuracy at fine grinding and initial polishing stages, for the main surface deviations are astigmatism or other asymmetrical aberrations. This method can guide the measurement point distribution, control the measurement error caused by distribution to be less than 1/5 of surface error, and can improve measurement accuracy efficiently.

To improve the measuring accuracy of Signal to Noise Ratio(SNR) of the third-generation low level image intensifiers, a transient low light level illuminometer was designed based on photon counting principles to measure the illuminance value of 1.08×10-4 lx from a circular area with diameter of 0.2 mm for the quasi-point imaging source on a photocathode. Firstly, the photon distributing probability and fluctuated deviation were analyzed for the quasi-point light source at a color temperature of 2 856 K, and the average photon flux was calculated. Then, the low light level illuminance measuring principle by the photon counting method was studied according to the photon flux and imaging characteristics. Finally, the composition of the transient quasi-point low light level illuminometer was introduced, and the SNR of a third-generation low light level image intensifier was measured. Experimental results indicate that the illuminance deviation and uncertainty of the SNR are 0.4% and 5.0%,respectively.It concludes that the proposed low light level illuminometer based on photon counting can effectively improve the accuracy of illuminance measurement for quasi-point low level light sources.

On the basis of optical design theory, this paper designs a small-scale and dual-field optical system with a half sphere tracking field. This optical system takes a Code optical path as the main system and consists of three parts: tele-system at front, ray tuning system in the middle, and imaging system in the back. The first part is a telescope compound for adjusting the diameter of the light beam; the middle part is Code optical path made up four mirrors, which is used to turn the direction of the light beam; and the last part is an imaging system for long focal and short focal imaging and for tracking and recognizing targets. The focal lengths of the system are 60 mm and 120 mm and their Modulation Transfer Functions(MTFs) are all above 0.5 at 5.8 lp/mm. By imaging tests, this optical system has better imaging quality and can capture the images form the large field and small one at the same time.

This paper studies the outage probability for parallel relay Free-space Optical(FSO) communication systems under a condition of strong turbulence. By considering the influences of atmospheric attenuation, atmospheric turbulence and pointing errors on the transmission performance of FSO communication systems, this paper establishes a composite channel model. Based on the model, an analytical expression is further derived for the end-to-end outage probability of parallel relay FSO communication systems. Finally,the effects of transmitted powers, pointing errors and communication distances on outage probability are analyzed through computer simulation. Simulation results show that parallel relay transmission is a promising technology to increase the outage performance and the de-rived analytical expression can provide sufficient precision for evaluating the outage performance of parallel relay free-space optical communication systems, which is helpful to the design of future free space optical communication systems.

To improve the performance of a high-speed dot- matrix pulse jet generator in a printing machine and to optimize the printing effect of the machine, a mathematical model for the high-speed pulse jet generator was established and a sliding mode observer was designed. By building a feedback system based on the observer, the sensorless control of the high-speed pulse jet generator was realized to track the desired trajectory exactly, reduce the seating velocity of the valve core and to eliminate the vibration and noise greatly without increasing the cost of hardware. The experimental results show that the seating velocity has been reduced from 0.55 m/s for open loop control to 0.02 m/s for close loop one, the vibration and noise are almost eliminated, and the jet printing effect is improved obviously. The design result meets the industrial production demand when it is applied to a marking system for steel products and it provides theory foundation for design of the control units of high-speed pulse jet generators.

This paper analyzed the zero-point displacement uncertainty determined by Heisenberg uncertainty principle in the silicon cantilever nano-resonators with the thicknesses of 12 nm and 38.5 nm. The analysis results show that the zero-point displacement uncertainty is inversely proportional to the thickness and width of the cantilever and proportional to the length of the cantilever, and the zero-point displacement uncertainty of the silicon cantilever nano-resonator with the thickness of 12 nm is 4.1×10-3 nm. Combining the parametric pumping quantum squeezing technique, the relationships between the quantum-squeezing factors of the silicon cantilever nano-resonators with different thicknesses and their structure dimensions, temperatures, pumping voltages were analyzed. The analysis results show that the quantum-squeezing factor is proportional to the temperature, and inversely proportional to the pumping voltage. When the temperature is 0.01 K and the pumping voltage equals 4 V, the quantum noise of the silicon cantilever nano-resonator with the thickness of 12 nm is reduced by 26.56 dB. The analysis results promote the improvement of the measurement accuracy of the ultra-thin cantilever nano-resonators under the influence of the quantum noises observably.

Several kinds of evaluation methods for the uncertainty in coordinate measurement are introduced and it points out that most of these methods are failed to the uncertainty evaluation for special objectives because of lack of theory support or practicability. Therefore, this paper investigates the uncertainty evaluation of gear measurement with Coordinate Measurement Machines (CMMs) by the Monte Carlo method. Firstly, a measuring model is established based on the files for the calibration and compensation of the specific CMM, then the mode is used to obtain measuring results with a large number of sample points. Using these simulated results, the uncertainties can be evaluated more conveniently. Finally,the Monte Carlo method is successfully used in evaluating measurement uncertainty of gear profiles and obtained stable results show that the maximal difference among the results is less than 0.03 μm when the typical uncertainty is 0.96 μm. The paper suggests that Monte Carlo method can support specific uncertainty measurement and can change the situation that common evaluation method can not be suitable for the commercial CMMs.

For tracking and locating robots in the pipeline inspection accurately, a wireless adaptive location model was presented to realize the 3D position of robots without the geometrical sizes of pipelines and electromagnetic parameters of ambient medium. Firstly, extremely low frequency electromagnetic fields of pipelines were described by a magnetic dipole model. Then, an adaptive antenna positioning model based on six sensors was proposed and electromagnetic transmitter and receiver circuits were designed.Based on the model,a linear equation containing six unknown numbers was derived and three kinds of algorithms were used to analyze and simulate the equation. Finally, engineering experiments were performed on the pipes with different thicknesses and burial depths. The experiment on a pipe wall thickness of 5.74 mm and burried deep from 0.8 to 0.2 m shows that the average position error is 18.7 cm,which has been decreased by 3.4 cm compared with that of the original model. The results can satisfy the requirements of systems for non-contact, real time and adaptive location.

A new style coordinate measuring system based on 3-PSS parallel mechanism was proposed to overcome the drawbacks and weaknesses of traditional Coordinate Measurement Machines(CMMs) and articulated arm CMMs and to realize 3D measurement with only one linear grating and one precision guide. A measurement model,a measuring error model as well as the error averaging effort of the parallel mechanism were investigated. Firstly,a 6-bar measurement model was achieved based on the theory of parallel kinematic mechanism. Then, the influence of bar length error and reading error from the liner grating were analyzed in detail and the hypostasis why parallel structure posses error averaging effort was revealed mathematically. Finally, the prototype CMM was introduced to its design, manufacturing and assemble and the experiment result was provided too.Results indicate that the measuring errors before compensation and instrument calibration in three dimensions are about 0.029 mm in x direction, 0.045 mm in y direction and 0.058 mm in z direction. Obtained results can provide the direction for the design of new CMM protypes.

To accurately measure the transmission directions of high power laser beams from a laser independent expanding beam system in the laser launching system,the equipment for measuring the parallelism error of independent expanding beam system is designed. Firstly, based on the speciality of the independent expanding beam system and the IR laser, the equipment uses a high resolution IR CCD for measuring and imaging. Then, the mechanical structure of the equipment is constructed by using aluminum alloys with light quality and high rigidity,and its activity parts are building on a linear moving platform with high precision. On the basis of the high resolution CCD and the precise displacement platform,the equipment can implement the dynamic and static measurement.The experimental results show that the equipment works stably and reliably and measuring precision is better than 2″.It satisfies the requirements of the laser launching system,and can provide basis for the assembly and application of the expanding beam systems.

For characterizing the nanostructure and controlling nano-manufacturing quality,a metrological Atomic Force Microscope(AFM) was designed and constructed in National Institute of Metrology. To trace the displacement to the SI unit, the relative position of sample and AFM probe is measured with homodyne 8-pass interferometers and the surface topology of the sample is measured by AFM at a contact mode. A cube with mirrors is fixed on the probe as the reference mirror of interferometers, so that the relative displacement of probe in the x -y direction to the sample is measured by interferometers. The sample stage is fixed on a corner block with mirrors on three sides and driven by a piezoelectric motion stage. Two interferometers is used to measure the displacement of sample and probe in z direction. The probe tip is positioned in the intersection of the interferometers in 3 directions to minimize the Abbe error. As the phase mixing from the defect of optical element will cause the nonlinear error,a harmonic separation method is introduced to fit the inteferometric signals and to correct the error. The measured results show that the nonlinear error has been reduced to 0.7 nm, which demonstrates this system has better performance.

An active disturbance rejection controller was designed in the lensbarrel of an aerial camera to reduce the disturbance caused by an eccentric cam of the lensbarrel. An extended state observer was designed to estimate the disturbance and then to generate control signals to compensate the disturbance influence. First, the disturbance characteristic of the cam was analyzed. And then, a mathematic model of lensbarrel was established and simplified. Based on bandwidth parameterization,the extended state observer and the control law with disturbance compensation were designed and a position controller was finished. Finally, an experiment on the lensbarrel was performed to test the disturbance rejection performance of the controller. As compared with the traditional first order square lag-lead compensation method used in aerial cameras, experiment results show that the active disturbance rejection controller can reduce the disturbance error about 50% with a lower controller gain about percentile. In conclusion,the disturbance rejection performance of the system is improved and the demand for controller gain is lowered at the same time. It is feasible and practical.

A scanning plasma etching system based on parallel probe actuation was developed to realize micro- and nano-scale etching. The electrical and optical emission spectra of a micro plasma reactor which was a key device in the system were measured to explore the characteristics of the plasma in the reactor. First, a metal-dielectric-metal structure microplasma reactor with an inverted pyramidal hollow cathode was fabricated based on Micro-electric-mechanic System(MEMS) technology. Then,a testing system was set up to measure the V-I curve and optical emission spectra of the microplasma generated at a SF6 gas pressure of 5-12 kPa and drived by a DC mode. Experimental result shows that the discharge current is increased in linearity with the discharge voltage. When the gas pressure increases from 5 kPa to 12 kPa, the discharge current is increased from 2.1~2.82 μA to 3.6~4.2 μA, which means that the microplasma is at an abnormal discharge mode. When the feature size of the reactor decreases from 150 μm to 30 μm, the characteristic line of fluorine(703.7 nm) is increased about 56%, which demonstrates that the plasma density is increased with reducing device sizes. The measurement result of electrical and optical emission spectra of microplasma indicates that the microplasam reactor is suitable for the scanning plasma etching of silicon.

To effectively evaluate the tracking ability of a photoelectric theodolite, a new tracking error model based on the Radial Basis Function(RBF) neural network was established. First, the nonlinear factors existing in the theodolite were described and the reason why the system was hard to be modeled based on theory was discussed. Then, the RBF neural network theory and the target system were introduced, and the RBF neural network model was built and verified in different parameters. Finally, the network model with new parameters and data was trained and the new network model was obtained through changing parameter periods. Experimental results indicate that the precision of the neural network is closely dependent on the target system parameters. When the half cone angle(a) and the tilt angle(b) of a dynamic target are 21.2° and 43.8°, respectively, and the moving period(T) is 8.5 s, the maximum model error is 3.18′ in the acceleration coming to the maximum. And for other time, the model error is less than 0.6′. Furthermore, when the a and b are 16.6°, 37.5°, and T is 13 s, the maximum model error is about 1.8′. With the network model, the maximum error between model output and real output is 2.4′ in the speed coming to maximum. And for other time, the maximum model error is less than 1.2′. The results indicate that the network model based on RBF neural network can replace a real system in a certain sense. It is feasible and has high accuracy and important value to the engineering practice.

To improve the capability of space-based surveillance for space targets， this paper researches the Moving Target Indicator (MTI) based on time-domain projecting image sequences for suppressing starry sky background.The MTI has been used in a spaceborn signal processor on the USA Midcourse Space Experiment for target detection and tracking. According to the in-depth study of MTI algorithm, a new method is proposed to suppress the background of cluttered cloud based on the standardized maximum projection of temporal difference. The mathematical principle and the operator design method of temporal projection are given. Then, considering the statistical characteristics of cluttered cloud, the two Improved MTIs(IMTIs),namely, the temporal difference operator on an adjacent frame and the estimated median operator, are introduced to the MTI to enhance the clutter suppression. Finally, the experimental method based on the cloud background data acquired is designed to analyze the algorithm performance of different projection methods as well as the main factors affecting on the algorithm. The experimental results show that the output Signal-to-clutter Ratio(SCR) of IMTI reaches more than 5.8 when the input SCR of a small target is less 2.0, which has been improved by 1 in average as compared with that of MTI.It concludes that the IMTI can effectively solve the dim target detection problem of cluttered cloud image background.

An evaluating method of freeform curve profile errors based on the Improved Genetic Algorithm(IGA) and quasi random sequence was proposed to inspect freeform curves and surface parts and to compute their profile errors efficiently and precisely. Firstly, according to the characteristics that the freeform curve was expressed by discrete points rather than an analytic function, the Non-uniform Rational B-spline (NURBS) was used to express the free curve and the IGA was proposed to reconstruct it. Then,the quasi random sequence was taken to generate parameter values uniformly and to calculate the shortest distance from a point to a reconstructed curve exactly.Furthermore, The computation methods of the control vertex and objective function value were described when freeform curve was reconstructed and the detailed steps were established for reconstructing the free curve and computing the shortest distance from the point to the curve based on the IGA and quasi random sequence. Finally, the curve profile errors of a simulation example and practical parts were calculated and measured. The results verify that the evaluation precision of freeform curve profile error is higher than 99%. The proposed method has the advantages of simple algorithm, rapid computation and high accuracy and it can be applied in engineering metrology.

Since the existing target orientation estimation methods for laser radars are not robust to the occlusion, a novel 3D orientation estimation method was proposed. The principles of the existing methods and the intrinsic characters of the surface structures for ground targets were analyzed carefully, then the feature of Projection Density Entropy (PDE) was introduced, and the relationship between PDE and target orientation was analyzed. Finally, a 3D orientation estimation method was formulated by iteratively rotating and projecting the target point cloud onto the coordinate planes together with PDE calculation. Comparative experiments were performed on the dataset containing point clouds of 25 ground targets, the performance in self-occlusion, occlusion and the noise were investigated, and the parameter tuning was discussed. The results show that the estimation error of this method is below 3° in self-occlusion, and also no more than 10 ° even in 80% occlusion. It is clear that the proposed method is robust to occlusion and converges quickly, thus is capable of estimating the 3D orientation of ladar targets in complex scenes.

The accuracy evaluation methods for a laser tracker developed by ourselves are investigated to solve the problem that the coordinate precision in a large-size space coordinate measuring system is difficult to be evaluated. In consideration of the great impacts of environmental conditions, equipment status, operator skills and other factors on measurement accuracy, this paper proposes a bundle adjustment method to evaluate the accuracy of the laser tracker under practical conditions. The Matlab is used to simulate the accuracy evaluation, and results show that the bundle adjustment can generally reflect the measurement accuracy of laser tracker measurement system . Furthermore, a practical experiment is performed on a laser tracker made from Faro company, and results show that the measuring accuracies of horizontal angle σH and vertical angle σV are 1.97″ and 2.61″,respectively, and measuring accuracy σD for the distance is 3.75×10-6.As compared with the instrument accuracy of the Faro (σH=2.0″,σV=2.0″,σD=4 μm), It proves that using bundle adjustment to evaluate the performance of the laser tracker developed is feasibility and correctness. The method will be useful to broaden application of laser tracker technology and to open a way to task-oriented uncertainty evaluation.

An exterior attitude calculation method by taking Rodrigues parmeter as the attitute representation parameter was presented to overcome the shortcomings of the constraints and complexity of traditional attitude calculation algorithms and to increase the real-time performance for the multi-linear CCD spatial object exterior attitude measurement system.A multi-linear CCD exterior attitude calculation model was deduced based on the high efficiency of the Rodrigues parameter and the relationship of the intersection vector between the line segments composed of point cooperation targets. In order to avoid the singularity in attitude calculation, a switching theory of the Rodrigues parameters is combined in the algorithm and the process of this attitude calculation method was also given. Experimental results indicate that the computational-complexity of the proposed algorithm is reduced by 37.6% as compared with that of the quaternion method on the premise of assuring precision, and it is superior to quaternion method in real-time performance. At the same time, it avoids the singularity problem.

To improve the resolution of projective image of a Thin Film Transistor-Liquid Crystal Display (TFT-LCD), a method was proposed by using a piezo-stage to drive the TFT-LCD movement in X and Y directions to implement the pixel-multiplexing of the TFT-LCD. The hardware configuration of the TFT-LCD was introduced, and the principle of improving the resolution of projective image by the pixel-multiplexing was presented. On the basis of accuracy demand of displacement movement to be 10 nm, the moving mechanism that can achieve a higher precision was chosen . Furthermore, three kinds of test schemes were proposed to prove the obtained results, and a experimental platform was constructed to verify the correction and efficiency of test principle. Experimental results show that the image resolution projected by the TFT-LCD has been doubled in X and Y directions, respectively, and total pixels are four times that of traditional imaging method. Proposed method changes the situation that the resolution of a star simulator is limited by that of the display device.

Subtracted blood volume spectrometry was employed to the noninvasive biochemical examination with near infrared spectroscopy(NIRS) to eliminate the influence of tissues.To raise the Signal to Noise Ratio(SNR) of the NIRS pulse wave signal needed by the spectral subtraction, an effective adaptive filter method was proposed to process the pulse wave signal. The principles of Least Mean Square(LMS) adaptive filter were described, and a new adaptive filtering way fit for the pulse wave signal of this experiment was proposed. Then, a 16-pixel near-infrared pulse wave acquisition system made by ourselves was used to collect the pulse wave signals of human body. Finally, the proposed adaptive filtering way was used to process the NIRS pulse wave signals and analyze the results. The result shows that the noise level of blood spectrum has reduced from 800 μAU to 12 μAU after spectral subtraction by using the proposed method, and the related coefficient of pulse wave of adjacent wavelength has raised from 0.994 0 to 0.999 9. The analysed result verifies that the method is effective in the NIR noninvasive biochemical examination area.

A machine vision system is proposed to measure the diameter of a mini milling cutter on line, and the measurement uncertainty is analyzed in this paper. The system consists of a back-light source, a rotate stage, a rotary encoder, a camera and corresponding software. While the milling cutter rotates, the camera is triggered by the rotary encoder and a series of images are captured. The sources of uncertainty and their effects are analyzed, including the parallelism of the light source, lens distortion, CCD noise, focusing situation, the geometric properties of tested objects and the algorithm design. According to results of experiments, the uncertainty mainly depends on the geometric property of the tested object when sampling rate is not enough, otherwise, it is mainly relative to the parallelism of the light source. In the experiment performed, the system uncertainty is 4 μm with a sampling rate of 33 frame/circle, both accuracy and efficiency meet the requirement of manufacturing.

An error model of phase discrimination based on spectral analysis is deduced to reduce the phase discrimination error for a phase-shift laser range finder, and the Hilbert transform is induced to data pre-processing to eliminate the estimation bias of phase difference. The bias and deviation of conventional spectrum analysis phase discrimination are analyzed. The analysis shows that the bias is influenced by initial phases and it can not be ignored in fast and precision measurement.This paper proposes an unbiased improvement method. The method uses a window function to design a simple Hilbert transformer to convert the objective of Discrete Fourier Transform into an analytic signal. Then the nearly unbiased phase difference measurement is achieved by spectral analysis only in increasing four addition and two shift operations. Simulation and experimental results indicate that the mean phase is the same as the real phase difference. When the signal to noise ratio is 40 dB, the measurement accuracy for the high speed phase discriminaton is 0.1°. When the modulation frequency is 100 MHz, the distance measurement accuracy is 0.4 mm. Results show that the Hilbert transform can help spectral analysis realize high accuracy phase difference measuring and the method can be applied to fast phase-shift laser range finders.

An arbitrary shape ROI coding method based on modified Set Partitioning in Hierarchical trees (SPIHTs) is proposed to solve the problems of arbitrary shape Region of Interest(ROI) coding algorithms in low reconstructed image quality and inefficiency at a low bit rate. The ROI mask is described by combining the similarity of spatial position among wavelet coefficients with the specific wavelet filter at an extremely low bit rate, which lays a foundation for improving coding efficiency. The modified SPIHT partitioning structure is used to improve the coding efficiency of sorting pass by grouping more ROI entries together. A quantization method based on each wavelet subband optimizes the output bit stream in ROI encoding and improves the reconstructed image quality by choosing the proper threshold for each subband. Experiment results show that the proposed method can support multiple arbitrary shape ROIs and can describe the ROI mask information of the whole image at very low bit rate (less than 0.04 bit/pixel). Furthermore, at the bit rate less than 0.5 bit/pixel,the proposed algorithm has improved its Peak Signal to Noise Ratio(PSNR) by 2-7dB,and reduced the encoding time above 30% as compared with those of Multiple Subband Bitplane Shift (MSBShift) algorithm based on JPEG2000. It is concluded that the proposed method has higher reconstructed image quality, faster coding speed and is fit for image application at the low bit rate.

A lossless compression algorithm based on distributed source coding was proposed to compress the airborne hyperspectral data effectively. In order to make full use of the spectral correlation of hyperspectral images,a multi-band prediction scheme was introduced to acquire the prediction values of the current block and to reduce the maximal absolute value of prediction error effectively. Then, by using the maximal absolute value to determine the coset index of pixels belonging to the current block,the lossless compression of hyperspectral images was realized by transmitting the coset index of the current block instead of its prediction error. Experimental results on hyperspectral images acquired by Airborne Visible Infrared Imaging Spectrometer (AVIRIS) show that the proposed algorithm can offer both high compression performance and low encoder complexity compared with those existing classical algorithms, which is available for on-board compression of hyperspectral images.