This paper analyzes the characteristics of the output gradient histogram and shortages of several traditional automatic threshold methods in order to segment the gradient image better.Then an improved double-threshold...This paper analyzes the characteristics of the output gradient histogram and shortages of several traditional automatic threshold methods in order to segment the gradient image better.Then an improved double-threshold method is proposed,which is combined with the method of maximum classes variance,estimating-area method and double-threshold method.This method can automatically select two different thresholds to segment gradient images.The computer simulation is performed on the traditional methods and this algorithm and proves that this method can get satisfying result.展开更多
In radar systems of automatic detection, an estimate of background clutter power is used to set the detection threshold. An interference saturated environment is frequently encountered in these systems (multiple targe...In radar systems of automatic detection, an estimate of background clutter power is used to set the detection threshold. An interference saturated environment is frequently encountered in these systems (multiple target situations). Therefore, the detection of signals in such an environment becomes one of the most important problems to be solved. The double-threshold algorithm is one of the more interesting detectors used in these situations. While the first threshold operation ensures that the calculation of the detection (second) threshold is based on a set of samples which is free of strong interferers and is therefore much more representative of the noise level, the second threshold is used to declare the presence or the absence of the radar target. The object of the present paper is to analyze the performance of such type of CFAR schemes when the radar receiver contains a noncoherent integrator amongst its basic elements. It is found that the processor detectabil ity loss is very low and the performance degradation, caused by interferers is quite small even if the number of outlying targets is large, given that the first threshold is properly chosen.展开更多
Single-pixel cameras, which employ either structured illumination or image modulation and compressive sensing algorithms, provide an alternative approach to imaging in scenarios where the use of a detector array is re...Single-pixel cameras, which employ either structured illumination or image modulation and compressive sensing algorithms, provide an alternative approach to imaging in scenarios where the use of a detector array is restricted or difficult because of cost or technological constraints. In this work, we present a robust imaging method based on compressive imaging that sets two thresholds to select the measurement data for image reconstruction. The experimental and numerical simulation results show that the proposed double-threshold compressive imaging protocol provides better image quality than previous compressive imaging schemes. Faster imaging speeds can be attained using this scheme because it requires less data storage space and computing time. Thus, this denoising method offers a very effective approach to promote the implementation of compressive imaging in real-time practical applications.展开更多
Aircraft engine component and sensor fault detection and isolation approach was proposed,which included fault type detection module and component-sensor simultaneous fault isolation module.The approach can not only di...Aircraft engine component and sensor fault detection and isolation approach was proposed,which included fault type detection module and component-sensor simultaneous fault isolation module.The approach can not only distinguish among sensor fault,component fault and component-sensor simultaneous fault,but also isolate and locate sensor fault and the type of engine component fault when the engine component fault and the sensor faults occur simultaneously.The double-threshold mechanism has been proposed,in which the fault diagnostic threshold changed with the sensor type and the engine condition,and it greatly improved the accuracy and robustness of sensor fault diagnosis system.Simulation results show that the approach proposed can diagnose and isolate the sensor and engine component fault with improved accuracy.It effectively improves the fault diagnosis ability of aircraft engine.展开更多
The double-threshold method has been widely used in ultrasonic flow measurement to determine time-of-flight(TOF)due to its low cost and ease of implementation.Performance of this method is negatively affected by the c...The double-threshold method has been widely used in ultrasonic flow measurement to determine time-of-flight(TOF)due to its low cost and ease of implementation.Performance of this method is negatively affected by the cycle-skip phenomenon which occurs frequently under inconstant working conditions,especially varied fluid temperature.This paper proposes a method to suppress the phenomenon to facilitate reliable determination of TOF in ultrasonic flow measurement.First,the double-threshold method is used to generate a feature point to segment the signal.Second,based on the correlation coefficient and signal power,judgement factors of individual signal periods are calculated to determine signal onset.Finally,a valid zero crossing which has a constant lag from the onset is selected to determine the TOF.Thus,the cycle-skip phenomenon is suppressed.Two additional modifications are proposed to eliminate the influence of varied signal frequency and low sampling rate.The proposed method was validated by an experiment based on an ultrasonic water flow sensor.Results showed that the frequently appearing cycle-skip phenomenon can be successfully suppressed by the proposed method.展开更多
Extreme value analysis is an indispensable method to predict the probability of marine disasters and calculate the design conditions of marine engineering.The rationality of extreme value analysis can be easily affect...Extreme value analysis is an indispensable method to predict the probability of marine disasters and calculate the design conditions of marine engineering.The rationality of extreme value analysis can be easily affected by the lack of sample data.The peaks over threshold(POT)method and compound extreme value distribution(CEVD)theory are effective methods to expand samples,but they still rely on long-term sea state data.To construct a probabilistic model using shortterm sea state data instead of the traditional annual maximum series(AMS),the binomial-bivariate log-normal CEVD(BBLCED)model is established in this thesis.The model not only considers the frequency of the extreme sea state,but it also reflects the correlation between different sea state elements(wave height and wave period)and reduces the requirement for the length of the data series.The model is applied to the calculation of design wave elements in a certain area of the Yellow Sea.The results indicate that the BBLCED model has good stability and fitting effect,which is close to the probability prediction results obtained from the long-term data,and reasonably reflects the probability distribution characteristics of the extreme sea state.The model can provide a reliable basis for coastal engineering design under the condition of a lack of marine data.Hence,it is suitable for extreme value prediction and calculation in the field of disaster prevention and reduction.展开更多
Spectrum sensing is studied for multi-user cognitive radio networks in this paper. An improved spectrum sensing method----energy-cooperative detection method is developed, which combines the double threshold energy de...Spectrum sensing is studied for multi-user cognitive radio networks in this paper. An improved spectrum sensing method----energy-cooperative detection method is developed, which combines the double threshold energy detecting method with the “OR” fusion decision rule. The simulation is done for both AWGN channel and Rayleigh channel, and the advantages of the improved method are verified.展开更多
基金Supported by the National Nature Science Foundation of China(50099620)the Project of Chenguang Plan in Wuhan(985003062)
文摘This paper analyzes the characteristics of the output gradient histogram and shortages of several traditional automatic threshold methods in order to segment the gradient image better.Then an improved double-threshold method is proposed,which is combined with the method of maximum classes variance,estimating-area method and double-threshold method.This method can automatically select two different thresholds to segment gradient images.The computer simulation is performed on the traditional methods and this algorithm and proves that this method can get satisfying result.
文摘In radar systems of automatic detection, an estimate of background clutter power is used to set the detection threshold. An interference saturated environment is frequently encountered in these systems (multiple target situations). Therefore, the detection of signals in such an environment becomes one of the most important problems to be solved. The double-threshold algorithm is one of the more interesting detectors used in these situations. While the first threshold operation ensures that the calculation of the detection (second) threshold is based on a set of samples which is free of strong interferers and is therefore much more representative of the noise level, the second threshold is used to declare the presence or the absence of the radar target. The object of the present paper is to analyze the performance of such type of CFAR schemes when the radar receiver contains a noncoherent integrator amongst its basic elements. It is found that the processor detectabil ity loss is very low and the performance degradation, caused by interferers is quite small even if the number of outlying targets is large, given that the first threshold is properly chosen.
基金supported by the National Natural Science Foundation of China(Nos.11675014,61605218,61601442,61575207,and 61474123)the National Major Scientific Instruments Development Project of China(No.2013YQ030595)+2 种基金the National Defense Science and Technology Innovation Foundation of Chinese Academy of Sciences,the Science and Technology Innovation Foundation of Chinese Academy of Sciences(No.CXJJ-16S047)the Program of International Science and Technology Cooperation(No.2016YFE0131500)the Advance Research Project(No.30102070101)
文摘Single-pixel cameras, which employ either structured illumination or image modulation and compressive sensing algorithms, provide an alternative approach to imaging in scenarios where the use of a detector array is restricted or difficult because of cost or technological constraints. In this work, we present a robust imaging method based on compressive imaging that sets two thresholds to select the measurement data for image reconstruction. The experimental and numerical simulation results show that the proposed double-threshold compressive imaging protocol provides better image quality than previous compressive imaging schemes. Faster imaging speeds can be attained using this scheme because it requires less data storage space and computing time. Thus, this denoising method offers a very effective approach to promote the implementation of compressive imaging in real-time practical applications.
基金Program Sponsored for Scientific Innovation Research of College Graduate in Jiangsu Province(CX10B_108Z)
文摘Aircraft engine component and sensor fault detection and isolation approach was proposed,which included fault type detection module and component-sensor simultaneous fault isolation module.The approach can not only distinguish among sensor fault,component fault and component-sensor simultaneous fault,but also isolate and locate sensor fault and the type of engine component fault when the engine component fault and the sensor faults occur simultaneously.The double-threshold mechanism has been proposed,in which the fault diagnostic threshold changed with the sensor type and the engine condition,and it greatly improved the accuracy and robustness of sensor fault diagnosis system.Simulation results show that the approach proposed can diagnose and isolate the sensor and engine component fault with improved accuracy.It effectively improves the fault diagnosis ability of aircraft engine.
基金Project supported by the Science Fund for Creative Research Groups of National Natural Science Foundation of China(No.51821093)。
文摘The double-threshold method has been widely used in ultrasonic flow measurement to determine time-of-flight(TOF)due to its low cost and ease of implementation.Performance of this method is negatively affected by the cycle-skip phenomenon which occurs frequently under inconstant working conditions,especially varied fluid temperature.This paper proposes a method to suppress the phenomenon to facilitate reliable determination of TOF in ultrasonic flow measurement.First,the double-threshold method is used to generate a feature point to segment the signal.Second,based on the correlation coefficient and signal power,judgement factors of individual signal periods are calculated to determine signal onset.Finally,a valid zero crossing which has a constant lag from the onset is selected to determine the TOF.Thus,the cycle-skip phenomenon is suppressed.Two additional modifications are proposed to eliminate the influence of varied signal frequency and low sampling rate.The proposed method was validated by an experiment based on an ultrasonic water flow sensor.Results showed that the frequently appearing cycle-skip phenomenon can be successfully suppressed by the proposed method.
文摘Extreme value analysis is an indispensable method to predict the probability of marine disasters and calculate the design conditions of marine engineering.The rationality of extreme value analysis can be easily affected by the lack of sample data.The peaks over threshold(POT)method and compound extreme value distribution(CEVD)theory are effective methods to expand samples,but they still rely on long-term sea state data.To construct a probabilistic model using shortterm sea state data instead of the traditional annual maximum series(AMS),the binomial-bivariate log-normal CEVD(BBLCED)model is established in this thesis.The model not only considers the frequency of the extreme sea state,but it also reflects the correlation between different sea state elements(wave height and wave period)and reduces the requirement for the length of the data series.The model is applied to the calculation of design wave elements in a certain area of the Yellow Sea.The results indicate that the BBLCED model has good stability and fitting effect,which is close to the probability prediction results obtained from the long-term data,and reasonably reflects the probability distribution characteristics of the extreme sea state.The model can provide a reliable basis for coastal engineering design under the condition of a lack of marine data.Hence,it is suitable for extreme value prediction and calculation in the field of disaster prevention and reduction.
文摘Spectrum sensing is studied for multi-user cognitive radio networks in this paper. An improved spectrum sensing method----energy-cooperative detection method is developed, which combines the double threshold energy detecting method with the “OR” fusion decision rule. The simulation is done for both AWGN channel and Rayleigh channel, and the advantages of the improved method are verified.
