The navigation system plays a pivotal role in guiding aircraft along designated routes,ensuring precise and punctual arrival at destinations.The integration of scene matching with an inertial navigation system enhance...The navigation system plays a pivotal role in guiding aircraft along designated routes,ensuring precise and punctual arrival at destinations.The integration of scene matching with an inertial navigation system enhances the capability of providing a dependable guarantee for success-ful accomplishment of flight missions.Nonetheless,assuring reliability in scene matching encoun-ters significant challenges in areas characterized by repetitive or weak textures.To tackle these challenges,we propose a novel method to assess the reliability of scene matching based on the dis-tinctive characteristics of correlation peaks.The proposed method leverages the fact that the sim-ilarity of the optimal matching result is significantly higher than that of the surrounding area,and three novel indicators(e.g.,relative height,slope of a correlation peak,and ratio of a sub peak to the main peak)are determined to conjointly evaluate the reliability of scene matching.The pro-posed method entails matching a real-time image with a reference image to generate a correlation surface.A correlation peak is then obtained by extracting the portion of the correlation surface exhibiting a significant gradient.Additionally,the matching reliability is determined by considering the relative height,slope,and ratio of the peak collectively.Exhaustive experimental results with two sets of data demonstrate that the proposed method significantly outperforms traditional approaches in terms of precision,recall,and F1-score.These experiments also establish the efficacy of the proposed method in achieving reliable matching in challenging environments characterized by repetitive and weak textures.This enhancement holds the potential to significantly elevate scene-matching-based navigation.展开更多
Intense human activities have greatly changed the flood generation conditions in most areas of the world, and have destroyed the consistency in the annual flood peak and volume series. For design flood estimation, coa...Intense human activities have greatly changed the flood generation conditions in most areas of the world, and have destroyed the consistency in the annual flood peak and volume series. For design flood estimation, coaxial correlation diagram and conceptual hydrological model are two frequently used tools to adjust and reconstruct the flood series under human disturbance. This study took a typical mountain catchment of the Haihe River Basin as an example to investigate the effects of human activities on flood regime and to compare and assess the two adjustment methods. The main purpose is to construct a conceptual hydrological model which can incorporate the effects of human activities. The results show that the coaxial correlation diagram is simple and widely-used, but can only adjust the time series of total flood volumes. Therefore, it is only applicable under certain conditions(e.g. There is a strong link between the flood peaks and volumes and the link is not significantly affected by human activities). The conceptual model is a powerful tool to adjust the time series of both flood peak flows and flood volumes over different durations provided that it is closely related to the catchment hydrological characteristics, specifically accounting for the effects of human activities, and incorporating expert knowledge when estimating or calibrating parameters. It is suggested that the two methods should be used together to cross check each other.展开更多
The code tracking loop is a key component for user positioning. The pseudorange information of Bei Dou B1 signals has been fused and changed for vector tracking, so a correlation output model for complex scenarios is ...The code tracking loop is a key component for user positioning. The pseudorange information of Bei Dou B1 signals has been fused and changed for vector tracking, so a correlation output model for complex scenarios is designed to prevent the propagation of error and valuate the signal performance. The relevant software and hardware factors that affect the output are analyzed.A single channel time-division multiplexing(TDM) method for multicorrelation data extraction is proposed. Statistical characteristics of the correlation output data for both vector and scalar structures are evaluated. Simulation results show that correlation outputs for both structures follow normal or Chi-squared distributions in normal conditions, and the Gamma distribution in harsh conditions. It is shown that a tracking model based on the multi-channel fusion hardly changes the probability distribution of the correlation output in the normal case, but it reduces the ranging error of the code loop, and hence the tracking ability of the code loop for weak signals is improved. Furthermore, vector tracking changes the pseudorange characteristics of channels anytime, and affects the mutual correlation outputs of the code loops in the abnormal case. This study provides a basis for the subsequent design of autonomous integrity algorithms for vector tracking.展开更多
Gamma-ray bursts (GRBs) are by far the most powerful explosions in the universe. Over the past two decades, several GRB energy and luminosity correlations were discovered for long gamma-ray bursts, which are bursts wh...Gamma-ray bursts (GRBs) are by far the most powerful explosions in the universe. Over the past two decades, several GRB energy and luminosity correlations were discovered for long gamma-ray bursts, which are bursts whose observed duration exceeds 2 seconds. One important correlation, the Amati relation, involves the observed peak energy, <em>E</em><sub><em>p,obs</em></sub>, in the <em>v</em>F<em><sub>v</sub></em> spectrum and the equivalent isotropic energy, <em>E</em><sub><em>iso</em></sub>. For many years, it was believed that the Amati correlation applied only to long GRBs. In this paper, we use a recent data sample that includes both long and short GRBs to re-examine the issue of whether the Amati correlation applies to long GRBs only. Our results indicate that although short bursts do not follow the Amati relation in the strict sense, they do exhibit a correlation between the intrinsic peak energy, <em>E</em><em><sub>p,i</sub></em>, and <em>E<sub>iso</sub></em> that is very similar to the Amati relation but with a different normalization and slope. The paper also discusses the physical interpretation of this correlation in the context of the internal shock model.展开更多
Gamma-ray bursts (GRBs) are the most intense and powerful explosions in the universe. Based on their observed duration, they are traditionally divided into long bursts whose observed duration equals or exceeds 2 s, an...Gamma-ray bursts (GRBs) are the most intense and powerful explosions in the universe. Based on their observed duration, they are traditionally divided into long bursts whose observed duration equals or exceeds 2 s, and short bursts whose observed duration is less than 2 s. Several GRB energy and luminosity correlations have been discovered for long gamma-ray bursts. Two important correlations are the Amati relation and the Yonetoku relation. The Amati relation is a correlation between the intrinsic peak energy, E<sub>p</sub><sub>,i</sub>, obtained from the νF<sub>ν</sub> spectrum and the equivalent isotropic energy, E<sub>iso</sub>, while the Yonetoku relation is a correlation between E<sub>p,i</sub> and the peak isotropic luminosity, L<sub>iso</sub>. In this paper, we use a recent data sample that includes both long and short GRBs to compare these two correlations for the two groups of bursts. We also compare the E<sub>iso</sub>-L<sub>iso</sub> plane for these two types of bursts. Our results indicate that both long and short bursts adhere to these two correlations but with different normalizations. We also find that the E<sub>iso</sub>-L<sub>iso</sub> plane is similar for both types of GRBs but is shifted to lower values of E<sub>iso</sub> for short GRBs.展开更多
基金supported by the National Natural Science Foundation of China (No.42271446).
文摘The navigation system plays a pivotal role in guiding aircraft along designated routes,ensuring precise and punctual arrival at destinations.The integration of scene matching with an inertial navigation system enhances the capability of providing a dependable guarantee for success-ful accomplishment of flight missions.Nonetheless,assuring reliability in scene matching encoun-ters significant challenges in areas characterized by repetitive or weak textures.To tackle these challenges,we propose a novel method to assess the reliability of scene matching based on the dis-tinctive characteristics of correlation peaks.The proposed method leverages the fact that the sim-ilarity of the optimal matching result is significantly higher than that of the surrounding area,and three novel indicators(e.g.,relative height,slope of a correlation peak,and ratio of a sub peak to the main peak)are determined to conjointly evaluate the reliability of scene matching.The pro-posed method entails matching a real-time image with a reference image to generate a correlation surface.A correlation peak is then obtained by extracting the portion of the correlation surface exhibiting a significant gradient.Additionally,the matching reliability is determined by considering the relative height,slope,and ratio of the peak collectively.Exhaustive experimental results with two sets of data demonstrate that the proposed method significantly outperforms traditional approaches in terms of precision,recall,and F1-score.These experiments also establish the efficacy of the proposed method in achieving reliable matching in challenging environments characterized by repetitive and weak textures.This enhancement holds the potential to significantly elevate scene-matching-based navigation.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41130639, 51179045, 41201028)the Nonprofit Industry Financial Program of MWR of China (201501022)
文摘Intense human activities have greatly changed the flood generation conditions in most areas of the world, and have destroyed the consistency in the annual flood peak and volume series. For design flood estimation, coaxial correlation diagram and conceptual hydrological model are two frequently used tools to adjust and reconstruct the flood series under human disturbance. This study took a typical mountain catchment of the Haihe River Basin as an example to investigate the effects of human activities on flood regime and to compare and assess the two adjustment methods. The main purpose is to construct a conceptual hydrological model which can incorporate the effects of human activities. The results show that the coaxial correlation diagram is simple and widely-used, but can only adjust the time series of total flood volumes. Therefore, it is only applicable under certain conditions(e.g. There is a strong link between the flood peaks and volumes and the link is not significantly affected by human activities). The conceptual model is a powerful tool to adjust the time series of both flood peak flows and flood volumes over different durations provided that it is closely related to the catchment hydrological characteristics, specifically accounting for the effects of human activities, and incorporating expert knowledge when estimating or calibrating parameters. It is suggested that the two methods should be used together to cross check each other.
基金supported by the National Natural Science Fundation of China(41474027)
文摘The code tracking loop is a key component for user positioning. The pseudorange information of Bei Dou B1 signals has been fused and changed for vector tracking, so a correlation output model for complex scenarios is designed to prevent the propagation of error and valuate the signal performance. The relevant software and hardware factors that affect the output are analyzed.A single channel time-division multiplexing(TDM) method for multicorrelation data extraction is proposed. Statistical characteristics of the correlation output data for both vector and scalar structures are evaluated. Simulation results show that correlation outputs for both structures follow normal or Chi-squared distributions in normal conditions, and the Gamma distribution in harsh conditions. It is shown that a tracking model based on the multi-channel fusion hardly changes the probability distribution of the correlation output in the normal case, but it reduces the ranging error of the code loop, and hence the tracking ability of the code loop for weak signals is improved. Furthermore, vector tracking changes the pseudorange characteristics of channels anytime, and affects the mutual correlation outputs of the code loops in the abnormal case. This study provides a basis for the subsequent design of autonomous integrity algorithms for vector tracking.
文摘Gamma-ray bursts (GRBs) are by far the most powerful explosions in the universe. Over the past two decades, several GRB energy and luminosity correlations were discovered for long gamma-ray bursts, which are bursts whose observed duration exceeds 2 seconds. One important correlation, the Amati relation, involves the observed peak energy, <em>E</em><sub><em>p,obs</em></sub>, in the <em>v</em>F<em><sub>v</sub></em> spectrum and the equivalent isotropic energy, <em>E</em><sub><em>iso</em></sub>. For many years, it was believed that the Amati correlation applied only to long GRBs. In this paper, we use a recent data sample that includes both long and short GRBs to re-examine the issue of whether the Amati correlation applies to long GRBs only. Our results indicate that although short bursts do not follow the Amati relation in the strict sense, they do exhibit a correlation between the intrinsic peak energy, <em>E</em><em><sub>p,i</sub></em>, and <em>E<sub>iso</sub></em> that is very similar to the Amati relation but with a different normalization and slope. The paper also discusses the physical interpretation of this correlation in the context of the internal shock model.
文摘Gamma-ray bursts (GRBs) are the most intense and powerful explosions in the universe. Based on their observed duration, they are traditionally divided into long bursts whose observed duration equals or exceeds 2 s, and short bursts whose observed duration is less than 2 s. Several GRB energy and luminosity correlations have been discovered for long gamma-ray bursts. Two important correlations are the Amati relation and the Yonetoku relation. The Amati relation is a correlation between the intrinsic peak energy, E<sub>p</sub><sub>,i</sub>, obtained from the νF<sub>ν</sub> spectrum and the equivalent isotropic energy, E<sub>iso</sub>, while the Yonetoku relation is a correlation between E<sub>p,i</sub> and the peak isotropic luminosity, L<sub>iso</sub>. In this paper, we use a recent data sample that includes both long and short GRBs to compare these two correlations for the two groups of bursts. We also compare the E<sub>iso</sub>-L<sub>iso</sub> plane for these two types of bursts. Our results indicate that both long and short bursts adhere to these two correlations but with different normalizations. We also find that the E<sub>iso</sub>-L<sub>iso</sub> plane is similar for both types of GRBs but is shifted to lower values of E<sub>iso</sub> for short GRBs.
