[ Objective] The study aimed to correct error of lightning location data with small amplitude. [ Method] Using the curve fitting toolbox of matlab mathematical software, the distribution of lightning location data in ...[ Objective] The study aimed to correct error of lightning location data with small amplitude. [ Method] Using the curve fitting toolbox of matlab mathematical software, the distribution of lightning location data in Chongqing during 1999 -2008 was fitted based on logarithmic normal distribution function, and the specific characters of lightning data with current amplitude from -10 to 10 kA were analyzed. [ Result] During 1999 - 2008, the frequency of lightning with current amplitude from -10 to 10 kA in Chongqing City accounted for 4.93% of total frequency, while the fre- quency of lightning with current amplitude from -5 to 5 kA accounted for only 1.27%, lower than 2%, according with the conventional deletion proportion in China. Lightning data with current amplitude from -5 to 5 kA caused a great disturbance to the fitting effect, so the fitting effect was the best after these lightning data was deleted. After the lightning location system of Chongqing City was upgraded in 2005, the frequency of lightning with current amplitude from -10 to 10 kA decreased, and there were obvious changes in the frequency of lightning with current amplitude from -10 to -5 kA and from 5 to 10 kA, while the frequency of lightning with current amplitude from -5 to 5 kA was small and stable, so these data could be deleted. [Conclusion] The research could provide theoretical references for error correction of lightning location data with small amplitude in Chongqing City.展开更多
In this paper,a parametric method of site error estimation is developed for a lightning location system (LLS) which consists of three or more direction finders (DFs) and one position analyzer (PA). The site error for ...In this paper,a parametric method of site error estimation is developed for a lightning location system (LLS) which consists of three or more direction finders (DFs) and one position analyzer (PA). The site error for each DF is a function of bearings measured by the DF, and is assumed to be limited-term harmonics. The problem of site error estimation is reduced to a non-linear unconstrained minimization problem by employing the eigen technique (Orville Jr., 1987). The site error can be found directly by minimizing the objective function. By using the data set obtained with the LLS of three DFs in Beijing area during the summer of 1988, the site error correction curves for all DFs were found. About 4900 lightning flashes detected by the three DFs were used. The results showed that about 95% of the flash residuals of the sample were within ± 1 degree after corrections. The lightning locations with site error corrections were more consistent with the corresponding radar echoes than those without corrections.展开更多
Subpixel centroid estimation is the most important star image location method of star tracker. This paper presents a theoretical analysis of the systematic error of subpixel centroid estimation algorithm utilizing fre...Subpixel centroid estimation is the most important star image location method of star tracker. This paper presents a theoretical analysis of the systematic error of subpixel centroid estimation algorithm utilizing frequency domain analysis under the con-sideration of sampling frequency limitation and sampling window limitation. Explicit expression of systematic error of cen-troid estimation is obtained, and the dependence of systematic error on Gaussian width of star image, actual star centroid loca-tion and the number of sampling pixels is derived. A systematic error compensation algorithm for star centroid estimation is proposed based on the result of theoretical analysis. Simulation results show that after compensation, the residual systematic errors of 3-pixel-and 5-pixel-windows’ centroid estimation are less than 2×10-3 pixels and 2×10-4 pixels respectively.展开更多
Abstract： In the case of Chang EⅢ high-speed flight, to ensure accurate lunar soit landing in a predetermined area, the key issue is the landing track and control strategy design. As we all know, the landing prcess ...Abstract： In the case of Chang EⅢ high-speed flight, to ensure accurate lunar soit landing in a predetermined area, the key issue is the landing track and control strategy design. As we all know, the landing prcess e need to meet the requirements of the key point＇ s conditions, as well as minimize fuel consumption. Hence,it is of great important to find Perilune and Apolune points. Based on energy conservation and Kepler＇ s second law, we can find Perilune and Apolune points and figure out their speeds respectively. We also can calculate the location of the landing site by the conditions of minimum fuel consumption. To achieve the least energy-consuming, Chang E Ⅲ must reach above the intentended landing spot at the end of the quick-adjust stage. As a result, you can use the main constraints and optimize fuel consumption using the genetic algorithm at the attempt to calculate horizontal displacement.展开更多
基金the Special Project for Public Welfare Industry(GYHY200806014)
文摘[ Objective] The study aimed to correct error of lightning location data with small amplitude. [ Method] Using the curve fitting toolbox of matlab mathematical software, the distribution of lightning location data in Chongqing during 1999 -2008 was fitted based on logarithmic normal distribution function, and the specific characters of lightning data with current amplitude from -10 to 10 kA were analyzed. [ Result] During 1999 - 2008, the frequency of lightning with current amplitude from -10 to 10 kA in Chongqing City accounted for 4.93% of total frequency, while the fre- quency of lightning with current amplitude from -5 to 5 kA accounted for only 1.27%, lower than 2%, according with the conventional deletion proportion in China. Lightning data with current amplitude from -5 to 5 kA caused a great disturbance to the fitting effect, so the fitting effect was the best after these lightning data was deleted. After the lightning location system of Chongqing City was upgraded in 2005, the frequency of lightning with current amplitude from -10 to 10 kA decreased, and there were obvious changes in the frequency of lightning with current amplitude from -10 to -5 kA and from 5 to 10 kA, while the frequency of lightning with current amplitude from -5 to 5 kA was small and stable, so these data could be deleted. [Conclusion] The research could provide theoretical references for error correction of lightning location data with small amplitude in Chongqing City.
文摘In this paper,a parametric method of site error estimation is developed for a lightning location system (LLS) which consists of three or more direction finders (DFs) and one position analyzer (PA). The site error for each DF is a function of bearings measured by the DF, and is assumed to be limited-term harmonics. The problem of site error estimation is reduced to a non-linear unconstrained minimization problem by employing the eigen technique (Orville Jr., 1987). The site error can be found directly by minimizing the objective function. By using the data set obtained with the LLS of three DFs in Beijing area during the summer of 1988, the site error correction curves for all DFs were found. About 4900 lightning flashes detected by the three DFs were used. The results showed that about 95% of the flash residuals of the sample were within ± 1 degree after corrections. The lightning locations with site error corrections were more consistent with the corresponding radar echoes than those without corrections.
文摘Subpixel centroid estimation is the most important star image location method of star tracker. This paper presents a theoretical analysis of the systematic error of subpixel centroid estimation algorithm utilizing frequency domain analysis under the con-sideration of sampling frequency limitation and sampling window limitation. Explicit expression of systematic error of cen-troid estimation is obtained, and the dependence of systematic error on Gaussian width of star image, actual star centroid loca-tion and the number of sampling pixels is derived. A systematic error compensation algorithm for star centroid estimation is proposed based on the result of theoretical analysis. Simulation results show that after compensation, the residual systematic errors of 3-pixel-and 5-pixel-windows’ centroid estimation are less than 2×10-3 pixels and 2×10-4 pixels respectively.
文摘Abstract： In the case of Chang EⅢ high-speed flight, to ensure accurate lunar soit landing in a predetermined area, the key issue is the landing track and control strategy design. As we all know, the landing prcess e need to meet the requirements of the key point＇ s conditions, as well as minimize fuel consumption. Hence,it is of great important to find Perilune and Apolune points. Based on energy conservation and Kepler＇ s second law, we can find Perilune and Apolune points and figure out their speeds respectively. We also can calculate the location of the landing site by the conditions of minimum fuel consumption. To achieve the least energy-consuming, Chang E Ⅲ must reach above the intentended landing spot at the end of the quick-adjust stage. As a result, you can use the main constraints and optimize fuel consumption using the genetic algorithm at the attempt to calculate horizontal displacement.
