To accurately estimate winter wheat yields and analyze the uncertainty in crop model data assimilations, winter wheat yield estimates were obtained by assimilating measured or remotely sensed leaf area index （LAI） v...To accurately estimate winter wheat yields and analyze the uncertainty in crop model data assimilations, winter wheat yield estimates were obtained by assimilating measured or remotely sensed leaf area index （LAI） values. The performances of the calibrated crop environment resource synthesis for wheat （CERES-Wheat） model for two different assimilation scenarios were compared by employing ensemble Kalman filter （EnKF）-based strategies. The uncertainty factors of the crop model data assimilation was analyzed by considering the observation errors, assimilation stages and temporal-spatial scales. Overalll the results indicated a better yield estimate performance when the EnKF-based strategy was used to comprehen- sively consider several factors in the initial conditions and observations. When using this strategy, an adjusted coefficients of determination （R2） of 0.84, a root mean square error （RMSE） of 323 kg ha-1, and a relative errors （RE） of 4.15% were obtained at the field plot scale and an R2 of 0.81, an RMSE of 362 kg ha-1, and an RE of 4.52% were obtained at the pixel scale of 30 mx30 m. With increasing observation errors, the accuracy of the yield estimates obviously decreased, but an acceptable estimate was observed when the observation errors were within 20%. Winter wheat yield estimates could be improved significantly by assimilating observations from the middle to the end of the crop growing seasons. With decreasing assimilation frequency and pixel resolution, the accuracy of the crop yield estimates decreased; however, the computation time decreased. It is important to consider reasonable temporal-spatial scales and assimilation stages to obtain tradeoffs between accuracy and computation time, especially in operational systems used for regional crop yield estimates.展开更多
Numerical diffusion or filter are used in most numerical models in order to eliminate small-scale (near two-grid intervals in wavelength) waves, However, conventional diffusion or filter schemes introduce the noise, a...Numerical diffusion or filter are used in most numerical models in order to eliminate small-scale (near two-grid intervals in wavelength) waves, However, conventional diffusion or filter schemes introduce the noise, and indeed few people realized, by filters themselves. For instance, most filters are troubled when they are put to use on meteorological fields with sharp gradient or with steep slope and consequently, the recurrence of undesirable numerical high-frequent oscillations (overshooting and undershooting) seems to be inevitable, Particularly when diffusion or filter is implemented in limited-area models, serious side effects on the limited-area boundaries often contaminate the modeling results. The merits and demerits are surveyed for commonly used diffusion or filter operations. A new type of monotonic digit filter is suggested to prevent overshooting and undershooting (due to the computational shock and Gibbs oscillation) nearby the discontinuous or nearly discontinuous locations when the filtering process was carried out, meanwhile the high selective property of damping is retained. Moreover, the new filter is designed on the implicit framework so that it can easily handle the problem of boundary diminishing in limited-area modeling.展开更多
The degree of dietary specialization has a fundamental impact on the ecological function and interactions of suspension feeders.While niche differentiation by food particle size is common among obligate suspension fee...The degree of dietary specialization has a fundamental impact on the ecological function and interactions of suspension feeders.While niche differentiation by food particle size is common among obligate suspension feeders,its role is not evident in facultative ones.In this study,we aimed at providing new insights on the matter by focusing on sympatric mysid species.As mysids use different mechanisms for raptorial and filter-feeding,they represent a more adequate model system than for example,the more extensively studied copepods.We made morpholog-ical measurements on the 4 coexisting invasive Ponto-Caspian mysid species to determine the areas and mesh sizes of their filters.We also quantified their clearance rates on the microalga Cryptomonas sp.in a laboratory experiment to reveal how morphological differences manifest in their overall filtering capacity.We found relatively small but consistent differences in the primary filter area among the species,indicating that morphological constraints due to the enclosed position of the setae might limit the possibility for differentiation.The primary filter mesh sizes were small in all 4 species(0.69-2.73μm)with moderate but consistent intraspecific differences,suggesting that the benefit of being able to capture small particles might outweigh the pressure for differentiation.The observed clearance rates were in accordance with the morphological characteristics of the species,highlighting that auxiliary filters(present in one of the species,Limnomysis benedeni)are needed to increase filtering capacity considerably.Our study confirmed that food particle size can contribute to the niche differentiation of facultative filter feeders,but also indicated that they can tolerate a higher overlap than obligate ones.The observed differences were related to the habitat preferences and predatory potentials of the species,suggesting that complementarity among the different niche axes might further facilitate theircoexistence.展开更多
When adaptive robust control（ARC） strategy based on backstepping design is applied in pneumatic servo control, accurate pressure tracking in motion is especially necessary for both force and position trajectories tr...When adaptive robust control（ARC） strategy based on backstepping design is applied in pneumatic servo control, accurate pressure tracking in motion is especially necessary for both force and position trajectories tracking ofrodless pneumatic cylinders, and therefore an adaptive robust pressure controller is developed in this paper to improve the tracking accuracy of pressure trajectory in the chamber when the pneumatic cylinder is moving. In the proposed adaptive robust pressure controller, off-line fitting of the orifice area and on-line parameter estimation of the flow coefficient are utilized to have improved model compensation, and meanwhile robust feedback and Kalman filter are used to have strong robustness against uncertain nonlinearities, parameter fluctuations and noise. Research results demonstrate that the adaptive robust pressure controller could not only track various pressure trajectories accurately even when the pneumatic cylinder is moving, but also obtain very smooth control input, which indicates the effectiveness of adaptive model compensation. Especially when a step pressure trajectory is tracked under the condition of the movement of a rodless pneumatic cylinder, maximum tracking error of ARC is 4.46 kPa and average tracking error is 0.99 kPa, and steady-state error of ARC could achieve 0.84 kPa, which is very close to the measurement accuracy of pressure transducer.展开更多
Data assimilation in agricultural remote sensing research is of great significance to integrate with remote sensing observations and model simulations for parameters estimation. The present investigation not only desi...Data assimilation in agricultural remote sensing research is of great significance to integrate with remote sensing observations and model simulations for parameters estimation. The present investigation not only designed and realized the Ensemble Kalman Filtering algorithm （EnKF） assimilation by combing the crop growth model （CERES-Wheat） with remote sensing data, but also optimized and updated the key parameters （LAI） of winter wheat by using remote sensing data. Results showed that the assimilation LAI and the observation ones agreed with each other, and the R2 reached 0.8315. So assimilation remote sensing and crop model could provide reference data for the agricultural production.展开更多
The NW part of Iran belongs to the Iranian plateau that is a tectonically active region within the Alpine-Himalayan orogenic belt. The intrusion of Oligocene parts in various faces caused the alteration and mineraliza...The NW part of Iran belongs to the Iranian plateau that is a tectonically active region within the Alpine-Himalayan orogenic belt. The intrusion of Oligocene parts in various faces caused the alteration and mineralization such as copper, molybdenum, gold and iron in the Siyahrood area. Granitoidic rocks with component of Granodiorite to alkali have been influenced by hydrothermal fluids. Alteration zones are important features for the exploration of deposits and the ASTER sensor is able to identify the type of alteration and its alteration zoning. This method can be a useful tool for detecting potential mineralization area in East Azarbaijan—Northwest of Iran. The purpose of this study is to evaluate ASTER data for mapping altered minerals in Siyahrood area in order to detect the potential mineralized areas. In this study, false color composite, and band ratio techniques were applied on ASTER data and argillic, phyllic, Iron oxide and propylitic alteration zones were separated. ASAR image processing has been used for lineaments and faults identified by the aid of directional filter. The structural study focused on fracture zones and their characteristics including strike, length, and relationship with alteration zones. The results of this study demonstrate the usefulness of remote sensing methods and ASTER multi-spectral data for alteration, and ASAR data are useful for lineament mapping.展开更多
In order to meet the application requirements of autonomous vehicles, this paper proposes a simultaneous localization and mapping （SLAM） algorithm, which uses a VoxelGrid filter to down sample the point cloud data, ...In order to meet the application requirements of autonomous vehicles, this paper proposes a simultaneous localization and mapping （SLAM） algorithm, which uses a VoxelGrid filter to down sample the point cloud data, with the combination of iterative closest points （ICP） algorithm and Gaussian model for particles updating, the matching between the local map and the global map to quantify particles＇ importance weight. The crude estimation by using ICP algorithm can find the high probability area of autonomous vehicles＇ poses, which would decrease particle numbers, increase algorithm speed and restrain particles＇ impoverishment. The calculation of particles＇ importance weight based on matching of attribute between grid maps is simple and practicable. Experiments carried out with the autonomous vehicle platform validate the effectiveness of our approaches.展开更多
机载激光雷达(Light Detection and Ranging,LiDAR)技术为矿区面状沉陷监测提供了高精度的三维空间数据支持。然而,在矿区复杂场景中,地物空间分布密集、地形梯度突变以及地物与地面点高程特征相似性高等问题,导致现有点云滤波方法精度...机载激光雷达(Light Detection and Ranging,LiDAR)技术为矿区面状沉陷监测提供了高精度的三维空间数据支持。然而,在矿区复杂场景中,地物空间分布密集、地形梯度突变以及地物与地面点高程特征相似性高等问题,导致现有点云滤波方法精度显著降低,严重制约了地面点云的提取精度与沉陷监测可靠性。为此,提出了一种基于弯曲能量优化的矿区机载LiDAR点云自适应滤波方法,实现了复杂矿区场景下地面点的精确提取,为矿区面状沉陷监测提供高精度的三维空间数据支持。首先,采用一维离散平滑样条法提取潜在种子地面点,并基于多尺度形态学开运算剔除潜在种子地面点中残留的非地面点;其次,基于地形弯曲能量与回弹比之间的定量关系,构建一种自适应复杂地形的布料刚度调节方法,动态生成高精度参考地形;最后,通过点至参考地形的高差阈值判定,完成地面点与非地面点的分离。为验证方法的有效性,在复杂矿区开展了多场景试验,结果表明:在Ⅰ类误差和Ⅱ类误差指标上,所提出的方法较现有方法的误差显著降低,平均总误差为6.08%,较现有方法降低了49.04%。该方法成功解决了复杂矿区场景下地面点云的高精度提取难题,为矿区面状沉陷监测、边坡稳定性分析等安全监测任务提供了可靠的数据支持,并为空天地一体化的矿山安全智能监测体系的构建提供了技术支撑。展开更多
基金supported by the National Natural Science Foundation of China (41401491,41371396,41301457,41471364)the Introduction of International Advanced Agricultural Science and Technology,Ministry of Agriculture,China (948 Program,2016-X38)+1 种基金the Agricultural Scientific Research Fund of Outstanding Talentsthe Open Fund for the Key Laboratory of Agri-informatics,Ministry of Agriculture,China (2013009)
文摘To accurately estimate winter wheat yields and analyze the uncertainty in crop model data assimilations, winter wheat yield estimates were obtained by assimilating measured or remotely sensed leaf area index （LAI） values. The performances of the calibrated crop environment resource synthesis for wheat （CERES-Wheat） model for two different assimilation scenarios were compared by employing ensemble Kalman filter （EnKF）-based strategies. The uncertainty factors of the crop model data assimilation was analyzed by considering the observation errors, assimilation stages and temporal-spatial scales. Overalll the results indicated a better yield estimate performance when the EnKF-based strategy was used to comprehen- sively consider several factors in the initial conditions and observations. When using this strategy, an adjusted coefficients of determination （R2） of 0.84, a root mean square error （RMSE） of 323 kg ha-1, and a relative errors （RE） of 4.15% were obtained at the field plot scale and an R2 of 0.81, an RMSE of 362 kg ha-1, and an RE of 4.52% were obtained at the pixel scale of 30 mx30 m. With increasing observation errors, the accuracy of the yield estimates obviously decreased, but an acceptable estimate was observed when the observation errors were within 20%. Winter wheat yield estimates could be improved significantly by assimilating observations from the middle to the end of the crop growing seasons. With decreasing assimilation frequency and pixel resolution, the accuracy of the crop yield estimates decreased; however, the computation time decreased. It is important to consider reasonable temporal-spatial scales and assimilation stages to obtain tradeoffs between accuracy and computation time, especially in operational systems used for regional crop yield estimates.
基金the Project of Natural Science Foundation of Jiangsu Province, BK99020 and the "973' Project of "CHERES" Gl998040907 the Natio
文摘Numerical diffusion or filter are used in most numerical models in order to eliminate small-scale (near two-grid intervals in wavelength) waves, However, conventional diffusion or filter schemes introduce the noise, and indeed few people realized, by filters themselves. For instance, most filters are troubled when they are put to use on meteorological fields with sharp gradient or with steep slope and consequently, the recurrence of undesirable numerical high-frequent oscillations (overshooting and undershooting) seems to be inevitable, Particularly when diffusion or filter is implemented in limited-area models, serious side effects on the limited-area boundaries often contaminate the modeling results. The merits and demerits are surveyed for commonly used diffusion or filter operations. A new type of monotonic digit filter is suggested to prevent overshooting and undershooting (due to the computational shock and Gibbs oscillation) nearby the discontinuous or nearly discontinuous locations when the filtering process was carried out, meanwhile the high selective property of damping is retained. Moreover, the new filter is designed on the implicit framework so that it can easily handle the problem of boundary diminishing in limited-area modeling.
基金The authors thank Peter Dobosy,Adam Egri,Bence Gergacz,Eszter Laczkovszki,Sarah Lecoq,Nicolas Malinge,and Karoly Palffy for their assistance in various phases of the research.Project no.132605 has been implemented with the support provided from the National ResearchDevelopment and Innovation Fund of Hungary,financed under the FK_19 funding scheme.VR acknowledges further support by the NKFIH-138215project.
文摘The degree of dietary specialization has a fundamental impact on the ecological function and interactions of suspension feeders.While niche differentiation by food particle size is common among obligate suspension feeders,its role is not evident in facultative ones.In this study,we aimed at providing new insights on the matter by focusing on sympatric mysid species.As mysids use different mechanisms for raptorial and filter-feeding,they represent a more adequate model system than for example,the more extensively studied copepods.We made morpholog-ical measurements on the 4 coexisting invasive Ponto-Caspian mysid species to determine the areas and mesh sizes of their filters.We also quantified their clearance rates on the microalga Cryptomonas sp.in a laboratory experiment to reveal how morphological differences manifest in their overall filtering capacity.We found relatively small but consistent differences in the primary filter area among the species,indicating that morphological constraints due to the enclosed position of the setae might limit the possibility for differentiation.The primary filter mesh sizes were small in all 4 species(0.69-2.73μm)with moderate but consistent intraspecific differences,suggesting that the benefit of being able to capture small particles might outweigh the pressure for differentiation.The observed clearance rates were in accordance with the morphological characteristics of the species,highlighting that auxiliary filters(present in one of the species,Limnomysis benedeni)are needed to increase filtering capacity considerably.Our study confirmed that food particle size can contribute to the niche differentiation of facultative filter feeders,but also indicated that they can tolerate a higher overlap than obligate ones.The observed differences were related to the habitat preferences and predatory potentials of the species,suggesting that complementarity among the different niche axes might further facilitate theircoexistence.
基金supported by National Natural Science Foundation of China (Grant No. 50775200)
文摘When adaptive robust control（ARC） strategy based on backstepping design is applied in pneumatic servo control, accurate pressure tracking in motion is especially necessary for both force and position trajectories tracking ofrodless pneumatic cylinders, and therefore an adaptive robust pressure controller is developed in this paper to improve the tracking accuracy of pressure trajectory in the chamber when the pneumatic cylinder is moving. In the proposed adaptive robust pressure controller, off-line fitting of the orifice area and on-line parameter estimation of the flow coefficient are utilized to have improved model compensation, and meanwhile robust feedback and Kalman filter are used to have strong robustness against uncertain nonlinearities, parameter fluctuations and noise. Research results demonstrate that the adaptive robust pressure controller could not only track various pressure trajectories accurately even when the pneumatic cylinder is moving, but also obtain very smooth control input, which indicates the effectiveness of adaptive model compensation. Especially when a step pressure trajectory is tracked under the condition of the movement of a rodless pneumatic cylinder, maximum tracking error of ARC is 4.46 kPa and average tracking error is 0.99 kPa, and steady-state error of ARC could achieve 0.84 kPa, which is very close to the measurement accuracy of pressure transducer.
基金supported by the National Natural Science Foundation of China (40701120)the Beijing Natural Science Foundation, China (4092016)the Beijing Nova, China (2008B33)
文摘Data assimilation in agricultural remote sensing research is of great significance to integrate with remote sensing observations and model simulations for parameters estimation. The present investigation not only designed and realized the Ensemble Kalman Filtering algorithm （EnKF） assimilation by combing the crop growth model （CERES-Wheat） with remote sensing data, but also optimized and updated the key parameters （LAI） of winter wheat by using remote sensing data. Results showed that the assimilation LAI and the observation ones agreed with each other, and the R2 reached 0.8315. So assimilation remote sensing and crop model could provide reference data for the agricultural production.
文摘The NW part of Iran belongs to the Iranian plateau that is a tectonically active region within the Alpine-Himalayan orogenic belt. The intrusion of Oligocene parts in various faces caused the alteration and mineralization such as copper, molybdenum, gold and iron in the Siyahrood area. Granitoidic rocks with component of Granodiorite to alkali have been influenced by hydrothermal fluids. Alteration zones are important features for the exploration of deposits and the ASTER sensor is able to identify the type of alteration and its alteration zoning. This method can be a useful tool for detecting potential mineralization area in East Azarbaijan—Northwest of Iran. The purpose of this study is to evaluate ASTER data for mapping altered minerals in Siyahrood area in order to detect the potential mineralized areas. In this study, false color composite, and band ratio techniques were applied on ASTER data and argillic, phyllic, Iron oxide and propylitic alteration zones were separated. ASAR image processing has been used for lineaments and faults identified by the aid of directional filter. The structural study focused on fracture zones and their characteristics including strike, length, and relationship with alteration zones. The results of this study demonstrate the usefulness of remote sensing methods and ASTER multi-spectral data for alteration, and ASAR data are useful for lineament mapping.
基金Supported by the Major Research Plan of the National Natural Science Foundation of China(91120003)Surface Project of the National Natural Science Foundation of China(61173076)
文摘In order to meet the application requirements of autonomous vehicles, this paper proposes a simultaneous localization and mapping （SLAM） algorithm, which uses a VoxelGrid filter to down sample the point cloud data, with the combination of iterative closest points （ICP） algorithm and Gaussian model for particles updating, the matching between the local map and the global map to quantify particles＇ importance weight. The crude estimation by using ICP algorithm can find the high probability area of autonomous vehicles＇ poses, which would decrease particle numbers, increase algorithm speed and restrain particles＇ impoverishment. The calculation of particles＇ importance weight based on matching of attribute between grid maps is simple and practicable. Experiments carried out with the autonomous vehicle platform validate the effectiveness of our approaches.
文摘机载激光雷达(Light Detection and Ranging,LiDAR)技术为矿区面状沉陷监测提供了高精度的三维空间数据支持。然而,在矿区复杂场景中,地物空间分布密集、地形梯度突变以及地物与地面点高程特征相似性高等问题,导致现有点云滤波方法精度显著降低,严重制约了地面点云的提取精度与沉陷监测可靠性。为此,提出了一种基于弯曲能量优化的矿区机载LiDAR点云自适应滤波方法,实现了复杂矿区场景下地面点的精确提取,为矿区面状沉陷监测提供高精度的三维空间数据支持。首先,采用一维离散平滑样条法提取潜在种子地面点,并基于多尺度形态学开运算剔除潜在种子地面点中残留的非地面点;其次,基于地形弯曲能量与回弹比之间的定量关系,构建一种自适应复杂地形的布料刚度调节方法,动态生成高精度参考地形;最后,通过点至参考地形的高差阈值判定,完成地面点与非地面点的分离。为验证方法的有效性,在复杂矿区开展了多场景试验,结果表明:在Ⅰ类误差和Ⅱ类误差指标上,所提出的方法较现有方法的误差显著降低,平均总误差为6.08%,较现有方法降低了49.04%。该方法成功解决了复杂矿区场景下地面点云的高精度提取难题,为矿区面状沉陷监测、边坡稳定性分析等安全监测任务提供了可靠的数据支持,并为空天地一体化的矿山安全智能监测体系的构建提供了技术支撑。
