As an important tool for marine exploration, the autonomous underwater vehicle(AUV) must home in and dock at a docking station(DS) to be recharged, repaired, or to exchange information at set intervals. However, the c...As an important tool for marine exploration, the autonomous underwater vehicle(AUV) must home in and dock at a docking station(DS) to be recharged, repaired, or to exchange information at set intervals. However, the complex and hostile underwater environment makes this process challenging. This study proposes a real-time method based on polarized optical guidance for determining the position and attitude of the AUV relative to its DS. Four polarized artificial underwater landmarks are positioned at the DS, which are recognized by the AUV vision system. Compared with light intensity, the polarization of a light beam is known to be better maintained at greater propagation distances, especially in underwater environments. The proposed method, which is inspired by the ability of marine animals to communicate, calculates the pose parameters in less than 10 ms without any other navigational information. The simulation results reveal that the angle errors are small and the position errors are no more than 0.116 m within 100 m in the coastal ocean. The results of underwater experiments further demonstrate the feasibility of the proposed method, which extends the operating distance of the AUV beyond what is currently possible while maintaining the precision of traditional optical guidance.展开更多
在全球变暖的背景下,极端气候事件的频率和强度持续上升,给生态系统和社会经济发展带来了严峻挑战。与单一极端事件相比,复合干热事件(Compound Dry and Hot Events,CDHEs),即干旱和高温热浪的联合影响,成为对植被生态功能的重要威胁。...在全球变暖的背景下,极端气候事件的频率和强度持续上升,给生态系统和社会经济发展带来了严峻挑战。与单一极端事件相比,复合干热事件(Compound Dry and Hot Events,CDHEs),即干旱和高温热浪的联合影响,成为对植被生态功能的重要威胁。然而,植被对复合干热事件的抵抗和恢复响应及其驱动机制仍不明确。基于1982—2022年的ERA5-Land气候再分析数据、归一化植被指数(Normalized Difference Vegetation Index,NDVI)数据以及中国植被类型数据,利用标准化降水蒸散发指数(Standardized Precipitation and Evapotranspiration Index,SPEI)、标准化温度指数(Standardized Temperature Index,STI),结合Frank Copula函数构建复合干热指数(Standardized Compound Dry and Hot Index,SCDHI),研究中国复合干热事件的时空分布特征及其强度、严重度等基本特征,探讨了不同植被类型对复合干热事件的响应,重点分析了抵抗性和恢复性。通过计算驱动因子的贡献率,量化了各驱动因子对复合干热事件中的作用。研究结果显示:(1)复合干热事件在时空分布上表现出显著的区域性差异,华北、华中及西南地区由于降水分布不均、气温较高、湿度较低,易发生高强度且持续时间长的复合干热事件,而长江流域受季风调控,复合干热事件的严重度较高;从时间变化趋势来看,植被抵抗性和恢复性整体变化不显著,但部分区域生态韧性有所下降;(2)不同植被类型对复合干热事件响应差异显著。高山植被、沼泽、针叶林、阔叶林、针阔叶混交林和草甸的抵抗性较高(中位数均超过1.7);而栽培植被、草原、草丛和灌丛的抵抗性相对较低。灌丛、栽培植被、草甸、草原和草丛恢复性较高;针叶林、阔叶林、针阔叶混交林、高山植被以及沼泽的恢复性相对较低;(3)复合干热事件的驱动因子贡献率呈现阶段性和区域性差异:在抵抗阶段,主要降水和饱和水汽压影响,尤其是在华北、华中和西南地区;在恢复阶段,降水对植被恢复有较大影响,特别在华北和东北地区。研究结果为区域生态管理和适应性调控提供了科学依据。展开更多
基金supported by the National Natural Science Foundation of China (NSFC)(Nos. 51675076,51505062)the Science Fund for Creative Research Groups of NSFC (No. 51621064)the Pre-Research Foundation of China (No. 61405180102)。
文摘As an important tool for marine exploration, the autonomous underwater vehicle(AUV) must home in and dock at a docking station(DS) to be recharged, repaired, or to exchange information at set intervals. However, the complex and hostile underwater environment makes this process challenging. This study proposes a real-time method based on polarized optical guidance for determining the position and attitude of the AUV relative to its DS. Four polarized artificial underwater landmarks are positioned at the DS, which are recognized by the AUV vision system. Compared with light intensity, the polarization of a light beam is known to be better maintained at greater propagation distances, especially in underwater environments. The proposed method, which is inspired by the ability of marine animals to communicate, calculates the pose parameters in less than 10 ms without any other navigational information. The simulation results reveal that the angle errors are small and the position errors are no more than 0.116 m within 100 m in the coastal ocean. The results of underwater experiments further demonstrate the feasibility of the proposed method, which extends the operating distance of the AUV beyond what is currently possible while maintaining the precision of traditional optical guidance.
文摘在全球变暖的背景下,极端气候事件的频率和强度持续上升,给生态系统和社会经济发展带来了严峻挑战。与单一极端事件相比,复合干热事件(Compound Dry and Hot Events,CDHEs),即干旱和高温热浪的联合影响,成为对植被生态功能的重要威胁。然而,植被对复合干热事件的抵抗和恢复响应及其驱动机制仍不明确。基于1982—2022年的ERA5-Land气候再分析数据、归一化植被指数(Normalized Difference Vegetation Index,NDVI)数据以及中国植被类型数据,利用标准化降水蒸散发指数(Standardized Precipitation and Evapotranspiration Index,SPEI)、标准化温度指数(Standardized Temperature Index,STI),结合Frank Copula函数构建复合干热指数(Standardized Compound Dry and Hot Index,SCDHI),研究中国复合干热事件的时空分布特征及其强度、严重度等基本特征,探讨了不同植被类型对复合干热事件的响应,重点分析了抵抗性和恢复性。通过计算驱动因子的贡献率,量化了各驱动因子对复合干热事件中的作用。研究结果显示:(1)复合干热事件在时空分布上表现出显著的区域性差异,华北、华中及西南地区由于降水分布不均、气温较高、湿度较低,易发生高强度且持续时间长的复合干热事件,而长江流域受季风调控,复合干热事件的严重度较高;从时间变化趋势来看,植被抵抗性和恢复性整体变化不显著,但部分区域生态韧性有所下降;(2)不同植被类型对复合干热事件响应差异显著。高山植被、沼泽、针叶林、阔叶林、针阔叶混交林和草甸的抵抗性较高(中位数均超过1.7);而栽培植被、草原、草丛和灌丛的抵抗性相对较低。灌丛、栽培植被、草甸、草原和草丛恢复性较高;针叶林、阔叶林、针阔叶混交林、高山植被以及沼泽的恢复性相对较低;(3)复合干热事件的驱动因子贡献率呈现阶段性和区域性差异:在抵抗阶段,主要降水和饱和水汽压影响,尤其是在华北、华中和西南地区;在恢复阶段,降水对植被恢复有较大影响,特别在华北和东北地区。研究结果为区域生态管理和适应性调控提供了科学依据。
