垂线偏差数据对于提高惯性导航精度具有重要意义,阐述了使用重力场球谐模型计算水平重力扰动的方法,使用EGM2008重力场球谐模型计算水平重力扰动,并将其与美国国家地理空间情报局提供的全球2.5′×2.5′垂线偏差网格数据进行对比,...垂线偏差数据对于提高惯性导航精度具有重要意义,阐述了使用重力场球谐模型计算水平重力扰动的方法,使用EGM2008重力场球谐模型计算水平重力扰动,并将其与美国国家地理空间情报局提供的全球2.5′×2.5′垂线偏差网格数据进行对比,验证了所述水平重力扰动计算方法的正确性。将水平重力扰动计算结果用于航空、车载惯性导航数据离线处理,结果表明EGM2008模型计算的水平重力扰动可用于补偿惯性导航;将水平重力扰动计算结果用于长航时船载惯性导航数据离线处理,结果表明惯性导航精度最大提升1.5 n mile,平均提升0.8 n mile。展开更多
Seagrass ecosystems support high biodiversity and productivity and constitute critical links to adjacent ecosystems. However, there is a growing concern that increasing recreational navigation may affect its ecologica...Seagrass ecosystems support high biodiversity and productivity and constitute critical links to adjacent ecosystems. However, there is a growing concern that increasing recreational navigation may affect its ecological processes and functions, which may affect its recreational and tourism values, compromising local economies and livelihoods. The long-term impacts (1996-2011) of recreational navigation on seagrass benthic community structure were assessed by addressing the question of whether long-term effects of recreational navigation had a significant impact on seagrass community structure and on its benthic faunal assemblages. Findings evidenced: 1) a consistent spatio-temporal gradient in the ecological conditions of seagrasses across the scoured areas, with increased percent seagrass cover, density and canopy height, and seagrass benthic biodiversity with increasing distance from disturbed areas;2) a decline in percent seagrass cover, and an increased macroalgal and cyanobacterial percent cover through time around the disturbed areas;3) a significant shift in seagrass assemblage biodiversity as a response to boating that followed the intermediate disturbance hypothesis;4) an adverse effect on the spatial distribution and survival of multiple benthic invertebrate taxa;and 5) a significant decline in cnidarians, echinoids, ophiuroids, holothurians, and gastropods, and an increase in polychaetes, platyhelminths, and hermit crabs, particularly in areas exposed to boating. Spatio-temporal variation in seagrass community structure explained the observed variation in benthic faunal assemblages. The long-term consequences on ecosystem functions and management needs are discussed to foster the conservation of seagrasses.展开更多
The normal gravity model of a hypersonic boost-glide vehicle in near space is studied in this paper with the aim of alleviating the influence of the gravity model error on the precision of the inertial navigation syst...The normal gravity model of a hypersonic boost-glide vehicle in near space is studied in this paper with the aim of alleviating the influence of the gravity model error on the precision of the inertial navigation system(INS)during flight.First,a spherical harmonic model of the Earth’s gravitational field is introduced and the normal gravity of the Earth is derived from it.Then,the coordinate transformation needed for the application of the gravity model to the near-space navigation algorithm is formulated.Subsequently,the gravity disturbance in near space and the impact of J_(2)and J_(4)gravity truncation errors are analyzed.Finally,different normal gravity models and different precisions of inertial measurement unit(IMU)are exploited to simulate the near-space navigation algorithm.Based on this,the influence of the independent and combined effects caused by the interference factors is analyzed,and the applicable conditions of the normal gravity model are discussed.展开更多
针对重力扰动引起惯性水平基准姿态测量误差进而导致天文/惯性组合导航系统定位精度下降的问题,提出天文/惯性组合系统中的重力扰动补偿方法。首先,基于导航误差模型分析了影响天文/惯性组合导航系统定位精度的主要因素。其次,推导了重...针对重力扰动引起惯性水平基准姿态测量误差进而导致天文/惯性组合导航系统定位精度下降的问题,提出天文/惯性组合系统中的重力扰动补偿方法。首先,基于导航误差模型分析了影响天文/惯性组合导航系统定位精度的主要因素。其次,推导了重力扰动、惯性水平基准姿态测量误差与天文导航定位误差之间的传播机理。然后,研究了重力扰动建模与修正方法,并将重力扰动补偿方法应用于惯性水平基准的导航解算回路中,实现重力扰动的有效补偿。跑车试验结果表明,所提重力扰动补偿方法可以将天文/惯性组合导航系统中定位误差的振荡幅值由1.6 n mile降低至0.5 n mile。展开更多
文摘垂线偏差数据对于提高惯性导航精度具有重要意义,阐述了使用重力场球谐模型计算水平重力扰动的方法,使用EGM2008重力场球谐模型计算水平重力扰动,并将其与美国国家地理空间情报局提供的全球2.5′×2.5′垂线偏差网格数据进行对比,验证了所述水平重力扰动计算方法的正确性。将水平重力扰动计算结果用于航空、车载惯性导航数据离线处理,结果表明EGM2008模型计算的水平重力扰动可用于补偿惯性导航;将水平重力扰动计算结果用于长航时船载惯性导航数据离线处理,结果表明惯性导航精度最大提升1.5 n mile,平均提升0.8 n mile。
文摘Seagrass ecosystems support high biodiversity and productivity and constitute critical links to adjacent ecosystems. However, there is a growing concern that increasing recreational navigation may affect its ecological processes and functions, which may affect its recreational and tourism values, compromising local economies and livelihoods. The long-term impacts (1996-2011) of recreational navigation on seagrass benthic community structure were assessed by addressing the question of whether long-term effects of recreational navigation had a significant impact on seagrass community structure and on its benthic faunal assemblages. Findings evidenced: 1) a consistent spatio-temporal gradient in the ecological conditions of seagrasses across the scoured areas, with increased percent seagrass cover, density and canopy height, and seagrass benthic biodiversity with increasing distance from disturbed areas;2) a decline in percent seagrass cover, and an increased macroalgal and cyanobacterial percent cover through time around the disturbed areas;3) a significant shift in seagrass assemblage biodiversity as a response to boating that followed the intermediate disturbance hypothesis;4) an adverse effect on the spatial distribution and survival of multiple benthic invertebrate taxa;and 5) a significant decline in cnidarians, echinoids, ophiuroids, holothurians, and gastropods, and an increase in polychaetes, platyhelminths, and hermit crabs, particularly in areas exposed to boating. Spatio-temporal variation in seagrass community structure explained the observed variation in benthic faunal assemblages. The long-term consequences on ecosystem functions and management needs are discussed to foster the conservation of seagrasses.
文摘The normal gravity model of a hypersonic boost-glide vehicle in near space is studied in this paper with the aim of alleviating the influence of the gravity model error on the precision of the inertial navigation system(INS)during flight.First,a spherical harmonic model of the Earth’s gravitational field is introduced and the normal gravity of the Earth is derived from it.Then,the coordinate transformation needed for the application of the gravity model to the near-space navigation algorithm is formulated.Subsequently,the gravity disturbance in near space and the impact of J_(2)and J_(4)gravity truncation errors are analyzed.Finally,different normal gravity models and different precisions of inertial measurement unit(IMU)are exploited to simulate the near-space navigation algorithm.Based on this,the influence of the independent and combined effects caused by the interference factors is analyzed,and the applicable conditions of the normal gravity model are discussed.
文摘针对重力扰动引起惯性水平基准姿态测量误差进而导致天文/惯性组合导航系统定位精度下降的问题,提出天文/惯性组合系统中的重力扰动补偿方法。首先,基于导航误差模型分析了影响天文/惯性组合导航系统定位精度的主要因素。其次,推导了重力扰动、惯性水平基准姿态测量误差与天文导航定位误差之间的传播机理。然后,研究了重力扰动建模与修正方法,并将重力扰动补偿方法应用于惯性水平基准的导航解算回路中,实现重力扰动的有效补偿。跑车试验结果表明,所提重力扰动补偿方法可以将天文/惯性组合导航系统中定位误差的振荡幅值由1.6 n mile降低至0.5 n mile。
