Global analysis of time-lag and -accumulation effects of climate on vegetation growth

Climate dominantly controls vegetation over most regions at most times, and vegetation responses to climate change are often asymmetric with temporal effects. However, systematic analysis of the time-lag and time-accumulation effects of climate on vegetation growth, has rarely been conducted, in particular for different vegetation growing phases. Thus, this study aimed to leverage normalized difference vegetation index (NDVI) to determine the spatiotemporal patterns of climatic effects on global vegetation growth considering various scenarios of time-lag and/or accumulation effects. The results showed that (i) climatic factors have time-lag and -accumulation effects as well as their combined effects on global vegetation growth for the whole growing season and its subphases (i.e., the growing and senescent phases). However, these effects vary with climatic factors, vegetation types, and regions. Compared with those of temperature, both precipitation and solar radiation display more significant time-accumulation effects in the whole growing season worldwide, but behave differently in the growing and senescent phases in the middle-high latitudes of the Northern Hemisphere; (ii) compared to the scenario without time effects, considering time-lag and -accumulation effects as well as their combined effects increased by 17 %, 15 %, and 19 % the overall explanatory power of vegetation growth by climate change for the whole growing season, the growing phase, and senescent phase, respectively; (iii) considering the time-lag and -accumulation effects as well as their combined effects, climate change controls 70 % of areas with a significant NDVI variation from 1982 to 2015, and the primary driving factor was temperature, followed by solar radiation and precipitation. This study highlights the significant time-lag and -accumulation effects of climatic factors on global vegetation growth. We suggest that these effects need to be incorporated into dynamic vegetation models to better understand vegetation growth under accelerating climate change.     

论电离层对GPS定位的影响

电离层是ＧＰＳ定位的主要误差源。本文论述电离层的特征和折射系数,以及电离层的下列影响：电离层码群延、电离层载波相位超前、电离层多普勒频移、振幅闪烁、电离层相位闪烁效应、磁暴对ＧＰＳ定位测量的影响、电离层对差分ＧＰＳ的影响和ＧＰＳ接收机的电离层改正。     

RINEX_HO: second- and third-order ionospheric corrections for RINEX observation files

When GNSS receivers capable of collecting dual-frequency data are available, it is possible to eliminate the first-order ionospheric effect in the data processing through the ionosphere-free linear combination. However, the second- and third-order ionospheric effects still remain. The first-, second- and third-order ionospheric effects are directly proportional to the total electron content (TEC), although the second- and third-order effects are influenced, respectively, by the geomagnetic field and the maximum electron density. In recent years, the international scientific community has given more attention to these kinds of effects and some works have shown that for high precision GNSS positioning these effects have to be taken into consideration. We present a software tool called RINEX_HO that was developed to correct GPS observables for second- and third-order ionosphere effects. RINEX_HO requires as input a RINEX observation file, then computes the second- and third-order ionospheric effects, and applies the corrections to the original GPS observables, creating a corrected RINEX file. The mathematical models implemented to compute these effects are presented, as well as the transformations involving the earth’s magnetic field. The use of TEC from global ionospheric maps and TEC calculated from raw pseudorange measurements or pseudoranges smoothed by phase is also investigated.     

论环境条件对航摄仪检定的影响

本文分析了航摄仪检定的环境条件(压力、温度)对内方位元素、畸变差的影响,并进行了不同环境压力和不同环境温度影响的检定实验。实验结果表明:环境压力和环境温度对航摄仪检定的影响是不容忽略的。本文针对国内目前航摄仪检定现状,提出了改进意见。     

重复轨道雷达干涉测量中的大气影响及其研究展望

在研究大气延迟物理机制的基础上，分析了大气效应对雷达干涉测量产生的影响，并对重复轨道雷达干涉测量中大气延迟的分析方式进行了归纳与探讨； 回顾了国内外关于InSAR大气影响的研究方法，着重对现有的大气误差改正方法进行了分类和比较，并对存在的问题进行了分析，对今后的研究方向提出了建议。     

The welfare benefit of a home’s location: an empirical comparison of spatial and non-spatial model estimates

This article compares results from non-spatial and new spatial methods to examine the reliability of welfare estimates (direct and multiplier effects) for locational housing attributes in Seattle, WA. In particular, we assess if OLS with spatial fixed effects is able to account for the spatial structure in a way that represents a viable alternative to spatial econometric methods. We find that while OLS with spatial fixed effects accounts for more of the spatial structure than simple OLS, it does not account for all of the spatial structure. It thus does not present a viable alternative to the spatial methods. Similar to existing comparisons between results from non-spatial and established spatial methods, we also find that OLS generates higher coefficient and direct effect estimates for both structural and locational housing characteristics than spatial methods do. OLS with spatial fixed effects is closer to the spatial estimates than OLS without fixed effects but remains higher. Finally, a comparison of the direct effects with locally weighted regression results highlights spatial threshold effects that are missed in the global models. Differences between spatial estimators are almost negligible in this study.     

航空重力向下延拓的误差影响分析

本文从分析航空重力向下延拓过程中偶然误差和系统误差的变化特性入手,进而提出处理办法。首先,利用试验说明移去恢复法局限性,同时表明需处理系统误差和偶然误差的必要性。然后,采用理论推演和数值模拟计算分别估计了系统误差和偶然误差影响,试验结果发现:系统误差影响和偶然误差影响均与数据格网间隔、向下延拓高度呈线性关系,当格网化间隔较小和延拓高度较高时系统误差影响和偶然误差影响较大。最后,提出使用半参数模型和正则化算法的两步法估计系统误差和减弱偶然误差影响,试验结果说明两步法处理向下延拓各类误差影响优于仅用半参数模型或正则化算法的结果,在试验数据的偶然误差标准差为2×10~(-5) m/s~2、恒值系统误差3×10~(-5) m/s~2和变值系统误差标准差约1.3×10~(-5) m/s~2时,以及向下延拓高度6.3 km和格网间隔6′的条件下,两步法向下延拓结果的精度可达2.3×10~(-5) m/s~2。     

电离层对星载SAR矩形包络线性调频信号的影响

讨论了电离层对星载SAR矩形包络线性调频信号的影响 ,推导出由电离层引起的图像偏移和峰值二次相位误差的计算公式 ,基于这些公式对P ,L ,C 3个波段的影响作了比较分析。结果表明 :电离层对P波段的影响很大 ,对L波段有一定影响 ,对C波段的影响基本可以忽略。     

NOAA－AVHRR图像大气影响校正方法研究及软件研制第一部分 原理和模型

大气影响是遥感定量化应用的主要障碍之一。本文首先分析了大气对遥感图像产生的各种影响并对影响程度进行了一般的阐述，然后在原理和方法上对典型的大气影响校正算法进行了总结。通过分析我们认为，为了校正遥感图像所受到的大气影响，定量地获取当时当地的大气条件是完成这一工作的必要条件，而且是非常重要的条件之一。为此，我们提出了利用ＮＯＡＡ星载垂直探测器资料即ＴＯＶＳ资料，结合使用气溶胶模型，通过大气辐射传输模型，建立地面辐射量与卫星测量值之间的关系，并完成了对ＮＯＡＡ－ＡＶＨＲＲ图像的大气影响校正。在此基础上对我们的模型和算法进行了详细论述。这一模型是一套适用于发展业务软件的校正模型，软件发展完善后将为ＮＯＡＡ－ＡＶＨＲＲ数据的定量化应用打下基础。     

GPS载波相位测量中的信号多路径效应影响研究

当利用GPS进行高精度变形监测时,GPS信号的多路径效应成为影响GPS变形监测精度和可靠性的一种不可忽略的误差源.本文针对GPS载波相位测量中的多路径效应影响进行理论和试验分析.论述载波相位测量中GPS多路径信号的特征,分析它对载波相位测量的影响,提出在坐标域用移动平均进行短基线静态GPS测量多路径误差探测的方法.通过实测数据进行分析,取得满意的效果.     

控制网中观测元素作用的分析

本文阐述测量控制网中观测元素作用分析的理论,通过有关的四个数字指标对此进行了多个网例的定量分析,讨论了观测元素的作用与网形、与观测精度匹配等的关系。文中还给出了必要观测分量的几何意义。     

新天文常数、系统对天文经纬度和方位角的影响

本文从理论上讨论了新天文常数、系统对恒星视位置影响的周期性、计算公式及其数值范围,并结合一等天文外业的实际情况,推导了新天文常数、系统对天文经纬度和方位角的影响公式及其数值范围,从而得出在任何年观测都可以使其影响忽略不计等结论。     

关于土地覆被遥感监测的几点思考

针对国内外土地覆被遥感监测中存在的突出问题展开讨论,分析土地覆被分类系统的目标适应性; 总结现有分类算法的特点及存在问题,分析小尺度和大尺度监测技术的差异性和效果; 研究不同尺度土地覆被监测所解决的应用问题及尺度空间变化下的分类效果; 分析现有监测体系的分类精度及产生误差的原因和解决方法.     

某特种工程中精密定位、定向的实现

针对某特种工程中长距离精密定位、定向的需要,从高等级GPS控制网精度、加密GPS控制网精度、坐标投影误差、板块漂移影响及工程放样误差等方面分析和估算误差影响,探讨达到精度指标要求的可能性。针对潜在的定位、定向的影响因素,提出合理的技术实现方案,评价采用该技术方案后,工程定位、定向实际达到的精度,并对特定区域内被监测目标的点位精度、有效覆盖范围误差做出推算。     

Critical error effects and analysis in carrier phase-based airborne GPS positioning over large areas

For high accuracy airborne differential GPS positioning over large areas, i.e. a monitor-remote separation over 50 km, residual errors from the atmosphere and orbit, as well as multipath effects are the main error sources which limit the potential positioning accuracy. The effects of these critical errors are quantified and analyzed using test data collected during an airborne positioning campaign. Four Trimble 4000 SSE receivers were used, with two serving as monitors and the other two as remote receivers installed in the aircraft. Monitor-aircraft separations of up to 200 km were experienced during the test. A formula is derived for analytical estimation of orbital error effects. Results and discussions relevant to the critical error analysis are presented with emphasis on their effects on the positioning results.     

敦煌地区大气水汽和气溶胶对获取地表温度的影响

大气中的水汽和气溶胶含量是影响热红外波段数据的主要因素。针对敦煌地区,本文首先利用ＬＯＷＴＲＡＮ－７辐射传输模型对１９９２年９月２５日敦煌市西戈壁的一幅Ｌａｎｄｓａｔ－５ＴＭ６波段的热红外图像数据进行了大气订正,获取了地表辐射温度。进而利用ＬＯＷＴＲＡＮ－７通过模拟计算研究了该地区大气水汽和气溶胶含量的变化对ＴＭ６波段地面温度获取结果的影响,给出了对于热红外图像进行大气订正的主要判据。另外,文中还对热红外波段地面比辐射率的影响也进行了简单分析     

小尺度地幔对流与海底地形抬升

根据建立的垂直于大洋中脊的二维热对流有限元数值模型，采用常粘性以及与温度相关的粘性两种粘性结构对小尺度地幔对流对海底地形的影响进行了重新研究。该模型的主要特点是采用开放边界条件，从而可以避免原有封闭模型因回流问题而产生的复杂效应。数据结果显示，在常粘性模型中，小尺度地幔对流可造成海底地形抬升；但对与温度相关的粘性模型，小尺度对流对地形几乎不产生影响。     

GPS卫星定轨中的摄动力影响分析

分析了地球重力场、海洋潮汐、行星摄动、地极潮汐、相对论加速度等对GPS轨道拟合及轨道外推造成的影响,认为在GPS定轨中除了顾及地球重力场及海洋潮汐对卫星轨道影响之外,还应注意地球重力场模型及海洋潮汐模型的选用问题;此外,在短弧定轨可以不考虑行星摄动、地极潮汐以及相对论加速度的影响,但长弧定轨中需考虑它们的影响。     

The effect on the geoid of lateral topographic density variations

Gravimetric geoid determination by Stokes formula requires that the effects of topographic masses be removed prior to Stokes integration. This step includes the direct topographic and the downward continuation (DWC) effects on gravity anomaly, and the computations yield the co-geoid height. By adding the effect of restoration of the topography, the indirect effect on the geoid, the geoid height is obtained. Unfortunately, the computations of all these topographic effects are hampered by the uncertainty of the density distribution of the topography. Usually the computations are limited to a constant topographic density, but recently the effects of lateral density variations have been studied for their direct and indirect effects on the geoid. It is emphasised that the DWC effect might also be significantly affected by a lateral density variation. However, instead of computing separate effects of lateral density variation for direct, DWC and indirect effects, it is shown in two independent ways that the total geoid effect due to the lateral density anomaly can be represented as a simple correction proportional to the lateral density anomaly and the elevation squared of the computation point. This simple formula stems from the fact that the significant long-wavelength contributions to the various topographic effects cancel in their sum. Assuming that the lateral density anomaly is within 20% of the standard topographic density, the derived formula implies that the total effect on the geoid is significant at the centimetre level for topographic elevations above 0.66 km. For elevations of 1000, 2000 and 5000 m the effect is within ± 2.2, ± 8.8 and ± 56.8 cm, respectively. For the elevation of Mt. Everest the effect is within ± 1.78 m.     

基于多路径效应的植被覆盖研究

测站周围的环境会对GPS观测产生多路径效应影响,利用TEQC软件分析武汉九峰台站的近十年的GPS数据,并对结果进行了频谱分析,发现GPS多路径效应与台站周围植被覆盖情况存在着一致的周年的变化规律。因此,可以利用GPS的多路径效应来研究植被覆盖率的变化。