Selection and quality assessment of Landsat data for the North American forest dynamics forest history maps of the US

Using the NASA Earth Exchange platform, the North American Forest Dynamics (NAFD) project mapped forest history wall-to-wall, annually for the contiguous US (1986–2010) using the Vegetation Change Tracker algorithm. As with any effort to identify real changes in remotely sensed time-series, data gaps, shifts in seasonality, misregistration, inconsistent radiometry and cloud contamination can be sources of error. We discuss the NAFD image selection and processing stream (NISPS) that was designed to minimize these sources of error. The NISPS image quality assessments highlighted issues with the Landsat archive and metadata including inadequate georegistration, unreliability of the pre-2009 L5 cloud cover assessments algorithm, missing growing-season imagery and paucity of clear views. Assessment maps of Landsat 5–7 image quantities and qualities are presented that offer novel perspectives on the growing-season archive considered for this study. Over 150,000+ Landsat images were considered for the NAFD project. Optimally, one high quality cloud-free image in each year or a total of 12,152 images would be used. However, to accommodate data gaps and cloud/shadow contamination 23,338 images were needed. In 220 specific path-row image years no acceptable images were found resulting in data gaps in the annual national map products.     

面向WebGL的矢量数据三维绘制技术

矢量数据的叠加显示能够提高三维虚拟地球的表达效果与分析能力。受限于GPU的计算精度,在三维虚拟地球中矢量数据绘制普遍存在抖动现象和深度冲突现象。对基于WebGL的矢量数据三维绘制中计算精度问题进行了分析,提出了使用CPU RTC技术和GPU RTE技术提高顶点变换的精度,使用多视锥渲染算法和深度平面技术解决深度缓存精度问题。实验证明,这几种技术和算法可以有效缓解抖动现象和深度冲突现象导致的视觉干扰,改善了各种尺度和范围的矢量数据在三维地形上的叠加显示效果。     

新太阳光压模型在GNSS定轨中的应用

太阳光压摄动是影响卫星定轨中重要的误差源,在GNSS导航卫星精密定轨过程中使用最为广泛的光压模型为ECOM模型。为了探究几种ECOM模型及其适用性,该文以超快速星历为起算轨道,分析对比经典ECOM-1模型与最新13参数ECOMC模型对GPS/BDS卫星轨道的影响。结果显示:相较于ECOM-1模型,ECOMC模型在GPS定轨中精度有所提升,特别体现在径向精度提升,单天与三天弧段在径向的解算精度分别提升了12.73%和24.74%;在BDS定轨中,采用ECOMC模型,部分GEO卫星在径向方向单天精度有12.38%的提升,而对于IGSO与MEO卫星二者精度差异不大;分析可得,由于星体结构不对称引起卫星在沿太阳-卫星方向作用的偶数阶短周期谐波扰动,引入卫星-太阳方向偶数阶项的参数估计可提升卫星径向精度。     

Surface gravitational field and topography changes induced by the Earth’s fluid core motions

Using a Love number formalism, the elastic deformations of the mantle and the mass redistribution gravitational potential within the Earth induced by the fluid pressure acting at the core–mantle boundary (CMB) are computed. This pressure field changes at a decadal time scale and may be estimated from observations of the surface magnetic field and its secular variation. First, using a spherical harmonic expansion, the poloidal and toroidal part of the fluid velocity field at the CMB for the last 40 years is computed, under the hypothesis of tangential geostrophy. Then the associated geostrophic pressure, whose order of magnitude is about 1000 Pa, is computed. The surface topography induced by this pressure field is computed using Love numbers, and is a few millimetres. The mass redistribution gravitational potential induced by these deformations and, in particular, the zonal components of the related surface gravitational potential perturbation (J₂, J₃ and J₄ coefficients), are calculated. Overall perturbations for the J₂ coefficient of about 10^–10, for J₃ of about 10^–11 and for J₄ are found of about 0.3×10^–11. Finally, these theoretical results are compared with recent observations of the decadal variation of J₂ from satellite laser ranging. Results concerning J₂ can be described as follows: first, they are one order of magnitude too small to explain the observed decadal variation of J₂ and, second, they show a significant linear trend over the last 40 years, whose rate of decrease amounts to 7% of the observed value.     

星载GPS载波相位周跳探测方法

在星载GPS载波相位测量中,周跳的探测与修复对最后的定位精度起着至关重要的作用。本文根据在星载条件下GPS载波相位测量的观测时间短、环境变化复杂、所得历元少和基本不受对流层延迟影响等特点,论述了适用于星载高动态环境GPS载波相位周跳探测和修复的方法,并指出各种方法的特点和适用要求。     

弹性椭球地球模型的海潮效应

本文推证了比较完整的弹性椭球地球模型的海潮负荷理论和计算公式,它对弹性球型地球模型海潮效应计算的发展起了一定的作用。     

过黄河渡槽的脉动风荷载模拟

根据脉动风压功率谱与脉动风速功率谱之间的关系,利用风压功率谱密度函数矩阵的分解,通过一组余弦函数的和对过黄河渡槽随机形式的脉动风荷载进行了计算机模拟。     

福州市温泉区地面沉降监测与沉降规律分析

应用精密水准测量方法，于１９９３年在温泉区取得三个周期的观测成果，结合以往资料进行综合分析，得出初步结论。并为福州市地下热水开采的控制、预防及减轻因沉降产生的地灾害方面提出有益的建议。     

Big Earth data: disruptive changes in Earth observation data management and analysis?

ABSTRACT

Turning Earth observation (EO) data consistently and systematically into valuable global information layers is an ongoing challenge for the EO community. Recently, the term ‘big Earth data’ emerged to describe massive EO datasets that confronts analysts and their traditional workflows with a range of challenges. We argue that the altered circumstances must be actively intercepted by an evolution of EO to revolutionise their application in various domains. The disruptive element is that analysts and end-users increasingly rely on Web-based workflows. In this contribution we study selected systems and portals, put them in the context of challenges and opportunities and highlight selected shortcomings and possible future developments that we consider relevant for the imminent uptake of big Earth data.     

Targeting rare earth element bearing mine tailings on Bangka Island,Indonesia, with Sentinel-2 MSI

A laboratory study on rare earth element bearing mine tailings, collected from Bangka Island, Indonesia, reported a new spectral absorption feature at 674 nm associated with Erbium. The present study aims to evaluate the capability of the European Space Agency’s Sentinel-2 MSI sensors to detect this absorption feature from space. An arithmetic band operation is performed on selected visible and near-infrared spectral bands of a Sentinel-2 image. The results show that Sentinel-2 MSI is capable of detecting the 674 nm Erbium-related absorption feature within the particular environmental setting of the study area.