首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Land cover change is increasingly affecting the biophysics, biogeochemistry, and biogeography of the Earth's surface and the atmosphere, with far-reaching consequences to human well-being. However, our scientific understanding of the distribution and dynamics of land cover and land cover change (LCLCC) is limited. Previous global land cover assessments performed using coarse spatial resolution (300 m–1 km) satellite data did not provide enough thematic detail or change information for global change studies and for resource management. High resolution (∼30 m) land cover characterization and monitoring is needed that permits detection of land change at the scale of most human activity and offers the increased flexibility of environmental model parameterization needed for global change studies. However, there are a number of challenges to overcome before producing such data sets including unavailability of consistent global coverage of satellite data, sheer volume of data, unavailability of timely and accurate training and validation data, difficulties in preparing image mosaics, and high performance computing requirements. Integration of remote sensing and information technology is needed for process automation and high-performance computing needs. Recent developments in these areas have created an opportunity for operational high resolution land cover mapping, and monitoring of the world. Here, we report and discuss these advancements and opportunities in producing the next generations of global land cover characterization, mapping, and monitoring at 30-m spatial resolution primarily in the context of United States, Group on Earth Observations Global 30 m land cover initiative (UGLC).  相似文献   

2.
Irrigation accounts for 70% of global water use by humans and 33–40% of global food production comes from irrigated croplands. Accurate and timely information related to global irrigation is therefore needed to manage increasingly scarce water resources and to improve food security in the face of yield gaps, climate change and extreme events such as droughts, floods, and heat waves. Unfortunately, this information is not available for many regions of the world. This study aims to improve characterization of global rain-fed, irrigated and paddy croplands by integrating information from national and sub-national surveys, remote sensing, and gridded climate data sets. To achieve this goal, we used supervised classification of remote sensing, climate, and agricultural inventory data to generate a global map of irrigated, rain-fed, and paddy croplands. We estimate that 314 million hectares (Mha) worldwide were irrigated circa 2005. This includes 66 Mha of irrigated paddy cropland and 249 Mha of irrigated non-paddy cropland. Additionally, we estimate that 1047 Mha of cropland are managed under rain-fed conditions, including 63 Mha of rain-fed paddy cropland and 985 Mha of rain-fed non-paddy cropland. More generally, our results show that global mapping of irrigated, rain-fed, and paddy croplands is possible by combining information from multiple data sources. However, regions with rapidly changing irrigation or complex mixtures of irrigated and non-irrigated crops present significant challenges and require more and better data to support high quality mapping of irrigation.  相似文献   

3.
Based upon a data set of 25 points of the Baltic Sea Level Project, second campaign 1993.4, which are close to mareographic stations, described by (1) GPS derived Cartesian coordinates in the World Geodetic Reference System 1984 and (2) orthometric heights in the Finnish Height Datum N60, epoch 1993.4, we have computed the primary geodetic parameter W 0(1993.4) for the epoch 1993.4 according to the following model. The Cartesian coordinates of the GPS stations have been converted into spheroidal coordinates. The gravity potential as the additive decomposition of the gravitational potential and the centrifugal potential has been computed for any GPS station in spheroidal coordinates, namely for a global spheroidal model of the gravitational potential field. For a global set of spheroidal harmonic coefficients a transformation of spherical harmonic coefficients into spheroidal harmonic coefficients has been implemented and applied to the global spherical model OSU 91A up to degree/order 360/360. The gravity potential with respect to a global spheroidal model of degree/order 360/360 has been finally transformed by means of the orthometric heights of the GPS stations with respect to the Finnish Height Datum N60, epoch 1993.4, in terms of the spheroidal “free-air” potential reduction in order to produce the spheroidal W 0(1993.4) value. As a mean of those 25 W 0(1993.4) data as well as a root mean square error estimation we computed W 0(1993.4)=(6 263 685.58 ± 0.36) kgal × m. Finally a comparison of different W 0 data with respect to a spherical harmonic global model and spheroidal harmonic global model of Somigliana-Pizetti type (level ellipsoid as a reference, degree/order 2/0) according to The Geodesist's Handbook 1992 has been made. Received: 7 November 1996 / Accepted: 27 March 1997  相似文献   

4.
We estimate seasonal global mean sea level changes using different data resources, including sea level anomalies from satellite radar altimetry, ocean temperature and salinity from the World Ocean Atlas 2001, time-variable gravity observations from the Gravity Recovery and Climate Experiment (GRACE) mission, and terrestrial water storage and atmospheric water vapor changes from the NASA global land data assimilation system and National Centers for Environmental Prediction reanalysis atmospheric model. The results from all estimates are consistent in amplitude and phase at the annual period, in some cases with remarkably good agreement. The results provide a good measure of average annual variation of water stored within atmospheric, land, and ocean reservoirs. We examine how varied treatments of degree-2 and degree-1 spherical harmonics from GRACE, laser ranging, and Earth rotation variations affect GRACE mean sea level change estimates. We also show that correcting the standard equilibrium ocean pole tide correction for mass conservation is needed when using satellite altimeter data in global mean sea level studies. These encouraging results indicate that is reasonable to consider estimating longer-term time series of water storage in these reservoirs, as a way of tracking climate change.  相似文献   

5.
For space geodetic techniques, operating in microwave band, ionosphere is a dispersive medium; thus signals traveling through this medium are in the first approximation affected proportional to inverse of the square of their frequencies. This effect allows gaining information about the parameters of the ionosphere in terms of Total Electron Content (TEC) or the electron density (N e ). TEC or electron density can then be expressed by means of spherical harmonic base functions to provide a Global Ionosphere Map (GIM). The classical input data for development of GIMs are obtained from dual-frequency observations carried out at Global Navigation Satellite Systems (GNSS) stations. However, GNSS stations are in-homogeneously distributed around the world, with large gaps particularly over the oceans; this fact reduces the precision of the GIM over these areas. On the other hand, dual-frequency satellite altimetry missions such as Jason-1 provide information about the ionosphere precisely above the oceans; and furthermore Low Earth Orbiting (LEO) satellites, such as Formosat-3/COSMIC (F/C) provide well-distributed information of ionosphere globally. This study investigates on global modeling of TEC through combining GNSS and satellite altimetry data with global TEC data derived from the occultation measurements of the F/C mission. The combined GIMs of vertical TEC (VTEC) show a maximum difference of 1.3–1.7 TEC units (TECU) with respect to the GNSS-only GIMs in the whole day. The root mean square error (RMS) maps of combined solution show a reduction of about 0.1 TECU in the whole day. This decrease of RMS can reach up to 0.5 TECU in areas where no or few GNSS observations are available, but high number of F/C measurement is carried out. This proves that the combined GIMs provide a more homogeneous global coverage and higher reliability than results of each single method. All comparisons and validations made within this study provide vital information regarding combination and integration of various observation techniques in the Global Geodetic Observing System of the International Association of Geodesy.  相似文献   

6.
Unmodeled sub-daily ocean S2 tide signals that alias into lower frequencies have been detected in the analysis of gravity recovery and climate experiment (GRACE) space gravity fields of GRGS. The most significant global S2 aliased signal occurs off the northwest coast of Australia in a shallow continental shelf zone, a region with high tidal amplitudes at a period of 161 days. The GRACE S2 aliased equivalent water height grids are convolved with Green’s functions to produce GRACE aliased tidal loading (GATL) vertical displacements. The analysis of hourly global positioning system (GPS) vertical coordinate estimates at permanent sites in the region confirms the presence of spectral power at the S2 frequency when the same ocean tide model (FES2004) was used. Thus, deficiencies in the FES2004 ocean tide model are detected both directly and indirectly by the two independent space geodetic techniques. Through simulation, the admittance (ratio of amplitude of spurious long-wavelength output signal in the GRACE time-series to amplitude of unmodeled periodic signals) of the GRACE unmodeled S2 tidal signals, aliased to a 161-day period, is found to have a global average close to 100%, although with substantial spatial variation. Comparing GATL with unmodeled S2 tidal sub-daily signals in the vertical GPS time-series in the region of Broome in NW Australia suggests an admittance of 110–130%.  相似文献   

7.
GPS Solutions - We investigate the feasibility of completing an aircraft precision approach using two global navigation satellite systems (GNSS) satellites from different constellations in...  相似文献   

8.
 It is suggested that a spherical harmonic representation of the geoidal heights using global Earth gravity models (EGM) might be accurate enough for many applications, although we know that some short-wavelength signals are missing in a potential coefficient model. A `direct' method of geoidal height determination from a global Earth gravity model coefficient alone and an `indirect' approach of geoidal height determination through height anomaly computed from a global gravity model are investigated. In both methods, suitable correction terms are applied. The results of computations in two test areas show that the direct and indirect approaches of geoid height determination yield good agreement with the classical gravimetric geoidal heights which are determined from Stokes' formula. Surprisingly, the results of the indirect method of geoidal height determination yield better agreement with the global positioning system (GPS)-levelling derived geoid heights, which are used to demonstrate such improvements, than the results of gravimetric geoid heights at to the same GPS stations. It has been demonstrated that the application of correction terms in both methods improves the agreement of geoidal heights at GPS-levelling stations. It is also found that the correction terms in the direct method of geoidal height determination are mostly similar to the correction terms used for the indirect determination of geoidal heights from height anomalies. Received: 26 July 2001 / Accepted: 21 February 2002  相似文献   

9.
The ‘global warming’ effect has been found to influence vegetation phenological processes. Heat island phenomenon associated with urbanized area presents a unique place to investigate its local warming effects. This study compares the date of budburst (DOBB) of street London plane trees (Platanus × acerifolia) between highly urbanized New York City (NYC) and relatively less urbanized Ithaca, New York in 2007 and 2008. It also linked DOBB with land surface temperature and fractional vegetation cover derived from Landsat satellite images. The DOBB in NYC and Ithaca differed significantly as budburst occurred 3 and 4 days earlier in NYC than in Ithaca in 2007 and 2008, respectively. The intensity of the heat island effect and its effect on tree phenology were greater in NYC. Results show that DOBB can be explained by temperature, and findings could be extrapolated to make inferences on the potential impact of global warming on vegetation communities.  相似文献   

10.
利用GRACE、卫星测高和海洋实测温盐数据,探讨了2003~2012年间全球海平面、比容海平面和海水质量等的变化特征,并讨论了南极冰盖和格陵兰冰盖消融对全球海平面变化的影响。全球海平面整体呈上升趋势,上升速度为2.72±0.07 mm/a,且存在显著的空间分布特征。全球海平面、比容海平面和海水质量等的变化还具有显著的季节性特征,其中全球海平面变化的年周期振幅为4.6±0.3 mm。使用经验正交函数分析(EOF)得到全球海平面和比容海平面的季节性变化在南北半球存在显著的差异,但海水质量季节性变化不存在这种差异。南极冰盖和格陵兰冰盖的消融速率分别为-75.7±12.3 Gt/a和-124.1±2.9 Gt/a,对海平面的长期趋势项贡献分别为0.21±0.03 mm/a和0.34±0.01 mm/a,仅占全球海水质量增加速度1.80±0.10 mm/a的12%和19%,总计占31%,因此,两极冰盖质量消融并不是2003-2012年间海水质量增加的最主要因素。  相似文献   

11.
杨必胜  梁福逊  黄荣刚 《测绘学报》2017,46(10):1509-1516
三维激光扫描直接对地球表面进行三维密集采样,可快速获取具有三维坐标(X,Y,Z)和一定属性(反射强度等)的海量、不规则空间分布三维点云,成为数字化时代下刻画复杂现实世界最为直接和重要的三维地理空间数据获取手段,在全球变化、智慧城市、全球制图等国家重大需求和地球系统科学研究中起到十分重要的作用。目前,在传感器技术和国家需求的双重驱动下,三维激光扫描在硬件装备、三维点云数据处理以及应用3个方面取得了巨大的进步,同时也面临新的挑战。本文以三维激光扫描的发展历史为线索,总结了三维激光扫描系统的现状、三维点云数据处理的关键进展以及在测绘地理信息等领域的典型应用,并分析了三维点云数据处理面临的挑战,最后展望了三维激光扫描与点云处理的发展趋势。  相似文献   

12.
We present a geoid solution for the Weddell Sea and adjacent continental Antarctic regions. There, a refined geoid is of interest, especially for oceanographic and glaciological applications. For example, to investigate the Weddell Gyre as a part of the Antarctic Circumpolar Current and, thus, of the global ocean circulation, the mean dynamic topography (MDT) is needed. These days, the marine gravity field can be inferred with high and homogeneous resolution from altimetric height profiles of the mean sea surface. However, in areas permanently covered by sea ice as well as in coastal regions, satellite altimetry features deficiencies. Focussing on the Weddell Sea, these aspects are investigated in detail. In these areas, ground-based data that have not been used for geoid computation so far provide additional information in comparison with the existing high-resolution global gravity field models such as EGM2008. The geoid computation is based on the remove–compute–restore approach making use of least-squares collocation. The residual geoid with respect to a release 4 GOCE model adds up to two meters and more in the near-coastal and continental areas of the Weddell Sea region, also in comparison with EGM2008. Consequently, the thus refined geoid serves to compute new estimates of the regional MDT and geostrophic currents.  相似文献   

13.
Position information obtained from standard global positioning system (GPS) receivers has time variant errors. For effective use of GPS information in a navigation system, it is essential to model these errors. A new approach is presented for improving positioning accuracy using neural network (NN), fuzzy neural network (FNN), and Kalman filter (KF). These methods predict the position components’ errors that are used as differential GPS (DGPS) corrections in real-time positioning. Method validity is verified with experimental data from an actual data collection, before and after selective availability (SA) error. The result is a highly effective estimation technique for accurate positioning, so that positioning accuracy is drastically improved to less than 0.40 m, independent of SA error. The experimental test results with real data emphasize that the total performance of NN is better than FNN and KF considering the trade-off between accuracy and speed for DGPS corrections prediction.  相似文献   

14.
A variety of DEM products are available to the public at no cost, though all are characterized by trade-offs in spatial coverage, data resolution, and quality. The absence of a high-resolution, high-quality, well-described and vetted, free, global consensus product was the impetus for the creation of a new DEM product described here, ‘EarthEnv-DEM90’. This new DEM is a compilation dataset constructed via rigorous techniques by which ASTER GDEM2 and CGIAR-CSI v4.1 products were fused into a quality-enhanced, consistent grid of elevation estimates that spans ∼91% of the globe. EarthEnv-DEM90 was assembled using methods for seamlessly merging input datasets, thoroughly filling voids, and smoothing data irregularities (e.g. those caused by DEM noise) from the approximated surface. The result is a DEM product in which elevational artifacts are strongly mitigated from the input data fusion zone, substantial voids are filled in the northern-most regions of the globe, and the entire DEM exhibits reduced terrain noise. As important as the final product is a well defined methodology, along with new processing techniques and careful attention to final outputs, that extends the value and usability of the work beyond just this single product. Finally, we outline EarthEnv-DEM90 acquisition instructions and metadata availability, so that researchers can obtain this high-resolution, high-quality, nearly-global new DEM product for the study of wide-ranging global phenomena.  相似文献   

15.
本文给出了北斗三号全球导航卫星系统定位导航授时、星基增强、精密单点定位、区域短报文通信、全球短报文通信和国际搜救共6类服务的测试评估方法,并利用实测数据对各类服务的核心指标进行了评估。结果表明,定位导航授时服务方面,空间信号测距误差0.23 m(RMS),空间信号可用性99.44%,空间信号连续性99.99%,PDOP可用性100%,B1C信号全球定位精度水平方向1.31 m、垂直方向2.13 m(95%),B1C信号全球定位可用性99.93%,B1C信号授时精度14.7 ns(95%);星基增强服务方面,定位精度水平方向1.03 m、垂直方向2.60 m(95%)、具有垂直引导能力的一类进近(APV-I)可用性100%;精密单点定位服务方面,定位精度水平方向0.17 m(95%)、垂直方向0.22 m(95%)、平均收敛时间9 min;区域短报文通信服务成功率99.6%,服务容量1530万次/h(上行)、935万次/h(下行);全球短报文通信服务成功率96.46%,服务容量40万次/h(上行)、21万次/h(下行);国际搜救服务方面,搜救信号接收成功率98.3%(发射功率37 dBm)。  相似文献   

16.
A global, 2-hourly atmospheric precipitable water (PW) dataset is produced from ground-based GPS measurements of zenith tropospheric delay (ZTD) using the International Global Navigation Satellite Systems (GNSS) Service (IGS) tropospheric products (~80–370 stations, 1997–2006) and US SuomiNet product (169 stations, 2003–2006). The climate applications of the GPS PW dataset are highlighted in this study. Firstly, the GPS PW dataset is used as a reference to validate radiosonde and atmospheric reanalysis data. Three types of systematic errors in global radiosonde PW data are quantified based on comparisons with the GPS PW data, including measurement biases for each of the fourteen radiosonde types along with their characteristics, long-term temporal inhomogeneity and diurnal sampling errors of once and twice daily radiosonde data. The comparisons between the GPS PW data and three reanalysis products, namely the NCEP-NCAR (NNR), ECMWF 40-year (ERA-40) and Japanese reanalyses (JRA), show that the elevation difference between the reanalysis grid box and the GPS station is the primary cause of the PW difference. Secondly, the PW diurnal variations are documented using the 2-hourly GPS PW dataset. The PW diurnal cycle has an annual-mean, peak-to-peak amplitude of 0.66, 0.53 and 1.11 mm for the globe, Northern Hemisphere, and Southern Hemisphere, respectively, with the time of the peak ranging from noon to late evening depending on the season and region. Preliminary analyses suggest that the PW diurnal cycle in Europe is poorly represented in the NNR and JRA products. Several recommendations are made for future improvements of IGS products for climate applications.  相似文献   

17.
We investigate global mean sea level (MSL) changes and different geophysical contributions at interannual and long-term (decadal) time-scales. Thermosteric effects of global MSL changes are estimated from ocean temperature anomaly data for the period 1955–2003 from the World Ocean Database 2001 (WOD01), plus additional data processed through June 2004. Estimates based on WOD01 show significant differences to previously published results based on similar temperature anomaly data from the World Ocean Database 1998 (WOD98), especially during the period overlapping with the TOPEX/Poseidon satellite altimeter mission. During this period (1993–2004), the WOD01-estimated thermosteric contribution of global MSL change is less than half of the estimate from WOD98 (1.3 ± 0.1 vs. 3.0 ± 0.6 mm/year), as compared to the rate of 2.6 ± 0.06 mm/year observed by satellite altimeters. The larger uncertainty in ocean temperature profiles and incomplete data collection in WOD98, especially in the later years (1997 and 1998) appear to be the major error sources to the overestimated steric effects by WOD98. During the entire 50-year period, the steric effect on global MSL change amounts to about 0.34–0.39 (±0.05) mm/year. Strong interannual and decadal variability exists in estimated thermosteric contributions to the global MSL change, and (surprisingly) the thermosteric effect does not show any pronounced contribution to the strong interannual variability during the 1997/1998 El Niño/La Niña event. Our analysis based on the National Centers for Environmental Prediction reanalysis atmospheric model and the National Oceanic and Atmospheric Administration Climate Prediction Center global land data assimilation system indicates that atmospheric water vapor and terrestrial water storage changes show strong interannual variability that is well correlated with observed global MSL change, and could have significant effects on interannual global MSL changes.  相似文献   

18.
Combinations of Earth-orientation measurements: SPACE97, COMB97, and POLE97   总被引：7，自引：2，他引：5  
Independent Earth-orientation measurements taken by the space-geodetic techniques of lunar and satellite laser ranging, very-long-baseline interferometry, and the global positioning system have been combined using a Kalman filter. The resulting combined Earth-orientation series, SPACE97, consists of values and uncertainties for universal time, polar motion, and their rates spanning the period 28 September 1976 to 3 January 1998 at daily intervals. The space-geodetic measurements used to generate SPACE97 have then been combined with optical astrometric measurements to form two additional combined Earth-orientation series: (1) COMB97, consisting of values and uncertainties for universal time, polar motion, and their rates spanning the period 20 January 1962 to 1 January 1998 at 5-day intervals, and (2) POLE97, consisting of values and uncertainties for polar motion and its rate spanning the period 20 January 1900 to 21 December 1997 at monthly intervals. Received: 10 August 1998 / Accepted: 31 May 1999  相似文献   

19.
An improved methodology for the extraction and mapping of urban built-up areas at a global scale is presented in this study. The Moderate Resolution Imaging Spectroradiometer (MODIS)-based multispectral data were combined with the Visible Infrared Imager Radiometer Suite (VIIRS)-based nighttime light (NTL) data for robust extraction and mapping of urban built-up areas. The MODIS-based newly proposed Urban Built-up Index (UBI) was combined with NTL data, and the resulting Enhanced UBI (EUBI) was used as a single master image for global extraction of urban built-up areas. Due to higher variation of the EUBI with respect to geographical regions, a region-specific threshold approach was used to extract urban built-up areas. This research provided 500-m-resolution global urban built-up map of year 2014. The resulted map was compared with three existing moderate-resolution global maps and one high-resolution map in the United States. The comparative analysis demonstrated finer details of the urban built-up cover estimated by the resultant map.  相似文献   

20.
中国地质灾害点多面广，且大多地处高位并被植被覆盖，传统的人工调查排查在一些地区进行地质灾害隐患识别已显得无能为力，这也是近年来绝大多数灾难性地质灾害事件都不在预案点范围内的主要原因。提出通过构建天-空-地一体化的“三查”体系进行重大地质灾害隐患的早期识别，再通过专业监测，在掌握地质灾害动态发展规律和特征的基础上，进行地质灾害的实时预警预报，以此破解“隐患点在哪里”“什么时候可能发生”这一地质灾害防治领域的难题和国家急切需求。“三查”体系首先通过光学遥感和合成孔径雷达干涉测量技术（interferometric synthetic aperture radar，InSAR）实现区域扫面性地质灾害隐患的普查，随后利用机载激光雷达测量技术（light laser detection and ranging，LiDAR）和无人机摄影测量实现高地质灾害风险区段和重大地质灾害隐患的详查，最后采用现场调查、地面与坡体内部监（探）测等手段，实现重大地质灾害隐患的复核确认和排除，即核查。监测预警则是通过InSAR和地面观测手段（如全球导航卫星系统、裂缝计等），在掌握滑坡崩塌的变形规律和阶段以及时间-空间变形特征的基础上，建立分级综合预警体系，并利用地质灾害实时监测预警系统，逐步实现地质灾害监测预警的实用化和业务化运行。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号