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Improvement of a 3. radar backscattering model using matrix-doubling method

science china Earth sciences 2010年第7期53卷 1029-1035页

作者： ni wenjian1,2, guo zhifeng1 & sun guoqing3.1 state key laboratory of remote sensing science, jointly {3. by the institute of remote sensing applications of chinese academy of sciences and beijing normal U{13.versity, beijing 100101, china 2 Graduate U{13.versity of chinese academy of sciences, beijing 100049, china 3.Department of Geography, U{13.versity of Maryland, College Park, MD 27042, USA 1. state key laboratory of {3. sensing science jointly sponsored by the Institute of Remote Sensing Applications of Chinese Academy of Sciences and Beijing Normal University Beijing 100101 China2. Graduate University of Chinese Academy of Sciences Beijing 100049 China3. Department of Geography University of Maryland College Park MD 27042 USA

Radiative transfer models have been widely used to simulate the radar backscattering from forested areas. A three-dimensional radar backscatter model of forest canopy developed in previous studies takes full account of spatial position of trees in a forest stand, and the interactions among crown, trunk and ground surface. The model predicted well for the co-polarized backscatter measurements, but underestimated the backscattering for cross-polarization, primarily because only the first-order scattering within tree crowns was considered in the model. The backscattering at cross-polarization depends strongly on multiple scatter- ing within tree crowns. To produce good estimations for cross-polarized component, the matrix-doubling method is employed here to compute multiple-scattering within the crown. The modified model is compared with the original model, and the field forest measurements and AIRSAR data are used for validation of the modified model. The cross-polarization backscattering is improved in different degrees for different crown structures and at different bands.

关键词： remote sensing forestry electromagnetic propagation radar backscattering model matrix-doubling

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Deforestation in Latin America in the 2000s predominantly occurred outside of typical mature forests

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The Innovation 2024年第3期5卷 88-98页

作者： Zhiyu Zhang wenjian ni Shaun Quegan Jingming Chen Peng Gong Luiz Carlos Estraviz Rodriguez Huadong guo Jiancheng Shi Liangyun Liu Zengyuan Li Yating He Qinhuo Liu Yosio Shimabukuro {3. sun key laboratory of remote {3. and Digital Earth Chinese Academy of SciencesBeijing 100101China University of chinese academy of {3. Shijingshan DistrictBeijing 100049China chinal of Mathematics and Statistics University of SheffieldSheffield S37RHUK Department of Geography and Program in Planning University of TorontoTorontoON M5S 3G3Canada Department of Earth sciences and Department of Geography University of Hong KongHong KongChina Forest science Department Luiz de Queiroz College of AgricultureUniversity of São PauloAv.Pádua Dias11Piracicaba 13418-900Brazil National Space science Center Chinese Academy of SciencesBeijing 100190China institute of Forest Resource Information Techniques Chinese Academy of ForestryBeijing 100091China Research institute of Forest Policy and Information Chinese Academy of ForestryBeijing 100091China remote sensing Department National Institute for Space Research(INPE)Av.dos Astronautas 1758São Josédos Campos 12227-010Brazil Department of Geographical sciences University of MarylandCollege ParkMD 20742USA

The role of tropical forests in the global carbon budget remains controversial,as carbon emissions from deforestation are highly *** high uncertainty arises from the use of either fixed forest carbon stock density or maps generated from satellite-based optical reflectance with limited sensitivity to biomass to generate accurate estimates of emissions from *** space missions aiming to accurately map the carbon stock density rely on direct measurements of the spatial structures of forests using lidar and *** found that lost forests are special cases,and their spatial structures can be directly measured by combining archived data acquired before and after deforestation by space missions principally aimed at measuring ***,using biomass mapping,we obtained new estimates of carbon loss from deforestation ahead of forthcoming space ***,using a high-resolution map of forest loss and the synergy of radar and lidar to estimate the aboveground biomass density of forests,we found that deforestation in the 2000s in Latin America,one of the severely deforested regions,mainly occurred in forests with a significantly lower carbon stock density than typical mature forests.

关键词： forest Latin lidar

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Assessment of Slope-Adaptive Metrics of GEDI Waveforms for Estimations of Forest Aboveground Biomass over Mountainous Areas

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Journal of remote sensing 2021年第1期2021卷 180-196页

作者： wenjian ni Zhiyu Zhang guoqing {3. state key laboratory of {3. sensing science Aerospace Information Research InstituteChinese Academy of SciencesBeijing 100101China University of chinese academy of {3. Beijing 100049China Department of Geographical sciences University of MarylandCollege ParkMD 20742USA

Waveform broadening effects of large-footprint lidar caused by terrain slopes are still a great challenge limiting the estimation accuracy of forest aboveground biomass(AGB)over mountainous ***-adaptive metrics of waveforms were proposed in our previous ***,its validation was limited by the unavailability of enough reference *** study made full validation of slope-adaptive metrics using data acquired by the Global Ecosystem Dynamics Investigation(GEDI)mission,meanwhile exploring GEDI waveforms on estimations of forest *** types of waveform metrics were employed,including slope-adaptive metrics(RHT),typical height metrics relative to ground peaks(RH),and waveform parameters(WP).In addition to terrain slopes,two other factors were also explored including the geolocation issue and signal start and ending points of *** showed that footprint geolocations in the first version GEDI data products were shifted to the left forward of nominal geolocations with a distance of about 24 m~3. m and were substantially corrected in the second version;the fourth and fifth groups of signal start and ending points of waveforms had worse performance than the rest of the four groups because they used the maximum and minimum signal thresholds,*** airborne laser scanner(ALS)data as reference,the root mean square error(RMSE)of terrain slopes extracted from the digital elevation model of the shuttle radar topography mission(SRTM DEM)was about 3..The coefficients of determination(R^(2))of estimation models of forest AGB based on RH metrics were improved from 0.48 to 0.68 with RMSE decreased from 19.7 Mg/ha to 15.4 Mg/ha by the second version *** RHT and WP metrics gave the best and the worst estimation accuracy,*** further improved R^(2) to 0.77 and decreased RMSE to 13.0 Mg/ha using terrain slopes extracted from SRTM DEM with a resolution of 1 arc second.R^(2) of estimation models based on RHT was finally

关键词： terrain estimation ground

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Characterization of ASTER GDEM elevation data over vegetated area compared with lidar data

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International Journal of Digital Earth 2015年第3期8卷 198-211页

作者： wenjian ni guoqing {3. Kenneth J.Ranson state key laboratory of {3. sensing science Institute of Remote Sensing and Digital EarthChinese Academy of SciencesBeijingChina Department of Geographical sciences University of MarylandCollege ParkMDUSA Biospheric sciences Branch NASA’s Goddard Space Flight CenterGreenbeltMDUSA

Current researches based on areal or spaceborne stereo images with very high resolutions(<1 m)have demonstrated that it is possible to derive vegetation height from stereo *** second version of the Advanced Spaceborne... 详细信息

Current researches based on areal or spaceborne stereo images with very high resolutions(state-of-the-art global elevation data-set developed by stereo ***,the resolution of ASTER stereo images(15 m)is much coarser than areal stereo images,and the ASTER GDEM is compiled products from stereo images acquired over 10 *** forest disturbances as well as forest growth are inevitable in 10 years time *** this study,the features of ASTER GDEM over vegetated areas under both flat and mountainous conditions were investigated by comparisons with lidar *** factors possibly affecting the extraction of vegetation canopy height considered include(1)co-registration of DEMs;(2)spatial resolution of digital elevation models(DEMs);(3.spatial vegetation structure;and(4)terrain *** results show that the accurate coregistration between ASTER GDEM and national elevation dataset(NED)is necessary over mountainous *** correlation between ASTER GDEM minus NED and vegetation canopy height is improved from 0.3.8 to 0.43.by degrading resolutions from 1 arc-second to 5 arc-second and further improved to 0.6 if only homogenous vegetated areas were considered.

关键词： vegetation canopy height ASTER GDEM NED photogrammetry stereo-mapping

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Regional Sampling of Forest Canopy Covers Using UAV Visible Stereoscopic Imagery for Assessment of Satellite-Based Products in Northeast china

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Journal of remote sensing 2022年第1期2022卷 311-324页

作者： Tianyu Yu wenjian ni Zhiyu Zhang Qinhuo Liu guoqing {3. state key laboratory of {3. sensing science Aerospace Information Research InstituteChinese Academy of SciencesBeijing 100101China University of chinese academy of {3. Beijing 100049China Department of Geographical sciences University of MarylandCollege ParkMD 20742USA

Canopy cover is an important parameter affecting forest succession,carbon fluxes,and wildlife *** global maps with different spatial resolutions have been produced based on satellite images,but facing the deficiency of reliable references for accuracy *** rapid development of unmanned aerial vehicle(UAV)equipped with consumer-grade camera enables the acquisition of high-resolution images at low cost,which provides the research community a promising tool to collect reference ***,it is still a challenge to distinguish tree crowns and understory green vegetation based on the UAV-based true color images(RGB)due to the limited spectral *** addition,the canopy height model(CHM)derived from photogrammetric point clouds has also been used to identify tree crowns but limited by the unavailability of understory terrain *** study proposed a simple method to distinguish tree crowns and understories based on UAV visible images,which was referred to as BAMOS for *** central idea of the BAMOS was the synergy of spectral information from digital orthophoto map(DOM)and structural information from digital surface model(DSM).Samples of canopy covers were produced by applying the BAMOS method on the UAV images collected at 77 sites with a size of about 1.0 km^(2) across Daxing’anling forested area in northeast of *** showed that canopy cover extracted by the BAMOS method was highly correlated to visually interpreted ones with correlation coefficient(r)of 0.96 and root mean square error(RMSE)of 5.7%.Then,the UAV-based canopy covers served as references for assessment of satellite-based maps,including MOD44B Version 6 Vegetation Continuous Fields(MODIS VCF),maps developed by the Global Land Cover Facility(GLCF)and by the Global Land Analysis and Discovery laboratory(GLAD).Results showed that both GLAD and GLCF canopy covers could capture the dominant spatial patterns,but GLAD canopy cover tended to miss scatte

关键词： maps Northeast Forest

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ICESat-2植被冠层高度和地表高程数据产品用于森林高度提取的效果评价

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遥感学报 2021年第6期25卷 1294-1307页

作者：董佳臣倪文俭张志玉孙国清中国科学院空天信息创新研究院遥感科学国家重点实验室北京100094 中国科学院大学资源与环境学院北京100049 美国马里兰大学地理系马里兰州College Park 美国20742

由美国宇航局(NASA)研制的新一代冰、云和陆地高程卫星(ICESat-2)于2018-09-15发射成功,其搭载的先进地形激光测高系统(ATLAS)采用微脉冲多波束光子计数激光雷达技术,可用于全球高程线采样数据的获取。目前公开发布了9种数据产品,其中... 详细信息

由美国宇航局(NASA)研制的新一代冰、云和陆地高程卫星(ICESat-2)于2018-09-15发射成功,其搭载的先进地形激光测高系统(ATLAS)采用微脉冲多波束光子计数激光雷达技术,可用于全球高程线采样数据的获取。目前公开发布了9种数据产品,其中包括植被冠层高度和地表高程数据产品(ATL08),为全球森林结构参数的估算提供了新的契机。本文以美国宾夕法尼亚州斯奈德县和印度尼西亚西加里曼丹吉打邦为研究区,在温带森林和热带雨林两种不同的生态系统立地条件下,对ICESat-2的ATL08数据产品用于森林高度估算的效果进行评价。首先建立了地形高程数据产品(ATL03.与ATL08数据产品的关联规则,以获取分别记录在这两种产品中的光子空间分布信息和分类信息;进而以机载小光斑激光雷达数据为参考,对ATL08数据产品的光子分类可靠性及其用于森林高度估算的准确性进行了分析评价。结果表明:(1)在温带森林情况下,ATL08数据产品提供的平均冠层高度和最大冠层高度与参考数据的相关系数(R~2)分别为0.54和0.61,相对误差分别为16.78%和10.71%,表明ATL08数据产品的光子分类结果能够用于刻画森林冠层结构和林下地形;(2)在热带雨林情况下,到达地面的光子数量相较于温带森林明显减少,地面光子类型识别的可靠性低,ATL08数据产品提供的平均冠层高度和最大冠层高度与参考数据的相关系数(R~)分别为0.21和0.19;(3.森林覆盖度的增大会导致ATL08计算的冠层高度误差增大,热带雨林平均冠层高度的误差随着坡度增大有增大趋势,在坡度为0°—10°、10°—20°和20°—3.°共3.情况下,误差分别为5.7 m、6.6 m和9.3.m。因此,在高森林覆盖度情况下,现有的ATL08数据产品难以直接用于森林高度的提取。

关键词： ICESat-2 ATLAS ATL08 森林结构参数

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