共查询到20条相似文献，搜索用时 328 毫秒
1.
湿地边界的界定研究是湿地科学的基础研究.湿地水文特征是界定湿地边界的唯一可靠标准.论文以洪河自然保护区为试验区,围绕湿地水文特征指标,构建了沼泽湿地的"淹埋深-历时-频率"阈值研究的理论和方法,并利用沼泽植被边界处的长时间序列的"水位-历时"过程线反演了湿地的"淹埋深-历时-频率阈值",并利用该阈值界定了湿地水文边界,主要研究结论如下:(1) McNemar's 统计检验表明,与单一极化SAR 数据集和不同波长极化SAR 整合数据集相比,ZY-3 多光谱和极化SAR 整合数据集显著提高了湿地植被的分类精度和识别能力,总体分类精度达到了94 .15% ,从用户精度上来看:浅水沼泽植被在单一的极化SAR 数据集中分类精度高于灌草植被和深水沼泽植被,Radarsat-2 和PALSAR 的整合数据集提高了灌草植被和深水沼泽植被的识别精度.从生产者精度上来看,浅水沼泽植被和深水沼泽湿在单一极化SAR 影像中的识别精度均高于灌草植被,ZY-3 和Radarsat-2 的整合数据集使灌草植被的精度提高了14 .7% ,达到了89 .41% . 相似文献
2.
针对以光谱特征差异为依据,提取森林湿地信息精度低的问题,该文采用兼容多源数据的分类回归树(CART)提取方法,并以大沾河国家森林湿地进行实证研究。基于Landsat8遥感数据、Radarsat-2极化雷达数据和地形辅助数据,采用SPM软件分别构建3种特征变量组合的CART决策树模型,并获取分类规则,最后根据规则对研究区的森林湿地信息进行提取。结果表明:3种特征变量组合中,兼容光谱、纹理、雷达与地形辅助数据的CART决策树的森林湿地信息提取精度最高,用户精度和制图精度分别达到了88.46%和82.14%。研究结果体现了雷达数据与地形辅助数据有助于提取森林湿地信息。 相似文献
3.
鄱阳湖是中国最大的淡水湖,也是国际重要湿地,对其生物量进行长期、定量研究有助于加深对区域乃至全球碳平衡的认识和理解。探讨了利用全极化Radarsat-2 C波段数据反演鄱阳湖湿地生物量的方法,改进了基于辐射传输理论的植被冠层散射模型,模拟了C波段湿地植被的后向散射特性;应用极化分解技术,增加了神经网络训练数据,并用后向反馈神经网络(BP)算法,反演了鄱阳湖湿地植被生物量。与野外实测生物量比较的结果表明:将改进的植被冠层散射模型和全极化分解得到的后向散射系数引入BP神经网络算法,能够有效降低生物量反演误差;全极化SAR数据在生物量反演中具有广阔的应用前景。 相似文献
4.
基于极化分解原理,获取了描述地物散射机制的特征参数,并组合成一些特征指数,如雷达植被指数等。这些特征指数具有反映体散射信息的能力,从而可间接获取植被长势、疏密程度及分布区域等信息。实验选择了鄱阳湖区Radarsat-2全极化数据,结合野外采集的样本数据,在分析该区植被特征的基础上,对不同特征参数进行了对比分析,对雷达植被指数与实地测量样本的生物量参数进行了相关分析。实验结果表明:文中给出的4种特征参数对植被引起的随机散射的描述总体趋势是一致的,但随着植被覆盖密度的增大,不同特征指数具有一定的差异,其中雷达植被指数最为准确,适用动态范围最大,并且与湿地植被生物量具有较高的线性相关性,可以定量地反映研究区的植被疏密及生物量差异信息。 相似文献
5.
现有的水下地形SAR(Synthetic Aperture Radar)探测模型尚未综合应用SAR的极化信息。本文基于Valenzuela的雷达散射截面表达式与袁业立提出的海波高频谱表达式,并结合全极化SAR相干斑抑制的极化白化滤波法,将极化信息有效地运用到水下地形SAR探测中去。最后,以中国台湾浅滩为例,分别利用Radarsat-2单一极化和全极化影像开展水下地形SAR探测研究,探测结果表明充分利用全极化信息的探测精度明显优于单一极化信息的探测精度,利用极化信息可以有效地提高水下地形SAR探测精度。 相似文献
6.
黄河三角洲湿地的动态变化监测对湿地资源合理利用、开发保护具有重要意义。采用C波段全极化高分三号（GF-3）合成孔径雷达数据与欧洲空间局哨兵二号（Sentinel-2B）多光谱数据,分析了黄河三角洲湿地7类地物的光谱、指数、极化散射以及纹理等特征信息,分别基于最大似然法（maximum likelihood,ML）、决策树（decision tree,DT）、支持向量机（support vector machine,SVM）方法实现了有监督分类,评估了两者协同与单独应用于湿地地物分类与识别的能力,结果表明,两者协同分类时,其总体精度分别可达90.4%、95.4%、95.7%,均明显高于两者单独分类的结果,证明了GF-3雷达数据与多光谱数据在湿地协同分类方面的可靠性和应用潜力。 相似文献
7.
以新疆渭库绿洲为研究区,对Radarsat-2全极化数据进行Freeman-Durden和H/α这2种目标极化分解处理,得到相应的特征参数,结合SVM-Wishart半监督分类方法对研究区土壤盐渍化信息进行提取,并利用目视判读和野外实地考察对分类结果进行分析验证。研究结果表明:①应用不同极化分解得到的特征参数进行影像类型识别和参数特征空间构建,不同参数信息识别度不同,且参数之间特征空间分布不同,其中H/α分解后特征参数构成的特征空间存在明显规律;②利用SVM-Wishart半监督分类方法对Freeman-Durden分解和H/α分解结果进行分类,Freeman-Durden分解后分类效果优于H/α分解分类效果,分类精度分别达88. 00%和78. 96%;③SVMWishart半监督分类优于传统的SVM分类效果,可以较好地提取研究区土壤盐渍化信息。SVM-Wishart半监督分类可对极化非相干分解后得到的特征参数进行较充分的挖掘,并使分类结果得到一定程度的提高,在区域土壤盐渍化信息提取中具有优势。 相似文献
8.
《国土资源遥感》2017,(2)
以Radarsat-2为例,提出了一种利用多极化SAR影像并结合后向散射模型提取建筑物高度的方法。以北京城区为实验区,首先,分析了SAR影像中建筑物二次散射所对应的亮线连通区域,并统计出该区域对雷达后向散射截面的贡献量;然后,基于平行六面体假设,将建筑物主长度及其与雷达方位向的夹角定量化,并给出计算不同极化散射矢量的方法;最后,利用几何光学-物理光学(geometrical optics-physical optics,GO-PO)模型一阶近似解的后向散射模型估计建筑物高度,并通过比较多个局部训练区提取结果,探讨不同极化信息的提取效果并给出最优极化组合。实验结果表明,通过极化特征组合比仅利用单极化信息提取建筑物高度的精度更高,81.43%建筑物误差小于5 m,均方根误差4.45 m,与ASTER GDEM相关系数为0.909 5,提取结果可靠。 相似文献
9.
极化合成孔径雷达数据蕴含了丰富的地物极化散射信息,已广泛应用于海上舰船目标检测研究。针对极化相干矩阵无法直接用于分析特定散射体物理特性的缺陷,利用Yamaguchi极化分解改进了极化Notch滤波器。将基于模型的极化分解方法引入Notch滤波器,利用表面散射、二次散射、体散射和螺旋体散射等散射机制的能量构造散射矢量代替极化相干散射矢量,并加入功率能量因子,构造新的极化SAR图像Notch滤波器。Radarsat-2全极化SAR图像实验结果表明,改进算法有效增强了舰船目标与海杂波背景间的对比度,检测性能优越。 相似文献
10.
由于SAR斜距成像几何方式及地形起伏的影响,原始SAR影像存在透视收缩、叠掩、阴影等严重的几何畸变和辐射畸变。其中,叠掩区具有强烈的后向散射回波,在极化SAR影像的分类研究中容易造成林地与居民地等地物混分,降低分类的精度。针对该问题,本文研究一种地形辐射校正方法,引入投影角计算后向散射系数γ0,有效地解决了地形起伏造成的辐射畸变问题。选取一景全极化Radarsat-2影像进行实验验证,分别对地形辐射校正前后的极化SAR影像进行了复Wishart监督分类。通过对分类结果的比较,表明经本文地形辐射校正方法处理后,极化SAR影像的分类精度得到了改善。 相似文献
11.
Mingshu Wang Marguerite Madden Ian Hendy Estradivari Gabby N. Ahmadia 《International Journal of Digital Earth》2017,10(4):457-468
ABSTRACTMangroves are critical in the ecological, economic and social development of coastal rural and urban communities. However, they are under threat by climate change and anthropogenic activities. The Sunda Banda Seascape (SBS), Indonesia, is among the world’s richest regions of mangrove biomass and biodiversity. To inform current and future management strategies, it is critical to provide estimates of how mangroves will respond to climate change in this region. Therefore, this paper utilized spatial analysis with model-based climatic indicators (temperature and precipitation) and mangrove distribution maps to estimate a benchmark for the mangrove biomass of the SBS in six scenarios, namely the Last Inter-glacial Period, the current scenario (1950–2000) and all four projected Representative Concentration Pathways in 2070 due to climate change. Despite mangroves gaining more biomass with climate change (the increase in CO2 concentration), this paper highlighted the great proportion of below-ground biomass in mangrove forests. It also showed that the changes in spatial distribution of mangrove biomass became more variable in the context of climate change. As mangroves have been proposed as an essential component of climate change strategies, this study can serve as a baseline for future studies and resource management strategies. 相似文献
12.
13.
Shufen Pan Guangsheng Chen Wei Ren Shree R. S. Dangal Kamaljit Banger Jia Yang 《International Journal of Digital Earth》2018,11(6):558-582
Terrestrial ecosystems play a significant role in global carbon and water cycles because of the substantial amount of carbon assimilated through net primary production and large amount of water loss through evapotranspiration (ET). Using a process-based ecosystem model, we investigate the potential effects of climate change and rising atmospheric CO2 concentration on global terrestrial ecosystem water use efficiency (WUE) during the twenty-first century. Future climate change would reduce global WUE by 16.3% under high-emission climate change scenario (A2) and 2.2% under low-emission climate scenario (B1) during 2010–2099. However, the combination of rising atmospheric CO2 concentration and climate change would increase global WUE by 7.9% and 9.4% under A2 and B1 climate scenarios, respectively. This suggests that rising atmospheric CO2 concentration could ameliorate climate change-induced WUE decline. Future WUE would increase significantly at the high-latitude regions but decrease at the low-latitude regions under combined changes in climate and atmospheric CO2. The largest increase of WUE would occur in tundra and boreal needleleaf deciduous forest under the combined A2 climate and atmospheric CO2 scenario. More accurate prediction of WUE requires deeper understanding on the responses of ET to rising atmospheric CO2 concentrations and its interactions with climate. 相似文献
14.
Ranganath R. Navalgund Raghavendra P. Singh 《Journal of the Indian Society of Remote Sensing》2011,39(3):281-295
Climate change is associated with earth radiation budget that depends upon incoming solar radiation, surface albedo and radiative forcing by greenhouse gases. Human activities are contributing to climate change by causing changes in Earth’s atmosphere (greenhouse gases, aerosols) and biosphere (deforestation, urbanization, irrigation). Long term and precise measurements from calibrated global observation constellation is a vital component in climate system modelling. Space based records of biosphere, cryosphere, hydrosphere and atmosphere over more than three decades are providing important information on climate change. Space observations are an important source of climate variables due to multi scale simultaneous observation (local, regional, and global scales) capability with temporal revisit in tune with requirements of land, ocean and atmospheric processes. Essential climatic variables that can be measured from space include atmosphere (upper air temperature, water vapour, precipitation, clouds, aerosols, GHGs etc.), ocean (sea ice, sea level, SST, salinity, ocean colour etc.) and land (snow, glacier, albedo, biomass, LAI/fAPAR, soil moisture etc.). India’s Earth Observation Programme addresses various aspects of land, ocean and atmospheric applications. The present and planned missions such as Resourcesat-1, Oceansat-2, RISAT, Megha-Tropiques, INSAT-3D, SARAL, Resourcesat-2, Geo-HR Imager and series of Environmental satellites (I-STAG) would help in understanding the issues related to climate changes. The paper reviews observational needs, space observation systems and studies that have been carried out at ISRO (Indian Space Research Organization) towards mapping/detecting the indicators of climate change, monitoring the agents of climate change and understanding the impact of climate change, in national perspectives. Studies to assess glacier retreat, changes in polar ice cover, timberline change and coral bleaching are being carried out towards monitoring of climate change indicators. Spatial methane inventories from paddy rice, livestock and wetlands have been prepared and seasonal pattern of CO2, and CO have been analysed. Future challenges in space observations include design and placement of adequate and accurate multi-platform observational systems to monitor all parameters related to various interaction processes and generation of long term calibrated climate data records pertaining to land ocean and atmosphere. 相似文献
15.
Background
Anthropogenic CO2 uptake by the ocean decreases the pH of seawater, leading to an 'acidification' which may have potential detrimental consequences on marine organisms [1]. Ocean warming or circulation alterations induced by climate change has the potential to slowdown the rate of acidification of ocean waters by decreasing the amount of CO2 uptake by the ocean [2]. However, a recent study showed that climate change affected the decrease in pH insignificantly [3]. Here, we examine the sensitivity of future oceanic acidification to climate change feedbacks within a coupled atmosphere-ocean model and find that ocean warming dominates the climate change feedbacks. 相似文献16.
Although climate change is highly prevalent in the media, people in Europe and the United States are often unsure about climate change terms, processes, and its personal consequences. In other words, climate change communication seems to be largely failing so far. Among other communication tools, maps are widely used for explanatory purposes by scientists and the media. Here two questions arise: first, whether high map complexity may be too intricate to be understood and discourage people from deciphering the map; and second, whether personal interest in climate change can be influenced by the phenomenon depicted or the map’s scale. In a survey conducted among 109 students in the USA, 63% of respondents preferred a simple map, but a substantial subset, 37%, asked for complexity to receive more information. Regional phenomena evoked more concern than far-off phenomena (concern level index difference of 0.93 on a 5-ranked Likert scale). The advantage of maps showing local areas could not be statistically confirmed. 相似文献
17.
Meng Qi Hu Fei Mao Han Sun Ying Yu Hou 《International Journal of Applied Earth Observation and Geoinformation》2011
Using NOAA/AVHRR 10-day composite NDVI data and 10-day meteorological data, including air temperature, precipitation, vapor pressure, wind velocity and sunshine duration, at 19 weather stations in the three-river-source region in the Qinghai–Tibetan Plateau in China from 1982 to 2000, the variations of NDVI and climate factors were analyzed for the purpose of studying the correlation between climate change and vegetation growth as represented by NDVI in this region. Results showed that the NDVI values in this region gradually grew from the west to the east, and the distribution was consistent with that of moisture status. The growing season came earlier due to climate warming, yet because of the reduction of precipitation, maximal NDVI during 1982–2000 did not show a significant change. NDVI related positively to air temperature, vapor pressure and precipitation, but negatively related to sunshine duration and wind velocity. Furthermore, the response of NDVI to climate change showed time lags for different climate factors. Water condition and temperature were found to be the most important factors effecting the variation of NDVI during the growing season in both the semi-arid and the semi-humid areas. In addition, NDVI had a better correlation with vapor pressure than with precipitation. The ratio of precipitation to evapotranspiration, representing water gain and loss, can be regarded as a comprehensive index to analyze NDVI and climate change, especially in areas where the water condition plays a dominant role. 相似文献
18.
Biodiversity Conservation in the REDD 总被引：1，自引：0，他引：1
Gary D Paoli Philip L Wells Erik Meijaard Matthew J Struebig Andrew J Marshall Krystof Obidzinski Aseng Tan Andjar Rafiastanto Betsy Yaap JW Ferry Slik Alexandra Morel Balu Perumal Niels Wielaard Simon Husson Laura D'Arcy 《Carbon balance and management》2010,5(1):1-9
Background
Forests occur across diverse biomes, each of which shows a specific composition of plant communities associated with the particular climate regimes. Predicted future climate change will have impacts on the vulnerability and productivity of forests; in some regions higher temperatures will extend the growing season and thus improve forest productivity, while changed annual precipitation patterns may show disadvantageous effects in areas, where water availability is restricted. While adaptation of forests to predicted future climate scenarios has been intensively studied, less attention was paid to mitigation strategies such as the introduction of tree species well adapted to changing environmental conditions.Results
We simulated the development of managed forest ecosystems in Germany for the time period between 2000 and 2100 under different forest management regimes and climate change scenarios. The management regimes reflect different rotation periods, harvesting intensities and species selection for reforestations. The climate change scenarios were taken from the IPCC's Special Report on Emission Scenarios (SRES). We used the scenarios A1B (rapid and successful economic development) and B1 (high level of environmental and social consciousness combined with a globally coherent approach to a more sustainable development). Our results indicate that the effects of different climate change scenarios on the future productivity and species composition of German forests are minor compared to the effects of forest management.Conclusions
The inherent natural adaptive capacity of forest ecosystems to changing environmental conditions is limited by the long life time of trees. Planting of adapted species and forest management will reduce the impact of predicted future climate change on forests. 相似文献19.
利用遥感和GIS研究内蒙古中西部地区环境变化 总被引：22，自引：1，他引：22
利用TM和MSS卫星遥感数据提取反映生态环境的植被、土壤亮度、湿度、热度指数，结合气候数据和其它地学辅助信息，在GIS的支持下建立环境质量评价模型；利用该模型评价了内蒙古中西部地区19876、1987、1996年跨越20年的环境变化，从区域平均环境质量指数的变化和各级指数分布的区域面积变化两方面说明了研究区20年来的环境退化；分析了气候因子对环境质量变化的影响，定量说明了半干旱地区影响环境变化的气候因子主要是湿润度，指出20年来人为因素对环境质量的影响呈现越来越大的趋势。 相似文献
20.
Muhammad Al-Amin Hoque Stuart Phinn Chris Roelfsema Iraphne Childs 《International Journal of Digital Earth》2018,11(3):246-263
Tropical cyclones and their devastating impacts are of great concern to coastal communities globally. An appropriate approach integrating climate change scenarios at local scales is essential for producing detailed risk models to support cyclone mitigation measures. This study developed a simple cyclone risk-modelling approach under present and future climate change scenarios using geospatial techniques at local scales, and tested using a case study in Sarankhola Upazila from coastal Bangladesh. Linear storm-surge models were developed up to 100-year return periods. A local sea level rise scenario of 0.34?m for the year 2050 was integrated with surge models to assess the climate change impact. The resultant storm-surge models were used in the risk-modelling procedures. The developed risk models successfully identified the spatial extent and levels of risk that match with actual extent and levels within an acceptable limit of deviation. The result showed that cyclone risk areas increased with the increase of return period. The study also revealed that climate change scenario intensified the cyclone risk area by 5–10% in every return period. The findings indicate this approach has the potential to model cyclone risk in other similar coastal environments for developing mitigation plans and strategies. 相似文献