近15年新疆伊犁河谷草地退化时空变化特征   总被引：1，自引：0，他引：1  

闫俊杰  刘海军  崔东  陈晨 《草业科学》2018,35(3):508-520

以伊犁河谷为研究区,利用MODIS NDVI数据及像元二分模型,反演草地植被覆盖度,以草地植被覆盖度为评价标准,结合数字高程模型(digital elevation model,DEM)数据及Getis-Ord Gi*冷/热点分析方法,对伊犁河谷2001-2015年草地退化的时空特征进行了分析。结果表明,1)受持续过度放牧及气候条件影响,2001-2015年伊犁河谷草地整体持续退化,15年内退化草地比例达46.18%,但退化以轻度为主;2)空间上退化草地的分布范围逐步向高海拔区域扩展,海拔1 500-3 000 m的中山和中高山区退化草地扩张最明显;3)草地生态保护政策的实施减缓了草地退化速度,草地退化与改善的空间差异逐渐明显,以退化为主的单一变化趋势有所改变;4)利用NDVI反演植被覆盖度对草地退化进行评价的方法存在对高植被覆盖区域草地退化敏感性相对较弱的缺陷。  相似文献   

2000-2010年锡林郭勒草原NPP时空变化及其气候响应   总被引：2，自引：0，他引：2  

刘海江  尹思阳  孙聪  彭福利  周澎 《草业科学》2015,(11):1709-1720

利用MODIS MOD17A3植被初级生产力数据产品及地面气象观测数据,研究分析了2000-2010年锡林郭勒盟草原NPP的时空变化特征、各气候因子的年际变化特征及NPP与气候因子的相关关系。结果表明,锡林郭勒盟草原NPP的分布由东向西逐渐减小,值大多分布在0~0.5 kg C·m-2;2001-2010年NPP呈现波动变化,整体呈增加趋势,空间分布上更加趋于均匀分布;2000-2010年,研究区内典型草原和荒漠草原各气候因子的变化趋势大致相同,4-9月累计平均气温、平均相对湿度和累计日照时数呈减小趋势,平均风速呈增加趋势,累计降水量典型草原呈轻微减少趋势,荒漠草原呈增加趋势,趋势斜率分别为-0.026和1.044 5,典型草原大部分气候因子的波动程度大于荒漠草原;研究区内两种类型的草原的NPP均与4-9月累计平均气温、平均日最低气温有较强的负相关关系(显著水平分别为P0.001和P0.01),与累计降水量、平均相对湿度有较强的正相关关系(显著水平为P0.01),与4-9月累计日照时数、平均风速呈负相关关系但相关关系较弱,荒漠草原对气候因子变化的响应总体不如典型草原敏感。  相似文献   

Developing the framework for a risk map for mite vectored viruses in wheat resulting from pre-harvest hail damage     

《Crop Protection》2016

There is a strong economic incentive to reduce mite-vectored virus outbreaks. Most outbreaks in the central High Plains of the United States occur in the presence of volunteer wheat that emerges before harvest as a result of hail storms. This study provides a conceptual framework for developing a risk map for wheat diseases caused by mite-vectored viruses based on pre-harvest hail events. Traditional methods that use NDVI were found to be unsuitable due to low chlorophyll content in wheat at harvest. Site-level hyperspectral reflectance from mechanically hailed wheat showed increased canopy albedo. Therefore, any increase in NIR combined with large increases in red reflectance near harvest can be used to assign some level of risk. The regional model presented in this study utilized Landsat TM/ETM+ data and MODIS imagery to help gap-fill missing data. NOAA hail maps that estimate hail size were used to refine the area most likely at risk. The date range for each year was shifted to account for annual variations in crop phenology based on USDA Agriculture statistics for percent harvest of wheat. Between 2003 and 2013, there was a moderate trend (R² = 0.72) between the county-level insurance claims for Cheyenne County, Nebraska and the area determined to be at risk by the model (excluding the NOAA hail size product due to limited availability) when years with low hail claims (<400 ha) were excluded. These results demonstrate the potential of an operational risk map for mite-vectored viruses due to pre-season hail events.  相似文献   

Monitoring desertification processes in Mongolian Plateau using MODIS tasseled cap transformation and TGSI time series     

LIU Qingsheng  LIU Gaohuan  HUANG Chong 《干旱区科学》2018,10(1):12-26

Most remote sensing studies assess the desertification using vegetation monitoring method. But it has the insufficient precision of vegetation monitoring for the limited vegetation cover of the desertification region. Therefore, it offers an alternative approach for the desertification research to assess sand dune and sandy land change using remote sensing in the desertification region. In this study, the indices derived from the well-known tasseled cap transformation(TCT), tasseled cap angle(TCA),disturbance index(DI), process indicator(PI), and topsoil grain size index(TGSI) were integrated to monitor and assess the desertification at the thirteen study sites including sand dunes and sandy lands distributed in the Mongolian Plateau(MP) from 2000 to 2015. A decision tree was used to classify the desertification on a regional scale. The average overall accuracy of 2000, 2005, 2010 and 2015 desertification classification was higher than 90%. Results from this study indicated that integration of the advantages of TCA, DI and TGSI could better assess the desertification. During the last 16 years, Badain Jaran Desert, Tengger Desert, and Ulan Buh Desert showed a relative stabilization. Otindag Sandy Land and the deserts of Khar Nuur, Ereen Nuur, Tsagan Nuur, Khongoryn Els, Hobq, and Mu Us showed a slow increasing of desertification, whereas Bayan Gobi, Horqin and Hulun Buir sandy lands showed a slow decreasing of desertification. Compared with the other 11 sites, the fine sand dunes occupied the majority of the Tengger Desert, and the coarse sandy land occupied the majority of the Horqin Sandy Land. Our findings on a three or four years' periodical fluctuated changes in the desertification may possibly reflect changing precipitation and soil moisture in the MP. Further work to link the TCA, DI,TGSI, and PI values with the desertification characteristics is recommended to set the thresholds and improve the assessment accuracy with field investigation.  相似文献   

Monitoring forage production for farmers’ decision making     

Gonzalo Grigera  Martín OesterheldFernando Pacín 《Agricultural Systems》2007

Objective management of grazing livestock production systems needs monitoring of forage production at the managerial unit level. Our objectives were to develop a system that routinely estimates forage above-ground net primary production (ANPP) at the spatial and temporal resolution required by farmers in the Pampas of Argentina, and to facilitate adoption of the system by end users as a managerial support tool. Our approach was based on the radiation use efficiency (RUE) logic, which proposes that ANPP is determined by the amount of photosynthetically active radiation absorbed by the canopy (APAR), and the efficiency with which that energy is transformed in above-ground dry matter (radiation use efficiency, RUE). APAR is the product of incoming photosynthetically active radiation (PAR) and the fraction absorbed by the canopy (fPAR). We estimated fPAR as a non-linear function of MODIS normalized difference vegetation index (NDVI). RUE was empirically estimated for the two principal forage resources of the region, yielding the following relations: ANPP = 0.6 × APAR + 12, (R² = 0.86; p < 0.001; n = 18) for the upland sown pastures, and ANPP = 0.27 × APAR + 26, (R² = 0.74; p < 0.001; n = 18) for the lowland naturalized pastures, with ANPP in g/m²/60 days and APAR in MJ/m²/60 days. The models were able to predict independent ANPP values with acceptable accuracy. Computational procedures were automated and run in a Relational Data Base Manager System that stored and managed all the information. The system is currently monitoring 212,794 ha in 83 farms and provides monthly ANPP values for the previous month and a history of the last 6 years. The data so generated show ANPP differences between the two major forage resources, considerable variability of a given month’s ANPP among years and paddocks, and contrasting among-farm differences in the efficiency of conversion of ANPP and forage supplements into beef production. The system was well accepted by end users who utilize it mainly for making near real time decisions according to last month ANPP, and explaining results of previous production cycles by incorporating ANPP as an explicative variable. However, there were differences among farmers in the degree of utilization, apparently related to the advisor’s attitude toward this new technology. Our results indicate that (1) forage production of large extensions can be monthly monitored at the paddock level by a small laboratory with capabilities in geographic information systems, and (2) advisors and farmers apply this information to their managerial decisions.  相似文献   

玉溪市林分植被覆盖变化及驱动力分析     

朱洪琴  王敬文  许彦红  期俊程  罗航  彭泽喜 《林业资源管理》2021,(1):121-131

林分植被覆盖在很大程度上能够反映林分生态系统的健康与否,其时空变化是林分生态系统发展方向的判断依据。对玉溪市2010—2019年林分植被覆盖的时空格局变化进行了分析,并利用单因素和多元回归分析方法分别建立回归模型探索了林分植被覆盖改善与退化的驱动因素。结果表明:林分植被覆盖整体呈向好趋势,各驱动因素与斜率均不是简单线性关系;道路和居民区与林分植被覆盖改善速度呈负相关、与退化速度呈正相关;DEM、坡度、大型水体、公益林管护与林分植被覆盖改善速度呈正相关、与退化速度呈负相关;坡向与林分植被覆盖改善速度呈正相关,地形起伏度与林分植被覆盖退化速度呈负相关。林分植被覆盖改善与退化的驱动力不尽相同,影响机制也存在差异,这为更好制定生态保护相关政策提供了有力的科学依据。  相似文献   

基于Google Earth Engine平台的关中冬小麦面积时空变化监测   总被引：1，自引：0，他引：1  

郭新  王乃江  张玲玲  郭永强  褚晓升  冯浩 《干旱地区农业研究》2020,38(3):275-280

以关中地区为研究区,基于Google Earth Engine(GEE)平台,根据冬小麦生育期内归一化植被指数(NDVI)时序曲线和物候特征,采用NDVI重构增幅算法和光谱突变斜率,构建了关中地区冬小麦提取模型并实现了冬小麦种植面积的提取。用农业统计面积验证提取结果表明:在市级和县级尺度上,决定系数R~2分别为0.82和0.62,一致性指标d分别为0.95和0.84,提取结果与实地调查数据的空间一致性精度为93.4%。结果显示:关中地区冬小麦主要分布在中部关中平原,冬小麦种植面积在2011—2017年呈下降趋势,减少了83.22×10~3 hm~2(8.47%)。综合考虑冬小麦NDVI时序曲线的"峰""谷"特征,具有一定的普适性,可为大面积连续年份冬小麦种植面积时空监测提供参考。  相似文献   

基于MODIS TVDI和模糊数学方法的藏北地区旱情等级遥感监测   总被引：1，自引：0，他引：1  

刘一哲  冯文兰  扎西央宗  梁丽  李潼 《干旱区研究》2020,(1):86-96

为了实现对藏北区域范围内春夏旱情的动态连续监测,基于温度植被干旱指数(TVDI)和模糊数学方法建立了遥感干旱的划分标准,研究时段为1980-2017年。首先利用MODIS产品数据计算TVDI,然后根据气象干旱等级监测结果,采用模糊数学法建立基于MODIS TVDI的干旱等级划分标准,并对监测结果进行精度验证,最后分析了近年来藏北地区旱情的时空变化特征。得到的主要结论:①基于归一化植被指数(NDVI)和增强植被指数(EVI)计算得到的温度植被干旱指数TVDIN和TVDIE,均与20 cm实测土壤水分含量在0.05的水平达到显著相关,TVDIE的决定系数更高;②基于TVDIE将旱情划分为无旱、轻旱、中旱、重旱、特旱5个等级,其中,据此标准获得的藏北地区旱情等级与气象干旱等级监测结果大体一致;③近年来藏北地区旱情整体不太严重,且总体趋缓,其中,2009年最严重,发生中旱及以上旱情的区域面积达24%,年内旱情在6月最严重。就旱情的空间分布特征而言,研究区西南部和中部干旱比较严重,北部和东南部相对较轻。研究成果可为藏北地区干旱监测提供数据支撑,遥感干旱等级的划分方法可为其他地区的干旱研究提供参考。  相似文献   

基于MODIS数据的河套灌区遥感干旱监测   总被引：4，自引：3，他引：1  

罗彪  刘潇  郭萍 《中国农业大学学报》2020,25(10):44-54

基于MODIS数据,以河套灌区为研究对象,计算灌区2000—2018年作物主要生育期内(5—8月)4种遥感干旱指数、温度植被干旱指数(TVDI)、植被供水指数(VSWI)、植被状态指数(VCI)、温度状态指数(TCI),并分析了4种干旱指数与0～20cm土壤相对含水量、降水量、灌区引水量相关性以及4种干旱指数之间的相互关系。结果表明:经过相关分析,TVDI与土壤相对含水量的相关性优于其他3种遥感干旱指数;在灌溉水量较多的灌区,遥感干旱指数与降雨量相关性较小而与灌区引水量呈现一定的相关关系。本研究发现TVDI在河套灌区有着良好的适用性。此外,在干旱监测中综合利用多种干旱指数进行分析对提高监测精度,科学合理地预报旱情具有重要意义。  相似文献   

基于多源遥感数据的综合干旱监测模型构建   总被引：1，自引：7，他引：1  

杜灵通  田庆久  王磊  黄彦  南岭 《农业工程学报》2014,30(9):126-132

在全球气候变化越来越复杂的大背景下,准确监测华北粮食主产区的旱情对区域农业生产有重要的指导意义。以往的遥感干旱监测方法多侧重于监测土壤或植被等单一干旱响应因子,反映综合信息的能力较差,为此该研究使用中分辨率成像光谱仪(moderate-resolution imaging spectroradiometer,MODIS)、热带降水测量计划(tropical rainfall measuring mission,TRMM)卫星等多源遥感数据,在综合考虑干旱发生发展过程中的土壤水分胁迫、植被生长状态和气象降水盈亏等因素的基础上,利用空间数据挖掘技术,构建综合干旱监测模型,并以山东省为例进行了试验验证。结果表明,模型监测出山东省近年来所经历的重大干旱过程与实际旱情一致,模型输出的旱情指标-综合干旱指数(synthesized drought index,SDI)与小麦的标准化作物单产变量的相关系数均大于0.7(P0.05);在小麦和玉米的生长期,综合干旱指数与作物受灾面积的相关系数在-0.67～-0.85之间,与标准化降水指数(standardized precipitation index,SPI)的相关系数在0.44～0.67之间,且通过了P0.01的极显著检验(3月份除外)。研究结果为综合评估区域干旱提供了一种新的方法。  相似文献