Regional soil organic carbon prediction model based on a discrete wavelet analysis of hyperspectral satellite data     

《International Journal of Applied Earth Observation and Geoinformation》2020

Most studies have the achieved rapid and accurate determination of soil organic carbon (SOC) using laboratory spectroscopy; however, it remains difficult to map the spatial distribution of SOC. To predict and map SOC at a regional scale, we obtained fourteen hyperspectral images from the Gaofen-5 (GF-5) satellite and decomposed and reconstructed the original reflectance (OR) and the first derivative reflectance (FDR) using discrete wavelet transform (DWT) at different scales. At these different scales, as inputs, we selected the 3 optimal bands with the highest weight coefficient using principal component analysis and chose the normalized difference index (NDI), ratio index (RI) and difference index (DI) with the strongest correlation with the SOC content using a contour map method. These inputs were then used to build regional-scale SOC prediction models using random forest (RF), support vector machine (SVM) and back-propagation neural network (BPNN) algorithms. The results indicated that: 1) at a low decomposition scale, DWT can effectively eliminate the noise in satellite hyperspectral data, and the FDR combined with DWT can improve the SOC prediction accuracy significantly; 2) the method of selecting inputs using principal component analysis and a contour map can eliminate the redundancy of hyperspectral data while retaining the physical meaning of the inputs. For the model with the highest prediction accuracy, the inputs were all derived from the wavelength range of SOC variations; 3) the differences in prediction accuracy among the different prediction models are small; and 4) the SOC prediction accuracy using hyperspectral satellite data is greatly improved compared with that of previous SOC prediction studies using multispectral satellite data. This study provides a highly robust and accurate method for predicting and mapping regional SOC contents.  相似文献   

Effect of farmland expansion on drought over the past century in Songnen Plain,Northeast China     

Yu  Wanhui  Zhang  Lijuan  Zhang  Hongwen  Jiang  Lanqi  Zhang  Ankang  Pan  Tao 《地理学报(英文版)》2020,30(3):439-454

The effects of human activities on climate change are a significant area of research in the field of global environmental change. Land use and land cover change(LUCC) has a greater effect on climate than greenhouse gases, and the effect of farmland expansion on regional drought is particularly important. From the 1910 s to the 2010 s, cultivated land in Songnen Plain increased by 2.67 times, the area of cultivated land increased from 4.92×10~4 km~2 to 13.14×10~4 km~2, and its percentage of all land increased from 25% to 70%. This provides an opportunity to study the effects of the conversion of natural grassland to farmland on climate. In this study, the drought indices in Songnen Plain were evaluated from the 1910 s to the 2010 s, and the effect of farmland expansion on drought was investigated using statistical methods and the Weather Research and Forecasting Model based on UK's Climatic Research Unit data. The resulting dryness index, Palmer drought severity index, and standardized precipitation index values indicated a significant drying trend in the study area from 1981 to 2010. This trend can be attributed to increases in maximum temperature and diurnal temperature range, which increased the degree of drought. Based on statistical analysis and simulation, the maximum temperature, diurnal temperature range, and sensible heat flux increased during the growing season in Songnen Plain over the past 100 years, while the minimum temperature and latent heat flux decreased. The findings indicate that farmland expansion caused a drying trend in Songnen Plain during the study period.  相似文献   

一次暴雨过程受不同系统影响的动力热力场结构特征     

任丽  关铭  李有缘  王深义 《气象科技》2019,47(6):959-968

本文使用常规观测资料、卫星云图、自动气象站降水量以及0.25°×0.25°的NCEP/NCAR再分析资料,对出现在东北地区北部受不同系统影响的连续2d暴雨过程的热力和动力场结构特征展开研究。结果表明:24日为暖锋锋生暴雨,暴雨范围大;25日为台风暴雨,暴雨出现在台风移动路径上,为狭长带状。暴雨是由MCS活动造成的,每次短时强降水均与TBB低值中心相对应,台风倒槽内的MCS强度比暖锋云系内的MCS弱,但是降水强度却更大。台风安比携带大量暖湿空气,其东侧的低空急流向北输送热量和水汽,水汽辐合集中在边界层内,台风暴雨的水汽辐合强度比暖锋暴雨更强烈,所造成的雨强更大。暖锋暴雨期间,小兴安岭迎风坡地形的辐合抬升作用明显;高层强辐散及地形辐合抬升作用对暴雨有较大贡献。台风暴雨期间,低空辐合,特别是水汽辐合作用对暴雨有较大贡献;辐合区位于台风倒槽附近,倒槽表现为冷锋性质。  相似文献   

基于NCEP CFSv2模式的黑龙江省夏季降水预测研究     

班晋  王波  李永生  赵佳莹 《气象与环境学报》2019,35(6):21-27

基于1982-2017年NCEP_CFSv2（NCEP Climate Forecast System version 2）模式预测资料对黑龙江省夏季降水进行降尺度预测。通过分析黑龙江省夏季降水与同期环流因子的关系、模式对关键区环流因子的预测,选取模式模拟与再分析资料相关较好、黑龙江降水实况与再分析资料关系较好的环流因子作为预测因子,结合最优子集回归法筛选因子,建立降尺度预测模型,最后采用交叉检验法进行预测效果检验和独立样本预测。结果表明：模式降尺度预测与实况的距平符号-致率为69%,6 a独立样本预测中有5 a预测正确,优于目前的业务预测效果。进-步研究发现,在模式能够准确预测环流因子的情况下,模式降尺度可以较好地预测黑龙江省夏季降水的趋势。此外,模式降尺度在拉尼娜年预测效果较好。  相似文献   

基于多模式集成冬半年气温预报偏差修正     

齐铎  刘松涛  赵广娜  高梦竹 《气象与环境学报》2022,38(3):119-126

卡尔曼滤波递减平均方法对模式直接输出的气温预报进行订正,能有效提高预报准确率,但有时会造成显著负订正的现象,使订正预报效果反而不及模式直接输出。利用消除偏差集合平均方法(BREM)选择最优滑动训练期对2019年10月至2020年4月ECMWF预报(EC)、经过卡尔曼滤波递减平均法订正的预报(EC_COR)及中央台网格指导预报(SCMOC)等3种气温预报在黑龙江省的结果进行集成,并将BREM方法对EC_COR的修正效果进行评估,结果表明:不同预报结果都表现为冬季和夜间预报的准确率更低,气温偏低的11月至翌年1月更倾向于表现出预报较实况系统性偏高的特点。BREM方法能有效地修正EC_COR对EC负订正的现象,且可显著高于任何一种参与集成的单一预报效果。可在对单一模式进行卡尔曼滤波递减平均订正的基础上,进一步提升预报质量。另外,利用集成方法对高质量预报产品的融合(不局限于模式直接输出预报或是订正预报)可获取较单一预报更优的预报结果。  相似文献   

西辽河流域归一化植被指数与气象因子相关性分析     

田宝星  刘丹  宫丽娟  赵放  季生太  赵慧颖  于成龙 《气象与环境学报》2021,37(3):88-93

为了解西辽河流域归一化植被指数(NDVI)的分布规律、变化趋势及对气候变化的响应,利用2000—2018年西辽河流域11个气象站逐日气象资料和MODIS归一化植被指数数据集,通过线性回归和相关分析,探讨了生长季各月NDVI与气象因子的时滞性,以及气象站周围10 km缓冲区内不同植被类型NDVI与气象因子的相关性。结果表明：西辽河流域年平均气温、最高气温、最低气温和降水量均呈上升趋势。NDVI呈上升趋势,植被有所改善,不同植被类型NDVI均呈增加趋势,耕地增加趋势最快,耕地长势受益于农事活动的完善和增进。NDVI空间分布呈现中间低,四周高特点。生长季各月NDVI与降水量存在明显的滞后性,滞后期为1个月;仅8月NDVI与前1个月平均气温和最高气温存在滞后性。不同植被类型NDVI与平均气温、最高气温的相关性密切。耕地NDVI与气象因子的相关性较好。研究结果可为维护西辽河流域生态系统平衡提供参考。  相似文献   

Planning of Water-Saving Green Space System Based on GIS Technology and Archydrodata Model     

Liu  Dongmin  Wang  Daqing  Du  Guoming  Yuan  Shuai  Yu  Chang  Zhao  Meng  Fang  Li  Fu  Yuchen  Zhang  Weiqian  Liu  Huimin 《Water Resources》2022,49(4):733-742

Water Resources - Following sponge city concept, taking Qunli New District as study object, and planning water-saving green space system (WGSS) that can use rainwater resources. GIS and ArcHydro...  相似文献   

2017-2018年冬季黑龙江省气温异常成因分析     

班晋  李永生  赵佳莹  孙镆涵 《黑龙江气象》2019,36(1):14-17,23

2017-2018年冬季全省平均气温为-19.7℃,较历年同期偏低2.2℃,为1981年以来的第3位,仅次于2000年和2012年。本文利用NCEP再分析资料,对2017-2018年黑龙江省冬季气温异常成因进行分析,结果表明大气环流的异常是造成黑龙江省冬季气温异常偏低的直接原因。东亚季风环流系统表现为:东亚冬季风强度偏强,西伯利亚高压偏强,500hPa东亚大槽异常偏深。分析下垫面外强迫因素,2017-2018年赤道中东太平洋出现拉尼娜事件,分析显示拉尼娜事件发生可能导致冬季风偏强,从而也是造成全省气温偏低的主要原因之一。  相似文献   

青藏高原定结盆地中更新世孢粉记录及其环境意义     

韩建恩  邵兆刚  裴军令  余佳  王津  张倩倩  朱大岗 《地质论评》2023,69(1):24-32

西藏定结盆地叶如藏布东岸剖面为一套灰与灰白色黏土质砂、粉砂、细砂与粗砂层所组成的湖相沉积地层,厚约41.3 m, ESR和U系测年数据显示该地层沉积时间介于距今551.6～202.4 ka的中更新世时期。该套地层的孢粉化石丰富,依据孢粉化石类型与丰度变化,自下而上可分为5个孢粉带。结合测年结果、孢粉和介形类记录,定结盆地中更新世的古环境变化阶段为：551.6～448.4 ka,气候温暖湿润,适宜植物生长;448.4～375.2 ka,气候向冷干转化;375.2～291.2 ka,气候波动频繁,呈现冷湿—冷干—冷湿的变化过程;291.2～261.0 ka,气候进一步趋于干冷;261.0～202.4 ka,气候波动频繁,表现为冷干—暖湿—冷干的变化过程。  相似文献   

黑龙江流域洪峰水位特征分析     

董淑华  姜雪  邢贞相  张玉国 《水文》2015,35(3):74-77

黑龙江流域地跨中、俄、蒙三国,沿岸地区洪水灾害频繁,在一定程度上制约了当地国民经济的发展。因此,有必要对流域的洪峰水位变化特征进行分析,为流域水资源管理提供可靠依据。结合SPSS对相邻两站的洪峰水位进行相关分析,相邻两水位站的相关系数均较大,成极显著相关,且有非常显著的统计学意义。经回归分析得出相邻两站间洪峰水位均成线性关系,且不包含常数项。降水量对洪峰水位影响分析表明,最大洪峰雨量的影响最为显著,其次是汛期雨量,相关关系最不显著的是年降水量。  相似文献