Accuracy assessment of NLCD 2011 percent impervious cover for selected USA metropolitan areas     

《International Journal of Applied Earth Observation and Geoinformation》2020

The emergence of high-resolution land cover data has created the opportunity to assess the accuracy of impervious cover (IC) provided by the National Land Cover Database (NLCD). We assessed the accuracy of the 900 m² NLCD2011 %IC for 18 metropolitan areas throughout the conterminous United States using reference data from 1 m² land cover data developed as part of the United States Environmental Protection Agency’s EnviroAtlas project. Agreement was assessed from two perspectives: 1) sensitivity to the size of the assessment unit used for the comparison, and 2) utility of NLCD %IC to serve as a proxy for high-resolution IC. The former perspective was considered because statistical relationships can be sensitive to assessment unit size and shape, and the latter perspective was considered because high resolution (reference) %IC data are not available nationwide. The utility of NLCD %IC as a proxy for the high resolution data was assessed for seven lattice (square) cell sizes ranging from 1 ha to 200 ha using four EnviroAtlas IC indicators: 1) %IC per 100 ha (1 km²); 2) %IC by Census block group; 3) %IC within a 15 m (radius) of the riparian zone, and; 4) %IC within a 50 m (radius) of the riparian zone. Agreement was quantified as per assessment unit deviation (NLCD %IC – reference %IC) and summarized as Mean Absolute Deviation (MAD) and Mean Deviation (MD) both within and across the 18 metropolitan areas. Ordinary least squares (OLS) regression (y = reference %IC and x = NLCD %IC) was also used to evaluate the quality of the NLCD %IC data. MAD was ≤ 5% for six of the seven lattice cell sizes. MAD was also ≤ 5% for Census block groups > 100 ha and for both riparian units. These results suggest that uncertainty attributable to the measurement of %IC was no greater than the uncertainty related to the effect of IC on aquatic resources that have been derived from studies of aquatic condition (e.g., benthic fauna) over a range of %IC. Overall, agreement was variable from one metropolitan area to the next. Agreement improved as assessment unit size increased and declined as the level of urbanization (NLCD %IC) increased. NLCD %IC tended to underestimate reference %IC overall, but NLCD %IC was sometimes greater than reference %IC in urbanized settings.  相似文献   

1960—2017年沈阳地区春播期降水变化特征     

慕臣英  张郁  徐全辉  宋晓巍  张菁  李石  高桐 《气象与环境学报》2019,35(3):106-111

基于1960—2017年沈阳市5个气象观测站4—5月降水量资料,采用线性趋势法和累积距平分析了沈阳市春播期(4—5月)降水量演变特征,并分析首场透雨及最大连续无有效降水日数演变特征及对春播期降水量影响,对春播期降水量资源变化特征进行相关分析。结果表明:近58a沈阳春播期降水量整体呈现弱的增加趋势,平均每10a增加3.1mm,2004年开始降水量迅速增加,且波动性较大,降水量异常偏多或偏少年份较多,易诱发春旱春涝事件。春播期首场透雨出现日期平均每10a偏晚0.051d,首场透雨日期偏晚,将导致春播期前期雨水条件不足,引起土壤干旱,不利于春播开展。最大连续无有效降水日数呈波动性增加趋势,平均每10a增加0.56d,对4月降水量影响较大,虽然春播期降水资源总量增加,但存在降水资源时间分配不均的问题,且长时间无有效降水事件频发,将导致春播期干旱灾害事件发生风险加大,导致适播期延后。  相似文献   

区域性CORS系统监测地表形变的可行性     

黄兵杰  郑凤娇  白洁  王勇 《测绘学院学报》2011,(3)

连续运行卫星定位服务系统(简称为CORS)已经在国内外广泛建立,CORS在维护区域大地测量基准和城市测绘工作中得到了非常广泛的应用。但在城市地面沉降监测方面,仍存在基准站的稳定性、测量精度对平面及高程形变影响等问题。这里提出了一套完整的基于CORS系统变形监测网的稳定性分析的方法和流程。采用秩亏自由网平差,以位移向量一次性范数最小原则求取监测网点最合理的位移量及权阵。采用正态分布函数对监测点的位移显著性进行检验。结合武汉市地面沉降监测项目,分析评价了武汉市连续运行卫星定位服务系统(简称为WHCORS)用于城市地表形变监测的可行性。  相似文献   

2010年早春浙江罕见连阴雨天气环流特征及成因分析   总被引：4，自引：0，他引：4  

张建海  曹艳艳 《高原气象》2011,30(6):1543-1553

利用客观分析资料分析了2010年早春浙江连阴雨天气的环流特征和热力、动力条件,并与历史同期天气状况进行了对比,结果表明：（1）乌拉尔山地区长波脊前偏北气流为连阴雨天气提供了冷空气条件,西太平洋副热带高压偏北偏西有利于其西北侧建立持久、稳定的水汽通道。（2）南北温差分布的变化导致高空西风急流出现分支,浙江位于北支急流南侧...  相似文献   

电性任意各向异性且分块连续变化CSAMT三维有限元数值模拟          下载免费PDF全文

李勇  林品荣  刘祖鉴 《地球物理学报》2019,62(10):3923-3933

考虑地球介质电导率任意各向异性且随空间位置连续变化的情况，本文实现了直接求解电磁场的可控源音频大地电磁测深（CSAMT）三维有限元数值模拟.首先给出了电导率任意各向异性介质中CSAMT二次电场满足的控制方程及其相应变分问题，然后采用任意六面体单元对研究区域进行剖分，在网格单元中对任意各向异性电导率进行线性插值，解决了实际工作中岩矿石电导率各向异性且连续变化的情况，将变分问题转化为线性代数方程组的求解.电导率各向异性且连续变化一维模型三维有限元数值模拟结果与电导率各向异性且分层均匀渐进模型解析解结果对比验证了方法的有效性；三维地电模型电导率随位置线性变化且各向同性、主轴各向异性、方位各向异性和倾斜各向异性的数值模拟结果表明，电导率各向异性且连续变化对CSAMT视电阻率和相位数据均有明显的影响.  相似文献   

1951—2018年衢州市椪柑采摘期连阴雨天气变化特征     

汪晨  毛程燕  龚理卿  王健疆 《气象与环境学报》2021,37(2):71-76

基于1951—2018年衢州市椪柑采摘期降水量、雨日、日照时数、相对湿度等逐日气象资料,应用统计分析和小波分析方法,分析椪柑采摘期连阴雨天气变化特征及其大气环流背景。结果表明：1951—2018年衢州椪柑采摘期连阴雨日数、次数和强度呈略微增加趋势、滑动3 d无雨次数呈减少趋势;滑动3 d无雨次数存在明显的5 a、7 a和15 a左右的年际和年代际周期变化规律,并且均呈现缩短趋势;椪柑采摘期连阴雨较强年亚欧地区呈两高一低的径向型环流,强冷空气南下活动较频繁、东移缓慢,偏南暖湿气流活跃,致使冷暖空气在中国长江中下游地区长时间交汇,导致连阴雨天气。  相似文献   

两次持续性暴雨天气的螺旋度对比分析     

蒙军 《中低纬山地气象》2022,46(5):29-35

本文利用常规观测资料、逐小时区域自动站观测资料、NCEP1°× 1°逐6小时再分析资料等对安顺2019年6月5-11日和9月5-10日的持续性暴雨天气进行分析,结果表明：（1）6月5-11日天气过程主要是由于两高之间不断有短波槽东移造成的,9月5-10日天气过程主要是由于副高稳定少动,西南涡在副高外围稳定维持较造成的;（2）垂直螺旋度垂直积分越大越有利于产生强的短时强降雨,垂直螺旋度强中心发展高度越高越有利于短时强降雨持续不断的产生;（3）水汽垂直螺旋度在这2次持续性暴雨天气过程中对短时强降雨的发生和降雨强度有很好的指示,水汽垂直螺旋度在短时强降雨出现前6小时出现增大,且中心值越大短时强降雨强度越强,在短时强降雨发生期间迅速减小;（4）6月5-11日天气过程中,质量垂直螺旋度值增大-减小得越多,出现的短时强降雨强度越强。  相似文献   

A CRPS-Based Spatial Technique for the Verification of Ensemble Precipitation Forecasts     

赵滨  张博  李子良 《热带气象学报(英文版)》2021,27(1):24-33

Traditional precipitation skill scores are affected by the well-known“double penalty”problem caused by the slight spatial or temporal mismatches between forecasts and observations. The fuzzy (neighborhood) method has been proposed for deterministic simulations and shown some ability to solve this problem. The increasing resolution of ensemble forecasts of precipitation means that they now have similar problems as deterministic forecasts. We developed an ensemble precipitation verification skill score, i.e., the Spatial Continuous Ranked Probability Score (SCRPS), and used it to extend spatial verification from deterministic into ensemble forecasts. The SCRPS is a spatial technique based on the Continuous Ranked Probability Score (CRPS) and the fuzzy method. A fast binomial random variation generator was used to obtain random indexes based on the climatological mean observed frequency, which were then used in the reference score to calculate the skill score of the SCRPS. The verification results obtained using daily forecast products from the ECMWF ensemble forecasts and quantitative precipitation estimation products from the OPERA datasets during June-August 2018 shows that the spatial score is not affected by the number of ensemble forecast members and that a consistent assessment can be obtained. The score can reflect the performance of ensemble forecasts in modeling precipitation and thus can be widely used.  相似文献   

Diel variations in the vertical distribution of copepods off the north coast of Spain   总被引：1，自引：0，他引：1  

de Puelles  M. L. Fernandez; Valdes  L.; Varela  M.; Alvarez-Ossorio  M. T.; Halliday  N. 《ICES Journal of Marine Science》1996,53(1):97-106

  相似文献   

Seasonal cycles and long-term trends of plankton in shelf and oceanic habitats of the Norwegian Sea in relation to environmental variables     

Jrg Aßmus  Webjrn Melle  Dag Tjstheim  Martin Edwards 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(21-22):1895

The plankton abundance data of the Continuous Plankton Recorder (CPR) route from Bergen or Rotterdam to Weather Station Mike (6444^′N, 2E) from 1949 to 1981 were analysed for long-term trends and seasonal production cycles, and were related to environmental data. The data were explored using the canonical correlation analysis and nonparametric techniques like the Nadaraya–Watson regression. While large copepods such as Calanus spp. and Metridia lucens did not show any temporal trends, a sharp decrease in the abundances of smaller copepods and phytoplankton was observed after 1960. The temporal trends were not related to the NAO, but did show a correlation with the wind direction. Seasonal abundance curves showed that production of both phytoplankton and zooplankton taxa started earlier in coastal water compared to Atlantic water. From the 1950s to the 1970s most taxa showed a delay in the start of the seasonal production cycles, indicating a reduction in the length of the productive cycle. This may to some extent explain the reduced abundance of smaller copepods, phytoplankton and other species during the 1960s and 1970s.  相似文献