基于多源数据的黑河流域日尺度蒸散发量模拟

植被蒸散发是地表水量平衡和热量平衡的重要参量,也是衡量植被生长状况和作物产量的重要指标,同时也是进行流域水资源优化配置的依据。遥感技术的快速发展使其成为区域尺度蒸散发模拟的重要手段。以黑河流域为例,构建遥感驱动的蒸散发模拟模型,结合多源遥感数据(MODIS、TRMM等)以及GLDAS全球陆面数据同化系统数据,对黑河流域2005、2010、2015年三个时期的潜在蒸散发和实际蒸散发进行了时间尺度为每日、空间尺度为1km的模拟。研究结果表明:潜在蒸散发月际变化明显,从5月开始增长,于7月达到峰值,然后逐渐减少;实际蒸散发在月份之间变化趋势明显,在2015年均达到了最高值;精度检验结果表明本研究采用的两个模型均达到了很好的效果,Kristensen-Jensen模型更适合用于黑河流域。本研究为黑河流域地表特征数据集提供了重要的日尺度蒸散发数据。     

Validation of 2015 Lake Erie MODIS image spectral decomposition using visible derivative spectroscopy and field campaign data

Timely identification of color-producing agents (CPAs) in Lake Erie is a challenging, but vital aspect of monitoring harmful algal blooms (HABs). In particular, HABs that include large amounts of cyanobacteria (CyanoHABs) can be toxic to humans, posing a threat to drinking water, in addition to recreational and economic use of Lake Erie. The optical signal of Lake Erie is complex (Becker et al., 2009; Moore et al., 2017), typically comprised of phytoplankton, cyanobacteria, colored dissolved organic matter (CDOM), detritus, and terrigenous inorganic particles, varying in composition both spatially and temporally. The Kent State University (KSU) spectral decomposition method effectively partitions CPAs using a varimax-rotated, principal component analysis (VPCA) of visible reflectance spectra measured using lab, field or satellite instruments (Ali et al., 2013; Ortiz et al., 2017, 2013). We analyze 2015 imagery acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor and field samples collected during the early 2015 cyanoHAB season. We identified four primary CPA spectral signatures, and the spatial distribution of each identified CPA, in the reflectance spectra datasets of both the MODIS and lab-measured water samples. The KSU spectral decomposition method results in mixtures of specific pigments, pigment degradation products, and minerals that describe the optically complex water. We found very good agreement between the KSU VPCA spectral decomposition results and in situ measurements, indicating that this method may be a powerful tool for rapid CyanoHAB monitoring and assessment in large lakes using instruments that provide moderate resolution imagery (0.3 to 1 km²).     

Spatial and temporal variability of inherent and apparent optical properties in western Lake Erie: Implications for water quality remote sensing

Lake Erie has experienced dramatic changes in water quality over the past several decades requiring extensive monitoring to assess effectiveness of adaptive management strategies. Remote sensing offers a unique potential to provide synoptic monitoring at daily time scales complementing in-situ sampling activities occurring in Lake Erie. Bio-optical remote sensing algorithms require knowledge about the inherent optical properties (IOPs) of the water for parameterization to produce robust water quality products. This study reports new IOP and apparent optical property (AOP) datasets for western Lake Erie that encapsulate the May–October period for 2015 and 2016 at weekly sampling intervals. Previously reported IOP and AOP observations have been temporally limited and have not assessed statistical differences between IOPs over spatial and temporal gradients. The objective of this study is to assess trends in IOPs over variable spatial and temporal scales. Large spatio-temporal variability in IOPs was observed between 2015 and 2016 likely due to the difference in the extent and duration of mid-summer cyanobacteria blooms. Differences in the seasonal trends of the specific phytoplankton absorption coefficient between 2015 and 2016 suggest differing algal assemblages between the years. Other IOP variables, including chromophoric, dissolved organic matter (CDOM) and beam attenuation spectral slopes, suggest variability is influenced by river discharge and sediment re-suspension. The datasets presented in this study show how these IOPs and AOPs change over a season and between years, and are useful in advancing the applicability and robustness of remote sensing methods to retrieve water quality information in western Lake Erie.     

基于改进遥感蒸散模型的西南地表蒸散研究

基于卫星遥感资料以及气象站点数据,利用基于地表净辐射、植被指数、月平均气温和月温差的混合型线性双源遥感蒸散模型估算了我国西南地区地表蒸散量,并与MODIS数据作对比验证。结果表明:改进后的遥感蒸散模型估算的蒸散值与MODIS监测的值具有很好相关性,其模拟精度依次为:秋季冬季夏季春季。利用改进后的模型研究了西南地表蒸散,发现近20 a来该地区实际蒸散呈现明显的增加趋势,春、夏两季蒸散量较大,占全年总量的62.3%,春季由东南向西北递减,广西大部分地区以及云南南部实际蒸散量较大,而川西则较小;夏季与秋季呈现由东向西递减的趋势,由广西、贵州、重庆向云南和四川递减;冬季则呈现由南向北递减的规律。     

不同空间分辨率遥感数据识别湖泊的误差分析

湖泊面积及空间分布是表征水情变化的重要指示因子,对研究气候变化和人类活动对水资源的影响具有重要作用。如何利用遥感影像进行湖泊制图和面积估算是当前遥感应用研究中的难点问题。从实际应用需求出发,采用GF-1/WFV(Wide Field View)、Landsat-8 OLI(Operational Land Imager)、MODIS(Moderate-Resolution Image Spectroradiometer)遥感数据,选用安徽省受人类活动影响较大的54个湖泊为研究区域,采用NDWI二值分割法得到湖泊水体信息,使用30,500 m和1 000 m 3种空间分辨率的遥感影像进行湖泊制图,探讨制图精度与湖泊形态之间的关系。结果表明:湖泊分形维数值越大,湖泊形态越复杂, Kappa系数越高,面积误差越小;遥感影像分辨率越高,湖泊制图结果的Kappa系数和总体精度越高。     

基于GF-1/WFV的钱塘江叶绿素a和总悬浮物浓度遥感估算

为了探究高分一号(GF-1)卫星对河流水体水质参数遥感反演的效果,使用GF-1卫星数据的16 m分辨率的GF-1/WFV传感器数据和地面实测数据,基于地面实测光谱反射率数据模拟WFV波段组合,构建水体叶绿素a和总悬浮物浓度遥感模型,从而对钱塘江流域杭州段水体水质参数进行估算。研究结果表明:基于B1-B3差值的二次多项式模型可用于叶绿素a浓度估算(R²=0.83,RMSE=0.74 μg/L),基于B3波段的二次多项式模型可用于总悬浮物浓度的估算(R²=0.92,RMSE=1 mg/L);通过模型应用于准同步的GF-1/WFV数据,较好反映了低潮位钱塘江杭州段水体叶绿素a和总悬浮物浓度的空间分布,为高分一号卫星数据遥感监测钱塘江水色参数做出了有益的探索性工作。研究方法及结果对其他流域河流水色遥感研究具有参考价值。     

基于卫星遥感的河道下垫面信息获取技术研究

在洪水泛滥过程中,河道下垫面会在一定程度上影响洪水的蔓延速度,因此,获取河道下垫面信息对建立合理的洪水淹没计算模型有很重要的意义。利用高分辨率卫星遥感技术与河道地物光谱数据库相结合的方法,可以快速、及时地监测河道下垫面信息的动态变化,获取大面积河道下垫面信息。将该方法运用到海城河流域,精确获取了海城河河道下垫面信息及其分布状况,并绘制了海城河城区段洪水演进曼宁图。计算结果可作为该地区高光谱数据库的重要依据,并为城市防洪提供准确的决策信息。     

遥感驱动的分布式实际径流模拟研究

以WBM/WTM(Water balance model/Water transport model)模型为基础,以遥感反演的月降水和月蒸发为主要数据源,开发了基于遥感的分布式水量平衡与传输模型(Remote sensing based Water balance/Water transport model,RSWB/WTM)。利用2002年-2007年的TRMM卫星的降水数据与2004年-2008年基于遥感反演的蒸散发数据,用该模型模拟了白洋淀流域阜平、中唐梅、紫荆关三个水文站的实际径流,对模型的模拟精度进行了评价。三个站的效率系数均大于0.54,其中中唐梅和紫荆关站的效率系数大于0.62。从R2来看,三个站分别是0.56、0.64和0.64。白洋淀流域水库、塘坝对实际径流的干扰较大,进而影响到了模型的模拟精度。另外,遥感反演降水与蒸发存在的不确定性也是影响模拟效率的原因之一。建立的完全以遥感为数据源的分布式水文模拟模型将为基于遥感的水资源评价提供新的技术手段。     

Satellite based lake bed elevation model of Lake Urmia using time series of Landsat imagery

This study presents a lake bed elevation model of Lake Urmia. In the course of model generation, a time series of the extent of the lake surface was derived from 129 satellite images with different acquisition dates based on the Landsat sensors Thematic Mapper (TM), Enhanced Thematic Mapper Plus (ETM+), and Operational Land Imager (OLI). Due to the rapid shrinking of the lake during the last two decades, lake surface areas ranging from 890 km² to 6125 km² could be covered. The water edge of the various lake extents was then linked to the observed water level on the day of the satellite image acquisition. The resulting contour lines, covering water levels between 1270.04 m and 1278.42 m a.s.l. and thus representing the lakebed morphology in its shallow parts, were merged with existing data (deeper parts) and interpolated to generate a lake bed elevation model. Finally, Lake Urmia’s Level-Area-Volume relationships were derived from the lake bed elevation model and compared to bathymetric data previously published.     

Flexible Working,Individual Performance,and Employee Attitudes: Comparing Formal and Informal Arrangements

In the context of a wider trend to individualize human resource management, this article examines the relationship between flexible working arrangements and individual performance. Drawing on a range of theories, this article also examines potential indirect effects on employee performance via job satisfaction and organizational commitment and analyzes whether these relationships vary according to whether the arrangement was set up through a formal process or negotiated informally between the employee and his or her line manager. Extant research has tended to focus on formal arrangements, however, informal arrangements are widespread and may better accommodate work‐life preferences, thereby potentially fostering more positive attitudes from employees. Survey data from 2,617 employees in four large organizations with well‐established flexible working policies are analyzed. Results from structural equation models show average positive indirect effects from informal flexible working, but also negative direct effects from formal flexible working. When two forms of flexible working amenable to being set up by both formal and informal means are examined separately, formal arrangements for flexibility over working hours are found to be negatively associated with performance, but also a source of greater job satisfaction; informal remote working arrangements have positive indirect effects via organizational commitment and job satisfaction on worker performance. © 2016 Wiley Periodicals, Inc.