基于SEBAL模型的西北农牧交错带生长季蒸散发估算及变化特征分析

蒸散发是土壤-植被-大气系统中水循环和能量交换的主要组成部分,准确估算区域蒸散发对农业用水调度与水资源的管理至关重要。利用MODIS数据产品结合地面气象站的观测资料,基于能量平衡原理建立的SEBAL(Surface Energy Balance Algorithms for Land)模型对西北农牧交错带2015年生长季(4—10月)的地表蒸散发量进行反演研究,并用Penman-Monteith(P-M)公式结合作物系数对模型的估算结果进行对比,结果表明:SEBAL模型估算结果与P-M公式之间的平均绝对误差为0.79mm/d,均方根误差为0.94mm/d,R~2=0.76,整体反演值偏高,但基本能满足本地区的研究需求。生长季区域日均蒸散发的变化范围为0.12—10.66mm/d,日蒸散量均值为4.31mm/d,呈东北、西南部较高,西部偏低的空间分布特征。将蒸散发估算值与地表特征参数统计分析发现蒸散发与NDVI和地表净辐射之间呈正相关,与地表温度和地表反照率之间呈负相关;不同土地利用/覆被类型的日蒸散发量由大到小依次为:耕地、林地、未利用地与草地。     

遥感数据支持下不同地表覆盖的区域蒸散

将地表能量平衡系统(SEBS)扩展成遥感日蒸散估算模型,利用MODIS遥感数据估算了黄淮海地区的区域蒸散,并在地理信息系统的支持下分析了不同地表覆盖下的区域蒸散统计分布特征.在缺乏各地表覆盖类型相应蒸散量实测值进行对比的情况下,以2001年4月17日估算的日蒸散量为例,通过各地表覆盖类型日蒸散量间的相互对比分析表明,SEBS估算的区域日蒸散量具有一定的合理性.分析结果表明：在黄淮海地区,荒地具有最低的蒸散量;森林、灌木、草地等地表覆盖类型具有中等的蒸散量;而水体、湿地以及耕地具有较高的蒸散量.可能由于包含绿地和水面,城镇用地的蒸散量也较高.土壤含水量的空间差异性导致森林、灌木、草地和耕地等地表覆盖类型的蒸散量具有明显的空间差异性.耕地蒸散量的空间差异性可以为制定合理、高效的农田灌溉计划提供指示作用.SEBS遥感日蒸散模型的局限性在于有可能低估水体和湿地等地表覆盖类型的蒸散量.     

基于NOAA PAL数据集的地表蒸散遥感估算方法

基于NOAA AVHRR气象卫星长时间序列10 d合成的PAL数据集（分辨率8 km×8 km）以及地表能量平衡原理和“VI-T_s”方法,建立了地表蒸散的遥感估算方法,该方法不需要地面气象观测数据的支持,所需参数可直接从遥感数据反演或推算,并选择国际上著名的遥感蒸散模型——SEBS模型对新建模型进行了验证比较.结果表明：新建模型和SEBS模型模拟的地表蒸散值及其季节性变化趋势非常一致,说明新构建模型的模拟结果比较可靠,能够反映地表蒸散的实际情况.新建地表蒸散遥感估算模型可操作性强,为利用长时间序列的卫星遥感数据研究我国乃至全球地表蒸散的时空变化规律提供了一个新的途径.     

长白山阔叶红松林蒸散量的测算

2001年7－9月应用水量平衡法对长白山阔叶红松林蒸散量进行了测定,同时应用波文比（BREB）法对其蒸散量进行了估算,两种方法得到的总蒸散量分别为288.18mm和214.94mm,均小于该时段的降雨量301.9mm。通过两种方法分别得出了各月平均日蒸散量,并通过第二种方法计算出每日的蒸散量及每日不同时刻的蒸散速率,从而对水量平衡法和BREB方法测算阔叶红松林蒸散量的可行性及其精度进行了验证。     

辽河三角洲湿地生长季蒸散量时空格局及影响因素

蒸散是湿地系统水分损失的重要途径之一,有效量化湿地蒸散量并对其时空格局进行研究具有重要意义。本文以Landsat数据和气象观测数据为基础,利用SEBAL模型估算辽河三角洲湿地1985—2017年共8期植被生长季的蒸散量,并分析其时空格局和影响因素。结果表明:(1)反演得到的蒸散量平均相对误差为9.01%,估测值与实测值相关系数为0.61,基本满足湿地蒸散研究需求;(2)研究区多年日蒸散量均值和相对变化率整体呈双峰态势,极小值出现在2005年,极大值出现在1989年和2014年;(3)日蒸散量具有水陆交界处最低、西部较低、中东部和南部高的趋势,具有显著的空间分异特征;(4)不同土地利用/覆被类型的蒸散量大小依次为:水体区湿地植被区非湿地植被区非植被区(除水体外),多年不同土地利用/覆被类型的蒸散量变化也呈双峰态势,日总蒸散量变化与土地利用转型有关,土地利用/覆被是导致湿地蒸散时空分异的重要因素;(5)平均蒸散量与太阳辐射、气温、风速、相对湿度四个气象因子加权值显著相关,相关系数为0.69,两者年际波动趋势基本一致,蒸散量变化与气象条件变动联系密切。     

中天山地区草地地表辐射收支演变规律

地表辐射对研究地表能量平衡及气候形成机制具有重要意义。利用中天山乌拉斯台地区陆气相互作用观测站2018年5月至2019年4月地表辐射数据,分析了中天山草地不同时间尺度和不同天气条件下的地表辐射与反照率变化特征。结果表明：(1)地表辐射月平均日变化除大气长波辐射较弱外,其余分量均呈单峰型,极值大小及时间存在差异,太阳总辐射与净辐射最大日峰值均出现在6月,为920.9与603.3 W/m~2,大气与地表长波辐射分别出现在7月和8月,为327.5 W/m~2与471.7 W/m~2,而反射短波辐射则出现在2月,为520.6 W/m~2。(2)太阳总辐射、反射短波辐射、大气与地表长波辐射年曝辐量分别为6860.62、2101.72、7171.25、10089.69 MJ/m~2;就季节变化而言,反射短波辐射曝辐量在冬季明显高于其它季节,其它分量则均表现为夏季>春季>秋季>冬季。(3)不同月份地表反照率日变化均呈“U”型曲线,年均值为0.393,最大与最小月均值分别出现在12月与8月,为0.760与0.217。这种变化体现在季节上则为冬季>秋季>春季>夏季。(...     

内蒙古荒漠草原地表反照率变化特征

基于2008年全年内蒙古荒漠草原的气象观测数据对荒漠草原地表反照率的变化特征分析发现,内蒙古荒漠草原的地表反照率在晴天呈早晚高、正午前后低的U形变化特征,降水引起的土壤含水量变化将导致地表反照率减小,云对地表反照率的影响比较复杂。荒漠草原地表反照率的月平均日变化类似于晴天条件下的日变化,大多数月份呈现早晚高正午前后低的U形变化趋势,仅在1-2月份及11-12月份呈现V形。地表反照率的季节变化较为明显。在生长季,由于存在植被覆盖使得地表反照率较低;而在冬季,地表反照率较高,特别是1\,2月份,其月均值分别为0.56和0.48,甚至高于沙漠。9月份地表反照率月均值达到最小值0.230, 7、8\,9月份地表反照率接近,分别为0.236、0.232和0.230。而且在生长季,荒漠草原的地表反照率高于退化草地、农田及麦田,低于沙漠的地表反照率,但是荒漠草原的地表反照率除7-10月份明显低于沙漠地表反照率外(相差大于0.02),生长季的其它月份与沙漠相差不大。晴天地表反照率随太阳高度角的增大而减小,当太阳高度角大于40°时,地表反照率趋于稳定,其与太阳高度角呈指数关系。土壤含水量的增大会导致地表反照率的减小,地表反照率与土壤含水量呈指数或线性关系。根据地表反照率与这两个因子之间的单因子关系式,建立了内蒙古荒漠草原晴天地表反照率随太阳高度角与土壤含水量变化的双因子参数化公式,而且太阳高度角和土壤含水量两者共同解释了地表反照率变化的68%左右。该公式可以较好地模拟内蒙古荒漠草原晴天地表反照率的变化。该公式是否可以进一步耦合到天气或气候模式中,还需要借助更多代表性的观测资料的验证,但是本研究无疑对陆面模式中地表反照率更准确的参数化及模拟提供了参考依据。     

浑太流域实际蒸散的时空变化特征及影响因素

基于浑太流域1970—2006年气象、水文资料,采用参数率定后的平流-干旱（AA）模型计算浑太流域蒸散.根据水量平衡法得到的蒸散结果对模型的原始参数进行调整,并在4个子流域进行验证.采用线性趋势分析、滑动平均法、克里金插值、灵敏度分析方法研究浑太流域蒸散的时空变化和影响因素.结果表明： AA模型经验参数（0.75）在浑太流域上的计算误差为11.4%,表明AA模型在浑太流域上是可行的;浑太流域年均蒸散量为347.4 mm,并以1.58 mm·(10 a)^-1的速率略呈上升趋势,但上升趋势不明显,年内呈单峰变化,峰值出现在7月;季节变化上,夏季最大,冬季最小,春季高于秋季;整个流域实际蒸散量呈现从西北至东南逐渐减少的分布特征,但差异不大;净辐射是影响浑太流域蒸散变化的主导因素.
     

河套灌区蒸散发时空变化特征及驱动力分析

蒸散发(Evapotranspiration, ET)是陆地与大气系统中水循环与能量交换的重要因素。为了提高估算区域尺度ET的精度, 更加准确的为气候演变研究、水资源管理、环境保护等提供现实数据与理论支撑, 论文基于2017—2018年Landsat8 OLI遥感影像与气象站数据, 运用SEBS (Surface Energy Balance System)模型估算河套灌区日尺度蒸散发, 采用Penman-Monteith公式计算结果对其进行精度验证, 并探讨其时空变化特征及驱动力。结果表明: (1) SEBS模型估算值与彭曼公式计算的5个气象站的平均相对误差分别为15.07%、17.94%、16.17%、9.93%、13.18%, 表明估算研究区日尺度蒸散发可以基于SEBS模型实现, 并且估算效果较好。(2)研究区内ET空间上呈现纬度递减变化, ET随着纬度的降低呈增大的趋势。(3)基于SEBS模型得到的日蒸散量与NDVI、地表反照率、地表温度等3个地表参数拟合系数从大到小依次排序为: 地表温度＞地表反照率＞NDVI。(4)日尺度SEBS模型得到的蒸散发与气象因素进行主成分分析, 与第一主成分密切相关的驱动因子为气温, 方差贡献率为40.434%。综合可见, SEBS模型能够很好的对河套灌区蒸散发进行模拟, 模拟潜在蒸散发量具有明显的年内分配特征, 在4—10月中整体表现为先增大再减小趋势, ET最高值出现在7月, ET的主要特征影响因子为气温。     

塔河森林生态系统蒸散发的定量估算

蒸散发是农业、气象、水文科学研究的重要参数,是全球水文循环过程的重要组成部分.本文应用改进的DHSVM分布式水文模型,利用光学遥感TM数据反演得到叶面积指数等地表数据,由数字高程模型求得坡度、坡向等地形指数因子,定量估算塔河地区2007年逐日蒸散发.应用BP神经网络建立逐日蒸散发量与逐日径流出口流量的关系,并建立研究区水量平衡方程,共同检验研究结果的准确性.结果表明:该模型可以较好地应用于本研究区.塔河流域年总蒸散量234.01 mm,蒸散发与季节有明显的相关性,夏季蒸散发值最高,日均蒸散发值1.56 mm,秋季、春季日均蒸散发值分别为0.30、0.29 mm,冬季蒸散发值最低.地表覆盖类型对蒸散发值影响明显,阔叶林的蒸散发能力强于针阔混交林,其次为针叶林.     

Estimating the regional evapotranspiration in Zhalong wetland with the Two-Source Energy Balance (TSEB) model and Landsat7/ETM+ images

This paper aims to integrate a numerical model, vegetation index, and regional evapotranspiration estimation to assess the water cycle in Zhalong wetland, China with the aid of remote sensing technologies. An interdisciplinary analysis was performed to study the eco-hydrological characteristics of the wetland ecosystem. In particular, a new solution for solving the Two-Source Energy Balance (TSEB) was developed and applied. This new solution method is based on a definition of the aerodynamic temperature in a two-layer ground surface structure. Following this new solution for TSEB, the outputs of the Surface Energy Balance Algorithm (SEBAL) may be used as the inputs for TSEB to avoid the complex calculations of the bulk boundary layer and soil surface resistance. The new solution method makes the implementation of TSEB much easier when bi-directional thermal infrared remote sensing images are not available. Daily evapotranspiration and vegetation index of the wetland were calculated from six scenes of Landsat7/ETM+ remote sensing images acquired during 2001 and 2002 in our case study. Spatial distribution of daily evapotranspiration was also provided to help realize the wetland condition. The seasonal changes of vegetation index and evapotranspiration for some typical wetland ground surfaces were analyzed and presented as well to explore the multitemporal variations of plant species holistically. Ultimately, such integrative analysis aids in understanding the general biological patterns associated with these wetland vegetation cover, while specific situations of the wetland ecosystem can be recognized.     

Diurnal and seasonal variations of surface albedo in a spring wheat field of arid lands of Northwestern China

Surface albedo greatly affects the radiation energy balance of croplands and is a significant factor in crop growth monitoring and yield estimation. Precise determination of surface albedo is thus important. This study aimed to examine the influence of growth stages (tillering, jointing, heading, filling and maturity) on albedo and its diurnal asymmetry by measuring diurnal albedo variations. Results indicated that the daily mean surface albedo generally exhibited an increased tendency during tillering to heading but decreased after heading. Surface albedos were much higher in the morning than the corresponding values of the same solar elevation angles in the afternoon when the solar elevation angle was less than 40°, indicating a diurnal asymmetry in surface albedo. However, less difference was found in surface albedos between forenoon and afternoon when the solar elevation angle was greater than 40°. Dew droplets on the leaf surface in the morning were assumed to be the main factor resulting in the diurnal asymmetry in albedo of spring wheat.     

Interannual and seasonal variations of energy and water vapor fluxes above a tropical seasonal rain forest in Xishuangbanna, SW China

The values and variation characteristics of energy components, their relationship with net radiation and the characteristics of water balance in the forest were analyzed, based on the observation data of energy fluxes, meteorological parameters and biomass in a tropical seasonal rain forest in Xishuangbanna from January 2003 to December 2004. The results show that annual net radiation was 3516.4 MJ/(m² · a) and 3516.6 MJ/(m² · a) in 2003 and 2004, respectively, of which 46% and 44% were used in latent heat flux, and 12% and 11% were lost as sensible heat flux. Annual mean canopy surface conductance was 10.3 mm/s and 10.0 mm/s in 2003 and 2004, respectively. Moreover, canopy surface conductance was lower in dry-hot seasons than in fog-cool and rainy seasons. Canopy surface conductance correlated significantly and positively with leaf area index, but negatively with water vapor pressure deficit. In general, canopy surface conductance was not affected directly by soil water content, but highly depended on soil moisture status when soil water content was below 0.15 m³/m³. Annual total evapotranspiration of this forest ecosystem in dry seasons was lower than that in rainy seasons, which was considered as one of the most important reasons that tropical seasonal rain forest could survive and flourish in Xishuangbanna at limit of water and heat.     

Interannual and seasonal variations of energy and water vapor fluxes above a tropical seasonal rain forest in Xishuangbanna, SW China

The values and variation characteristics of energy components, their relationship with net radiation and the characteristics of water balance in the forest were analyzed, based on the observation data of energy fluxes, meteorological parameters and biomass in a tropical seasonal rain forest in Xishuangbanna from January 2003 to December 2004. The results show that annual net radiation was 3516.4 MJ/(m² · a) and 3516.6 MJ/(m² · a) in 2003 and 2004, respectively, of which 46% and 44% were used in latent heat flux, and 12% and 11% were lost as sensible heat flux. Annual mean canopy surface conductance was 10.3 mm/s and 10.0 mm/s in 2003 and 2004, respectively. Moreover, canopy surface conductance was lower in dry-hot seasons than in fog-cool and rainy seasons. Canopy surface conductance correlated significantly and positively with leaf area index, but negatively with water vapor pressure deficit. In general, canopy surface conductance was not affected directly by soil water content, but highly depended on soil moisture status when soil water content was below 0.15 m³/m³. Annual total evapotranspiration of this forest ecosystem in dry seasons was lower than that in rainy seasons, which was considered as one of the most important reasons that tropical seasonal rain forest could survive and flourish in Xishuangbanna at limit of water and heat.     

黑河流域高寒草甸生态系统水分收支及蒸散发拆分研究

水分收支是对水循环要素降水、蒸发蒸腾、径流以及土壤贮储水量变化等的定量刻画,对水资源的可持续开发及利用至关重要。基于黑河流域阿柔观测站2014和2015年水文气象观测数据,运用水量平衡理论,定量的评估了高寒草甸生态系统的水分收支动态,并结合双源模型对高寒草甸生态系统蒸散发(植被蒸腾和土壤蒸发)进行拆分及评价。研究结果表明(1)在生长季(5—9月)植被蒸腾是高寒草甸生态系统主要的耗水形式,2014和2015年生长季平均蒸散比(T/ET)分别为0.74和0.79;(2)土壤水分的剧烈变化主要发生在0—40 cm处,且受冻融过程影响显著;(3)在降水较多的年份(2014)高寒草甸生态系统水分收支基本平衡,且不受冻融影响的月份(6—9)有地表径流产生约42 mm;在正常年份(2015),生态系统呈现水分亏缺,亏缺量约为134 mm,6—9月约亏缺26 mm;(4)模型估算蒸散发(ET)与实测蒸散发具有很好的一致性,相关系数可达0.90,敏感性分析表明模型输入变量对蒸散发(ET)及蒸散比(T/ET)产生的误差较小,双源模型可以很好地实现对高寒草甸生态系统蒸散发(ET)的拆分。     

A simulation test of Smith's “degrees of freedom” correction for comparative studies

Computer simulation was used to test Smith's (1994) correction for phylogenetic nonindependence in comparative studies. Smith's method finds effective N, which is computed using nested analysis of variance, and uses this value in place of observed N as the baseline degrees of freedom (df) for calculating statistical significance levels. If Smith's formula finds the correct df, distributions of computer-generated statistics from simulations with observed N nonindependent species should match theoretical distributions (from statistical tables) with the df based on effective N. The computer program developed to test Smith's method simulates character evolution down user-specified phylogenies. Parameters were systematically varied to discover their effects on Smith's method. In simulations in which the phylogeny and taxonomy were identical (tests of narrow-sense validity), Smith's method always gave conservative statistical results when the taxonomy had fewer than five levels. This conservative departure gave way to a liberal deviation in type I error rates in simulations using more than five taxonomic levels, except when species values were nearly independent. Reducing the number of taxonomic levels used in the analysis, and thereby eliminating available information regarding evolutionary relationships, also increased type I error rates (broad-sense validity), indicating that this may be inappropriate under conditions shown to have high type I error rates. However, the use of taxonomic categories over more accurate phylogenies did not create a liberal bias in all cases in the analysis performed here. The effect of correlated trait evolution was ambiguous but, relative to other parameters, negligible. © 1995 Wiley-Liss, Inc.     

沿海防护林体系热效应的遥感分析

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