大孔径闪烁仪和涡动相关仪观测显热通量之间的尺度关系

利用北京昌平小汤山2002年、2004年涡动相关仪和大孔径闪烁仪的观测数据,借助解析足迹模型计算的源区,分析均匀、非均匀下垫面上涡动相关仪和大孔径闪烁仪观测显热通量之间的差异和关系.结果表明:地表的均匀与非均匀性质,直接影响涡动相关仪和大孔径闪烁仪观测的显热通量的差异大小.在分析均匀、非均匀地表上2种仪器源区重叠面积及重叠区域内足迹值大小与观测通量值之间的关系后,构建一个非均匀地表上2台涡动相关仪与1台闪烁仪观测通量之间的尺度关系式.     

近岸海洋气象平台涡动相关数据处理与质量控制

涡动相关方法在海洋—大气界面通量过程的观测研究中得到广泛应用。通量观测的数据质量很大程度上取决于环境条件和订正方法的正确应用,因此需要对数据进行处理与质量控制。基于博贺海洋气象平台上方2层涡动相关系统约7个月的湍流观测数据,分析了目前未能在数据采集平台上实时运行的几种订正方法对通量结果的影响。分析表明：在通量值较小时,...     

黑河流域不同下垫面水热通量特征分析

"黑河流域遥感—地面观测同步试验"在黑河上中游地区不同下垫面上建立了多个自动气象站和涡动相关仪及大孔径闪烁仪通量观测站。选取草地、森林及农田3种下垫面的观测资料,分析了水、热和CO2通量特征。结果表明:黑河流域内不同下垫面能量收支各分量(净辐射、感热、潜热和土壤热通量等)有明显的日变化特征;各通量观测站观测结果如季节变化趋势等差异明显,反映了不同下垫面地气交换特征的不同。黑河上游阿柔冻融观测站和中游临泽草地站两套大孔径闪烁仪(LAS)的观测与涡动相关仪有关结果有较好的对应关系。结合浅层土壤热储存量的计算等分析了地表能量平衡的闭合情况。LAS观测的感热通量一般大于涡动相关仪的测量值;两者的差异主要由下垫面的非均一性、通量贡献源区大小不同以及影响大气湍流通量观测的涡旋尺度不同等原因引起。     

黑河流域观测通量的空间代表性研究

地表湍流通量包括显热通量和潜热通量,它的准确测定对天气气候预报、农业节水和水资源管理等意义重大。目前应用较为广泛的通量测量技术有涡动相关仪(EC)和大孔径闪烁仪(LAS),前者是单点观测,观测范围通常只有几百米;后者近年来得到长足的发展,可以观测从几百米到十几公里尺度上的区域湍流通量。建立了EC和LAS通量解析足迹模型,详细介绍了足迹模型的理论依据和建立方法,并对二者模型的异同进行了阐释。在黑河流域遥感—地面观测同步试验中,以高寒与干旱区伴生的黑河流域为试验区,包括寒区水文试验、森林水文试验和干旱区水文试验,使用足迹模型分别分析了临泽草地站、阿柔冻融观测站的EC、LAS观测通量的源区,结合风向变化规律,对二者通量观测差异进行分析解释;分析了盈科灌区绿洲站、大野口关滩森林站的EC观测数据,以及阿柔冻融观测站的EC、LAS观测数据,选择具有代表性的月份,进行观测站点的空间代表性分析。结果表明:对通量观测站点进行空间代表性分析是十分必要的,可得到观测站点通量源区的时空变化特征,同时足迹模型在通量观测数据的分析中有很大的实用价值,可为今后通量观测数据的应用提供参考。     

大孔径闪烁仪在黑河流域的应用分析研究

大孔径闪烁仪(LAS)是近年来发展较快的一种新型通量测量仪器,用以观测较大尺度上的感热通量变化.”黑河流域遥感-地面观测同步试验”项目在黑河上、中游地区不同下垫面貌一新建立了多个地面站,除常规气象参数、各辐射分量、土壤温湿梯度和热流以及涡动相关（EC）通量外,还在黑河上游阿柔冻融站及中游临泽草地站架设有大孔径闪烁仪.依据有关观测,着重分析大孔径闪烁仪所测感热通量的日、季变化特征.阿柔站所用数据时间段为2008年3月至2009年12月,临泽草地站为2008年5～8月.在与涡动相关通量数据进行对比分析中,除依据解析模式计算分析EC及LAS的源区差异及有关影响外,对不同大气稳定度下大孔径闪烁仪观测资料的质量控制、感热通量的计算方法等做了仔细分析,以提高LAS通量结果的总体质量.长期观测资料分析表明,大孔径闪烁仪与涡动相关仪的感热通量及其时间变化有较好的对应关系.部分时段的较明显差异,主要由二者源区所含下垫面类型的不同引起.多数情况下,LAS所测感热通量比EC的有关结果偏大,可能因为LAS的源区一般远比EC的大,大孔径闪烁仪所测通量有天然的面积平均效果.     

大孔径闪烁仪研究区域地表通量的进展

地表湍流通量包括感热通量和潜热通量的准确测定对天气气候、农业、水文和水资源管理等意义重大。在几公里到几十公里尺度上有代表性的区域湍流通量的观测研究,特别在非均匀下垫面情况下,仍然非常困难。近年来蓬勃发展的大孔径闪烁仪（LAS）为这一问题的解决提供了全新手段。在介绍大孔径闪烁仪原理的基础上,综述了国内外利用大孔径闪烁仪开展区域地表通量观测研究的进展,包括在不同地表的LAS测量与涡动相关方法有关结果的对比,影响测量精度的关键因子分析,以及在区域地表通量遥感估算模型检验中的应用等,最后对大孔径闪烁仪的应用前景进行了展望。     

春末黄土高原半干旱区地表能量闭合的观测研究

利用兰州大学半干旱气候与环境监测站的连续观测数据,分析了该站的数据质量情况和黄土高原半干旱区的近地层湍流通量特征及地表能量平衡能量闭合状况.结果表明:兰州大学半干旱气候与环境监测站(SACOL)湍流通量的平均时间取30min为宜.该站利用EdiRe获得的湍流通量较TK2和CR5000数据自动记录器输出的湍流通量结果要好.黄土高原半干旱区近地层湍流能量与地表含水量状况明显相关,地表干燥时感热通量处于主导地位,接近于干旱区的特征;地表湿润时感热通量和潜热通量则相当,接近于湿润地区的特征.地表能量平衡分析表明,兰州大学黄土高原半干旱环境监测站观测的地表能量闭合度高达85%,与已有的观测相比,能量闭合情况属于较好水平.     

海河流域不同下垫面上大孔径闪烁仪观测显热通量的时空特征分析

基于海河流域密云站、馆陶站和大兴站2008-2009年大孔径闪烁仪的观测数据,结合涡动相关仪和自动气象站的同步观测,经过数据筛选、质量评价、数据处理及插补等步骤,得到了3个站点不同时间尺度的显热通量和蒸散量.首先分析了3个站点1月、4月、7月、10月不稳定状态下大孔径闪烁仪通量观测的空间代表性及源区内不同下垫面的通量贡献率,并结合下垫面作物生长状况比较分析了3个站点不同季节大孔径闪烁仪观测显热通量与净辐射的月平均日变化趋势,不同下垫面上两者变化趋势一致,且馆陶站的显热通量在各月中都为最低,1月、7月密云站的显热通量与大兴站较为接近.同时3个站点2008-2009年9:00～15:00显热通量日平均值的季节变化趋势表明,相对于密云站单峰状的季节变化,源区内下垫面的植被类型和植被生长状况导致馆陶站和大兴站的显热通量都表现出明显的三峰变化.最后,以馆陶站大孔径闪烁仪和涡动相关仪观测的30 min显热通量数据为例,结合涡动相关仪的能量闭合率,大孔径闪烁仪和涡动相关仪通量足迹源区的重叠程度和非重叠部分的地面非均一性,对不同尺度显热通量观测的差异原因进行了讨论.     

大孔径闪烁仪观测数据的处理方法研究

大孔径闪烁仪可以获取公里级尺度的显热/潜热通量,其观测数据在农林业、水文、气象等领域的研究中具有越来越重要的作用.以海河流域2008年密云站和馆陶站大孔径闪烁仪的观测数据为例,讨论了数据筛选与处理方法,以及大气不稳定状态下不同处理方法对显热通量造成的影响.结果表明:空气折射指数结构参数应结合电压信号的方差进行计算、采用逐日的日平均波文比系数进行湿度订正、结合空间权重函数计算有效高度、选取Andreas(1988)稳定度函数计算显热通量等是可信的.通过对不同插补方法的比较可知,采用非线性回归方法和以零值替代的方法对不稳定状态和稳定状态下30 min缺失的显热通量进行插补,采用动态线性回归方法对日显热通量的缺失进行插补是可行的.为了解决由于冬天净辐射和显热通量较小,造成能量平衡方程余项法计算的蒸散量产生较大误差的问题,可采用根据大孔径闪烁仪与涡动相关仪观测的日蒸散量建立的关系式进行估算.基于上述方法的研究,形成了一套较为完整的大孔径闪烁仪观测数据的处理流程,保证了在不同下垫面、不同的天气状况条件下都能获取质量可靠、数据连续的大孔径闪烁仪观测的显热/潜热通量.     

涡动相关仪观测蒸散量的插补方法比较

涡动相关仪在长时间连续观测中,观测数据会有不同程度的缺失.应用6种不同的插补方法(平均昼夜变化法MDV,非线性回归方法NLR,动态线性回归方法DLR,查表法LUT,FAO-PM方法,HANTS方法)对北京密云站2007年涡动相关仪观测蒸散量数据进行了插补.结果表明:LUT方法在不同数据缺失时均得到较好结果(均方差小于8 W/m2);MDV和NLR方法更适合于短时间数据缺失的插补:DLR和FAO-PM方法在观测数据出现连续波动时插补结果较差.由LUT、DLR、NLR、HANTS、FAO-PM方法得到的年蒸散量分别为395.8 mm、409.9 mm、393.5 mm、390.7 mm、399.4 mm,差异在2.3～19.2 mm之间变化.对比分析了LUT方法得到的年蒸散量(潜热通量)与净辐射、降水量以及LAS观测潜热通量间的变化规律,表明插补结果合理.     

Limitations and improvements of the energy balance closure with reference to experimental data measured over a maize field

The use of energy fluxes data to validate land surface models requires that energy balance closure conservation is satisfied, but usually this condition is not verified when the available energy is bigger than the sum of turbulent vertical fluxes. In this work, a comprehensive evaluation of energy balance closure problems is performed on a 2012 data set from Livraga obtained by a micrometeorological eddy covariance station located in a maize field in the Po Valley. Energy balance closure is calculated by statistical regression of turbulent energy fluxes and soil heat flux against available energy. Generally, the results indicate a lack of closure with a mean imbalance in the order of 20%. Storage terms are the main reason for the unclosed energy balance but also the turbulent mixing conditions play a fundamental role in reliable turbulent flux estimations. Recently introduced in literature, the energy balance problem has been studied as a scale problem. A representative source area for each flux of the energy balance has been analyzed and the closure has been performed in function of turbulent flux footprint areas. Surface heterogeneity and seasonality effects have been studied to understand the influence of canopy growth on the energy balance closure. High frequency data have been used to calculate co-spectral and ogive functions, which suggest that an averaging period of 30 min may miss temporal scales that contribute to the turbulent fluxes. Finally, latent and sensible heat random error estimations are computed to give information about the measurement system and turbulence transport deficiencies.     

Validation of theoretical footprint models using experimental measurements of turbulent fluxes over maize fields in Po Valley

Representative source area of turbulent fluxes measured by eddy covariance stations is an important issue which has not yet been fully investigated. In particular, the validation of the analytical footprint models is generally based on the comparison with Lagrangian model predictions, while experimental results are not largely diffused in literature. In this work, spatial distribution of carbon dioxide, latent and sensible heat fluxes across two different maize fields in Po Valley, is used to validate two theoretical footprint models. Experiments are performed in two totally different scenarios at bare and vegetated soils using two eddy covariance systems: one fixed station which is located about in the middle of the field and a mobile station which is placed at various distances from the field edge to investigate the horizontal variation of the vertical scalar fluxes. The first objective of this work is to provide detailed information about the spatial distribution of turbulent fluxes across Po Valley characteristic fields at bare and vegetated soils, highlighting peculiarities and uniqueness. The second objective consists in the comparison between mobile measurements of carbon dioxide, latent and sensible heat fluxes and the predictions of two analytical footprint models widely used in literature. Contemporaneously, the latter objective will permit to understand what is the best footprint model which, under typical Po Valley atmospheric turbulent conditions, describes a representative source area compatible with the field dimensions and the turbulent flux distributions. The results show that both models are in good agreement with experimental measurements. The results also show that the spatial distribution of turbulent fluxes is strongly influenced by the presence of vegetation in the field. Moreover, the representative source area is different for different scalar fluxes. Another result is about 10:1 fetch-to-height obtained for both field situations.     

复杂条件下湍流通量的观测与分析

随着气候与环境问题的突出，地球生态系统与大气间的CO2、水汽和能量交换引起更大关注。全球通量网和其它研究计划已在不同地区建立了大量通量站；并主要利用涡动相关方法进行通量的观测与分析。许多通量站设在地形起伏、斑块植被地区，且由于长期连续运转，不可避免地会遇到许多不利气象条件。国内各部门应用的涡动相关方法通量观测系统已有数百套。此方法似乎简单，而较准确的有代表性的通量取得却涉及许多问题。国外近10年来有关研究很活跃，国内则显得相对薄弱。仪器和台站很多，却缺乏合乎国际规范的处理程序和质量控制体系，影响到资料共享和合作研究。应根据国际最新进展和部分台站资料，在做成较规范的湍流资料处理程序的基础上，建立包括通量源区分析的质量控制与保证系统。对地形和植被都较复杂的情况，结合国际上几个较典型的通量站和国内祁连山大野口等通量站特点，做了简要介绍。      

Overview of the UAV—Based Eddy Covariance Fluxes Measurements Technique

Airborne Eddy Covariance (EC) method is one of the most effective ways to measure the turbulent fluxes over regional scale directly. The turbulent fluxes from airborne EC method have the same spatial scale with the pixel scale of remote sensing image and the grid scale of land-surface models, which is very important for the simulation of regional or global land-surface fluxes. UAV-based eddy covariance method could achieve the observation of turbulent fluxes in a multi-period and multi-sorties way, and the observation result is reliable and the application is inexpensive. It is an important development direction for airborne flux observation technique. After the introduction of the main technical characteristics of the airborne EC method, this paper reviewed the worldwide progress in UAV-based fluxes measurements system from these aspects of the specifications of the UAVs, the integrated instruments, and the analysis of the application cases. Then, the main sources of uncertainty affecting the UAV-based fluxes measurements were discussed. At last, the shortcomings of the current UAV-based flux observation system were summarized. A brief outlook about UAV-based fluxes measurements technique was also given.     

Analysis of the Characteristics of Turbulent Flux and Its Footprint Climatology at An Agricultural Site

Based on quality controlled data from eddy covariance system and automatic weather station collected at Guantao farmland site from 2008 to 2010, the characteristics of diurnal, seasonal and annual variations of turbulent flux were reported. The corresponding source areas of flux measurement at different temporal scales were analyzed in detail, using arithmetic-averaged and flux-weighted footprint climatology calculation method, respectively. The main findings are as follows. Firstly, sensible heat and latent heat flux both show consistent diurnal variation throughout the year, while CO₂ fluxes only have significant diurnal variation in growing season with an opposite trend. The seasonal variation of the turbulent flux is mainly affected by the crop type and its growth status in different phenological periods. During growing season, latent heat flux and CO₂ flux are the dominant flux exchange items whose value are significantly higher in their middle growth stage than other ones during which latent heat and CO₂ flux exchange of the summer corn is stronger than winter wheat. Secondly, with combined effects of wind, turbulence and surface condition, the source area of flux measurement change most significantly at daily scale, less obvious at seasonal scale and smallest at annual scale. Finally, compared with arithmetic-averaged footprint climatology method, flux-weighted footprint climatology is a more reasonable method to calculate the source areas of the flux measurement, in that they account for the time change of the actual turbulent flux. The arithmetic-averaged results are most likely to overestimate the size of source area during small observed flux due to its weak turbulent exchange.     

A Preliminary Study of the Validation of Land Surface Models with Large Aperture Scintillometer Data

The application of large aperture scintillometer observations to the validation of land surface models has important significances in better understanding and describing the influences of land surface processes on climate change. With observational data from stations, field survey data, and remote sensing data, the land surface processes of Miyun and Arou, two typical flux observation stations in northern China, were simulated by SiB2 model at the spatial scale of 1km². The simulation was validated by the sensible heat fluxes obtained by Large Aperture Scintillometer (LAS) and Eddy Covariance measurement (EC). The results showed that: ①SiB2 has given a good simulation of the sensible heat flux as well as its diurnal variation and seasonal variation; ②The validation of large scale simulation by LAS can avoid the disadvantage of EC, such as energy disclosure and spatial scale differences with model simulation, and could give better results.     

生态系统碳通量估算中耦合涡度协方差与遥感技术研究进展

陆地生态系统CO^₂和水热通量的长期观测研究一直是国际上关注的热点问题。截止目前,利用微气象学原理的涡度协方差技术是唯一能直接测定生物圈与大气间物质与能量通量的标准方法,成为国际通量观测网络的主要技术。但是涡度协方差技术的测定仍然是一种小尺度观测方法,其观测结果难于直接外推到更大尺度。同时,缺乏区域、跨尺度生态系统及其时空动态观测数据一直是限制碳循环研究的主要障碍,而遥感技术的发展可望在不远的将来使大尺度、高分辨生态系统变化的长期定量观测成为可能。这些问题在当今集中体现在如何建立通量—遥感的跨尺度观测体系,并有效地将有限的通量站点测量数据与大尺度遥感资料以及生态模型有机地结合。总结过去耦合涡度协方差技术与遥感技术的工作,主要在以下3个层面展开：①涡度协方差技术与遥感技术对碳通量估算的相互验证;②涡度协方差技术为遥感反演提供地面参数;③遥感观测解译辅助分析通量贡献区（footprint）。集中在这3个方面进行探讨,通过总结各方面的研究特点与进展,可望为未来在这个领域开展工作理顺思路。     

珠江流域岩石风化作用消耗大气/土壤CO2量的估算

以流域的岩性、径流量和水化学分析数据为主要资料,利用基于GIS空间分析的GEM-CO2模型,估算珠江流域陆地岩石风化作用消耗大气/土壤空气中的CO2,评价河流流域的碳汇能力。结果表明,珠江流域因岩石溶蚀和风化作用消耗大气/土壤中的CO2量为252×109 mol·a-1(571×103 mol·km-2·a-1),从岩性分析,碳酸盐岩区大气/土壤CO2消耗量为180×109 mol·a-1(1030×103 mol·km-2·a-1),占总量的71.4%。二级流域以西江流域CO2消耗量最大,占珠江流域总CO2消耗量79.4%,北江、东江分别占总量的13.0%、4.9%。珠江流域大气/土壤CO2消耗量大约为世界大河流域平均值的2.3倍。