多光谱多角度遥感数据综合反演叶面积指数方法研究

叶面积指数是陆地生态系统的一个十分重要的结构参数。用遥感数据求取叶面积指数可以利用光谱的信息,比如通过植被指数来拟合一个经验关系,但很多植被指数明显受土壤背景的影响,对于有明显行结构的农作物,土壤的影响很难消除,植被指数的方法误差较大。多角度遥感包含了大量的地面目标的立体结构信息,具备求解植被特征参数的潜力,但通常多角度遥感反演对光谱信息的利用不足。与以往的反演方法相区别,该文利用行播作物二向反射模型,将多角度与多光谱数据结合进行行播作物LAI反演实验,并对反演算法进行了详细的敏感性分析实验,结果表明采用多角度、多光谱遥感数据相结合的方法可以有效反演行播作物的叶面积指数。     

Fate of polycyclic aromatic hydrocarbon (PAH) contamination in a mangrove swamp in Hong Kong following an oil spill

The fate of polycyclic aromatic hydrocarbon (PAH) contamination in a mangrove swamp (Yi O) in Hong Kong after an oil spill accident was investigated. The concentrations and profiles of PAHs in surface sediments collected from five quadrats (each of 10 m×10 m) covering different degrees of oil contamination and the most contaminated mangrove leaves were examined in December 2000 (30 days after the accident) and March 2001 (126 days later). The concentrations of total PAHs in surface sediments ranged from 138 to 2135 ng g⁻¹, and PAHs concentrations decreased with time. In the most contaminated sediments, total PAHs dropped from 2135 (30 days) to 1196 ng g⁻¹ (120 days), and the decrease was smaller in less contaminated sediments. The percentage reduction in sediment PAHs over three months (44%) was less significant than that in contaminated leaves (85%), indicating PAH in or on leaves disappeared more rapidly. The PAH profiles were very similar in sediments collected from quadrats Q1 and Q2 with benzo[a]anthracene and pyrene being the most abundant PAH compounds, but were different in the other three quadrats. The proportion of the light molecular weight PAHs to total PAHs increased after three months, especially phenanthrene. Results suggest that physical and photo-chemical weathering (tidal washing and photo-oxidation) of crude oil in surface sediments and on plant leaves were important processes in the first few months after the oil spill. The PAH contamination in Yi O swamp came from both petrogenic and pyrolytic sources. The petrogenic characteristic in the most contaminated sediment was confirmed with high values of phenanthrene to anthracene ratio (>10) and low values of fluoranthene to pyrene ratio (0.3–0.4).     

冬小麦灌浆期旗叶光曲线及叶绿素荧光参数研究

利用叶绿素荧光这一光合作用的敏感指针,以河南农业大学试验基地栽种的冬小麦"西农979"灌浆期的旗叶为材料,采用Mini-PAM叶绿素荧光仪测定其光合作用的叶绿素荧光参数的日变化和对不同温度胁迫的响应,以及光响应曲线,求出光饱和点I0和半饱和光强Ik,研究其光合器官的光合作用特征。结果表明:1)在灌浆期冬小麦的光饱和点为2236.5μmol/(m2·s),半饱和光强Ik为647.7μmol/(m2·s),表明灌浆期的冬小麦旗叶对强光的耐受力较强。2)在日变化的测量中出现高温胁迫现象,Fv/Fm、q P、q L和Y(NO)指示光合作用对高温胁迫的响应波动较大;Y(II)在10:00达到全天最大值,随温度的升高不断下降,r ETR、q N、NPQ、Y(NPQ)均与Y(II)对高温胁迫的响应相互验证,对环境温度变化较为敏感,是评价冬小麦光合作用的重要指标。3)对不同温度胁迫的响应,q N、NPQ、Y(NPQ)和Y(NO)随温度升高存在转折点,且均为36℃,该温度下冬小麦旗叶光合器官开始失活或被破坏,在温度达到41℃以上时这种破坏趋于稳定,且十分严重。     

利用光化学反射植被指数估算光能利用率研究的进展

植被光能利用率(LUE)是估计植被初级生产力(GPP)和净初级生产力(NPP)模型的一个重要输入,准确地估计LUE对于生态学研究有重要的意义.由于LUE随环境的变化关系十分复杂,现有的LUE估算模型过于粗糙简单,而通过遥感直接估计LUE将会更加可靠.研究表明,光化学反射植被指数(PRI)与LUE有很好的相关性,故PRI在利用遥感估计LUE方面具有极大的潜力.但是很多研究也发现了PRI-LUE的关系不够稳健,受许多因素的干扰,比如物种构成、冠层结构及大气等.因此,PRI的广泛应用还需要更多的研究.本文首先介绍了PRI的定义及PRI随LUE变化的生理机制,再综述了一些利用遥感手段建立PRI-LUE关系的例子,然后分析了影响PRI-LUE关系的各种干扰因素,最后对PRI研究取得的成果、存在的问题以及发展前景作了总结.     

Contrasting vegetation changes in dry and humid regions of the Tibetan Plateau over recent decades

An overall greening over the Tibetan Plateau(TP) in recent decades has been established through analyses of remotely sensed Normalized Difference Vegetation Index(NDVI), though the regional pattern of the changes and associated drivers remain to be explored. This study used a satellite Leaf Area Index(LAI) dataset(the GLASS LAI dataset) and examined vegetation changes in humid and arid regions of the TP during 1982–2012. Based on distributions of the major vegetation types, the TP was divided roughly into a humid southeastern region dominated by meadow and a dry northwestern region covered mainly by steppe. It was found that the dividing line between the two regions corresponded well with the lines of mean annual precipitation of 400 mm and the mean LAI of 0.3. LAI=0.3 was subsequently used as a threshold for investigating vegetation type changes at the interanual and decadal time scales: if LAI increased from less than 0.3 to greater than0.3 from one time period to the next, it was regarded as a change from steppe to meadow, and vice versa. The analysis shows that changes in vegetation types occurred primarily around the dividing line of the two regions, with clear growth(reduction) of the area covered by meadow(steppe), in consistency with the findings from using another independent satellite product. Surface air temperature and precipitation(diurnal temperature range) appeared to contribute positively(negatively) to this change though climate variables displayed varying correlation with LAI for different time periods and different regions.     

冬早熟大蒜叶枯病流行的气象条件分析

根据弥渡县农业技术推广中心多年的观测试验资料,分析了冬早熟大蒜叶枯病流行的规律与气象条件的关系,发现病害与种植区域、种植年度、播期早迟、降雨过程和日照有关。初步提出防治的主要措施,供冬早熟蒜区参考。     

Improved Land Use and Leaf Area Index Enhances WRF-3DVAR Satellite Radiance Assimilation: A Case Study Focusing on Rainfall Simulation in the Shule River Basin during July 2013

The application of satellite radiance assimilation can improve the simulation of precipitation by numerical weather prediction models. However, substantial quantities of satellite data, especially those derived from low-level(surface-sensitive)channels, are rejected for use because of the difficulty in realistically modeling land surface emissivity and energy budgets.Here, we used an improved land use and leaf area index(LAI) dataset in the WRF-3 DVAR assimilation system to explore the benefit of using improved quality of land surface information to improve rainfall simulation for the Shule River Basin in the northeastern Tibetan Plateau as a case study. The results for July 2013 show that, for low-level channels(e.g., channel 3),the underestimation of brightness temperature in the original simulation was largely removed by more realistic land surface information. In addition, more satellite data could be utilized in the assimilation because the realistic land use and LAI data allowed more satellite radiance data to pass the deviation test and get used by the assimilation, which resulted in improved initial driving fields and better simulation in terms of temperature, relative humidity, vertical convection, and cumulative precipitation.     

新疆沙冬青(Ammopiptanthus nanus)和蒙古沙冬青(A. monglicus)叶片解剖特征及抗旱性

以新疆沙冬青(Ammopiptanthus nanus)幼苗叶片、蒙古沙冬青(A.monglicus)幼苗及成年叶片为研究对象,采用石蜡切片法将叶片解剖并固定,再用光学显微观察法对其抗旱性结构分析比较,旨在探讨沙冬青属植物叶片在干旱环境的生态适应机制。采用方差分析法对各指标的差异性进行比较分析,通过Pearson's相关系数法分析各指标间相关关系。结果表明:(1)新疆沙冬青与蒙古沙冬青幼苗叶片厚度无显著差异;新疆沙冬青幼苗叶片的角质层厚度及上、下表皮厚度及栅栏组织厚度均显著大于蒙古沙冬青幼苗;新疆沙冬青幼苗叶片的海绵组织厚度和主脉直径均显著小于蒙古沙冬青。蒙古沙冬青成年植株叶片厚度、角质层厚度、栅栏组织厚度及主脉直径均显著大于幼苗,上、下表皮厚度及海绵组织厚度均小于幼苗。(2)沙冬青属植物叶片栅栏组织厚度与叶片厚度显著正相关;下表皮厚度、角质层厚度、海绵组织厚度与叶片厚度相关性不显著。为了更好适应分布区环境,新疆沙冬青叶片比蒙古沙冬青具有更强的抗旱性,蒙古沙冬青成年植株叶片的抗旱性优于幼苗。沙冬青属植物叶片的加厚主要通过栅栏组织的加厚实现。     

科尔沁沙地几种常见植物茎叶吸水特征

植物通过茎叶吸水能够极大地改善自身水分条件。为研究科尔沁沙地植被茎叶吸收水分变化特征,于2017年7-8月选取科尔沁沙地常见植物差不嘎蒿（Artemisia halodendron）、小叶锦鸡儿（Caragana microphylla）、猪毛菜（Salsola collina）,通过自然降雨、茎叶隔雨、根部隔雨的控制试验,运用压力室法测定了降雨前后的植物水势（Ψ）变化。结果表明：（1）根部隔雨试验中,差不嘎蒿、小叶锦鸡儿和猪毛菜降雨后的水势值与降雨前相比分别升高了约66.7%、59.5%和87.9%,在降雨后第2天的水势值与降雨前相比分别升高了约73.2%、86.7%和90.6%。（2）差不嘎蒿和猪毛菜在不同部位隔雨试验中的茎叶水势值差异不明显（P>0.05）,小叶锦鸡儿茎叶水势值存在显著差异（P<0.05）。（3）差不嘎蒿、小叶锦鸡儿和猪毛菜都存在茎叶吸水现象。小叶锦鸡儿比差不嘎蒿和猪毛菜更能够适应科尔沁沙地的生存环境。     

叶面积指数间接测量方法

叶面积指数是对地遥感的关键参数。间接测量法快速高效,已广泛应用于叶面积指数的地面测量和遥感验证中,服务于众多行业和领域,表现为论文被引数远远大于发文数。从理论基础、代表算法、测量仪器、影响因素几个方面全面总结了叶面积指数间接测量方法的发展和现状,指出聚集/尺度效应、叶倾角分布、木质组分、地形效应是影响测量精度的关键因素,针对这些影响因素对未来发展方向进行了展望。