Non-destructive estimation of potato leaf chlorophyll from canopy hyperspectral reflectance using the inverted PROSAIL model

Optimizing nitrogen (N) fertilization in crop production by in-season measurements of crop N status may improve fertilizer N use efficiency. Hyperspectral measurements may be used to assess crop N status by estimating leaf chlorophyll content. This study evaluated the ability of the PROSAIL canopy-level reflectance model to predict leaf chlorophyll content. Trials were conducted with two potato cultivars under different N fertility rates (0–300 kg N ha⁻¹). Canopy reflectance, leaf area index (LAI) and leaf chlorophyll and N contents were measured. The PROSAIL model was able to predict leaf chlorophyll content with reasonable accuracy later in the growing season. The low estimation accuracy earlier in the growing season could be due to model sensitivity to non-homogenous canopy architecture and soil background interference before full canopy closure. Canopy chlorophyll content (leaf chlorophyll content × LAI) was predicted less accurately than leaf chlrophyll content due to the low estimation accuracy of LAI for values higher than 4.5.     

基于室内光谱测量的玉米单叶偏振与二向性反射关系研究

本研究利用多角度光度计实测了玉米单叶的偏振反射比与二向反射比数据。该光度计能够在不同的观测天顶角、入射天顶角和方位角下测量目标物的偏振反射和二向反射,获得地物目标在2π空间的多角度观测数据。通过分析实测的偏振反射和二向反射数据,得出了玉米单叶的偏振反射与二向反射之间关系密切,最大与最小偏振反射比之和的平均数约等于同等观测条件下玉米叶片的二向反射比。该研究成果为植被遥感监测做出了一种新的尝试,并且对偏振光遥感、多角度遥感的深入研究与应用提供了依据。     

A review on reflective remote sensing and data assimilation techniques for enhanced agroecosystem modeling

During the last 50 years, the management of agroecosystems has been undergoing major changes to meet the growing demand for food, timber, fibre and fuel. As a result of this intensified use, the ecological status of many agroecosystems has been severely deteriorated. Modeling the behavior of agroecosystems is, therefore, of great help since it allows the definition of management strategies that maximize (crop) production while minimizing the environmental impacts. Remote sensing can support such modeling by offering information on the spatial and temporal variation of important canopy state variables which would be very difficult to obtain otherwise.In this paper, we present an overview of different methods that can be used to derive biophysical and biochemical canopy state variables from optical remote sensing data in the VNIR-SWIR regions. The overview is based on an extensive literature review where both statistical–empirical and physically based methods are discussed. Subsequently, the prevailing techniques of assimilating remote sensing data into agroecosystem models are outlined. The increasing complexity of data assimilation methods and of models describing agroecosystem functioning has significantly increased computational demands. For this reason, we include a short section on the potential of parallel processing to deal with the complex and computationally intensive algorithms described in the preceding sections.The studied literature reveals that many valuable techniques have been developed both for the retrieval of canopy state variables from reflective remote sensing data as for assimilating the retrieved variables in agroecosystem models. However, for agroecosystem modeling and remote sensing data assimilation to be commonly employed on a global operational basis, emphasis will have to be put on bridging the mismatch between data availability and accuracy on one hand, and model and user requirements on the other. This could be achieved by integrating imagery with different spatial, temporal, spectral, and angular resolutions, and the fusion of optical data with data of different origin, such as LIDAR and radar/microwave.     

利用多角度POLDER偏振资料实现陆地上空大气气溶胶光学厚度和地表反照率的同时反演 I. 理论与模拟

陆地上空标量辐射对地表反射率和大气气溶胶散射都具有很强的敏感性,而偏振反射只对大气气溶胶敏感,对地表不敏感。根据这个原理并结合POLDER(POLarization and Directionality of Earth Reflectance)资料的特点,作者提出综合利用标量辐射和偏振反射信息来实现陆地上空大气气溶胶和地表反照率的同时反演。首先,利用多角度偏振辐射观测提取大气气溶胶光学参数,再利用标量辐射测量对偏振反演结果作进一步筛选和订正,同时获得地表反射率。数值模拟试验结果证明,仅利用偏振信息只能获取大气气溶胶信息,而且其结果误差较大,特别是对于散射作用较强的短波长通道如670 nm误差更大,但经过标量辐射订正后的结果得到明显改善,气溶胶光学厚度和地表反射率与真实值之间相关系数都达到0.99以上。为提高查找表的计算效率,提出并建立了反演方案所需要的半参数化数值表,利用内插方法寻求气溶胶光学厚度和地表反射率的数值解的反演方法。     

大型沉水植物狐尾藻不同盖度的光谱特征

地物特征与其光谱特征的关系是解译遥感影像的关键。本研究利用ASD便携式地物光谱仪对上海崇明国际湿地公园人工湖中的沉水植物狐尾藻的反射光谱进行了初步研究。结果表明,随狐尾藻盖度的增加,其光谱反射率、一阶和二阶导数红边斜率的峰值也相应增加,不同盖度狐尾藻的光谱反射率的差异主要表现在500—650nm和700—900nm波段范围。分别对狐尾藻盖度与这些波段的光谱反射率及根据一阶和二阶导数获得的光谱指数进行回归分析,得到了较好的线性关系。应用回归分析得到的线性方程,可以根据测定的光谱反射率定量反演水体中的狐尾藻盖度。研究结果可为监测大型沉水植物的高光谱遥感影像解译和分类提供技术支撑,为大尺度遥感监测沉水植物的分布和动态变化提供科学依据。     

高温超高压模拟实验研究--Ⅱ.高温高压下烷烃产物的演化特征

对不成熟泥炭样品进行了高压（0.1～2 GPa) 、高温( 200 ℃～400 ℃）模拟实验,并对实验后样品的烷烃产物进行了分析。结果显示,同一压力条件下,温度升高,烷烃参数表现出更成熟的特征;温度较低时（200 ℃）,压力升高,烷烃参数表现出不成熟,温度较高时（400 ℃）,除个别特殊点之外,压力增大,烷烃参数愈来愈不成熟,说明温压条件都是影响有机质成熟的重要因素,压力的存在会抑制有机质的成熟作用。用模拟实验手段来探讨压力的作用和影响,具有重要的理论及实际意义。     

Upper Limit of Iodine Oxide in the Lower Stratosphere

It has been suggested that iodine oxides, IOx, could play a significant role in the ozone destruction in the lower stratosphere. To investigate this suggestion, spectra from nine SAOZ uv-visible spectrometer balloon flights were examined for the IO absorption signature between 405 and 450 nm. IO was not detected, either at mid- or high latitude, in the morning or the evening, in summer or winter. An upper limit of 0.2 parts per trillion by volume (pptv) at 20 km and 0.1 pptv at 15 km at the 95% confidence level (2), was derived from the best measurements at 90° SZA at sunset and sunrise. Since a photochemical model shows that 70% of inorganic iodine should be in the form IO at that time, it is concluded that unless iodine chemistry is different from that assumed at the moment, the role of iodine in stratospheric ozone depletion is small.     

北京市平原区2015年—2019年0.8 m地表反射率数据集

地表反射率产品作为最重要的定量遥感产品,是很多参量化遥感产品的基础数据源,可以被广泛应用于林业、农业、水资源、生态环境、城市环境等典型应用领域。对于米级高分辨率的遥感影像,国内外不提供反射率影像产品。目前主流的国产高分数据源大部分都是蓝、绿、红、近红4个波段的多光谱数据,缺少短波红外波段,难以满足陆地区域浓密植被算法或者清洁水体的短波红外信号近似看作零的假设条件,要完成精确大气校正、生产大范围的GF-2影像拼接的地表反射率产品,是一个挑战。为了更好的推广高分地表反射率的应用,本研究针对北京市平原区,运用全色和多光谱融合、几何精校正和相对辐射一致化算法,以Sentinel-2为参考影像,生成了一套几何精校正后的0.8 m地表反射率影像集。该数据集时间范围为2015年—2019年,每年一期,包含年度产品的覆盖情况及分布矢量,共计184景地表反射率影像,数据量总共为1.63 TB。     

低轨卫星增强北斗三号导航星座性能分析

针对低轨卫星星座有待合理化设计的问题,深入研究了低轨卫星星座增强北斗三号系统定位性能。分析轨道高度、轨道倾角、星座构型对星座覆盖性能的影响,仿真北斗三号、GPS和3种不同类型的低轨星座,研究各低轨星座与北斗三号、GPS的组合系统在所选7个测站以及全球范围内的可见卫星数和PDOP值分布。结果表明低轨卫星对北斗三号的增强效果主要与低轨卫星数目有关,且不同轨道倾角的组合低轨星座有利于均衡系统在全球范围内的可见卫星数与PDOP值分布。低轨卫星有望通过改善卫星观测几何构型提高北斗三号系统的定位性能,且增强效果与低轨星座构型密切相关。     

Optical detection of Prorocentrum donghaiense blooms based on multispectral reflectance

Prorocentrum donghaiense is one of the most common red tide causative dinoflagellates in the Changjiang （Yangtze） River Estuary and the adjacent area of the East China Sea. It causes large-scale blooms in late spring and early summer that lead to widespread ecologic and economic damage. A means for distinguish- ing dinoflagellate blooms from diatom （Skeletonema costatum） blooms is desired. On the basis of measure- ments of remote sensing refectance [Rrs（λ）] and inherent optical parameters, the potential of using a mul- tispectral approach is assessed for discriminating the algal blooms due to P. donghaiense from those due to S. costatum. The behavior of two reflectance ratios [R1 = Rrs（560）/Rrs（532） and Re = Rrs（708）/Rrs（665）], suggests that differentiation of P. donghaiense blooms from diatom bloom types is possible from the current band setup of ocean color sensors. It is found that there are two reflectance ratio regimes that indicate a bloom is dominated by P. donghaiense; （1） R1 〉 1.55 and R2 〈 1.0 or （2） R1 〉 1.75 and R2 ≥ 1.0. Various sensitivity analyses are conducted to investigate the effects of the variation in varying levels of chlorophyll concentration and colored dissolved organic matter （CDOM） as well as changes in the backscattering ratio （bbp/bp） on the efficacy of this muitispectral approach. Results indicate that the intensity and inherent op- tical properties of the algal species explain much of the behavior of the two ratios. Although backscattering influences the amplitude of Rrs（λ）, especially in the 530 and 560 nm bands, the discrimination between P. donghaiense and diatoms is not significantly affected by the variation of bbp/bp. Since aCDOM （440） in coastal areas of the ECS is typically lower than 1.0 m-1 in most situations, the presence of CDOM does not interfere with this discrimination, even as SCDOM varies from 0.01 to 0.026 nm-1. Despite all of these effects, the dis- crimination of P. donghaiense blooms from diatom blooms based on multispectral measurements of Rrs（λ） is feasible.