基于反射峰面积的水体叶绿素遥感反演模拟研究

叶绿素浓度是水体富营养化状态的重要指标,也是水色遥感反演的水质参数之一。水体中叶绿素浓度的遥感反演主要是建立实测光谱和实测水质参数二者之间的关系模型,利用遥感影像进行叶绿素浓度的信息提取。传统的叶绿素浓度遥感反演受区域性和季节性的影响,反演精度不高,而且反演模型不具普适性,需对叶绿素光谱特征进行分析,建立高精度的反演模型。本文采用Hydrolight数据模拟了不同叶绿素浓度(1~200 µg·L^-1)的水体在可见光近红外的反射波谱曲线,通过分析叶绿素的光谱特征选取了特征波段或波段组合,并建立了叶绿素浓度反演模型。研究表明,除反射峰波长模型外,反射峰面积模型、三波段模型、红光线高度模型等均能较好地反演叶绿素浓度。在不同叶绿素反演模型中,除红光线模型外,最优的是反射峰面积模型,其决定系数为0.9689,反演误差为25.25 µg·L^-1;其次是三波段模型,其决定系数为0.9637,反演误差为10.66 µg·L^-1。究其原因,三波段模型考虑了水体中非色素悬浮物、黄色物质及水体后向散射对叶绿素浓度反演造成的影响;反射峰面积模型除此之外还综合考虑了叶绿素散射效率的影响。     

叶绿素a浓度反演模型：堆栈自编码器粒子群优化BP神经网络

内陆水体叶绿素a浓度是衡量水体富营养化程度的主要指标，是影响水体反射率光谱特征的重要因素之一。本文以白洋淀烧车淀、圈头乡各村庄等水域为研究区，采集了高光谱数据和水样，并在实验室测定叶绿素a等水质参数，应用于白洋淀区域的叶绿素a高光谱遥感反演。针对线性降维方法特征提取能力不足和神经网络构建叶绿素a遥感反演模型时学习效率低、泛化能力差的问题，提出了堆栈自编码器粒子群优化BP神经网络模型。该模型利用堆栈自编码器强大的非线性变换能力，通过最小化重构误差来学习高光谱数据特征，在实现数据降维的同时最大程度保留原始光谱数据中的水体辐射信息，提取出实测水体光谱的深度特征，将BP神经网络初始权重作为粒子的位置向量，通过粒子群算法搜寻网络初始权重的最优值，降低出现局部极值的概率，提高模型的稳定性和反演的精确度。堆栈自编码器粒子群优化BP神经网络模型(R²=0.82,RMSE=2.65μg/L,MAE=1.89μg/L)相较于对高光谱数据不降维的BP神经网络模型(R²=0.75,RMSE=3.16μg/L,MAE=2.39μg/L)、基于主成分分析法降维的BP神经...     

高分六号影像在内陆水体叶绿素a反演中的应用潜力分析

GF-6 WFV影像具有宽覆盖、高时空分辨率、高光谱分辨率等特点,目前在农业和林业遥感领域都有一定应用,但是在水质遥感中的应用潜力还缺乏系统的评估。本文以潘家口和大黑汀水库为研究区,采用2019年9月24—25日获取的潘家口和大黑汀水库叶绿素a浓度、实测遥感反射率和准同步GF-6 WFV影像,构建了潘家口和大黑汀水库叶绿素a浓度经验反演模型,探索GF-6 WFV在内陆水体叶绿素a浓度遥感监测中的应用潜力。研究结果表明,基于GF-6 WFV模拟光谱构建的潘家口和大黑汀水库叶绿素a浓度经验模型决定系数均在0.90以上,GF-6 WFV影像在水体叶绿素a遥感监测中具有应用潜力,尤其是新增的黄波段和红边波段1,有助于提高GF-6 WFV影像叶绿素a浓度遥感监测能力;GF-6 WFV影像大气校正误差降低了叶绿素a浓度遥感监测精度,GF-6 WFV影像水体大气校正精度有待改进,以提升GF-6 WFV影像水质遥感监测能力。     

富营养化的太湖水体叶绿素a浓度模型反演

半经验模型反演叶绿素a浓度是目前遥感反演水体叶绿素a浓度的主要方法。但是,大量研究结果表明,太湖水体浑浊,富营养化严重,各种半经验模型的反演精度和模型适用性有较大差异。因此,研究一种既满足一定精度要求,又具有时间普适性的叶绿素a浓度反演算法,对提高模型适用性,促进遥感的反演应用具有重要意义。本研究通过2005年6-10月地面实测数据,建立太湖叶绿素a浓度一阶微分反演模型、波段比值反演模型和三波段反演模型,对比各模型反演效果,认为波段比值模型与三波段模型具有较好的反演效果。运用2006年11月和2007年11月实测数据对这三种模型加以检验,结果表明,三波段模型反演高富营养化的太湖水体,不仅精度高,平均误差仅为实测浓度差的8.3%,而且适用性较强,不同年份数据的检验结果证明平均误差均低于实测浓度差的20%。因此,三波段模型是这三种反演模型中效果最好的一类模型。     

太湖水质参数MODIS的遥感定量提取方法

本文利用MODIS数据的可见光、近红外波段和准实时的地面采样数据,分别利用线性回归模型和神经网络模型反演了太湖的叶绿素a和悬浮物浓度.结果表明,利用MODIS数据的波段组合(M2/M8)和(M2/M9)可估算太湖的叶绿素a浓度;而MODIS数据的波段组合(M12/M17)、(M13/M17)及MODIS(M4)波段能定量估算太湖的悬浮物浓度,但估算精度仍不能满足实际需要.因此,构建了一个以MODIS可见光及近红外波段为输入,以太湖水质参数为输出的2层BP神经网络模型反演太湖的水质参数,大大提高了反演精度.     

湖泊水体叶绿素a含量估算的波段宽度变化影响分析——以太湖为例

为研究不同波段宽度遥感数据对监测水体叶绿素a含量的影响,以太湖水体实测高光谱遥感反射率数据为基础,分析计算不同波段宽度下遥感反射率的归一化值与叶绿素a浓度之间的相关系数。随着波段宽度在75.93nm范围内不断递增,最大相关系数逐渐减小,最大正相关波段向长波方向移动,最大负相关波段向短波方向移动。而波段宽度在31.6nm范围内变化时,最大正相关波段和最大负相关波段都会保持相对稳定。通过对不同波段处相关系数平均值和标准差的对比分析认为,718.77^~34.58nm为叶绿素a遥感监测的最佳波段范围。这将对遥感传感器的波段设置,以及实际水体叶绿素a遥感监测时的波段选择,具有重要的参考价值。     

南方红壤侵蚀区长汀县不同生态恢复年限下芒萁叶绿素含量的高光谱估算模型

芒萁是南方红壤侵蚀区生态恢复重要的地带性草本植物,对生态系统修复具有重要作用,监测其叶绿素含量能有效诊断生长健康状况。本文以福建省长汀县朱溪流域6个不同生态恢复年限下的芒萁叶片高光谱反射数据以及实测叶绿素含量为数据源,借助高光谱遥感技术分析不同恢复年限芒萁叶片原始光谱特征,筛选出光谱敏感波段并构建光谱指数,基于相关性分析,建立芒萁叶绿素单变量以及多元逐步回归模型,并确定最佳估算模型。结果表明：高光谱指数建立的单变量估算模型中,改进红边归一化植被指数（mNDVI₇₀₅）、叶面叶绿素指数（LCI）、红边指数（Vog）、比值光谱指数（RVI_603/407）、NDVI[603,407]高光谱指数建立的二次模型精度高,建模决定系数R²均超过了0.8,其中以高光谱指数为自变量建立的多元回归模型拟合R²值（0.886）最高。综合建模精度和模型验证精度,LCI指数构建的单变量模型以及基于高光谱指数的多元回归模型是估算芒萁叶片叶绿素含量最佳模型。本研究建立的叶绿素高光谱估算模型对快速、无损地监测水保植物芒萁生长具有重要意义。     

湛江港海域叶绿素a浓度的高光谱遥感反演

基于表观光学法研究冬季湛江港海域高光谱遥感叶绿素a浓度的反演模型构建,结果表明,该海域单波段遥感反射率与叶绿素a浓度相关性低,波段比值和遥感反射率的一阶微分法可提高叶绿素a浓度反演精度。665nm处的遥感反射率一阶微分值与叶绿素a浓度相关性良好,相关系数可达0.84。一阶微分相关系数大于0.8的波段大部分处于叶绿素a红光强烈吸收区域,对于富营养化的湛江港海域采用一阶微分方法构建叶绿素a浓度的遥感反演模型具有合理性。     

太湖浮游藻类的后向散射分离及其叶绿素a浓度反演

浮游藻类的后向散射是水体光谱构成的重要组成部分,作为水体辐射传输模型中的重要参数,高精度的藻类后向散射系数对水体叶绿素a浓度的遥感反演精度至关重要。本文以简化的辐射传输模型-生物光学模型为基础,尝试性分离了太湖浮游藻类的后向散射系数。通过藻类后向散射规律分析,建立了浮游藻类吸收、后向散射特征的叶绿素a反演模型,改善了叶绿素a浓度的遥感反演精度。分析表明：藻类颗粒物的后向散射系数与吸收系数之间存在反比关系,且在560 nm、700 nm附近存在明显的散射峰,与叶绿素a浓度之间相关性显著;低密度藻类水体总悬浮颗粒的后向散射以非色素颗粒为主导,适合采用经典的指数模型模拟后向散射系数,而藻类密度较高的富营养化水体,水体总悬浮颗粒的后向散射以藻类颗粒为主导,传统的指数模型已不适用;采用分离藻类后向散射系数的方法,使得叶绿素a浓度的反演值与真实值相关系数从0.66提高到0.98,相对误差从55%降低到38%,均方根误差(RMSE)也由60.95 μg/L降低至13.98 μg/L。其真实性检验表明,与经典指数模型方法相比,利用藻类颗粒后向散射分离方法反演叶绿素a浓度,能够显著改善反演精度。     

安阳南断裂带土壤H2、Rn地球化学特征

为研究安阳南断裂带土壤气体地球化学特征及构造地球化学背景，采用野外流动测量的方法对安阳南断裂带宗村段开展2期土壤H₂和Rn的重复观测。结果表明，第1期H₂和Rn的浓度范围分别为（0.66~58.56）×10^-6 和15~123 kBq/m³，背景值分别为6.87×10^-6和52.49 kBq/m³；第2期H₂和Rn的浓度范围分别为（0.36~29.73）×10^-6和28.2~103 kBq/m³，背景值分别为0.89×10^-6和47.49 kBq/m³。2期H2和Rn的测量结果均显示，在距测量起点210~300 m处气体浓度出现高值异常，气体在断裂带附近较为富集，对断层位置有一定的指示作用，利用断层气H2和Rn探测隐伏断裂的浅层位置在该区具有可行性。     

Relationship Between Zooplankton Community Characteristics and Environmental Conditions in the Surface Waters of the Western Pacific Ocean During the Winter of 2014

Understanding the effects of environmental heterogeneity on zooplankton communities has been a hot topic for several decades. However, relatively little is known about the responses of zooplankton communities to environmental conditions at large scales from inshore waters to the open ocean. Here, we used the abundance, biovolume, taxa and size spectra of zooplankton collected from the surface waters of the western Pacific Ocean during the winter of 2014 to study the relationship between zooplankton community characteristics and environmental conditions using multiple linear regression(MLR) analysis and redundancy analysis(RDA). According to a hierarchical cluster analysis based on hydrographic conditions, the study area was classified into five water masses. Significant correlations were identified between the limited nutrients and the zooplankton abundance and biovolume from inshore waters to the open ocean. Non-metric multidimensional scaling(NMDS) revealed two distinct zooplankton assemblages. In the northern inshore, Copepoda and Euphausiacea were the dominant zooplankton taxa and in other water masses, Chaetognatha and gelatinous zooplankton were the dominant zooplankton taxa in addition to Copepoda. Our results suggested that, on a large scale from inshore waters to the open ocean in the western Pacific Ocean, the spatial distribution of zooplankton taxa was mainly influenced by environmental conditions, while in the inshore waters, it was due to the top-down effect of the dominant zooplankton taxa. Finally, the slope of the normalized biovolume size spectra(NBSS) was negatively correlated with chlorophyll-a(Chl-a) concentration and PO_4~(3-)-P concentration in the inshore waters, which indicated that the higher the trophic level the dominant zooplankton taxa were, the steeper the NBSS slope was.     

Field Detection of Chlorophyll-a Concentration in the Sea Surface Layer by an Airborne Oceanographic Lidar

An airborne oceanographic lidar, with a frequency-tripled Q-switched Nd: YAG laser of 355 nm, has been designed to measure chlorophyll-a (Chl-a) concentration in the sea surface layer by the Ocean Remote Sensing Institute, OUC. The field experiment was carried out in the bay which is located south of the Liaodong Peninsula on the 10th of September 2005. After the flight, the raw data were processed and analyzed by the fluorescence-to-Raman ratio method with seawater attenuation coefficients calculated from signal profiles. The results of Chl-a concentration measurements by lidar are shown. The measurements in clear sea water were also compared with those of Chl-a concentration by a Moderate Resolution Imaging Spectroradiometer (MODIS).     

Field Detection of Chiorophyll-a Concentration in the Sea Surface Layer by an Airborne Oceanographic Lidar

An airborne oceanographic lidar, with a frequency-tripled Q-switched Nd： YAG laser of 355 nm, has been designed to measure chlorophyll-a （Chl-a） concentration in the sea surface layer by the Ocean Remote Sensing Institute, OUC. The field experiment was carried out in the bay which is located south of the Liaodong Peninsula on the 10th of September 2005. After the flight, the raw data were processed and analyzed by the fluorescence-to-Raman ratio method with seawater attenuation coefficients calculated from signal profiles. The results of Chl-a concentration sea water were also compared with those of Chl-a concentration by measurements by lidar are shown. The measurements in clear a Moderate Resolution Imaging Spectroradiometer （MODIS）.     

Climatology and seasonal variability of satellite-derived chlorophyll a around the Shandong Peninsula

The chlorophyll a(Chl a) is an important indicator of marine ecosystems. The spatiotemporal variation of the Chl a greatly aff ects the mariculture and marine ranching in coastal waters of the Shandong Peninsula. In the current study, the climatology and seasonal variability of surface Chl-a concentration around the Shandong Peninsula are investigated based on 16 years(December 2002–November 2018) of satellite observations. The results indicate that the annual mean Chl-a concentration is greater in the Bohai Sea than in the Yellow Sea and decreases from coastal waters to off shore waters. The highest Chl-a concentrations are found in Laizhou Bay(4.2–8.0 mg/m 3), Haizhou Bay(4.2–5.9 mg/m 3) and the northeast coast of the Shandong Peninsula(4.4–5.0 mg/m 3), resulting from the combined eff ects of the intense riverine input and long residence time caused by the concave shape of the coastline. The seasonal Chl-a concentration shows a signifi cant spatial variation. The Chl-a concentrations in these three subregions generally exhibit an annual maximum in August/September, due to the combined eff ects of sea surface temperature, river discharge and sea surface wind. In the southeast coast region, however, the Chl-a concentration is lowest throughout the year and reaches a maximum in February with a minimum in July, forced by the seasonal evolution of the Yellow Sea Cold Water and monsoon winds. The interannual Chl-a concentration trends vary among regions and seasons. There are signifi cant increasing trends over a large area around Haizhou Bay from winter to summer, which are mainly caused by the rising sea surface temperature and eutrophication. In other coastal areas, the Chl-a concentration shows decreasing trends, which are clearest in summer and induced by the weakening land rainfall. This study highlights the diff erences in the Chl-a dynamics among regions around the Shandong Peninsula and is helpful for further studies of coupled physical-ecological-human interactions at multiple scales.     

变异函数对泛克里金法的细粒子比星-地融合影响研究

泛克里金方法进行星-地融合可有效提高MODIS FMF的精度,然而由于地基站点稀少造成融合前需要利用长时间序列数据获取变异函数的主要参数（块金值、基台值和变程）,故不能满足基于卫星瞬时观测遥感PM_2.5的PMRS模型的需求。本文对2010年12月至2016年11月中国中东部地区的数据进行了变异函数参数的计算和分析,结果表明不同年份相关距离变化情况相一致,夏季显著高于冬季,基台值呈现与相关距离相反的趋势。通过利用2016年冬季变异函数中的变程（控制实验）和2011-2016年冬季变异函数的变程季均值（对比实验）作为初始值,对2016年冬季中国中东部地区MODIS FMF和地基FMF进行了融合,弃一交叉验证结果显示控制实验下FMF融合结果与地基FMF偏差最大值由0.552降低至0.198左右（对比实验下最大偏差为0.218）,平均误差相近（分别为0.070、0.080）。2种实验估算的PM_2.5平均值（分别为77.6、78.8 μg/m³）仅相差1.2 μg/m³,与在位测量的PM_2.5观测值相比,误差平均值均为37.4 μg/m³。由此可见,融合结果对初始变程值的变化敏感度不高,在季节相同的情况下,变程的多年季均值可有效替代相应季节的变程值。     

辽宁朝阳-北票断裂跨断层水准与断层土壤气地球化学特征对比分析

对朝阳-北票断裂上的北票黄花营子水准场地和朝阳桃花吐水准场地进行跨断层土壤气Rn、CO₂、CO和H₂浓度测量,结果表明,黄花营子水准场地土壤气Rn、CO₂、CO和H₂浓度变化范围分别为1.027~14.35 kBq/m³、0.1%~0.77%、0.2~1.4 ppm和21.45~303.4 ppm;桃花吐水准场地土壤气Rn、CO₂、CO和H₂浓度变化范围分别为1.88~18.15 kBq/m³、0.23%~4.53%、0.2~2.6 ppm和12.03~399 ppm。土壤气地球化学分析结果表明,Rn、CO₂、CO和H₂浓度在水准测线范围内具有准同步高值异常变化特征,且测线内多点浓度高于异常下限,揭示朝阳-北票主干断裂在2处水准测线范围内经过,水准数据自2018年以来出现的张性变化真实可靠,主要与构造活动作用增强有关。