鄱阳湖叶绿素a浓度遥感定量模型研究

叶绿素a浓度是反映湖泊水体营养状况的重要指标,本研究通过分析水体叶绿素a浓度与高光谱反射特征的相互关系,采用一阶微分值和峰值比值法分别建立了叶绿素a的高光谱定量反演模型,在此基础上与同步MODIS数据敏感波段建立卫星定量反演模型。结果表明:叶绿素a荧光峰出现在波段690nm-700nm,波段696nm一阶微分值相关系数最大;波段700nm与波段680nm的比值与其对数相关性较好,MODIS数据波段2和波段1比值的指数模型为最佳的回归模型。     

冠层光能利用率的叶绿素荧光光谱探测

设计了玉米生长期日变化试验,同步获取玉米冠层光谱和通量观测数据,探究从植被发射荧光光谱角度实现植被光能利用率可靠反演的可能性。运用涡度相关法获取群体生态系统净生产力(NEP),通过呼吸作用拟合得到冠层总初级生产力(GPP);在此基础上结合吸收光合有效辐射(APAR)获取冠层光能利用率(LUE);同时,利用叶绿素荧光光谱分离算法,提取了光合作用叶绿素荧光绝对强度和相对强度。结论表明,植被发射荧光光谱与光合有效辐射(PAR)显著正相关,760nm波段荧光与PAR的复相关系数R2在0.99以上;叶绿素荧光绝对强度与NEP和GPP显著正相关,荧光和NEP对环境日变化具有类似的响应特征;688nm和760nm植被发射的叶绿素荧光相对强度与LUEGPP存在可靠负相关关系,即叶绿素荧光强度越大,光能利用率越低。同时,通过比较几种植被指数与各种光合参量的相关性表明,叶绿素荧光能够更好的跟踪植被光合状态的变化,更适宜于植被光能利用率的探测。     

水面菲涅尔反射对~761 nm叶绿素荧光估算的影响

叶绿素荧光是光合作用的有效探针,可用于海洋浮游植物的监测与定量评估。太阳诱导叶绿素荧光覆盖可见光—近红外650—800 nm,在～685 nm与～740 nm表现出两个形态不同的荧光峰特征。基于～685 nm荧光峰的叶绿素浓度反演算法较为成熟,但在高悬浮物和高叶绿素浓度的水体中,算法的有效性不足。基于叶绿素荧光在氧气吸收谱段(O2-A)的填充作用,水体遥感反射率光谱～761 nm峰值中包含有太阳诱导叶绿素荧光信号,能用于水体叶绿素浓度的估算,但该反射峰形态特征还取决于传感器的光谱分辨率。本研究基于不同光谱分辨率的大气吸收谱线特征,模拟了水体遥感反射率光谱(750—775 nm)上太阳诱导叶绿素荧光的信号响应特征;分析了利用遥感反射率(～761 nm)计算叶绿素荧光的原理,阐明了不同光谱分辨率条件下水体叶绿素荧光信号在反射光谱上的形态变化规律。采用水面以上测量法获取的离水光谱辐亮度,包含了水面的菲涅尔反射信号,由于真实的菲涅尔系数难以准确测量,这给基于～761 nm处遥感反射率峰值的荧光信号估算带来不确定性影响。研究表明,假定菲涅尔系数为0时,虽然～761 nm叶绿素荧光信号与其浓度具有较好的线性统计关系,但却带来较大的不确定性;这种不确定的影响,在低浓度叶绿素水体中表现明显,在高浓度叶绿素水体中,影响相对较小;准确估算菲涅尔系数,有助于减少这种不确定性影响。对基于遥感反射率～761 nm叶绿素荧光信号的深入探讨,将能推动未来水体叶绿素荧光的识别与利用。     

HY-1C卫星COCTS近海水体遥感反射率产品真实性检验

中国HY-1C卫星水色水温扫描仪(COCTS)从2018年9月发射至今已积累了大量的全球观测数据,本文利用AERONET-OC实测数据集对COCTS近海水体遥感反射率(Rrs)产品进行了真实性检验。本文对实测光谱数据集进行归一化处理,按光谱特征分为A (清洁)、B (比较清洁)、C (轻微浑浊)、D (比较浑浊)这4种光学水体类型,对COCTS Rrs产品在这4类水体的精度进行评价。结果表明:COCTS反演Rrs在A、B两种水体类型中存在轻微高估(平均绝对百分比误差APD (Average absolute Percent Difference)分别为38.79%、44.44%),在C类水体轻微低估(APD=40.85%),而在D类水体显著低估(APD=47.14%)。COCTS不同波段Rrs产品在4类水体的精度亦存在差异,其中412 nm、443 nm波段在A类水体中和实测数据一致性相对较好(APD均小于30%);520 nm、565 nm波段在C、D两类水体中和实测数据一致性相对较好(APD均小于30%);670 nm波段在4种水体均呈现显著低估。由于AERONET-OC波段和CO...     

基于光谱特征的三峡坝区水色要素反演

基于野外测定的水质参数,通过研究三峡坝区水体中水色要素浓度与反射率之间的关系,选择反演叶绿素、悬浮物、溶解性有机物的最佳波段,建立了反演水色要素浓度的遥感定量模型。研究表明,在波段比值的基础上进行幂次修正的波段组合反射率与SS浓度相关性较好(R2=0.76),可以用来估算悬浮物浓度;悬浮物浓度影响叶绿素浓度的反演精度,通过在模型中增加一个红绿波段比值指数项的方法能够抑制或削弱悬浮物的影响,提高了叶绿素浓度的反演精度(R2=0.75);DOC反演模型中,绿光波段与红光波段反射率的对数值能较好的估算DOC浓度,且与log(DOC)相关程度最高,决定系数为0.85,反演精度较高。     

太湖梅梁湾下行漫衰减系数的Monte Carlo模拟及分析

漫衰减系数常用于计算水体浑浊度和划分水体等级,是水中生物进行光合作用等生态过程中的重要参数。本文假设水体固有光学特性(IOPs)不随垂直剖面变化,水体表面为镜面。通过Monte Carlo方法模拟追踪光子在水中的运动过程,统计大量光子在不同深度上的能量分布,计算出下行漫衰减系数Kd值。结果表明:在450 nm,550 nm和650 nm波长处模拟的Kd值基本上小于实测Kd值,对应后向散射概率为3%的散射相函数模拟的相对误差最小,适合用于构建太湖水体的Kd值反演模型。进一步分析入射天顶角、b/a值对Kd值变化的影响,结果发现:在b/a较大的情况下,散射相函数成为影响Kd值变化的主要因素。当b/a值大于9时,入射天顶角从10°变化到80°时,Kd值的变化率小于10%,可忽略入射天顶角的变化对Kd值的影响。利用单一散射相函数模拟不同波长处的Kd值,发现悬浮颗粒物浓度较高且以无机颗粒物为主体时,450—550 nm内模拟值大于实测值,550—650 nm内则相反,说明随着波长的增加,水体中颗粒物的散射呈现出前向散射减弱、后向散射增强的变化趋势。在反演不同波长处的Kd值时需考虑到散射相函数的光谱变化所造成的误差。     

光谱波段宽度对森林叶片叶绿素含量反演的影响分析

随着传感器技术的发展,高光谱数据光谱的波段宽度逐渐变窄,如何从海量的光谱数据中找到最优的光谱波段反演叶绿素含量,成为研究的难点问题。本文在测量华中农业大学狮子山6种主要树种的光谱数据和叶绿素含量的基础上,利用叶绿素指数(CI)和回归方法反演叶绿素含量,并分析了波段宽度对反演叶绿素含量结果的影响,结果发现波段宽度会影响到叶绿素反演的精度,当波段宽度为30nm时,叶绿素含量与"红边"区域(700nm-730nm)和近红外区域(770nm-800nm)叶绿素指标(CI)间的线性关系较好,决定系数可达到77.62%,均方根误差为10.6ug/cm2。     

长时序Landsat的北极Lena河DOC浓度变化及驱动力分析

北极Lena河是世界第十长河,也是北极地区第二大河,其年径流量约占北冰洋淡水总量的20%,同时将陆地生态系统上的大量有机物携带进海洋,并且在全球碳循环中起到非常重要的作用。卫星遥感数据是监测河流有机碳循环的重要数据源,特别是在无冰期的高纬度地区。本研究的目的是:(1)建立一种高精度反演算法估算北极Lena河的溶解有机碳DOC (Dissolved Organic Carbon)浓度;(2)分析长时间序列遥感影像中DOC浓度的变化特征;(3)探讨北极Lena河的DOC浓度变化的主要驱动因素。本文中主要构建了一种基于谷歌地球引擎GEE的遥感反演算法,利用1999年—2018年的Landsat影像反演得到了北极Lena河的有色溶解有机物CDOM(Chromophoric Dissolved Organic Matter)浓度。基于CDOM与DOC这两种水体成分的实地测量值之间的强相关性(R2=0.873),本文将CDOM反演结果转换为DOC浓度。在此基础上,本文分析了近20年的北极Lena河无冰期DOC的时空动态变化。研究结果表明反演算法所表现的性能证实了使用Landsat系列不同传感器长时间监测河流DOC变化的能力。利用增强回归树模型分析了北极Lena河的DOC变化的是土地覆盖变化、流域坡度、气象因子、人类活动以及纬度地带性等众多驱动因素的共同影响,而季节性,地域性和规模性也会影响DOC浓度与上述驱动因素之间的定量关系。总之,本文的结果可以提高监测北极地区不同河流中DOC变化及其通量的能力,并加深对北极碳循环的了解。     

不同养分供应状况对水稻荧光光谱特征的影响及其在遥感应用上的意义

在不同的养分供应状况下,对水稻在几个生育期的荧光光谱特征的研究表明:氮素供应的减少会引起水稻叶片荧光光谱中蓝绿波段峰的强度在有效分蘖期时降低,无效分蘖期始升高,并使红波段峰的强度和特征峰之间的强度比值(如440nm/550nm)在各生育期均有所降低;利用水稻叶片荧光光谱特征的变化监测其养分供应状况是可能的;监测波段以400—800nm为宜,监测时期应为分蘖盛期一孕穗期。     

利用夫琅和费暗线探测自然光条件下的植被光合作用荧光研究

自然光照条件下测定的植被反射的辐照度光谱既包括太阳光诱导荧光的发射光谱，又包括叶片对入射光的反射光谱，研究如何从冠层光谱中提取荧光光谱有十分重要的应用价值。首先，论文介绍了夫琅和费暗线探测自然光条件下的光合作用荧光的基本原理和方法。其次，将太阳大气的夫琅和费暗线拓展到地球大气，发现地物光谱仪测定的冠层辐照度光谱中688nm和760nm两个氧气吸收形成的夫琅和费暗线特征明显，且荧光较强，所以利用这两个波段的夫琅和费暗线可以探测自然光条件下的光合作用荧光。第三，研究并分析了夫琅和费暗线方法计算的688nm和760nm波段的荧光特性，结果表明该方法计算的荧光是可靠的，它与光合有效辐射（PAR）关系密切，复相关系数达到了0．9；冬小麦冠层荧光光谱在760nm和688nm波段的荧光大小基本相等，而地锦冠层荧光光谱在688nm波段的荧光强度是760nm的3倍左右，表明荧光光谱能够更加敏感地反映植被物种或生理生化状况的差别。最后，将夫琅和费暗线方法计算的688nm和760nm波段的荧光数据与激光脉冲调制荧光仪测定Fv／Fm荧光参数进行了统计分析，结果表明它与Fv／Fm存在极显著的负相关关系。所以利用夫琅和费暗线方法能够探测植被冠层荧光，并有可能替代传统的测定方法，并推广到航空航天平台，实现荧光探测从接触式点测量方式到航空或卫星遥感大面积监测的技术飞越。     

Tracing high time-resolution fluctuations in dissolved organic carbon using satellite and buoy observations: Case study in Lake Taihu,China

Field measurements of dissolved organic carbon (DOC) concentration and remote-sensing reflectance were conducted to develop a regional, empirical red-blue algorithm to retrieve surface DOC from Geostationary Ocean Color Imager (GOCI) data for Lake Taihu, China. The auxiliary data (in-situ observations of the optical properties and water quality, buoy measurements of hydrodynamic data and water chemical parameters) were used to investigate the spatial and temporal variations in DOC. GOCI was shown to be capable of successfully obtaining hourly variations in DOC, with a root mean square error percentage (RMSP) of 17.29% (RMSE = 0.69 mg/L) for the match-up data. The GOCI-derived DOC in Lake Taihu confirms that the highest DOC concentration is in northwest Lake Taihu, followed by Meiliang Bay, Gonghu Bay and northeast Lake Taihu. Hourly DOC variation is significant and presents a different trend for each lake segment due to the variety of influencing factors. Discharge of DOC from surrounding rivers is an important factor to the variation of DOC in northeast Lake Taihu. However, organic products of algae will be the primary contributor to DOC when algal bloom occurred. During the period of algal bloom, high DOC levels in Lake Taihu can lead to hypoxia when coupled with high temperatures and low disturbance.     

内陆水体藻类叶绿素浓度与反射光谱特征的关系

通过研究内陆水体反射光谱特征与藻类叶绿素浓度之间的关系,建立藻类叶绿素高光谱定量遥感模型。在实验地太湖地区,采用高分辨率地物光谱仪实地测量了湖水在可见光和近红外波段（３００－１１００ｎｍ）的反射光谱曲线,并且同时采样分析叶绿素、总悬浮固体物质浓度等水质参数。研究发现在叶绿素浓度较高时（〉５μｇ／Ｌ）,水体光谱反射比Ｒ７０５ｎｍ／Ｒ６７５ｎｍ、叶绿素在７００ｎｍ附近反射峰的位置等与叶绿素浓度有较好的     

Retrieval of CDOM and DOC Using In Situ Hyperspectral Data: A Case Study for Potable Waters in Northeast China

Chromophoric dissolved organic matter (CDOM), the light absorbing fraction of dissolved organic carbon (DOC), together with phytoplankton and total suspended matter are the main optically active components could be retrieved by remote sensing data. Generally, different composition of DOC and CDOM corresponds to different water surface reflectance. Absorption properties of CDOM and retrieval models for CDOM and DOC were investigated with data from potable reservoirs located in the central of Jilin Province. Water sampling field surveys were conducted on 15, 16 and 19 of September 2012 across the Shitoukoumen, Erlonghu and Xilicheng reservoirs, respectively. Both empirical regression (single band model and band ratio model) and partial least squares coupled with back-propagation artificial neural models (PLSBPNN) were established to estimate CDOM absorption coefficient at 355 nm [a_CDOM(355)] and DOC concentration with in situ measured remote sensing reflectance. It was found that the band ratio models and PLSBPNN model performed well for estimating DOC concentration while the band ratio models yielded the best result in retrieval CDOM. Moreover, all the three models performed better on the DOC concentration estimation than the performance on a_CDOM(355). Band ratio models outperformed (R ² ?=?0.55) other models for estimating CDOM absorption coefficient, while PLSBPNN model outperformed other models with respect to DOC estimation (R ² ?=?0.93). High spectral slope values indicated that CDOM in the potable waters primarily comprised low molecular weight organic substances; while sources of DOC were mainly coming from exogenous input, which was the main reason lead to the difference of model performances on DOC and a_CDOM(355) estimation. The algorithms developed in this study is needed to be tested and refined with more in situ spectral data, also future work is still needed to be undertaken for characterizing the dynamic of the potable water quality with remotely sensed imagery.     

Estimating dissolved organic carbon concentration in turbid coastal waters using optical remote sensing observations

Dissolved Organic Carbon (DOC) is an important component in the global carbon cycle. It also plays an important role in influencing the coastal ocean biogeochemical (BGC) cycles and light environment. Studies focussing on DOC dynamics in coastal waters are data constrained due to the high costs associated with in situ water sampling campaigns. Satellite optical remote sensing has the potential to provide continuous, cost-effective DOC estimates. In this study we used a bio-optics dataset collected in turbid coastal waters of Moreton Bay (MB), Australia, during 2011 to develop a remote sensing algorithm to estimate DOC. This dataset includes data from flood and non-flood conditions. In MB, DOC concentration varied over a wide range (20–520 μM C) and had a good correlation (R² = 0.78) with absorption due to coloured dissolved organic matter (CDOM) and remote sensing reflectance. Using this data set we developed an empirical algorithm to derive DOC concentrations from the ratio of R_rs(412)/R_rs(488) and tested it with independent datasets. In this study, we demonstrate the ability to estimate DOC using remotely sensed optical observations in turbid coastal waters.     

Historical effects of dissolved organic carbon export and land management decisions on the watershed-scale forest carbon budget of a coastal British Columbia Douglas-fir-dominated landscape

Background

To address how natural disturbance, forest harvest, and deforestation from reservoir creation affect landscape-level carbon (C) budgets, a retrospective C budget for the 8500 ha Sooke Lake Watershed (SLW) from 1911 to 2012 was developed using historical spatial inventory and disturbance data. To simulate forest C dynamics, data was input into a spatially-explicit version of the Carbon Budget Model-Canadian Forest Sector (CBM-CFS3). Transfers of terrestrial C to inland aquatic environments need to be considered to better capture the watershed scale C balance. Using dissolved organic C (DOC) and stream flow measurements from three SLW catchments, DOC load into the reservoir was derived for a 17-year period. C stocks and stock changes between a baseline and two alternative management scenarios were compared to understand the relative impact of successive reservoir expansions and sustained harvest activity over the 100-year period.

Results

Dissolved organic C flux for the three catchments ranged from 0.017 to 0.057 Mg C ha^?1 year^?1. Constraining CBM-CFS3 to observed DOC loads required parameterization of humified soil C losses of 2.5, 5.5, and 6.5%. Scaled to the watershed and assuming none of the exported terrestrial DOC was respired to CO₂, we hypothesize that over 100 years up to 30,657 Mg C may have been available for sequestration in sediment. By 2012, deforestation due to reservoir creation/expansion resulted in the watershed forest lands sequestering 14 Mg C ha^?1 less than without reservoir expansion. Sustained harvest activity had a substantially greater impact, reducing forest C stores by 93 Mg C ha^?1 by 2012. However approximately half of the C exported as merchantable wood during logging (~176,000 Mg C) may remain in harvested wood products, reducing the cumulative impact of forestry activity from 93 to 71 Mg C ha^?1.

Conclusions

Dissolved organic C flux from temperate forest ecosystems is a small but persistent C flux which may have long term implications for C storage in inland aquatic systems. This is a first step integrating fluvial transport of C into a forest carbon model by parameterizing DOC flux from soil C pools. While deforestation related to successive reservoir expansions did impact the watershed-scale C budget, over multi-decadal time periods, sustained harvest activity was more influential.

     

南海水色遥感的主因子分析

分析了叶绿素、黄色物质和无机悬浮颗粒等要素对海水光谱反射率的贡献,并由这些要素的光学特性正演光谱反射率,与实测结果符合较好。在此基础上,利用主成分分析方法,通过对光谱反射率数据的特征向量变换和主因子回归,建立了反演南海海水叶绿素和溶解有机碳的遥感算法。与实测结果的比较表明,叶绿素和溶解有机碳的相对误差分别达１７５％和３７４％。     

Assessment of the abnormal growth of floating macrophytes in Winam Gulf (Kenya) by using MODIS imagery time series

The objective of this research study is to assess the capability of time-series of MODIS imagery to provide information suitable for enhancing the understanding of the temporal cycles shown by the abnormal growth of the floating macrophytes in order to support monitoring and management action of Lake Victoria water resources.The proliferation of invasive plants and aquatic weeds is of growing concern. Starting from 1989, Lake Victoria has been interested by the high infestation of water hyacinth with significant socio-economic impact on riparian populations.In this paper, we describe an approach based on the time-series of MODIS to derive the temporal behaviour, the abundance and distribution of the floating macrophytes in the Winam Gulf (Kenyan portion of the Lake Victoria) and its possible links to the concentrations of the main water constituencies.To this end, we consider the NDVI values computed from the MODIS imagery time-series from 2000 to 2009 to identify the floating macrophytes cover and an appropriate bio-optical model to retrieve, by means of an inverse procedure, the concentrations of chlorophyll a, coloured dissolved organic matter and total suspended solid.The maps of the floating vegetation based on the NDVI values allow us to assess the spatial and temporal dynamics of the weeds with high time resolution.A floating vegetation index (FVI) has been introduced for describing the weeds pollution level.The results of the analysis show a consistent temporal relation between the water constituent concentrations within the Winam Gulf and the FVI, especially in the proximity of the greatest proliferation of floating vegetation in the last 10 years that occurred between the second half of 2006 and the first half of 2007.The adopted approach will be useful to implement an automatic system for monitoring and predicting the floating macrophytes proliferation in Lake Victoria.     

Developing water quality retrieval models with in situ hyperspectral data in Poyang Lake,China

Applying remote sensing techniques to develop the retrieval models and further to obtain the spatiotemporal information of water quality parameters is necessary for understanding, managing, and protecting lake ecosystems. This study aimed to calibrate and validate the retrieval models for estimating the concentrations of chlorophyll a (C_CHL), suspended particulate matter (C_SPM), and dissolved organic carbon (C_DOC) with the in situ hyperspectral measurements in Poyang Lake, China in 2010 and 2011. The model calibration and validation results indicated that: (1) for C_CHL retrieval, significantly strong and moderate correlations existed between the measured and estimated values (with the correlation coefficient r = 0.92 and r = 0.76) using the exponential model and the three-band model, respectively, with biased estimation observed for the exponential model; (2) for retrieving C_SPM, there was a strong correlation between the measured and estimated values (r = 0.95) using the exponential model; and (3) no significant correlation between measured and estimated C_DOC values was found with our developed models. More work is needed to allow the water quality of Poyang Lake to be accurately and steadily estimated, especially for C_CHL and C_DOC.     

基于环境因素的沿岸水域叶绿素遥感探测研究

海洋叶绿素的调查一直是海洋生物资源与海洋生态学的研究重点。遥感技术是海洋叶绿素调查的有力工具。利用遥感光谱信号探测海水叶绿素在大洋水体(一类水体)中十分成功,但在沿岸水体(二类水体)的精度却不高,主要是由于悬浮泥沙、黄色物质等的干扰太大。从叶绿素的生存条件入手,提出了利用海水叶绿素环境生存因子作为辅助因素的方法建立叶绿素遥感探测模型。并以珠江口海域作为研究对象展开试验,结果表明:环境因子的引用,使模型的误差从32·48%降为17·96%,精度大大提高,从而证明该方法的可行性和有效性。     

Application of Aqua MODIS sensor data for estimating chlorophyll a in the turbid Case 2 waters of Lake Erie using bio-optical models

There is considerable interest in accurately estimating water quality parameters in turbid (Case 2) and eutrophic waters such as the Western Basin of Lake Erie (WBLE). Lake Erie is a large, open freshwater body that supports diverse ecosystem, and over 12 million people in the mid-western part of the United States depend on it for drinking water, fisheries, navigational, and recreational purposes. The increasing utilization of the freshwater has deteriorated the water severely and currently the lake is experiencing recurring harmful algal blooms (HABs). Improving the water quality of Lake Erie requires the use of robust monitoring tools that help water quality managers understand sources and pathways of influxes that trigger HABs. Satellite-based remote sensing sensor such as the moderate resolution imaging spectroradiometer (MODIS) may provide frequent and synoptic view of the water quality indices. In this study, data set from field measurements was used to evaluate the performance of 14 existing ocean color algorithms. Results indicated that MODIS data consistently underestimated the chlorophyll a concentrations in the WBLE, with the largest source of errors from dissolved organic matter and xanthophyll accessory pigments in this data set. Most of the global algorithms, including OC4v4 and the Baltic model, generated near-identical statistical parameters with an average R² of ~0.57 and RMSE ~2.9 μg/l. MODIS performed poorly (R² ~0.18) when its NIR/red bands were used. A slightly improved model was developed using similar band ratio approach generating R² of ~0.62 and RMSE ~1.8 μg/l.