基于海洋一号D卫星海岸带成像仪的赤潮遥感监测特征

为进一步加强对赤潮等海洋生态灾害的动态监测,科学支撑海洋防灾减灾工作,文章基于海洋一号D卫星搭载的海岸带成像仪数据,选取北部湾、茂名近岸和陵水湾为研究区域,分析2021年2月发生的4例赤潮事件的遥感影像、叶绿素a浓度和赤潮指数特征。研究结果表明：遥感影像可清晰呈现赤潮分布状况,叶绿素a浓度和赤潮指数的异常值范围与遥感影像一致,赤潮水体的叶绿素a浓度和赤潮指数整体高于非赤潮水体。     

Effects of an artificial oyster shell reef on macrobenthic communities in Rongcheng Bay,East China

An artificial oyster shell reef was deployed in Rongcheng Bay, East China. However, the effects of this reef on the surrounding macrobenthic communities were unknown. We compared sedimentary factors, macrobenthic biomass, abundance, and community composition and ecological indicators between the reef and non-reef areas over a one year period. The mean values for chlorophyll a （Chl a）, total organic matter （TOM）, total organic carbon （TOC）, and total nitrogen （TN） content in surface sediments in the reef area were slightly higher than those in the non-reef area. The Chl a levels differed significantly between the two areas, but the TOM, TOC, and TN were not significantly different. The abundance of crustaceans was significantly different between the two areas, but the abundance and biomass ofpolychaetes, echinoderms, mollusk did not differ significantly. The permutational multivariate analysis of variance （PERMANOVA） revealed that the macrobenthic community differed significantly through time and analysis of similarity multivariate analyses （ANOSIM） revealed that the macrobenthic community differed significantly in some months. The ecological indicators revealed that the environmental quality of the reef area was slightly better than that of the non-reef area. Overall, our results suggest that the artificial oyster shell reef may change the macrobenthic community and the quality of the environment. Despite the lack of an effect in the short term, long-term monitoring is still needed to evaluate the effects of artificial oyster shell reefs on macrobenthic communities.     

The distribution of chlorophyll a and its influencing factors in different regions of the Bering Sea

The distribution of chlorophyll a(Chl a) and its relationships with physical and chemical parameters in different regions of the Bering Sea were discussed in July 2010. The results showed the seawater column Chl a concentrations were 13.41–553.89 mg/m2 and the average value was 118.15 mg/m2 in the study areas. The horizontal distribution of Chl a varied remarkably from basin to shelf in the Bering Sea. The regional order of Chl a concentrations from low to high was basin, slope, outer shelf, inner shelf, and middle shelf. The vertical distribution of Chl a was grouped mainly from single-peak type in basin, slope, outer shelf, and middle shelf, where the deep Chl a maxima(DCM) layer was observed at 25–50 m, 30–35 m, 36–44 m, and 37–47 m, respectively. The vertical distribution of Chl a mainly had three basic patterns: standard single-peak type, surface maximum type, and bottom maximum type in the inner shelf. The analysis also showed that the transportation of ocean currents may control the distribution of Chl a, and the effects were not simple in the basin of the Bering Sea. There was a positive correlation between Chl a and temperature, but no significant correlation between Chl a and nutrients. The Bering Sea slope was an area deeply influenced by slope current. Silicate was the factor that controlled the distribution of Chl a within parts of the water in the slope. Light intensity was an important environmental factor in controlling seawater column Chl a in the shelf, where Chl a was limited by nitrate rather than phosphate within the upper water. Meanwhile, there was a positive relationship between Chl a and salinity. Algal blooms broke out at Sta. B6 of the southwestern St. Lawrence Island and Stas F6 and F11 in the middle of the Bering Strait.     

基于经验模型的Hyperion数据植被叶绿素含量反演

对于反演植被叶绿素含量而言,基于Hyperion等高光谱传感器数据、利用经验方法建模是一种快速准确的方法。利用多种植被的实测数据以及Hyperion模拟数据,分析植被反射率及其变化形式与叶绿素含量的相关性,并进一步针对红边参数、植被指数等分析植被反射率与叶绿素含量的关系,选取最准确的经验建模方法。经过对比,改进的简单比值指数(modified simple ratio,MSR)与叶绿素含量相关性最高,其回归模型能比较准确地反演出叶绿素含量。通过Hyperion图像、利用MSR指数与实测叶绿素含量得到回归模型,建立区域叶绿素含量分布图;并对张掖地区植被叶绿素含量进行了反演,反演结果具有较高精度,相对误差低于5%。     

浅议赤潮

海洋是一种生物与环境、生物与生物之间相互依存，相互制约的复杂生态系统。系统中的物质循环、能量流动都是相对稳定，动态平衡的。当赤潮发生时这种平衡遭到干扰和破坏。在植物性赤潮发生初期，由于植物的光合作用。水体会出现高叶绿素a、高溶解氧、高化学耗氧量。赤潮造成的环境改变，使一些海洋生物不能正常生长，导致一些生物逃避甚至死亡，破坏了原有的生态平衡。     

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。     

温室黄瓜低温气象灾害指标

以黄瓜品种津优35号(Jingyou 35)为试材,于2011年设计不同低温（5、7、9、11 ℃,以25 ℃为对照）处理的人工环境控制试验,系统研究不同低温胁迫对黄瓜叶片光合作用特性及抗氧化酶活性的影响。结果表明：黄瓜叶片最大光合速率随低温胁迫程度的增加依次降低;在不同低温胁迫下,随胁迫时间的延长,黄瓜叶片光补偿点不断升高,光饱和点不断降低;在5 ℃、7 ℃和9 ℃低温处理下,随胁迫时间的延长,光系统Ⅱ最大光化学效率呈下降趋势,光化学淬灭不断降低,非光化学淬灭的变化趋势相反;黄瓜叶片中的超氧化物歧化酶活性随着处理温度的降低先升高后下降;过氧化物酶活性在9 ℃处理24 h后达到最高;过氧化氢酶活性随着处理温度的降低而升高;丙二醛含量大于对照,随胁迫程度的增加先升高,后略有下降。通过研究建立了温室黄瓜低温气象灾害指标,划分为4个等级,分别为轻度、中度、重度和极重,可为设施农业气象服务提供科学依据。     

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。     

基于MODIS的巢湖叶绿素a空间分布

利用MODIS影像数据,对水华现象出现的重要物质——巢湖水体叶绿素a信息进行反演。在对数据进行预处理后,采集影像相应位置的像元灰度值,与现实中在对应位置观测的湖水叶绿素a浓度进行相关性拟合分析,得到叶绿素a浓度与像元灰度值的相关性方程与相关系数。在建立相关性模型时采用了单波段和波段比值法,得到的最高相关系数为R2=0.881 8,表明利用这种方法反演巢湖水体叶绿素a浓度空间分布具有一定的可靠性。选择相关系数性较高的2个拟合方程反向演算MODIS影像,最后成功得到巢湖湖面当日叶绿素a浓度分布状况图,为巢湖防治水华发生提供了比较准确可靠的信息。