Spectral unmixing of coral reef benthos under ideal conditions

Hyperspectral remote sensing has shown promise for detailed discrimination of coral reef substratum types, but, by necessity, it samples at pixel scales larger than reef substratum patch sizes. Spectral unmixing techniques have been successful in resolving subpixel areal cover in terrestrial environments. However, the application of spectral unmixing on coral reefs is fundamentally challenging, due not only to the water column, but also to the potentially large number of spectrally similar and ecologically significant end-member (substratum) classes involved. A controlled ex-situ experiment was conducted using field-spectrometer data to assess the accuracy of spectral unmixing techniques to estimate the areal cover of small-scale (<0.25 m²) assemblages of reef substrata (e.g., changes in cover between massive corals, branching corals, bleached corals, macroalgae, and coralline red algae). Mixture compositions were obtained precisely by analysis of digital images collected by a camera calibrated to the field of view of the spectrometer. Linear unmixing techniques were applied to derive estimates of substratum proportions using the full spectral resolution data and various transformations of it, including derivatives and down sampling (merging adjacent wavelengths into broader spectral bands). Comparison of actual and estimated substratum proportions indicate that spectral unmixing may be a practical approach for estimating subpixel-scale cover of coral reef substrata. In the most accurate treatment, coefficients of determination across all mixture sets were high for most end-member classes (37 of 52 cases with r ² >0.64, i.e. r >0.8). The most successful analyses were based on derivatives of down-sampled data, implying that spectral unmixing benefits more from spectral smoothing and judicious choice of band locations than from high spectral resolution per se. Although these results show that changes in coral and algal cover can be determined by unmixing their spectra, the method is not yet an operational remote sensing tool. Primary empirical research is needed before taking the next step, which is to incorporate a water column, of variable depth, above the sea bed.     

浅谈化学生态学

一、概述化学生态学是最近一、二十年才发展起来的新的生态学分支学科,是一门研究化学物质的生态作用,揭示生物与环境关系本质的科学。目前,它虽然还处在幼年阶段,但它展示的方向和表现出的作用,却使生态学、生理学、化学、环境科学、农学、林学等许多领域内的科学家感到兴趣,在国际上引起相当的重视。在我国,有的单位也开始了这方面的研究工作。     

Assessing photosynthetic efficiency in an experimental mangrove canopy using remote sensing and chlorophyll fluorescence

This study examined the ability of the photochemical reflectance index (PRI) to track changes in effective quantum yield (Δ F/F _m ′), non-photochemical quenching (NPQ), and the xanthophyll cycle de-epoxidation (DPS) in an experimental mangrove canopy. PRI was correlated with (Δ F/F _m ′) and NPQ over the 4-week measurement period and over the diurnal cycle. The normalised difference vegetation index (NDVI) was not correlated with any aspect of photochemical efficiency measured using chlorophyll fluorescence or xanthophyll pigments. This study demonstrated that photochemical adjustments were responsible for controlling the flow of energy through the photosynthetic apparatus in this mangrove forest canopy rather than canopy structural or chlorophyll adjustments.     

Space remote sensing for spatial vegetation characterization

The study area, Madhav National Park (MP) represents northern tropical dry deciduous forest. The national park, due to its unique location (nearest to township), is under tremendous biotic pressure. In order to understand vegetation structure and dynamics, vegetation mapping at community level was considered important. Prolonged leafless period and background reflection due to open canopy poses challenge in interpretation of satellite data. The vegetation of Madhav National Park was mapped using Landsat TM data. The ground data collected from sample points were subjected to TWINSPAN analysis to cluster sample point data into six communities. The vegetation classification obtained by interpretation (visual and digital) of remote sensing data and TWINSPAN were compared to validate the vegetation classification at community level. The phytosociological data collected from sample points were analysed to characterize communities. The results indicate that structural variations in the communities modulate spectral signatures of vegetation and form basis to describe community structure subjectively and at spatial level.     

Satellite observation of Keppel Islands (Great Barrier Reef) 2002 coral bleaching using IKONOS data

An examination of IKONOS satellite imagery of the Keppel Islands (Great Barrier Reef) acquired before and during a coral bleaching event indicates that severe bleaching of reefs can be detected as an increase in brightness in the band 1 (blue) and band 2 (green) IKONOS spectral bands (4-m resolution). The bleaching was not detected in band 3 (red), band 4 (near-infrared), or in the 1-m panchromatic band data. A total of 0.74 km² of bleached coral was identified, with detection occurring in waters as deep as 15 m. The procedure requires that one of the scenes be radiometrically normalized to match the reference scene prior to image differencing. A relative radiometric normalization was used in this case because variable cloud cover present in the image acquired during the bleaching event prevented reliable modeling of atmospheric effects. The success at coral bleaching detection at Keppel Islands represents both a best-case and a cloud-challenged scenario. It was a best-case scenario in that coral cover was extensive (70–90% live coral cover, mostly acroporids) and the bleaching level was extreme (92–95% of coral cover white bleached). It was a cloud-challenged scenario in terms of having extensive and highly variable cloud cover present in the image acquired during the bleaching event. Color difference images reveal extensive areas of bleached coral at sites away from our study area, indicating that this platform and methodology may be a valuable tool for mapping high coral cover areas during bleaching events. Additional studies and technique refinements would be required to test the detection limits of bleaching with IKONOS imagery or to develop a spectrally based bleaching detection index.An erratum to this article can be found at     

Spectral reflectance of coral

Spectral reflectance (R) of corals is a fundamental parameter to coral reef remote sensing. We explore general trends as well as geographic and taxonomic variabilities of coral R using a data set consisting of 5,199 Rs measured in situ at depths of up to 15 m for 195 coral colonies at 11 sites worldwide. Coral R ranges in magnitude from ~0.5% at 400 nm to near 100% at 700 nm; mean coral R rises from ~2.5% at 400–500 nm to ~8% between 550 and 650 nm. All corals measured in this study exhibit one of two basic shapes of R, which we label the brown and blue modes. We postulate that brown-mode R is determined by pigment absorption solely by zooxanthellae, while blue-mode R arises through expression of a non-fluorescing coral-host pigment. Taxonomic and geographic variabilities are approximately equal to global variability, both in magnitude and shape, indicating that coral R is independent of taxonomic or geographic differences. We reason that this is to be expected, since R is determined by pigments that are conservative across geographic and taxonomic boundaries.     

Coral spawning in the western Pacific Ocean is related to solar insolation: evidence of multiple spawning events in Palau

Coral reproductive schedules have long been related to concomitant increases in regional sea surface temperature (SST). Yet, corals also mass spawn in the tropics, where SSTs vary little throughout the year. Here we show that the rise toward and fall from solar insolation maxima, which is the electromagnetic energy incident on the surface of the earth, coincide with coral spawning events in tropical Palau. Two insolation maxima (a consequence of the vernal and autumnal equinoxes) in the tropics lead to multiple spawning events per year. SSTs are poor predictors of coral spawning in the tropics. Multiple spawning events increase the rate of genetic recombination, which in turn may facilitate the likelihood of speciation and explain, in part, the high coral diversity in the tropics. We also show that mass spawning coincides with near-maximum solar insolation (5.0–7.2 kWh/m²/day) events from 33°N to 30°S in the western Pacific Ocean, and should be considered as one of the primary variables driving coral reproductive cycles.     

基于GIS的浙江省水稻遥感估产最佳时相选择

水稻遥感估产最佳时相选择应包括水稻种植面积估算最佳时相和水稻产量预报最佳时相两部分。在水稻遥感估产最佳时相选择中,由于首次引入GIS技术提取水稻可能种植区域,缩小了研究范围,植被种类也较简单一,因此仅用农作物物候历即可确定水稻种植面积估算最佳时相,而不需要考虑所有的植被类型。利用盆栽试验和小区试验研究水稻产量与不同时期的农学参数、农学参数与植被指数及水稻产量与植被指数的关系,结果表明,水稻产量与农业参数、农学参数与光谱变量的关系均以孕穗以抽穗期最好,水稻产量与光谱变量的关系则从分蘖盛期到抽穗期的极显著。因此,以孕穗期到抽穗期作为建立水稻遥感估产模型的最佳时期。再利用1998年各地的水稻发育期观测资料,确定各区水稻产量遥感最佳时相。     

Satellite remote sensing for ecological analysis of forested landscape

The spatial characterisation and vertical analysis are together considered important to evaluate structure of forested landscapes. In recent years, increased human impacts have resulted in changes in landscape and structure of the forest ecosystem. The present study is aimed to analyse impacts of disturbance on landscape structure using satellite remote sensing and a geographic information system (GIS) in Madhav National Park of India. The Landsat TM data have been used to identify vegetation types. The patch characteristics of the vegetation like size, shape, porosity and patch density have been studied. The physical and humanmade features have divided the national park in three zones. These zones are also utilised as management zones by the State Forest Department. The study indicates that the central zone is distinctly different from the south and north zones. The patch size and porosity have been found to be most important parameters to discriminate differences in the ecological status of three different zones of the park. The patchiness and shape provide supportive information and characterise the patches of the zones. The structural analysis of the vegetation revealed effect on species diversity and biomass distribution in the different disturbance regimes.     

遥感在林冠动态监测研究中的应用

 林冠动态大致包括三方面的内容,即由病虫害、林火等引起的林冠变化、由大风等灾害引起的林隙动态、以及树冠和林冠的正常变化等。遥感在林冠动态研究中的地位和作用已被广泛认知,国内外在此方面的研究已积累了丰富经验。进行林冠动态研究所利用的遥感数据主要有Landsat TM卫     

Satellite observations of main oceanographic processes to identify ecological associations in the Northern Arabian Sea for fishery resources exploration

Ecological associations are the inter-relationship between the species and their environment. Oceanographic processes like upwelling events and formation of eddies, rings, and fronts have been monitored using National Oceanic and Atmospheric Administration Advanced Very High Resolution (NOAA AVHRR) and Indian Remote Sensing Satellite-P4-Ocean Colour Monitor (IRS-OCM) data. Sea Surface Temperature (SST) and chlorophyll concentration (CC) images were derived from AVHRR and OCM, respectively. Upwelling event was monitored using AVHRR-SST by detecting the differences in surface water temperature. The formation of eddies, rings, cyclonic eddies, and anti-cyclonic eddies and their biological responses were studied using CC. Eddies and rings were found with high phytoplankton production in the form of bloom, which provide grazing ground for fishes. The anti-cyclonic eddies were found with very low CC, indicating the biological deserts in the ocean. The impacts of these processes on fish catch were studied using fishing operations data procured from Fishery Survey of India. In this paper, the occurrence of different oceanographic processes, their persistence, and relevance with catch statistics of fishery resources in the study area are discussed. The study explains the potentials of satellite remote sensing to establish the habitat linkage between oceanographic processes and fishery resources. Guest editor: V. D. Valavanis Essential Fish Habitat Mapping in the Mediterranean     

基于遥感影像的植被指数研究方法述评

随着遥感技术的发展,植被指数作为用来表征地表植被覆盖和生长状况的度量参数,已经在环境、生态、农业等领域有了广泛的应用。本文在分析植被指数形成机制及影响因子的基础上,对其具有一定技术突破的典型植被指数进行了归纳分类与比较分析,并评价了各自的优势和局限性。植被指数按遥感数据采集的平台可以分为航空植被指数和航天植被指数两大类,其中航天植被指数又可以分为基于波段简单线性组合的植被指数、消除影响因子的植被指数和针对高光谱遥感及热红外遥感的植被指数三类。最后就植被指数应用中存在的问题以及发展前景谈了一些看法:植被指数数目繁琐重复,急待规范条理化;植被指数应用领域不同,使用者时要慎重;植被指数影响因子很多,具体使用时应适时修正;植被指数公式繁琐阻碍其应用,应开发植被指数产品;遥感技术日新月异,积极研发新的植被指数。     

Studying marine microorganisms from space

Microorganisms are but a few micrometers in diameter and are not visible to the naked eye. Yet, the large numbers of microorganisms present in the oceans and the global impact of their activities make it possible to observe them from space. Here a few examples of how microorganisms can be studied from satellites are presented. The first case is the best known: the main pigment used in photosynthesis (chlorophyll a) can be determined from satellites. These kinds of studies have contributed a tremendous amount of understanding about the distribution and dynamics of primary production in the oceans. Two other examples will concern analysis of heterotrophic prokaryotic production and estimates of dimethyl sulfide (DMS) concentration and flux to the atmosphere. These three processes are of fundamental importance for the functioning of the biosphere. Marine microbes carry out about half of the total primary production in the planet. A substantial fraction of the respiration in the oceans is due to the activity of heterotrophic prokaryotes. Finally, the flux of DMS to the atmosphere is believed to constitute one of the mechanisms by which the biota can regulate climate. The global implications of microbial processes in the oceans can only be addressed with the help of satellites. Electronic Publication     

植物叶绿素含量的遥感模型及用陆地卫星数据所作的二维分布图

为了确定全球和区域尺度的植物叶绿素含量的多少和分布,遥感方法是一种很好的途径。有些遥感科学家直接利用归一化植被指数(NDVI)等植被指数推算叶绿素含量。实践表明,这种做法的缺点有:1.植被指数NDVI中的近红外波段反射率与叶绿素含量基本无关,这样NDVI中的主信息并没有表达叶绿素含量,其信噪比显著降低;2.存在明显的信息不确定性,同一个植被指数NDVI可能有两种状态:较高叶面积指数伴有较低叶绿素含量或者是较低叶面积指数伴有较高叶绿素含量。通过实践,作者推导出可用LANDSAT和NOAA影像图灰度值推算植被叶绿素含量遥感模型。并在中国科学院禹城遥感实验场实际应用中得到验证:用其模型推算植被叶绿素含量的精度比NDVI有较明显提高,不确定性有明显的降低。     

植物物候研究进展

植物物候直接反映了气候变化的影响,是植被动态模拟的关键.在遥感和模型技术的推动下,植物物候与全球变化关系的研究日益受到人们的关注.文中从植物物候与环境因子的相互关系、植物物候对全球变化的响应以及植物物候的遥感监测方面,综合论述了植物物候的研究进展,找出植被物候研究的不足,进而提出未来植被物候的研究方向.     

多波段卫星遥感海洋赤潮水华的方法研究

The spectral characteristics of the coastal waters in East China Sea was studied using in situ measurements, andt he multiband algorithms of remote sensing for bloom waters was discussed and developed. Examples of red tide detection using the algorithms in the East China Sea were presented. The results showed that the algorithms could provide information about the location and the area coverage of the red tide events.     

应用神经网络和多谱段遥感数据对大屿山岛土地覆盖分类的研究

 土地覆盖是植物群落研究的重要参数,反映植物群落的生长状况及其所处生存环境的优劣。小尺度常规的测定方法费力、费时,而且是破坏性的,不能动态监测其变化。而对于大尺度的测定,常规方法无能为力,只能采用遥感方法。应用人工神经网络和多谱段遥感数据对香港大屿山岛进行土地覆盖的分类,设计了一个合适的多层感知器前向反馈神经网络用于土地覆盖分类,并将分类结果与传统的最大似然分类方法所得的结果作比较,结果表明神经网络方法在分类精度上有了很大的提高。