Suspended solids analysis using ERTS-A data

The magnetic digital tapes of the imagery obtained by ERTS-A on September 23, 1972, have been analyzed for selected areas of the Potomac River. A statistical analysis of all four bands has been carried out. The results show that band III is useful in determining the water-to-land interface. Data on bands II suggest the existence of three distinct types of water—those having low, medium, and high reflecti vity. From previously published results and ground truth measurements the areas of hight reflectivity were identified as containg high concentrations of suspended solids. Areas of low reflectivity were identified as having relatively lower concentrations of suspended solids. A commonly used computer technique with some additional refinements has been used to generate thematic maps which identify the above areas and show their geographical distribution.     

Analytical algorithms for lake water TSM estimation for retrospective analyses of TM and SPOT sensor data

Suspended matter in inland waters is related to total primary production and fluxes of heavy metals and micropollutants such as PCBs. Synoptic information on suspended matter cannot be obtained from an in situ monitoring network since suspended matter is a spatially inhomogeneous parameter. This problem can be solved by the integrated use of remote sensing data, in situ data and water quality models. To enable retrospective model and remote sensing data comparison of suspended matter concentration and distribution, a methodology is required for processing satellite images that is independent of in situ measurements. Analytical optical modelling, based on knowledge of the in situ inherent optical properties, leads to reliable multi-temporal algorithms for estimating suspended matter concentration in lakes for the data from the SPOT and Landsat TM sensors. This methodology allows multi-temporal, multi-site and multi-instrument comparison of TSM maps derived from satellite imagery. This means that satellite sensor data can now become an independent measurement tool for water management authorities. The remote sensing maps showed that large gradients in TSM were observed for the various lakes as well as temporal changes of these spatial gradients. In situ point samples are shown to be not representative for suspended matter in the lakes.     

Estimating the extent of drained supraglacial lakes on the Greenland Ice Sheet

Supraglacial lakes are a common feature of the ablation zone of the Greenland Ice Sheet and have significant implications for the water budget of the area, because when they drain they can increase the speed at which ice moves to lower elevations. One valuable tool in assessing the water balance of ice sheets is to track the volume of lakes as they form, through in situ measurements or by determining lake area and depth from aircraft or spacecraft imagery. However, since supraglacial lakes drain unpredictably and rapidly, it is possible that they can form and drain without being observed. Therefore, it is valuable to create tools that can detect the previous presence of supraglacial lakes after they have drained. Three methods of distinguishing drained supraglacial lakes in Landsat Enhanced Thematic Mapper Plus (ETM+) satellite imagery and hyperspectral airborne imagery were analysed: spectral signature analysis on raw data, band ratio analysis, and textural analysis. All three methods show promise that they could be used to detect former (i.e. drained) supraglacial lakes, thereby refining estimates of the water balance of the Greenland Ice Sheet and providing valuable data to climate models.     

The impact of bottom brightness on spectral reflectance of suspended sediments

Two experiments were conducted outdoors to investigate how bottom brightness impacts the spectral response of a water column under varied suspended sediment concentrations. A white aluminum panel placed at the bottom of the tank was used as the bright bottom, and a flat-black tank liner served as the dark bottom. Sixteen levels of suspended sediment from 25 to 400 mg litre ^-1 were used in each experiment. Spectral data were collected using a Spectron SE-590 spectroradiometer. The major findings include the following: the bright bottom had the greatest impact at visible wavelengths; when suspended sediment concentrations exceeded 100 mg litre ^-1, the bright bottom response was found to be negligible; and, substrate brightness has minimal impact between 740 and 900 nm, suggesting that these wavelengths are best for measuring suspended sediment concentrations by means of remote sensing.     

Estimating suspended sediment concentrations in turbid coastal waters of the Santa Barbara Channel with SeaWiFS

A technique is presented for estimating suspended sediment concentrations of turbid coastal waters with remotely sensed multi-spectral data. The method improves upon many standard techniques, since it incorporates analyses of multiple wavelength bands (four for Sea-viewing Wide Field of view Sensor (SeaWiFS)) and a nonlinear calibration, which produce highly accurate results (expected errors are approximately ±10%). Further, potential errors produced by erroneous atmospheric calibration in excessively turbid waters and influences of dissolved organic materials, chlorophyll pigments and atmospheric aerosols are limited by a dark pixel subtraction and removal of the violet to blue wavelength bands. Results are presented for the Santa Barbara Channel, California where suspended sediment concentrations ranged from 0–200+ mg?l^?1 (±20?mg?l^?1) immediately after large river runoff events. The largest plumes were observed 10–30?km off the coast and occurred immediately following large El Niño winter floods.     

运用SPOT数据进行河流水体悬浮固体浓度的研究——以台湾淡水河为例

根据含沙水体的光谱特征,通过对比分析认为ＳＰＯＴ影像是河流水质遥感的理想数据源,其中１ 波段和２ 波段对反映水体悬浮固体比较敏感。根据遥感影像灰度值与水中悬浮固体含量之间的相关关系,运用ＳＰＯＴ影像的１、２ 波段和实测数据将淡水河悬浮固体含量分为４ 级,并对结果进行了评价。通过对悬浮固体污染等级图的分析,得出淡水河１０％ 以下的水体悬浮固体含量较高。悬浮固体含量从上游向下游递增,流经城市的河段悬浮物含量高,说明水体悬浮物含量受植被覆盖和人为作用影响。     

An algorithm for the retrieval of suspended sediment concentrations in the Irish Sea from SeaWiFS ocean colour satellite imagery

A study was conducted in the Irish Sea with the aim of deriving an algorithm for the retrieval of suspended sediment concentrations from ocean colour imagery obtained from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). In situ observations of the diffuse attenuation coefficient, K_d , and irradiance reflectance, R, were obtained at wavelengths coincident with the SeaWiFS visible wavebands using a Profiling Reflectance Radiometer (PRR600, Biospherical Instruments Inc., San Diego). Results showed that surface reflectance at 665 nm (R₆₆₅ ), rather than variations in the intrinsic colour of the ocean (using colour ratios), was the most widely applicable method of obtaining suspended sediment concentrations from ocean colour imagery in this region. The derived algorithm enabled the estimation of mineral suspended sediment (MSS) concentrations from ocean colour in the Irish Sea, accurate to within 1 mg l^?1 (see equation below). Furthermore, the application of this algorithm to a SeaWiFS image of the Irish Sea accurately reproduced known regions of high turbidity with realistic MSS concentrations.

MSS=0.0441R ² ₆₆₅ + 1.1392R ₆₆₅ + 1.7459

(R ²=0.9105, n=124, RMS error=0.907)

Specific absorption and scattering coefficients were derived for all optically active in-water constituents, namely yellow substance (YS), mineral suspended sediments (MSS) and phytoplankton pigments (C). An optical model based on the empirically derived absorption and scattering coefficients reproduced the observed relationship between MSS and R ₆₆₅. Model results highlighted the relative insensitivity of reflectance at 665 nm to variations in the concentrations of other in-water constituents, suggesting that the algorithm may be applicable to the Irish Sea throughout the year.     

Mapping glacial lakes partially obscured by mountain shadows for time series and regional mapping applications

Mountain shadows in optical satellite images complicate the mapping of glacial lakes. Due to the rugged topography in periglacial alpine regions, many glacial lakes, especially smaller lakes, are partially shaded by mountain shadows in remotely sensed images. Shadows not only reduce the accuracy of lake mapping but also make changes in lake area hard to detect. In this paper, the characteristics of mountain shadows in remotely sensed imagery are explored, and their spatial relationships with regards to glacial lakes are modelled. Building on the previously developed Glacial Lakes Iterative Local Mapping (GLILM) method, a new water mapping approach is presented. The new method utilizes log-transformed spectral data and a normalized difference water index, NDWI_blue, for delineating the boundaries of lakes within shadowed regions. The application of this approach is explored within the context of mapping lakes across space and time using Landsat images in the glacially dominated Tianshan mountainous of Central Asia. The results demonstrate that glacial lakes, both in sunlit and in shaded areas, can be mapped reliably, and that the results are useful for lake change analysis studies.     

基于地表参数真实性的GF-1和SPOT-7多光谱影像质量评价

目的 遥感影像中地表信息表达真实程度决定了影像信息提取和定量化应用水平,传统的从像素灰度和视觉特性角度的影像质量评价方法难以评价影像对地表信息表达能力,本文从地表反射率和NDVI（normalized difference vegetation index）两种地表参数真实性角度评价GF-1和SPOT-7多光谱影像质量。方法 提出了一种基于地表参数真实性的多光谱影像质量评价方法,完成GF-1和SPOT-7卫星对实验区同步成像,地面同步测量大气光学特性和典型地物样区光谱,获取同步观测数据并对多光谱影像进行辐射误差处理,计算地物样区在影像上的反射率和NDVI,通过与地面实测光谱数据比较分析了地表参数真实性,评价GF-1和SPOT-7多光谱影像质量。结果 人工靶标中GF-1影像在4个波段反射率误差均在5%内,精度优于SPOT-7;植被地物中SPOT-7影像在蓝绿红波段反射率误差在4%内,近红外波段误差在15%内,NDVI误差在16%内,反射率和NDVI精度均优于GF-1;硬地地物中GF-1影像在4个波段反射率误差在6%内,精度优于SPOT-7;评价结果表明SPOT-7多光谱影像对植被类地物光谱表达真实度更高,GF-1对硬地类地物光谱表达真实度更高。结论 提出的基于地表参数真实性的遥感影像质量评价方法,能够有效地从地物光谱信息表达精度的角度评价影像质量。     

基于高光谱数据和MODIS影像的鄱阳湖悬浮泥沙浓度估算

本文旨在寻找悬浮泥沙浓度的MODIS遥感影像估算模型,并利用实测的高光谱数据对其敏感波段和反演模型进行测试和验证。以鄱阳湖为研究区域,利用光谱数据进行分析,为利用遥感影像建模提供依据。进一步利用同步进行的鄱阳湖水质采样分析与MODIS影像中等分辨率各个波段反射率及其组合进行相关分析,寻找反演悬浮泥沙浓度的敏感波段。实验表明,MODIS的第一波段反射率对于悬浮泥沙浓度有很好的匹配(R² = 0.91; n = 25),进而建立了鄱阳湖地区的悬浮泥沙浓度遥感定量估算模型。利用估算模型和鄱阳湖地区历史MODIS影像,得到了鄱阳湖悬浮泥沙浓度分布图。基于对汛期鄱阳湖悬浮泥沙浓度的连续监测,可对长江倒灌入鄱阳湖现象的形态进行观测。     

Spectral reflectance characterization of shallow lakes from the Brazilian Pantanal wetlands with field and airborne hyperspectral data

The relationships between field water reflectance spectra and physico-chemical data of seven freshwater and five saltwater lakes from the Brazilian Pantanal wetlands were characterized. Selection of the lakes was based on previous inspection of the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) images. Principal component analysis (PCA) was used to identify homogeneous groups of lakes, in which the regression relationships were evaluated. The continuum removal method was applied to characterize minor spectral variations in the depth of the absorption bands present in field and image spectra. The results showed lakes with very distinct spectral characteristics. The transition from the freshwater to the saltwater lakes was characterized by lower values of depth and Secchi depth, larger concentrations of dissolved organic carbon (DOC), total suspended sediments (TSS), calcium (Ca), magnesium (Mg), sodium (Na) and potassium (K), and higher values of pH and electrical conductivity. The saline lakes presented a higher overall reflectance in the 400–900?nm range than the freshwater lakes, as indicated by the first principal component. From the optically active constituents analysed, DOC better explained variations in water reflectance. The discrimination of the saltwater lakes along the second principal component was due to the decrease in the chlorophyll (Chl) and to the increase in the DOC concentrations from the greenish to the bluish saline lakes. The AVIRIS instrument was able to detect the narrow 630?nm absorption band present in field water reflectance spectra.     

The effect of dissolved “yellow substance” on the quantitative retrieval of chlorophyll and total suspended sediment concentrations from remote measurements of water colour

Abstract

The effect of the dissolved “yellow substance” on the quantitative retrieval of chlorophyll and suspended sediment concentrations from remote measurements of water colour, has been investigated through a sensitivity analysis applied to theoretical simulations. Two different models for yellow substance absorption, derived from experimental observations, have been used in the computation. The results obtained showed important effects, leading to the conclusion that the presence of yellow substance must be taken into careful account in the process of inferring water composition from its colour signature.     

PS-InSAR公共主影像选择方法的研究

PS InSAR干涉中公共主影像的选择关系到干涉的质量。本文在综合考虑时空基线距和多普勒质心频率基线对干涉图去相关影响的基础上,提出以综合相关系数为测度的公共主影像最佳选择方法。借助欧空局提供的20景大同地区ENVISAT SLC SAR图像,进行PS InSAR公共主影像的优化选取实验。通过计算发现,指数权比对公共主影像的选择影响不大,因此建议在实际应用过程中,可直接按等指数权比计算综合相关系数,以此确定最佳公共主影像。     

A novel technique to detect turbid water and mask clouds in Greenland fjords

The existing National Aeronautics and Space Administration (NASA) Moderate Resolution Imaging Spectroradiometer (MODIS) MOD35_L2 cloud mask performance was assessed using imagery of Kangerlussuaq Fjord, Greenland. It was found to perform suboptimally, especially near glacially fed river mouths, due to sediment-laden water being highly reflective in near-infrared wavelengths. In situ observations of suspended sediment concentration (SSC) were compared against MODIS band 1 and 2 reflectance and show a reflectance saturation effect past which increasing SSC values fail to increase the reflectance of water. A new mask optimized for turbid waters uses the reflectance saturation effect observed in high-SSC water. This new mask and a custom adaption of individual tests within the existing MOD35_L2 cloud mask were tested. The new mask outperforms the standard MOD35_L2 mask and the combination of new and custom masks was shown to screen out clouds very well in Greenland fjords. It is thought that with local measurements of MODIS band 1 and 2 reflectance values of turbid water to serve as training data, this mask should perform equally well in other turbid coastal waters.     

Discrimination of adelgid-damage on single balsam fir trees with aerial remote sensing data

Compact Airborne Spectrographic Imager (CAS1) multi-spectral and panchromatic images were acquired in July 1992 over two forest plots infested by the balsam woolly adelgid (Adelges piceae) in western Newfoundland. A panchromatic image (pixel size approximately 25cm) was used as a georeference for the coarser resolution multi-spectral data which were resampled to 1m and 0-5m, then carefully tied to a detailed plot plan showing the locations of 159 trees. Field observations for each of these trees included a ranking for adelgid damage class according to a standard Forest Insect and Disease Survey (FIDS) scheme. A discriminant analysis of the multi-spectral CASI imagery (together with semi-variance parameters and texture derivations) indicated that damage caused by the balsam woolly adelgid on balsam fir (Abies balsamea) trees could be detected and separated into severity classes with a range of accuracy between 40-76 per cent depending on the classification scheme and the type of remote sensing variables available to perform discrimination. The ‘best’ discriminant results obtained were based on a single pixel sample extracted from a 0-5?m multi-spectral image comprised of six bands centred on 454, 550, 590, 662, 836, and 895nm. A central theme of this continuing effort is that the combination of multi-spectral, spatial and high spectral resolution image processing may provide further insight into optimal damage detection—and subsquent hazard ratings—using digital remote sensing imagery.     

A 20-year Landsat water clarity census of Minnesota's 10,000 lakes

A 20-year comprehensive water clarity database assembled from Landsat imagery, primarily Thematic Mapper and Enhanced Thematic Mapper Plus, for Minnesota lakes larger than 8 ha in surface area contains data on more than 10,500 lakes at five-year intervals over the period 1985–2005. The reliability of the data was evaluated by examining the precision of repeated measurements on individual lakes within short time periods using data from adjacent overlapping Landsat paths and by comparing water clarity computed from Landsat data to field-collected Secchi depth data. The agreement between satellite data and field measurements of Secchi depth within Landsat paths was strong (average R² of 0.83 and range 0.71–0.96). Relationships between late-summer Landsat and field-measured Secchi depth for the combined statewide data similarly were strong (r² of 0.77–0.80 for individual time periods and r² = 0.78 for the entire database). Lake clarity has strong geographic patterns in Minnesota; lakes in the south and southwest have low clarity, and lakes in the north and northeast tend to have the highest clarity. This pattern is evident at both the individual lake and the ecoregion level. Mean water clarity in the Northern Lakes and Forest and North Central Hardwood Forest ecoregions in central and northern Minnesota remained stable from 1985 to 2005 while decreasing water clarity trends were detected in the Western Corn Belt Plains and Northern Glaciated Plains ecoregions in southern Minnesota, where agriculture is the predominant land use. Mean water clarity at the statewide level also remained stable with an average around 2.25 m from 1985 to 2005. This assessment demonstrates that satellite imagery can provide an accurate method for obtaining comprehensive spatial and temporal coverage of key water quality characteristics that can be used to detect trends at different geographic scales.     

Toward universal multispectral suspended sediment algorithms

A data acquisition and analysis program has been undertaken to demonstrate the feasibility of remote multispectral techniques for monitoring suspended sediment concentrations in natural water bodies. Two hundred surface radiance measurements (400–1000 nm) were made at Lake Mead with coincident water sampling for laboratory analysis. Water volume spectral reflectance is calculated from the recorded surface radiance and volume reflectance-suspended sediment relationships investigated. Statistical analysis indicates that quantitative estimates of nonfilterable residue and nephelometric turbidity can be obtained from volume spectral reflectance data with sufficient accuracy (based on U.S. Environmental Protection Agency standards) to make the multispectral technique feasible for sediment monitoring. Algorithms exhibit sufficient universality to indicate they can be implemented in many cases with little or no ground truth for calibration.     

基于HSI变换和QPSO变换的图像融合算法

提出了一种基于HSI和QPSO（即基于量子行为的粒子群优化算法）的图像融合方法,HSI变换方法对多光谱图像和全色图像进行融合会丢失较多的光谱信息。利用QPSO算法来求解HSI变换中光谱强度分量的最优变换问题。由于采用了QPSO算法,使最后变换后的图像与多光谱图像和全色图像都有很强的相关性。实验表明,此方法所得到的融合图像优于传统HSI变换。     

Suspended sediment dynamics from repetitive Landsat data

Abstract

Repetitive Landsat CCT data were used to monitor the motion of non-uniformly distributed suspended sediments in a New Zealand tidal basin. The movement of such suspended sediment was followed using all four MSS bands with non-uniformly distributed suspended sediment being differentiated from bottom features by the data from two satellite overpasses. As pan of this study penetration depths of 45-50±5 cm and 10-15 ±5 cm were found for channels MSS 5 and MSS 6 over the sediment-laden tidal inlet. The difference in penetration depths within each MSS band was ascribed to differing concentrations of uniformly distributed suspended sediments between the two overpasses.     

水污染遥感监测

不同水质的水体在遥感影像上有较明显的反映。通过分析TM影像上不同水质水体的视反射率特征,发现1-4波段的视反射率(R1、R2、R3和R4)对不同的水质比较敏感。利用R2/R1>1可以区分出较高悬浮泥沙区域,R4/R3可以作为水体有机污染的指标。以黄河三角洲地区的小清河口为例,利用不同时相的TM影像,对水污染的遥感提取进行了尝试,得到了小清河口的水污染分布。