基于Landsat／TM和ETM＋的理塘草地沙化趋势及其驱动力分析

文章利用1989、1994、2000和2005年的4期Landsat／TM,ETM＋遥感影像,在几何校正、辐射定标、大气校正的基础上计算了归一化植被指数（NDVI）,建立最小二乘法线性回归方程对多时相NDVI进行同化处理,基于二分模型提取植被覆盖度并转换成荒漠化指数（DI）,对理塘县城附近约103．1km2范围的分类研究结果表明：（1）分为无沙化、轻度、中度、重度和严重沙化5级,其中2005年中度、重度和严重沙化面积分别为2．562km2、2．925km2和1．576km2;中度沙化比1989年减少9．69％,重度和严重沙化分别增多35．79％和161．8％;（2）2005年中度以上沙化面积比1989年增加1．470km2,增加了26．3％,年增加率为1．47％;（3）沙化面积呈前期小、中期大幅增加、后期增加减缓的总体趋势;（4）降水量和风速因子的变化趋势有利于缓解沙化,气温变化趋势没有反映出对沙化的促进作用。人类活动是造成沙化趋于恶化的主要因素;（5）沙化增加趋势与同类研究结果一致。     

Assessment of Chlorophyll-a Concentration and Trophic State for Lake Chagan Using Landsat TM and Field Spectral Data

In this study, we present the digital evaluation of Landsat TM data and field spectral measurements for retrieving chlorophyll-a (chl-a) concentration and trophic state index in Lake Chagan of Northeast China. Chl-a concentration of the lake can be estimated from the band ratio (TM4/TM3) and the field spectral data at 670 nm (absorption peak) and at 700 nm (reflectance peak). The results show that the best determination coefficient (R ²) is 0.67 from the TM data, by which chl-a distribution can be mapped. Based on chl-a determination from laboratory analysis, field spectral and TM data, the modified trophic state index (TSI_M) was applied to assess the lake’s trophic state. With the available data in Lake Chagan, each algorithm demonstrates the similar result for assessing the lake’s chl-a and trophic state. Our results indicate that Landsat TM and field spectral data could be used effectively to determine chl-a concentration and evaluate the trophic state of Lake Chagan in the study.     

Classifying environmentally significant urban land uses with satellite imagery

We investigated Bayesian networks to classify urban land use from satellite imagery. Landsat Enhanced Thematic Mapper Plus (ETM(+)) images were used for the classification in two study areas: (1) Marina del Rey and its vicinity in the Santa Monica Bay Watershed, CA and (2) drainage basins adjacent to the Sweetwater Reservoir in San Diego, CA. Bayesian networks provided 80-95% classification accuracy for urban land use using four different classification systems. The classifications were robust with small training data sets with normal and reduced radiometric resolution. The networks needed only 5% of the total data (i.e., 1500 pixels) for sample size and only 5- or 6-bit information for accurate classification. The network explicitly showed the relationship among variables from its structure and was also capable of utilizing information from non-spectral data. The classification can be used to provide timely and inexpensive land use information over large areas for environmental purposes such as estimating stormwater pollutant loads.     

Image Themes and Frames in US Print News Stories about Climate Change

Research on frames in climate change (CC) news coverage has advanced substantially over the past decade, but the emerging understanding of the framing role of visual imagery that often accompanies news texts remains fragmented. We report on a set of image frames identified through content analysis of 350 images associated with 200 news articles from 11 US newspaper and magazine sources from 1969 through late 2009. We reliably identified and quantified the occurrence of 118 image themes. We then hierarchically clustered the themes based on their co-occurrence in images to identify an integrated framework of 42 image frames. We highlight frames associated with particular types of images (e.g., photographs and maps) or geographic regions. From among the full set of frames, we identify 15 that commonly appear in US CC news imagery and discuss the ways in which image frames make salient (or render invisible) particular categories of people, geographic regions, aspects of science, and spheres of activity.     

土地利用/覆被变化对小流域地表温度的影响

遥感和GIS技术被用于检测白家湾河流域土地利用/覆被变化,并评估土地利用/覆被变化对白家湾河流域地表温度的影响。不同时期的Landsat TM和ETM+影像被用于确定土地利用/覆被变化格局,并对矿点增长及相关的植被覆盖减少情况进行量化。采用Landsat数据的热红外波段进行地表温度的反演。结果表明:(1)小流域内不同土地利用/覆被类型上地表温度具有差异;(2)由于不同时期不同人为干扰造成的影响不同,不同时期土地利用/覆被类型间的地表温度差异不同。(3)在整个研究区域内,平均地表温度和NDVI之间呈负相关关系,各种土地利用/覆被类型上的平均地表温度和NDVI都呈现负相关性,但一些土地利用/覆被类型与NDVI的相关性高于平均水平。(4)植被覆盖情况越好,对稳定地表温度所起的作用越大。     

基于Landsat系列卫星分析1985—2015年东平湖叶绿素a浓度变化趋势

基于Landsat-5 TM数据和地面同步水质监测数据发现,近红外波段与红色波段比值与叶绿素a实测浓度存在较高相关性,并以此建立了提取水体表层叶绿素a浓度的遥感信息模型。经验证,该模型用于叶绿素a浓度反演的精度良好,平均相对误差为14.5%。将该模型应用于Landsat卫星系列数据,提取了东平湖1985-2015年每年度丰水期叶绿素a浓度信息,得到共31幅东平湖叶绿素a浓度分布图,并对其进行了时空分析。结果表明：1985-2015年,东平湖叶绿素a平均浓度范围为32.4~81.4 μg/L,空间分布上一般表现为湖周边浅水区高于湖中心深水区,且空间差异变化明显;时间序列上,东平湖叶绿素a浓度表现出一定的波动性,在1987、1988、1992年出现较高值,总体看来,在95%置信水平上秩相关系数为-0.592,浓度呈下降趋势。     

基于Landsat TM的澳门城市热场影响因素分析

利用2004年10月19日Landsat TM数据提取澳门城区城市用地类型信息,反演城市地表温度,在此基础上通过主成分回归方法分析澳门城市热场的影响因素.结果表明,澳门城市热场受到硬化地表指数的影响较大,其次为植被比例.地表温度与硬化地表指数、道路密度呈显著正相关(P＜0.05),与归一化植被指数、植被比例及水体比例呈显著负相关(P＜0.05).     

WATER RESOURCES INVESTIGATIONS IN WEST CENTRAL IRAN USING LANDSAT DATA1

ABSTRACT: Extensive investigations have been undertaken to determine the utility of Landsat data for detecting and analyzing hydrologic characteristics of an interior watershed of Iran that drains to Daryachehye-Namak (salt lake). This interior playa serves as the terminus for surface water discharging to it from the Karaj, Shur, Saveh, and Ghom Rivers and ground water from their underlying aquifers. These drainage systems encompass heavily populated and industrial sectors of west central Iran, including Tehran. The result of this investigation demonstrates the applicability of Landsat data for mapping and monitoring water regimen as an aid in interpreting hydrologic conditions throughout this arid region. Fluctuation of water area in a playa lake, occupying the lowest part of this closed basin, was monitored on repetitive Landsat coverage. As the result of field investigations combined with optical and digital analyses of the Landsat data, fluctuating water depths were determined in order to estimate the volume of water present in this lake during various seasons. A comparison between stream discharge rates and the estimated volume of standing water make it possible to quantitatively evaluate the hydrologic regimen and to detect the significance of ground water discharge.     

A COMPUTERIZED DATA BASE FOR FLOOD PREDICTION MODELING1

ABSTRACT: A computerized geographic information system (GIS) was created in support of data requirements by a hydrologic model designed to predict the runoff hydrograph from ungaged basins. Some geomorphologic characteristics (i.e., channel lengths) were manually measured from topographic maps, while other parameters such as drainage area and number of channels of a specified order, land use, and soil type were digitized and manipulated through use of the GIS. The model required the generation of an integrated Soil Conservation Service (SCS) curve number for the entire basin. To this end, soil associations and land use (generated from analysis of Landsat satellite data) were merged in the GIS to acquire a map representing SCS runoff curve numbers. The volume of runoff obtained from the Watershed Hydrology Simulation (WAHS) Model using this map was compared to the volume computed by hydrograph separation and found to be accurate within 19 percent error. To quantify the effect of changing land use on basin hydrology, the GIS was used to vary percentages from the drainage area from forest to bare soil. By changing the basin runoff curve numbers, significant changes in peak discharge were noted; however, the time to peak discharge remained essentially independent of change in area of land use. The GIS capability eliminated many of the more traditional manual phases of data input arid manipulation, thereby allowing researchers to concentrate on the development and calibration of the model and the interpretation of presumably more accurate results.     

不同土地利用类型的地表特征参量的遥感反演研究——以猫跳河流域为例

利用2007年5月Lansat5 TM数据,运用单通道算法,基于全国遥感监测土地利用/覆盖分类体系,对贵州省猫跳河流域的地表特征参量进行了反演,得到不同土地利用类型下的典型地表特征参数值。在3种主要的土地利用类型中,林地的植被指数最高、地表温度最低,农田的植被指数最低而地表温度最高,草地介乎林地和农田之间。城镇建设用地主要表现为热岛效应,而水域则主要表现为地表温度（LST）和归一化植被指数（NDVI）的双低特征。进一步对二级土地利用类型的分析表明,由于结构、功能的不同,土地利用二级类在地表特征参量方面也表现出了有规律地变化。有助于深入认识不同土地利用类型的物理特征,可以丰富主要土地利用类型的影像分类的先验知识,有望将不同土地利用方式的生态环境效应研究推进一步