Experiment on Driving Precipitable Water Vapor from Ground-Based GPS Network in Chengdu Plain

The estimates of total zenith delay are derived using Bernese GPS Software V4. 2 based on GPS data every 30 s from the first measurement experiment of a ground-based GPS network in Chengdu Plain of Southwest China during the period from July to September 2004. Then the estimates of 0.5 hourly precipitable water vapor (PWV) derived from global positioning system (GPS) are obtained using meteorological data from automatic weather stations (AWS). The comparison of PWV derived from GPS and those from radiosonde observations is given for the Chengdu station, with RMS (root mean square) differences of 3.09m. The consis- tency of precipitable water vapor derived from GPS to those from radiosonde is good. It is concluded that Bevis’ empirical formula for estimating the weighted atmospheric mean temperature can be applicable in Chengdu area because the relationship of GPS PWV with Bevis’ formula and GPS PWV with radiosonde method shows a high correlation. The result of this GPS measurement experiment is helpful both for accumu- lating the study of precipitable water vapor derived from GPS in Chengdu areas located at the eastern side of the Tibetan Plateau and for studying spatial-temporal variations of regional atmospheric water vapor through many disciplines cooperatively.     

Experiment on driving precipitable water vapor from ground-based GPS network in Chengdu Plain

The estimates of total zenith delay are derived using Bernese GPS Software V4. 2 based on GPS data every 30 s from the first measurement experiment of a ground-based GPS network in Chengdu Plain of Southwest China during the period from July to September 2004. Then the estimates of 0.5 hourly precipitable water vapor (PWV) derived from global positioning system (GPS) are obtained using meteorological data from automatic weather stations (AWS). The comparison of PWV derived from GPS and those from radiosonde observations is given for the Chengdu station, with RMS (root mean square) differences of 3.09m. The consistency of precipitable water vapor derived from GPS to those from radiosonde is good. It is concluded that Bevis’ empirical formula for estimating the weighted atmospheric mean temperature can be applicable in Chengdu area because the relationship of GPS PWV with Bevis’ formula and GPS PWV with radiosonde method shows a high correlation. The result of this GPS measurement experiment is helpful both for accumulating the study of precipitable water vapor derived from GPS in Chengdu areas located at the eastern side of the Tibetan Plateau and for studying spatial-temporal variations of regional atmospheric water vapor through many disciplines cooperatively.     

基于MODIS遥感数据的水体提取算法研究

针对MODIS遥感数据采用多波段普间关系算法提取水体容易与阴影混淆,产生提取不精确的问题。作者将对多波段普间关系水体提取算法进行研究,并以鄱阳湖为实验对象,使用改进后的多波段普间关系算法对水体进行提取。实现提升水体提取精度的目标。     

MODIS observations of water color of the largest 10 lakes in China between 2000 and 2012

Forel-Ule (FU) index of water color is an important parameter in traditional water quality investigations. We retrieved the FU index of the largest 10 lakes in China during 2000-2012 from MODerate-resolution Imaging Spectroradiometer surface reflectance product (MOD09) images. Since FU index is an optical parameter, it can be derived from optical remote sensing data by direct formulas, which is invariant with region and season. Based on validation by in situ measured reflectance data, the FU index products are reliable, with average relative error of 7.7%. FU index can be used to roughly assess water clarity: the clearer a water body is, and the bluer it is in color, the smaller its FU index is. FU index can also be used to roughly classify trophic state into three classes: oligotrophic, mesotrophic, and eutrophic. We analyzed the spatial, interannual, and seasonal variations of the FU index and its implications for water clarity and trophic state, and the findings are mostly consistent with the results from related literature. All in all, it might be a feasible way to roughly assess inland water quality by FU index in large region and over long time period.     

基于MODIS数据的水体提取研究

通过对遥感图像各类地物的光谱和水体在中等分辨率的EOS／MODIS上的波谱特征的分析,论述了水体最为明显的波段组合,研究了如何从不同时期（枯水期、丰水期）的中等分辨率MODIS遥感影像提取水体的方法,并以武汉市梁子湖为例,对水体提取范围和精度进行比较和分析。实验表明：遥感图像经空间变换后再利用相同的方法提取的水体,更容易区分水体和阴影,产生的噪声也少,提取的水体范围更准确、计算的水域面积精度更高。     

长时序大范围内陆水体光学遥感研究进展

地球表面的江河、湖泊和水库等内陆水体是水资源的主要组成部分,由气候变化和人类活动所引起的内陆水体分布和水质时空变化等问题已成为各国科学家和政府关注的热点.相比常规实地采样监测手段,卫星遥感在长时序、大范围内陆水体监测方面具有重要优势.受到海洋水色遥感理论和方法的推动,同时也得益于内陆水体光学特性数据的不断积累,近年来内...     

空间地球科学视角下的全球水循环研究

空间地球科学是利用空间观测的手段,研究地球系统、各子系统之间以及各要素和过程之间的相互作用、变化机制及其发展演化的一门综合性、交叉性学科,为科学家开展地球系统科学研究提供新手段、新思路和全新视角.空间地球科学的发展推动航天技术、遥感和测绘科学、地球系统科学包括气象、海洋、水文、生态等一系列学科的发展,是全球变化背景下促...     

农作物长势综合遥感监测方法

作物收获之前进行大范围作物生长状况评价 ,可以尽早的获得有关作物产量信息。介绍了中国农情遥感监测系统的综合作物长势监测方法。以遥感数据标准化处理、云标识、云污染去除和非耕地去除为基础 ,生成质量一致的遥感数据产品集 ,提取区域作物生长过程。作物长势监测分为实时作物长势监测和作物生长趋势分析。实时的作物长势监测可以定性和定量地在空间上分析作物生长状况 ,分级显示作物生长状况 ,分区域统计水田和旱地中不同长势占的比重。作物生长趋势分析可以进行年际间的生长过程对比 ,从时间轴上反映作物持续生长的差异性 ,统计全国、主产区、省和区划单元 4个尺度的耕地、水田、旱地作物生长过程曲线年际间差异 ,从而为早期的产量预测提供信息。通过处理流程的系统化 ,建设了运行化的作物长势遥感监测分析系统 ,为用户构建了综合的作物实时生长状况 ,苗情的生长趋势分析环境。同时可以依据野外地面实测信息对遥感监测结果进行标定和检验。 1998年以来 ,系统在满足日常运行的前提下 ,技术方法逐渐改进和完善 ,监测结果的精度和可靠性不断得到提高。     

基于新型水体指数(NWI)进行水体信息提取的实验研究

基于遥感数据构建的水体指数模型可用于水体信息的提取。本文在对水体及其背景地物进行光谱特征分析的基础上,结合水体在近红外和中红外波段(相当于Landsat TM/ETM+影像的Band 4,Band 5和Band 7)同时具有强吸收这一典型特征,提出了一种新型的水体指数NW I(New W ater Index)。将该指数在含不同水体类型的遥感影像上进行实验,均获得了较好的提取效果。利用文献样本数据所作的实验表明,NW I具有很强的普适性,可用于水体信息的快速提取,且具有较高的精度。     

高分二号的沈阳市黑臭水体遥感识别

中国城市黑臭水体情况严重,基于遥感监测黑臭水体刚刚起步,很多问题待解决。以沈阳市城市建成区内主要河流为研究区,于2015年—2016年开展地面调查,获取了浑河和蒲河46个一般水体的样点,和辉山明渠、满堂河、细河以及微山湖路附近、丁香湖北部50个黑臭水体的样点数据,包括水面光谱和主要水质参数。分析了黑臭水体与一般水体的光谱特征,发现城市黑臭水体反射率光谱在绿光—红光波段变化比一般水体平缓,基于这一特点提出了一种基于反射率光谱指数BOI(Black and Odorous water Index)的黑臭水体识别模型,并将其与红绿波段比值指数进行对比,具有更好的识别精度。结果表明:(1)基于遥感反射率(Rrs)计算的BOI小于0.065时,可判为黑臭水体。(2)由于GF2水体图像精确大气校正存在困难,可以利用瑞利散射校正反射率(Rrc)替代R_(rs),BOI小于阈值0.05时,可判别为黑臭水体;同时模拟证明,当气溶胶光学厚度逐渐增大时,黑臭水体与一般水体的光谱差异将逐渐减小,因此这种方法主要适用于比较清晰的图像、气溶胶光学厚度比较小(如AOT(550)≤0.5时)。(3)基于R_(rc)的BOI模型可以较好的应用于GF2图像上,具有较好的识别精度。对2015年—2016年3景GF-2影像提取的结果显示,满堂河和新开河黑臭现象得到逐步改善,辉山明渠黑臭现象依然严峻。本文发展的黑臭水体遥感识别算法主要是基于沈阳黑臭水体的光谱特征,仅在沈阳市进行了验证,将来还需在其他城市进一步验证,并且需要更多地考虑多种因素对水体反射率的影响。     

湖北省水环境监测平台设计

在参考国内外相关基于WebGIS的环境监测系统的基础上,设想一个针对湖北省的利用遥感技术并基于WebGIS的水环境监测系统,并设计其架构与功能,可为今后相关的研究应用打下基础。     

Evaluating the performance of high-resolution satellite imagery in detecting ephemeral water bodies over West Africa

Pastoralism is a major occupation in Africa’s Sahel region, which spans from Senegal in the west to Ethiopia in the east and has a semi-arid climate. Pastoralists from the region are usually nomadic, moving regularly in search of water and pasture, often for hundreds of kilometers. Traditionally, pastoralists have relied on historical knowledge and transhumance pathways to reach the water bodies (WB). Due to climatic conditions, a vast majority of the WBs in this region are small, sporadic, and ephemeral, therefore there is a need to map and frequently monitor water availability. Remote sensing observations can be used to complement current monitoring efforts. High-resolution near-daily imagery from the recently launched PlanetScope (PS) constellation of small satellites has the potential to complement the existing medium-resolution and infrequent but well established and extensively calibrated sensors like Landsat. The aim of this study is to investigate the performance and applicability of high-resolution PS data to detect and monitor WBs in the Ferlo region of West Africa, in comparison to Landsat-8 imagery. The results indicate that for cloud-free days, PS data was comparable (r >0.88; ubRMSE <0.01) to Landsat, but due to inadequate cloud masking, the results were poor for cloudy days (r < 0.49 and ubRMSE>0.058). The PS images were able to detect nearly 95% of the WBs, whereas Landsat was able to identify only 32% at the water fraction threshold >40%. Initial results from this study show that the high spatial and temporal resolution PS datasets show promise in monitoring WBs in arid regions of West Africa.     

基于AdaBoost算法的遥感影像水体信息提取

AdaBoost算法利用每个特征构造一个简单分类器,然后将简单分类器进行训练组合成一个强分类器。算法能够充分利用每个分类器的优势并避免其劣势,得到一个最佳判别,达到提高分类精度的目的。本文利用TM影像,将影像各波段灰度、水体指数和谱间关系特征相结合,构成提取水体的强分类器,实现水体提取。实验结果表明,算法能够非常有效地、高精度地提取水体信息。     

基于水体光学分类的二类水体水环境参数遥感监测进展

二类水体主要包括内陆及近岸水体,受浮游植物、悬浮颗粒、有色可溶性有机物等多种因素影响,光学特性复杂多变,难以建立统一的水环境参数遥感定量估算模型.针对水体的光学特征,进行水体光学分类,进而反演水环境参数的方法,不仅能够提高参数估算精度,而且便于模型在同类水体中推广应用.水体光学分类方法主要包括基于固有光学特征的光学分类...     

一种利用高光谱像元分解技术提取水体边界的方法

针对水体边界混合像元导致的精度损失问题,提出了一种基于高光谱混合像元分解的水体边界提取方法。该方法结合高光谱影像水体边界混合像元特有的光谱特征,削弱诸多因素对水体边界像元识别的影响,获取水体边界混合像元,降低了混合像元分解的计算量。通过混合像元的高精度分解及水体边界像元分割,进一步逼近水体的真实边界,能显著提高水体边界界定的精度。试验结果表明:用该方法进行水体提取,精度明显优于水体指数法,略优于支持向量机法,总体精度为93.86%,Kappa系数为0.87。     

Agricultural growing season calendars derived from MODIS surface reflectance

In order to secure the necessary image acquisitions for global agricultural monitoring applications, we must first articulate Earth observation (EO) requirements for diverse agricultural landscapes and cropping systems. Crucial to this task is the identification of agricultural growing season timing at a meaningful spatial scale, so as to better define the necessary periods of image acquisition. To this end, 10 years of MODIS Terra Surface Reflectance imagery have been used to determine phenological transition dates including start of season, peak period, and end of season at 0.5° globally. This is the first set of global, satellite-derived, cropland-specific calendar dates for major field crops within a 0.5°, herein called agricultural growing season calendars Preliminary comparison against ground-based crop-specific calendars is performed, highlighting the utility of this approach for articulating growing season timing and its interannual and within-region variability. This research provides critical inputs for defining the EO requirements for the Global Agricultural Monitoring initiative (GEOGLAM), an effort by the Group on Earth Observations (GEO) to synergize existing national and regional observation systems for improved agricultural production and food security monitoring.     

防城港-钦州的海岸线遥感监测与时空分析

海岸线是海陆动态的分界线.国内外对防城港-钦州海岸线的时空变迁研究甚少.基于Landsat系列卫星遥感数据,利用ENVI(environment visualizing images)、Arc-Map平台,采用归一化水体指数半自动提取5期海岸线,定量、定性分析海岸线时空演变.研究发现:①1999-2018年海岸线增长了...     

利用MODIS遥感影像获取近地层气温的方法研究

由于冠层叶片群体效应,在1km的空间尺度上遥感获取浓密植被陆面温度与气温近似相等。根据这个原理对利用遥感手段获取气温进行了尝试,提出利用NDVI-Ts空间获取气温的方法,计算气温空间分布模式,同时对Prihodko和Goward提出的气温遥感获取模型(简称P-G模型)进行试验并与NDVI-Ts空间法进行了对比。根据Parton和Logan提出的气温尺度转换模型,利用气象站观测最高气温和最低气温获取Terra卫星过境时刻气温作为“测定值”,对遥感获取的气温进行检验,得到以下结论:P-G模型计算气温与观测结果相比偏高,而NDVI-Ts法计算结果偏低,但是其总体误差范围相当,大约为 4℃;与P-G模型相比,尽管NDVI-Ts空间法获得的气温在精度上对P-G模型没有多大的改善,但这种方法能够更加充分利用遥感获取的信息,而且在计算机运算效率上也有很大的改进,NDVI-Ts空间法相对于P-G模型具有一定优势。     

长江中游洪涝灾害特征的MODIS时序监测与分析

通过250m分辨率的MODIS时序数据,监测自2000年以来长江中游的鄱阳湖和洞庭湖地区的洪水淹没范围及其动态变化。基于同期TM数据对MODIS监测结果进行验证,精度为94.6%,达到了理想的洪灾淹没范围提取结果。监测结果显示,2010年鄱阳湖的淹没面积相对较大,而东洞庭湖和西南洞庭湖在2002年的淹没面积相对较大。三湖在一次淹没波动持续时间上最长可达5～6个月;洪涝灾害发生时间大多集中在4～11月份,其中以6～8月份最为频繁,夏季是该地区洪涝灾害的高发期。     

高分遥感数据在城市园林绿化规划实施监测中的应用

我国高分遥感数据的丰富完善,为开展我国高分卫星数据在相关行业领域的应用奠定了基础。本文研究了高分遥感数据在城市园林绿化规划实施监测中的应用,为建设国家园林城市、国家生态园林城市评选及城市绿地系统规划落实提供参考依据。