摘要：
In view of the low accuracy of traditional adjustment, an improved multiple-group adjustment method in indirect adjustment is proposed in this paper. In the process of improved multiple-group adjustment, the first group is first adjusted, and then the adjustment result of the first group and the observation value of the second group are adjusted together, which makes the results in the first-group adjustment meet the overall adjustment results. Finally, the posteriori unit-weight variance value, the coordinated factor matrix of the adjustment result, and the unknown function weight reciprocal are calculated. The experimental results show that the accuracy of multiple-group adjustment in the indirect grouping adjustment will be more accurate than the traditional indirect adjustment method. Moreover, this work provides important ideas and techniques for handling the goniometric triangular network of control surveys.
摘要：
Multifractal detrended fluctuation analysis (MFDFA) method can examine higher-dimensional fractal and multifractal characteristics hidden in time series. However, removal of local trends in MFDFA is based on discontinuous polynomial fitting, resulting in pseudo-fluctuation errors. In this paper, we propose a two-stage modified MFDFA for multifractal analysis. First, an overlap moving window (OMW) algorithm is introduced to divide time series of the classic MFDFA method. Second, detrending by polynomial fitting local trend in traditional MFDFA is replaced by ensemble empirical mode decomposition (EEMD)-based local trends. The modified MFDFA is named OMW-EEMD-MFDFA. Then, the performance of the OMW-EEMD-MFDFA method is assessed by extensive numeric simulation experiments based on a p-model of multiplicative cascading process. The results show that the modified OMW-EEMD-MFDFA method performs better than conventional MFDFA and OMW-MFDFA methods. Lastly, the modified OMW-EEMD-MFDFA method is applied to explore multifractal characteristics and multifractal sources of daily precipitation time series data at the Mapoling and Zhijiang stations in Dongting Lake Basin. Our results showed that the scaling properties of the daily precipitation time series at the two stations presented a long-range correlation, showing a long-term persistence of the previous state. The strong q-dependence of indicated strong multifractal characteristics in daily precipitation time series data at the two stations. Positive values demonstrate that precipitation may have a local increasing trend. Comparing the generalized Hurst exponent and the multifractal strength of the original precipitation time series data with its shuffled and surrogate time series data, we found that the multifractal characteristics of the daily precipitation time series data were caused by both long-range correlations between small and large fluctuations and broad probability density function, but the broad probability density function was dominant. This study may be of practical and scientific importance in regional precipitation forecasting, extreme precipitation regulation, and water resource management in Dongting Lake Basin.
关键词：
Land cover change;Dongting Lake;support vector machine;Landsat TM/OLI
摘要：
Land cover in Dongting Lake region has been faced high variations during recent decades. Therefore , there has a strong need to investigate and understand the land cover changes in Dongting Lake region between land cover types. In this study, support vector machine (SVM) classification method was employed to detect changes in land cover dynamic in Dongting Lake region using Landsat images for the year 1995, 2006 and 2015. Land cover information was classified to five categories: waterbody, wetland, built-up, cropland and forestland. Quantitative analysis , change detection matrix and land cover dynamic degree were utilized for investigating and assessing the land cover changes in Dongting Lake region. The overall accuracy (OA) and kappa coefficient of the land cover classification results were over 96% and 0.9, respectively. The results indicated that in 1995 about 11.32% of study area was covered by water-body together with 13.31% of wetland. Nearly 50% of the area was covered by cropland and remaining 2.59% was covered by built-up. During the period 1995-2015, the change rate of the waterbody was evaluated at-0.29%, at-0.67% for the wetland and at-2.47% for the built-up. On the contrary, the for-estland and cropland increased by 0.72% and 0.03%, respectively. In addition, the results of this study can provide scientific information for government to formulate policy for sustainable land use management in Dongting Lake region. Land cover change, Dongting Lake, support vector machine , Landsat TM/OLI Land cover changes affect global climate, species diversity and ecosystem balance, which can accelerate land degradation and reduce ecosystem services [1, 2]. It has become a serious environmental problem. Over the past few decades, land cover in Dongting Lake region experienced tremendous changes by natural processes, as well as anthropo-genic activities [3]. In particular, anthropogenic activities , such as reclaiming cropland from lakes and returning cropland to lakes, have become a major concern of land cover changes in Dongting Lake region [4]. Therefore, a clear understanding of the spatial and temporal changes of land cover types in the Dongting Lake region in recent two decades is important. Remote sensing has been monitoring and capturing the earth land's surface every day and night by providing spatial and temporal images over large and inaccessible area for more than six decades [5]. Therefore, remote sensing became an acknowledged technology for monitoring the land cover changes. Some optical remote sensing products, such as Moderate Images Spectrometer (MODIS), Advanced Very High-Resolution Radiometer (AVHRR), and Satellite Pour 1'Obervation de la Terre (SPOT) with resolution at 250 m to 1 km, are the very suitable data resources for studying information of earth surface [1, 6-11]. Despite short revisiting cycle and large swath width, these low-resolution products are mainly available on the detecting of large scale coarse land cover changes, but the transformation details of land cover types and its ratio remains unknown which usually occurs at a small scale. In order to settle these problems and detail monitoring earth's land cover changes, medium remote sensing satellite data, such as Landsat Thematic Mapper (TM) [12, 13], Landsat Enhanced Thematic Mapper Plus (ETM+) [7, 14] and Landsat Operational Land Im-ager (OLI) [12, 15], with resolution of 30 m but re-visiting cycle of 16 day, have been widely utilized for mapping land cover and monitoring its changes. Numerous researches have been conducted and various algorithms have been developed for detecting land cover changes especially over Dongting Lake region using remote sensing satellite technologies. Li et al. [16] employed the Geographical Information System (GIS) and Remote Sensing (RS) technologies to study the characterized long-term land cover changes in Dongting Lake region using the Landsat images from 1978, 1989, 1998. Their results indicated that land cover patterns in Dongting Lake region had been greatly altered by empoldering. Three land type had changed remarkably. The cultivated land decreased,
关键词：
Surface water area variation;flood inundation frequency;Dongting Lake;The Three Gorges Reservoir;remote sensing monitoring;Landsat
摘要：
Dongting Lake is the second largest freshwater lake in China, with rapid seasonal surface water area fluctuations in the middle reach of the Yangtze River and downstream from the Three Gorges Reservoir (TGR). The marked variation of the lake's surface water area is considered to have been affected by the TGR over the past decades. In this study, Landsat TM/ETM+/OLI time-series imagery data were employed to estimate the wet season total surface water area variation in South Dongting Lake and East Dongting Lake from 1988 to 2016. The surface water area was extracted from Landsat data using Modified Normalized Difference Water Index (MNDWI). The results indicated that the surface water area variation was accordant with the variation of precipitation and runoff of Xiangtan, Taojiang, Taoyuan, Shimen, Shadaoguan, Mituosi, Ouchikou and Chenglingji five hydrological stations. Most of the large surface water areas were observed during the pre-TGR period, whereas the small surface water areas were observed during the post-TGR period. Surface water area data, precipitation and runoff from the four hydrological stations (except Shimen station) all indicated downward trends, with reduction rates of 5.866 km(2).year(-1), 0.802 mm.year(-1), 3.950 10(8)m(3).year(-1), 2.834 10(8)m(3).year(-1), 0.377 10(8)m(3).year(-1), 1.282 10(8)m(3).year(-1), 2.715 10(8)m(3).year(-1) , 0.318 10(8)m(3).year(-1) and 16.114 10(8)m(3).year(-1), respectively. The results of correlation analyses indicated precipitation and water from the Yangtze river may affect the fluctuation in the surface water area to a large extent. The results of flood inundation probability analysis indicated that approximately 502.9 km(2) of the study area was in the high flood hazard zone. In addition, the results of this study can provide scientific information to understand the effect of the TGR on downstream lakes and achieve better water resources and flood hazard management in this region.
期刊：
2017 2ND INTERNATIONAL CONFERENCE ON FRONTIERS OF SENSORS TECHNOLOGIES (ICFST),2017年:198-203
通讯作者：
Zhang, Xike
作者机构：
[Zhang, Xike; Zhang, Qiuwen] Huazhong Univ Sci & Technol, Sch Hydropower & Informat Engn, Wuhan 430074, Hubei, Peoples R China.;[Zhang, Xike] Hunan City Univ, Sch Municipal & Mapping Engn, Yiyang 413000, Peoples R China.;[Zhang, Gui] Cent South Univ Forestry & Technol, Sch Sci, Changsha 410004, Hunan, Peoples R China.;[Gui, Zifan] Shenzhen Garden Management Ctr, Shenzhen 518000, Peoples R China.
通讯机构：
[Zhang, Xike] H;Huazhong Univ Sci & Technol, Sch Hydropower & Informat Engn, Wuhan 430074, Hubei, Peoples R China.;Hunan City Univ, Sch Municipal & Mapping Engn, Yiyang 413000, Peoples R China.
会议名称：
2nd International Conference on Frontiers of Sensors Technologies (ICFST)
会议时间：
APR 14-16, 2017
会议地点：
Shenzhen, PEOPLES R CHINA
会议主办单位：
[Zhang, Xike;Zhang, Qiuwen] Huazhong Univ Sci & Technol, Sch Hydropower & Informat Engn, Wuhan 430074, Hubei, Peoples R China.^[Zhang, Xike] Hunan City Univ, Sch Municipal & Mapping Engn, Yiyang 413000, Peoples R China.^[Zhang, Gui] Cent South Univ Forestry & Technol, Sch Sci, Changsha 410004, Hunan, Peoples R China.^[Gui, Zifan] Shenzhen Garden Management Ctr, Shenzhen 518000, Peoples R China.
关键词：
river network extraction;NDWI;object-oriented classification method;Landsat-5
摘要：
Landsat data have the characteristics of high resolution and wide spectrum, and have been widely used to extract river network. Based on the feature analysis and pretreatment of Landsat-5 Thematic Mapper (TM) data, in this paper, we studied and realized the extraction of river network in Hunan Province, analyzed and dealt with the extraction results of river network. The main research works are as follows: The Landsat-5 TM images were pre-processed by using ENVI5.3 software over the study area in 2011. Radiometric correction, image mosaic and subset were carried out. The Normalized Difference Water Index (NDWI) and object-oriented classification method were used to extract the river network, and then the extraction results of the two methods of residential area, vegetation area and cloud-containing area were analyzed. The results showed that the extraction of river network based on object-oriented classification method was more complete, and the inaccuracy and omission extraction of river network were much less than that based on NDWI. And then, editor tool in ArcGIS was used to delete the non-river network region and connect the non-connected area of the river network.
