Use of geomorphological units to improve drainage network extraction from a DEM : Comparison between automated extraction and photointerpretation methods in the Carraixet catchment (Valencia, Spain)

Drainage networks are one of the main elements characterizing basins, and network topology and geometry form the basis of many hydrological and geomorphological models (eg Geomorphological Unitary Hydrograph). The identification and manual delineation of channel networks from maps or aerial photographs requires much time and effort. In the last two decades, algorithms and procedures for automated extraction of drainage networks from digital elevation data have been developed and implemented in many specialized software applications. Nevertheless, automatically delineated channel networks do not always show close agreement with manually delineated networks. This paper describes a comparative analysis between a drainage network automatically extracted from a gridded digital elevation model, and the drainage network delineated manually from stereographic pairs of aerial photographs. The analysis showed that the automatic extraction technique may be adequate for catchment headwaters, but is inappropriate in the middle and lower basins, especially for alluvial fans and calcareous platforms. The paper suggests improving the automatic extraction technique by adapting it to operate with different parameters for each of the geomorphological units within the catchment.     

Monitoring of salt affected soils — A case study using aerial photographs,salyut‐7 space photographs,and landsat TM data

Soils of part of Ukai‐kakarapar Command area, Gujarat (India) have been mapped at 1:25, 000 scale using aerial photographs of December 1977. It was observed that about 36.3% of the area was affected by soil salinity/alkalinity. The test area has been remapped using Salyut‐7 space photographs taken during Indo‐Soviet joint flight in April, 1984. The area affected by soil salinity/alkalinity was found to be substantially higher (80.3%). The earlier mapping using aerial photographs was done when the soil surface was compartively moist (December 1977) as compared to date of Salyut‐7 photography (April 1984), when the soil surface was likely to be devoid of moisture and the salts moved to the surface. To have easy comparision with the map prepared by using aerial photographs, Landsat TM data of December, 1985 was used in which 45.7% of the total area was mapped as salt affected. The extent of area delineated using Landsat TM was higher than that of 1977 but much lesser than the area delineated using Salyut‐7 (MKF‐6M) photographs. This indicated that the increase in the extent of salt affected area in the map prepared using the MKF‐6M photographs might be partly due to actual increase in the salinity/alkalinity and partly due to the seasonal affects. Among the various bands of MKF‐6M, band ‐4 was found to be the best for delineating the salt affected soils. The boundaries were sharper in the FCC and band No.4 of MKF‐6M than in the aerial photographs.     

Integrated resource study for conservation and management of Ropar wetland ecosystem, Punjab

Integrated resource study in Ropar wetland ecosystem was undertaken to analyse physiography, drainage, landuse and vegetation status. Various thematic maps have been prepared using black and white aerial photographs on 1:20,000 scale and IRS 1A LISS-II (FCC) on 1:50,000 scale. The Ropar wetland ecosystem is comprised of six major landforms i.e. Siwalik hills, Valley, Piedmont plain, Alluvial plain, River terraces and River courses. The study area show high drainage density with sub dendritic and sub parallel drainage. The area has poor vegetative cover which results in extensive erosion and sedimentation of Ropar lake. The water spread and. qualitative turbidity level in the notified wetland area was also monitored. Anthropogenic pressure, industrial pollution, sedimentation, eutrophication, illegal fishing and flooding have been identified as major threats to the wetland. Keeping in view the threats to Ropar wetland, the conservation measures have been suggested.     

Colour infrared aerial photographs as data base for reconnaissance soil mapping and land suitability grouping

Colour infrared and panchromatic B & W aerial photographs at 1∶25,000 scale over part of Anantapur district of Andhra Pradesh were interpreted stereoscopically for delineating soilscape units. Soils and land properties were evaluated for suitability of the land for agriculture i.e. paddy and wheat. The results indicate that the relative case in delineating physiographic units offered by colour infrared air-photos does not commensurate with their cost. In the study area, 19.57 and 14.78 per cent area have been found to be suitable for paddy and wheat, respectively.     

Agriculture field characterization using aerial photograph and satellite imagery

Successfully delineating management zones that differ in crop productivity is an important component of site-specific management. We compared the effectiveness of the digitally scanned color aerial infrared photographs and digital Landsat Thematic Mapper (TM) data for delineating within-field zones. The zones delineated using normalized difference vegetation index (NDVI) from TM data explained 34% of field yield variance compared with 9% for that from digitally scanned color aerial infrared photograph data. The zones from NDVI using Landsat TM were better able to capture spatial differences in plant growth and relatively stable soil attribute of surface soil organic carbon.     

草尾河灵官嘴“跌水”成因的遥感研究

在收集地理、地质及水文等资料并对其进行详细整理分析的基础上，利用多时相卫星数据和航片，在相应数字图像处理软件 的支持下，对草尾河进行系统的遥感地质解译，并从地学和水动力学两方面研究了草尾河航道灵官嘴“跌水”形成的原因，预测了发 展演化趋势，为草尾河的航道疏浚提供参考资料。     

无人机航测在长江岸线测绘中的应用

无人机航测是一项新兴的测绘技术,以其测图效率高、受地面约束小、自动化成图等优点深受测绘生产单位的青睐。本文利用拓普康天狼星Sirius Pro无人机对泰州的长江岸线进行了航测,生成了高分辨率影像图、数字高程模型、数字地表模型,经检验航测成果的精度满足大比例尺测图的要求,为长江岸线的测绘提供了新的测绘方法,对无人机航测实践具有很好的指导借鉴作用。     

Partial polygon pruning of hydrographic features in automated generalization

This article demonstrates a working method to automatically detect and prune portions of waterbody polygons to support creation of a multi‐scale hydrographic database. Water features are sensitive to scale change, therefore multiple representations are required to maintain visual and geographic logic at smaller scales. Partial pruning of polygonal features – such as long, sinuous reservoir arms, stream channels too narrow at the target scale, and islands that begin to coalesce – entails concurrent management of the length and width of polygonal features as well as integrating pruned polygons with other generalized point and linear hydrographic features to maintain stream network connectivity. The implementation follows data representation standards developed by the US Geological Survey (USGS) for the National Hydrography Dataset (NHD). Portions of polygonal rivers, streams, and canals are automatically characterized for width, length, and connectivity. This article describes an algorithm for automatic detection and subsequent processing, and shows results for a sample of NHD subbasins in different landscape conditions in the US.     

Mass movement studies in Kosi catchment,mepal — A semi quantitative approach using aerial photographs

An area of about 5000 sq. km. in the upper parts of river basin of Sun Kosi falling in Nepal has been studied using medium and small scale aerial photographs of two different dates. The temporal variations in relation to mass movements that occur in the study area have been demarcated. The areas which have undergone increased erosion by slope failure and gully erosion over a period of 22 years are evaluated. An attempt has been made to quantify the increase in area of mass movement taking the advantage of three dimensional model of terrain as seen in the aerial photos.     

GIS Methodology for Characterizing Historical Conditions of the Willamette River Flood Plain, Oregon

Recent environmental developments have stimulated an interest in conservation and restoration of the historical Willamette River flood plain, both to protect against flooding and to provide wildlife habitat. In order to best utilize scarce resources, we characterized historical and modern river channel and flood‐plain conditions to evaluate changes and help prioritize restoration sites. Using cartographic and photographic data sources, we developed a Geographic Information System (GIS) to map active channels, side channels, islands and tributaries for four separate dates, as well as riparian and flood‐plain vegetation characteristics for pre‐European settlement and modern time periods. Coverages based on flood records and other boundaries were used to partition the flood plain into spatial subsets for analysis. The GIS allowed comparisons between historical and present conditions for a variety of environmental factors. Much of the pre‐settlement channel complexity has been removed. Total channel length in 1995 was 26% less than in 1850, with almost 58% of the river's side channels disconnected from the system. In addition, we found a 72% loss of flood‐plain forest from 1850 to 1995, since it was converted to agricultural and urban land uses. Selected river and flood‐plain variables were made available for a spatial model to prioritize potential locations for flood‐plain restoration.     

A note on the avulsion of Ghagghar river in the alluvial plains of Punjab and Haryana,North-West India

Ghagghar river in the alluvial plains of Punjab and Haryana, north-west India exhibits the phenomenon of avulsion in its middle and lower reaches. Study of aerial photographs shows that it has abandoned a 25 km long meander belt between Badshahpur and south of Jaswantpura which lies to the north of the present channel. The present channel course lies at a lower elevation on the flood plain away from the levee deposits which acted as an alluvial ridge.     

航测大比例尺数字化测图中的若干问题

在航测全数字化测图软件还比较昂贵的情况下，立足现有高备，运用测绘新技术，进行大比例尺航测数字化成因，获取数字地图，为城市地理信息系统提供基础信息，对中小城市的测绘工作是一种较好的选择。     

REMOTE SENSING IN THE MORPHOMETRIC ANALYSIS OF CHANNELS AND FLOODPLAINS

The first of two papers devoted to the analysis and mapping of river channels and floodplains describes Soviet work in the photogrammetric and cartometric analysis of floodplain morphology based on remote sensing imagery. The emphasis of the present paper is on the creation of digital terrain models for the automated measurement and mapping of floodplain features. Considerable attention is focused upon analysis of indicators of channel and floodplain dynamics (channel deposition, bankside erosion, meanders) appearing on aerial photographs. The results of channel analyses based on aerial photographic and field methods (determinations of channel width, depth, etc.) are compared for a test site. Translated from: Geomorfologiya, 1986, No. 4, pp. 51-57.     

Use of aerial photographs in mapping alkali soils with respect to their management in a part of north-west India

An area of 6000 ha covering four villages was adopted by the Central Soil Salinity Research Institute, Karnal under Operational Research Project to transfer the technology of alkali soil reclamation in the farmer’s fields. This necessitated mapping and characterisation of alkali soils of the area. Use of black and white photographs in 1∶25,000 scale proved effective in delineating alkali soils quickly and inexpensively. The physiography and photo elements like tone, landuse, drainage and parcelling facilitated identification and demarcation of four mapping units viz; P₁, P₃, P₄ and C. The unit P represented nearly flat upland alluvial plain while C represented low lying filled up old channel. The alkali soils confined mainly to the upland plain were recorded in white toned barren stretches and accounted for 36.6 percent of surveyed area. In addition, patchy occurrence of alkali soils admist the cultivated fields giving mottled appearance on the photographs was noticed over 11.3 percent area. In this case the photo scale proved limiting for demarcating alkali and non-alkali soils separately. The prtactical utility of the soil inventory in planning reclamation and management of alkali soil in the area has also been discussed.     

Georelief Transfiguration in Areas Affected by Open‐cast Mining

Open‐cast mining activity causes the largest georelief transfigurations all over the world. Large localities in north‐west Bohemia (the Czech Republic) are affected. In this area, we focus on a very significant case: the royal town Most, which has been turned into a lake. The main aim of this article is the reconstruction of the original georelief in different time periods together with analysis showing the process of landscape devastation. The workflow and analysis is based on precise elevation data obtained from aerial photographs and old maps. The georelief development is reconstructed using the digitized contour lines contained in Derived state‐map 1:5,000 (SMO5) from the years 1953, 1972, and 1980; maps of the 3^rd Military Survey (year 1936); and digital surface models (DSM) extracted, using the pixel correlation method, from aerial images (year 1953 and 2008). The most important results of the analysis are digital terrain models showing the evolution of the landscape which may be used for many purposes in landscape development analysis, historical applications, visualization or landscape reclamation.     

Investigating Issues in Map Accuracy When Using an Object-Based Approach to Map Benthic Habitats

In a recent study, benthic habitat maps were created of the Texas Gulf Coast from digital aerial imagery. The images were classified using an object-based image analysis (OBIA) approach and a classification and regression tree (CART) technique. The map was manually edited, changing 26% of the polygons' labels. Accuracy assessments of the unedited map and the edited map revealed the two were not significantly different. The research in this paper evaluates why these maps may have similar accuracies. Our analyses indicate that the small segmentation scale parameter used over-segmented the imagery, reducing the effectiveness of the CART technique and editing.     

Digital Aerial Orthobase for Cadastral Mapping

Large scale aerial photographs were acquired for one entire district of Andhra Pradesh in the southern India encompassing approx. 10,000 sq.kms. The voluminous data was processed using digital photogrammetry techniques to generate seamless digital orthoimages as a base map for cadastral mapping applications. Historically the cadastral mapping was carried out with traditional surveying methods such as ETS, theodolites not at regular intervals. With the advent of modern surveying & remote sensing techniques, generation of Digital Cadastral Database for Land Information System (LIS) is possible. The trends of cadastral mapping started with individual plan of survey of parcels with local datum and arbitrary map projections. This study essentially required an accurate and standard spatial reference for seamless cadastral mapping over the entire Area of Interest (AOI) in single datum and projection. Towards this a spatial reference in World Geodetic System (WGS 84) datum with Universal Transverse Mercator (UTM) projection was established. The terrain in the study area is moderately undulating and the relief due to manmade features was not so significant. The aerial orthobase was found suitable for delineating and measuring the individual parcels information. A good GCP configuration, triangulation accuracy and reliable and consistent Digital Elevation Model (DEM) was ensured the generation of Digital aerial orthobases with an accuracy of better than 25cm over a distance of 1000m. The orthobase was used for identification, delineation of the cadastre parcels and most importantly to validate the aerial orthobase with the field measurements.     

Assessment of an ASTER-generated DEM for 2D hydrodynamic flood modeling

Flood modeling often provides inputs to flood hazard management. In the present work we studied the flooding characteristics in the data scarce region of the Lake Tana basin at the source of the Blue Nile River. The study required to integrate remote sensing, GIS with a two-dimensional (2D) module of the SOBEK flood model. The resolution of the topographic data in many areas, such as the Lake Tana region, is commonly too poor to support detailed 2D hydrodynamic modeling. To overcome such limitations, we used a Digital Elevation Model (DEM) which was generated from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) image. A GIS procedure is developed to reconstruct the river terrain and channel bathymetry. The results revealed that a representation of the river terrain largely affects the simulated flood characteristics. Simulations indicate that effects of Lake Tana water levels propagate up to 13 km along the Ribb River. We conclude that a 15 m resolution ASTER DEM can serve as an input to detailed 2D hydrodynamic modeling in data scarce regions. However, for this purpose it is necessary to accurately reconstruct the river terrain geometry and flood plain topography based on ground observations by means of a river terrain model.     

THE MAPPING AND STUDY OF THE ISSYK-KUL' SHORELINE WITH AIR PHOTOS

Efforts to monitor and map the changing water level and shoreline of a large mountain lake in Central Asia with aerial photographs are described. The essence of the work involved the mapping of the shoreline and position of river deltas from air photos from various years during the period 1949-1980, at uniform scale and at a level of accuracy permitting the quantitative (cartometric) as well as qualitative assessment of change. The sequence of work in compilation of map-diagrams for different parts of the shoreline involved the preliminary referencing of photos to a map, photo interpretation and compilation of large-scale “graphic diagrams,” preparation of a cartographic base, reduction and placement of diagrams on the base, and transformation of the image as a whole. Results of analysis of these map-diagrams are summarized. Translated from: Vestnik Leningradskogo Universiteta, ser. 7: geologiya, geografiya, 1986, No. 2, pp. 44-48.     

GIS支持的长江安徽段干流河道演变的遥感分析

长江是我国的黄金水道,对长江安徽段河道演变的研究将有助于岸线资源的开发利用、河势变化分析及河道整治。本文运用RS与GIS方法对四期遥感TM影像图,采用目视解译和微机图像处理相结合的方法,分析研究了1980年以来长江干流安徽段河道的时空变化特征和规律。研究表明1980年以来长江干流安徽全河段总体河势保持相对稳定,未发生长河段的主流线大幅度摆动现象,但局部河段的河势仍不断调整,有的河段河势变化还相当剧烈。1980～2000年长江河道多处表现为泥沙的淤积作用,在分汊型河道边缘滩州和江心洲淤长作用明显,2000～2008年河道表现出明显的冲刷状态,主要原因在于上游来沙量的减少和下游的岸滩防护工作有效开展。2000～2008年,河流上段内滩洲冲刷速率大于下段。