Management of Water Resources Problem generally involves GIS AND REMOTE SENSING APPLICATION IN WATER RESOURCES. Geographical Information System (GIS)

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1 GIS AND REMOTE SENSING APPLICATION IN WATER RESOURCES Arup K. Sarma Professor Civil Engineering Department Indian Institute of Technology Guwahati Management of Water Resources Problem generally involves Acquiring topographic information of inaccessible area Terrain modeling Hydrological modeling for quantity and quality Hydrodynamic modeling for flow simulation Study of Spatiotemporal variation Providing management strategy in map form Scope of Remote Sensing Acquiring topographic data of any location High Resolution data Stereo data Visual and Digital data analysis Recording temporal changes Geographical Information System (GIS) Data Information Information System Geographical Information System 1

2 Definition Geographic Information System can be regarded as a special form of Information System that provides the required information by processing and analyzing geographic data. Data are said as geographically referenced when they are registered to an accepted geographical coordinate system. A widely accepted and generalized definition of GIS can be given as (USGS, 1997): Definition of GIS Geographic Information System is a computer system capable of assembling, storing, manipulating, displaying geographically referenced information, i.e., data identified according to their locations. History of Development GIS is a relatively new branch of Information Technology. Land Information System (LIS) is a similar system. In 1960s Canadian Geographic Information System (CGIS) was developed. In 1973, the United State Geological Society started development of the Geographical Information Retrieval and Analysis System (GIRAS) to handle and analyze land use and land cover data. With the development in the application of topology for analyzing spatial data, GIS became a more useful tool. In 1982, Environmental System Research Institute (ESRI) released the popular GIS software ArcInfo. With Advancement in the Operating System, Computer Graphics, DBMS, Computer-Human Interaction, and Graphical User Interface Design, GIS has now become a versatile, sophisticated and user friendly software. Scope of GIS GIS (Geographical Information System) has the capacity of Capturing data Storing data Querying data Analyzing data and Displaying data in various format 2

3 Capturing and storing data Real world features exist in two basic forms: Object and Phenomena. Objects are the features having identifiable boundaries. Objects like road, river, building etc. falls in this category. Phenomena are generally distributed continuously over a large area. Terrain, temperature, rainfall etc. falls in this category. Depending on the nature of data and nature of application, data are stored either in a field-based model (Raster model) or in an object-based model(vector model). MAP and GIS Geographic coordinate system of earth Latitude and Longitude (Graticule) 3D coordinate system a projection system is necessary to represent the actual 3D surface in a 2D space. This leads to Map Projection Map Projection Both perspective and non-perspective projections are used perspective projection is strictly geometric in nature, During transformation of spherical earth into a flat plane, important properties like Area, Shape, Distance, and Direction get disturbed Therefore, different projection systems have been designed to maintain one or two of these properties correctly the projection surface can be plane, cylindrical or cone, each a developable surface that can be open out as a sheet. Map projection is therefore, classified into basic three classes: 1) Cylindrical, 2) Conical, 3) Planer or Azimuthal. Again the developable surface may be placed in three different way relative to the globe: 1) Normal aspect, 2) Transverse aspect, and 3) Oblique aspect. The view obtained from any projection will be different depending on the position of the observer s station (or source of light). 3

4 Projection system 1) Cylindrical, 2) Conical, 3) Planer or Azimuthal. Transvers Mercator/ Cylindrical: Conformal and true local direction Polyconic/ Conical: for equidistant along each standard parallel Azimuth Equidistant/Planar: Equidistant and true direction from the map center Other components of GIS HARDWARE Hardware capacity affects the processing speed, ease of use and the type of output available SOFTWARE This includes not only the actual GIS software, but also various database, drawing, statistical, imaging or other software PROCEDURES Analysis requires well-defined, consistent method to produce correct result Raster Model Spatial phenomena are represented either by regular tessellations or irregular tessellation. Tessellations are geometric representation of figures that completely cover a flat. However, for digital representation of spatial field-based data, regular tessellation (square or rectangular), which is known as RASTER model is commonly used. Higher the resolution (Expressed as dpi, dot per inch) better is the data quality. A computer graphics represented by a 24 bit word length can give almost true colour. To store the information of a cell, for each of the colour Red, Green and Blue, 8 bits are reserved. A 8 bit (say ) can yield (2 8 = 256) combination. Thus the computer graphics can recognize 256 ranges of Red colour. Similarly 256 Green and 256 Blue 4

5 Vector Model Object-based spatial data can be exact or inexact. Object having distinct boundary are called exact object. object having fuzzy boundary are called inexact object. Graphical elements point, lines and polygon mostly represent the object-based spatial database. As these elements have dimension and direction, object-based data representation is labeled as VECTOR model. In vector model spatial objects are identified individually and represented mathematically (by coordinates). Vector data models in GIS can be built on two common and interrelated concepts: 1) the decomposition of spatial object into basic graphical elements 2) The use of topology (spatial relationship) to represent spatial object in addition to the use of geometry. A vector data model in its simplest form can be as shown below. Feature ID Feature Type xy 10 point xy 21 line x 1 y 1, x 2 y 2, x 3 y 3, x n y n(string) 31 Polygon x 1 y 1, x 2 y 2,.. x n y n (Closed loop) Vector model Vs Raster model CONCEPT OF LAYER In georelational data model, geographic data are abstracted into a series of independently defined layers. Each of these layers represents a selected set of closely associated spatial object such as roads, stream, and land cover types. The spatial object in a geographic space can be classified and stored separately according to the form of the basic graphical elements on the basis of the entity type. Layers generally store the path to a data source as well as the display property of that data source. 5

6 Concept of Layer QUERY AND ANALYSIS back The query and analysis in GIS has improved a lot due to application of concept of topology. Topology is the branch of mathematics that studies those properties of geometric figures that are unchanged when the shape of a figure is twisted, stretched, shrunk, or otherwise distorted without breaking (West et al, 1982). Properties like adjacency, containment, and connectivity are of this kind Basic topological properties ArcInfo Coverage stores data using a topological structure explicitly defining the following spatial relationship Adjacency Containment Connectivity Some capabilities of GIS Network Analysis A B A B Digital Terrain Model Table containing topological information Hydrological tools Krigging back 6

7 Road Network of IIT Guwahati Network Analysis Flood prone area Alternative major road back Digital Terrain Model Systematic Vs Adaptive There are two approaches for digital data sampling for terrain model Systematic sampling: Terrain data are sampled at regularly spaced intervals to form a Digital Elevation Model (DEM) Adaptive sampling: Terrain data are sampled selectively at salient ground points to form a Triangulated Irregular Network (TIN) However, there are well-established methods for conversion of DEM and TIN to and from one another. 7

8 Creating DEM for IITG Campus Digitized contour map Creating DEM for IITG Campus (Contd.) Elevation database created from the digitized contour file Creating TIN for IITG Campus (contd.) TIN elevation data created from the features data set Creating DEM for IITG Campus (contd.) DEM (5m resolution) back 8

9 Creating a depression less DEM Flow Direction Grid of IITG A DEM free of sinks is a depression less DEM. Presence of sinks may result in erroneous flow direction grid. Since flow direction grid is the first step in deriving the hydrologic characteristics of a surface, sinks should be filled. Flow Accumulation grid for IITG Watershed delineation for IITG 9

10 Delineating stream networks delineated from a DEM using the output from the FLOWACCUMULATION function. By applying a threshold value to the results of FLOWACCUMULATION using a GRID algebraic expression, a stream network can be delineated. Vectorizing A raster linear network can be accurately converted to an arc coverage using STREAMLINE. STREAMLINE is designed primarily for vectorization of stream networks, or any other grid representing a raster linear network for which directionality is known. In the output coverage, all arcs will point downstream. Grid Stream Network Coverage (i) Preparation of a Base map Application of Krigging A study on Fluoride back 10

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