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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

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Definition• Geographic Information System can beregarded as a special form of InformationSystem that provides the required informationby processing and analyzing geographicdata.• Data are said as geographically referencedwhen they are registered to an acceptedgeographical coordinate system.• A widely accepted and generalized definitionof 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) wasdeveloped.• In 1973, the United State Geological Society starteddevelopment of the Geographical Information Retrieval andAnalysis System (GIRAS) to handle and analyze land use andland cover data.• With the development in the application of topology foranalyzing 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, ComputerGraphics, DBMS, Computer-Human Interaction, and GraphicalUser 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

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Capturing and storing data• Real world features exist in two basic forms:– Object and Phenomena.– Objects are the features having identifiableboundaries. Objects like road, river, building etc.falls in this category.– Phenomena are generally distributed continuouslyover a large area. Terrain, temperature, rainfalletc. falls in this category.– Depending on the nature of data and nature ofapplication, data are stored either in a field-basedmodel (Raster model) or in an object-basedmodel(Vector model).MAP and GIS

• Geographic coordinate system of earth

– Latitude and Longitude (Graticule)

– 3D coordinate system– a projection system is necessary torepresent the actual 3D surface in a 2Dspace.• 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).

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Projection system1) Cylindrical, 2) Conical, 3) Planer or Azimuthal.

Transvers Mercator/ CylindricalTransvers Mercator/ CylindricalTransvers Mercator/ CylindricalTransvers Mercator/ Cylindrical: Conformal and true local directionConformal and true local directionConformal and true local directionConformal and true local directionPolyconic/ Conical:Polyconic/ Conical:Polyconic/ Conical:Polyconic/ Conical: for equidistant along each standard parallelfor equidistant along each standard parallelfor equidistant along each standard parallelfor equidistant along each standard parallelAzimuth Equidistant/PlanarAzimuth Equidistant/PlanarAzimuth Equidistant/PlanarAzimuth Equidistant/Planar: Equidistant and true direction from the map Equidistant and true direction from the map Equidistant and true direction from the map Equidistant and true direction from the map centercentercentercenterOther 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 01110101) can yield (28 = 256) combination. Thus the computer graphics can recognize 256 ranges of Red colour. Similarly 256 Green and 256 Blue

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Vector Model• Object-based spatial data can be exact orinexact.• Object having distinct boundary are calledexact object.• object having fuzzy boundary are calledinexact object.• Graphical elements point, lines and polygonmostly represent the object-based spatialdatabase. As these elements have dimensionand direction, object-based datarepresentation is labeled as VECTOR model.• In vector model spatial objects are identifiedindividually and represented mathematically(by coordinates).Vector data models in GIS can be built on two commonand interrelated concepts: 1) the decomposition ofspatial object into basic graphical elements 2) The useof topology (spatial relationship) to represent spatialobject in addition to the use of geometry. A vector datamodel in its simplest form can be as shown below.

Feature ID Feature Type xy

10 point xy

21 line x1y1, x2y2, x3y3,… xnyn(String)

31 Polygon x1y1, x2y2, .. xnyn (Closed loop)

Vector model Vs Raster modelCONCEPT OF LAYER

• In georelational data model, geographic data areabstracted into a series of independently definedlayers.

• Each of these layers represents a selected set ofclosely associated spatial object such as roads,stream, and land cover types.

• The spatial object in a geographic space can beclassified and stored separately according to theform of the basic graphical elements on the basisof the entity type.

• Layers generally store the path to a data source aswell as the display property of that data source.

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Concept of Layer

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QUERY AND ANALYSIS

• 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

B

A

A

B

Adjacency Containment Connectivity

Table containing topological information

ArcInfo Coverage stores data using a topological structure explicitly

defining the following spatial relationship

Some capabilities of GIS

• Network Analysis

• Digital Terrain Model

• Hydrological tools

• Krigging back

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Road Network of IIT Guwahati Network Analysis

Flood prone area

Alternative major

road

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Digital Terrain Model

• There are two approaches for digital datasampling for terrain model

– Systematic sampling: Terrain data are sampledat regularly spaced intervals to form a DigitalElevation Model (DEM)

– Adaptive sampling: Terrain data are sampledselectively at salient ground points to form aTriangulated Irregular Network (TIN)

Systematic Vs Adaptive

However, there are well-established methods for conversion of DEM

and TIN to and from one another.

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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)

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Creating a depression less DEM

• 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 Direction Grid of IITG

Flow Accumulation grid for IITGWatershed delineation for IITG

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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.

Stream Network

Grid Coverage

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(i) Preparation of a Base map Application of Krigging

A study on Fluoride

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