DIGITAL ELEVATION MODEL (DEM), ITS DERIVATIVES & APPLICATIONS Summer training project Carried out at Regional Remote Sensing Centre-West NRSC/ISRO, Jodhpur (1st June – 3rd July, 2015) Submiitted BY- Submitted to- Shadaab Er. Sagar s. salunkhe (B. Tech – aerospace Eng. ( Scientist/engineer ‘sd’, With sp. In avionics rrsc – w, nrsc/isro, Upes, Dehradun) jodhpur)

Contents What is a DEM? How are DEMs generated? What are the types of DEM Available? 1/7/2015 What are the various derivatives of DEM? What can DEMs be used for?

What is a DEM? Digital Elevation Model (DEM) is the digital representation of the land surface elevation with respect to any reference datum 1/7/2015

How is a DEM generated? A) From airborne or satellite remote sensing: RADAR Interferometry with 2 receivers, 60m apart A) From airborne or satellite remote sensing: Stereo images, RADAR or LIDAR data are used in a semi-automated process to create a DEM. 1/7/2015 Airborne Laser-scanning or LIDAR

How is a DEM generated? B) From terrestrial measurements with precise land survey instruments. These spot measurements are then interpolated into an elevation surface. With this method, it is costly and time-consuming to cover bigger areas. 1/7/2015

Digital hill-shade models generated from a Lidar scan. DEM, DTM and DSM... A digital terrain model is a topographic model of the bare earth –terrain relief - that can be manipulated by computer programs. Digital Surface Model measures the height values of the first surface on the ground. This includes terrain features, buildings, vegetation and power lines etc. DSM's therefore provide a topographic model of the earth's surface. Digital Surface Model Digital Terrain Model 1/7/2015 Digital hill-shade models generated from a Lidar scan.

Types of Digital Elevation Models… (a) Gridded DEM (b) TIN DEM (c) Contour-based DEM Gridded Digital Elevation Model (GDEM) consists of regularly placed, uniform grids with the elevation information of each grid TIN is a robust way of storing the spatially varying information. It uses irregular sampling points connected through non-overlapping triangles. The vertices of the triangles match with the surface elevation of the sampling point and the triangles (facets) represent the planes connecting the points. Contours represent points having equal heights/ elevations with respect to a particular datum such as Mean Sea Level (MSL). In the contour-based structure, the contour lines are traced from the topographic maps and are stored with their location (x, y) and elevation information. 1/7/2015

What are the various derivatives of DEM? Aspect Aspect identifies the downslope direction of the maximum rate of change in value from each cell to its neighbors. It can be thought of as the slope direction. Slope For each cell, the Slope tool calculates the maximum rate of change in value from that cell to its neighbors 1/7/2015

Phnom Penh Mapping Meetup Feb. 2013 Contour Contours are lines that connect locations of equal value in a raster dataset that represents continuous phenomena such as elevation, temperature, precipitation, pollution, or atmospheric pressure. Cut-fill A cut-and-fill operation is a procedure in which the elevation of a landform surface is modified by the removal or addition of surface material 1/7/2015 Bernd Eversmann, GIZ-CIM

Using View-shed and Observer Points for visibility analysis A view-shed identifies the cells in an input raster that can be seen from one or more observation locations. Each cell in the output raster receives a value that indicates how many observer points can be seen from each location 1/7/2015

Scientific applications What are DEMs used for? Scientific applications topographic mapping A DEM is needed for ortho-rectification of an image, the process of removing the effects of sensor tilt and relief to obtain a photographic map with uniform scale. Ortho-photo production 1/7/2015

What are DEMs used for? Operational Applications Flood modeling Development of data layers 1/7/2015

Military applications What are DEMs used for? Military applications Visibility analysis Surface navigation 1/7/2015

Phnom Penh Mapping Meetup Feb. 2013 Commercial applications 3D representations Tele - communication 1/7/2015 Bernd Eversmann, GIZ-CIM

Thank you! 1/7/2015