Indian Journal of Geo Marine Sciences Vol. 46 (07), July 2017, pp. 1339-1351 Comparative analysis of digital elevation models: A case study around Madduleru River Subbu Lakshmi. E1 & Kiran Yarrakula2* Centre for Disaster Mitigation and Management, VIT University, Vellore, Pin 632014, India *[E-mail: [email protected]] Received 14 July 2016 ; revised 28 November 2016 High resolution DEM is generated from Cartosat-1 stereo data. The performance of different DEMs is evaluated based on error statistics. To identify the hill profiles, the TIN plots have generated and compared for SRTM, Cartosat -1, and SOI toposheet. The study divulges that, elevation values of Cartosat-1 DEM are better in flat terrain and SRTM images in hilly region produced better, when compared each other. [Keywords: Cartosat-1 DEM, SRTM-DEM, Google earth, Survey of India Toposheet, Accuracy Assessment, Digital elevation model] Introduction corresponding image points are identified in the Cartosat-1 DEM with 2.5m spatial particular stereo images In general, the accuracy resolution and vertical resolution 7.5m is intended of Cartosat-1 DEM seems to be fine in the flat to be used for generating DEM. The ground terrain which is helpful to interpret the land control points and geometric model are the features13. Past few years many scientists and essential components required for generating researchers have done a series of local and global DEM from stereo data1. DEM in variety of assessments of these elevation products. Many application such as land use land cover to analyze new technologies are giving opportunities for the spatio-temporal change on the river2&3, generating digital elevation models in remote cadastral mapping, to assess the vertical sensing to determine Earth surface elevation at characteristics of topographical variability of increasing resolution for larger areas14. DEMs are urban built-up landscape4&5and Hydrological very useful that reflect the importance of the modeling to obtain information about flow lines, availability of global, consistent, and high quality slope, watershed boundary, elevation, DEM. In this paper an attempt has been made to contour6&7&8and other GIS applications. Elevation examine the accuracy of DEM derived from data generated from the satellite imageries is Cartosat-1 DEM, SRTM DEM, Google earth and evaluated by cross checking the elevation values SOI toposheet for proper planning. Existing obtained from topographic maps9. Assessment satellite based DEMs still show large drawbacks can also be done by checking the elevation values with respect to consistency, availability, cost, of the contour generated using satellite images degree of resolution, and coverage. DEMs should with elevation data obtained from differential act as a carrier of geoinformation representing global positioning system (DGPS) and global terrain features associated to the earth surface. It positioning system (GPS) 10&11. The cost of DGPS should provide innovative mechanism for data is very expensive12, provides very good operational applications to carry out more issue accuracy of less than 1m. In the present study, due and analysis operations to investigate the complex to unavailability of DGPS data, the elevation interactions among geospatial features and values are feed using toposheet and the processes identified at the Earth surface15. Here 1340 INDIAN J. MAR. SCI., VOL. 46, NO. 07, JULY 2017 mainly, we are assessing the quality of Cartosat-1 data through comparison with three other data sets. To assess the accuracy of DEM, a random of 59 control points are selected from the study area and interpreted the elevation values at each point. In this study elevation data of Cartosat-1 DEM, SRTM DEM, Google earth and SOI toposheet values are compared for the region of Anantapur and Kadapa districts of Andhra Pradesh, India. Materials and Methods The DEM comparison has been performed for the region of Anantapur and Kadapa districts, Andhrapradesh, India. Dorigallu and Gorivikanuma, Kokkarajukonda are the main hill areas covered by the dense forest extending from west to east in the study area. The height of this forest area varies from 372m to 755m. High resolution Cartosat-1 stereo data is used for DEM generation and it is compared with SRTM DEM with vertical resolution of 30m. Google earth and SOI toposheet with 1:50,000 scales are also used Fig. 1 Geographic location of the study area for DEM comparison. Figure 1 shows geographic location of the study area. Table 1 shows product details of the images. Table1 Data resource description S.NO Image Resolution Satellite Area Date of procurement used 1 PAN 2.5m IRS-1C (Cartosat-1) Anantapur and March 2010 Kadapa 2 SRTM 3-ARC Shuttle Radar Anantapur and September 2014 DEM seconds Kadapa 3 Google 0.15(Highest) Digital globe (Astrium, SPOT) Anantapur and January 2014 Earth Kadapa 4 SOI 1:50,000 Photogrammetric interpretation Anantapur and Procured in scale of aerial photography, LIDAR and Kadapa 2013.Updated for major toposheet other remotesensing techniques. details during 2014-2015 DEM is mainly used for representing the extraction of sensor information from RPC file is terrain surface in 3D form and to interpret the done to carry out the interior and exterior topographic features16. High resolution Cartosat-1 orientations18. Rational function is chosen as stereo kit with rational polynomial coefficient category of geometric model19. Stereo image pair (RPC) file is used to develop digital elevation is loaded which is in TIFF (Tagged image file model. Cartosat -1 ortho image is a panchromatic format) form. Then RPC coefficients are specified image with spatial resolution of 2.5m17. For DEM for the Band A and Band F images using the extraction, a block file is created for the image Survey of India Toposheet (SOI) 57J/3 by identity. The type of geometric model Cartosat-1 checking the minimum and maximum elevation RPC is assigned for the created blocks. The values of the study area. Pyramid layers for the LAKSHMI & YARRAKULA: COMPARATIVE ANALYSIS OF DIGITAL ELEVATION MODELS 1341 image in the block file will get activated of SRTM DEM, the contour is generated using 3D automatically. The pyramid layers are used to analyst option in ARC GIS software. By optimize image display during automatic tie point providing corresponding latitude and longitude collection and also in DEM extraction process. values of the chosen 59 points, the elevation Tie points are automatically generated using LPS values of the particular location is taken from the software and it act as a 3D reference point to SRTM contour, and these values are compared compute the quality of digital elevation model. To with contours generated from Cartosat -1 DEM. In establish the relationship between stereo images, case of toposheet, using latitude and longitude the sensor and ground in the block, the values of 59 chosen points, the corresponding triangulation process is done by providing ground elevation values are identified in toposheet and control points (GCPs) 20. GCP are the points on these values are then compared with Cartosat-1 the earth surface of known location (latitude, elevation values. Figure 2 shows the detailed longitude, elevation). Accurate ground control methodology for generating digital elevation points in the overlap area would results in uniform model using Cartosat-1 stereo data. DEM with high accuracy21. In the present work, the ground coordinates of GCPs are derived from Collection of CARTOSAT-1 stereo Collection of SRTM Identifying study area from image DEM Google earth satellite image of IRSP6 Resourcesat-II. Tie points are generated in the overlap area between Create block project (.blk) Generating contour for the Using selected 59 data in LPS 9.0 software study area using ARCGIS points for the study area the two stereo images. Sometimes the ground software analyzing the elevation values control points are taken as check points for Set Geometric model as Cartosat RPC Generating contour using generating DEM. The points with known ground ARCGIS software positions are check points used for assessing the Set projection type and Datum Using selected 59 data 22 points for the study area accuracy . Elevation values are derived from analyzing the elevation Load stereo image pair values toposheet for the corresponding well defined GCP points. The block triangulation is performed after Tie point generation adding GCP and elevation values. The block Triangulation triangulation estimates the position of each image Adding GCP, check point (for absolute DEM) in a block at the time of image capturing and establishes the relationship between images within Block adjustment and 23 processing a block sensor model and the ground . The triangulation process is run to check the accuracy Generation of contour from Cartosat 1 DEM of GPCs and tie points. Then the block Ortho image generation adjustment is carried out that simultaneously process all the images within the block which Using selected 59 data points for the study area minimize the error. Finally the DEM is extracted analyzing the elevation values with DEM cell size of 10m, after checking the accuracy of GCP and tie points by using DEM Accuracy assessment of different DEM elevation extraction. Reference coordinate system, values projection type, vertical and horizontal datum are used as Geographic lat/long, UTM, and WGS84 respectively. Once the DEM is generated, Fig. 2 Detailed methodologies for the comparative analysis of automatically the contour can be extracted from