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Refining IKONOS DEM for Dehradun region using Photogrammetry based DEM Editing methods, orthoimage generation and Quality assessment of Cartosat-1 DEM
* 1 , 2 , 1
1  Indian Institute of Remote Sensing, Dehradun, India
2  Indian Institute of Technology, Roorkee, India


The correct representation of the topography of terrain is an important requirement to generate photogrammetric products such as orthoimages and maps from high-resolution (HR) or very high resolution (VHR) satellite datasets. The refining of the digital elevation model (DEM) for the generation of orthoimage is a vital step with a direct effect on the final accuracy achieved in the orthoimages. The refined DEM has potential applications in various domains of Earth sciences such as geomorphological analysis, flood inundation mapping, hydrological analysis, large scale mapping in an urban environment, etc., impacting the resulting output accuracy. Manual editing is done in the presented study for the automatically generated DEM from IKONOS data consequent to the satellite triangulation with a root mean square error (RMSE) of 0.46, using the rational function model (RFM) and an optimal number of ground control points (GCPs). The RFM includes the rational polynomial coefficients (RPCs) to build the relation between image-space and ground-space. The automatically generated DEM initially represents the digital surface model (DSM) which is used to generate a digital terrain model (DTM) in this study for improving orthoimages for an area of approximately 100 km2. DSM frequently has errors due to mass points in hanging (floating) or digging, which need correction while generating DTM. The DTM assists in the removal of the geometric effects (errors) of ground relief present in the DEM (i.e., DSM here) while generating the orthoimages and thus improves the quality of orthoimages, specially in areas like Dehradun which is having highly undulating terrain with a large number of natural drainages. The difference image of reference i.e. edited IKONOS DEM (now representing DTM) and automatically generated IKONOS DEM, i.e. DSM has a mean difference of 1.421 m. The difference DEM (dDEM) for the reference IKONOS DEM and generated Cartosat-1 DEM at 10m posting interval (referred to as Carto10 DEM), results in a mean difference of 8.74 m.

Keywords: Digital surface model; Digital terrain model; Difference DEM; Rational Function Model; Satellite Triangulation; Hanging (floating) mass points; digging mass points