Cartosat-1 Stereo Data Research Articles

Resolving Biases in DEM Differencing for Estimation of Change in Elevation of Glacier Surfaces Using Cartosat-I Stereo Data

Understanding the impact of climatic variations on Himalayan-Karakoram glaciers has now become a necessity for planning water resources of Indus-Ganga–Brahmaputra basins. One of the most important parameters to assess this is the mass balance of glaciers. Besides ground-based studies of mass balance, differencing of Digital Elevation Models (DEMs) is now commonly employed for estimating the long-term changes for this purpose. Before applying this approach, it is necessary to evaluate the accuracy of elevation changes of glacier surfaces with respect to terrain parameters and the DEMs used. This study demonstrates the factors governing DEM differencing using an example of four glaciers of Zanskar region by comparing DEMs extracted from Cartosat-1 stereo data of ablation season of the years 2005 and 2015. A strong relation has been observed between slope of the terrain and elevation changes between the two DEMs on non-glaciated stable terrain (R2 = 0.8144). The regression equation thus developed has been used to correct elevation changes on glacier surface. Lowering of ablation zone of the four sample glaciers over a period of ten years has been of the order of 3.92, 11.17, 4.99 and 4.39 m. The results obtained by using Cartosat-I DEMs have also been validated using ASTER DEMs of similar time interval.

Accuracy Assessment of Digital Elevation Model Generated by SAR Stereoscopic Technique Using COSMO-Skymed Data

Radargrammetry technique using the stereoscopic synthetic aperture radar (SAR) images is used for the generation of a digital elevation model (DEM) of a region requires only the amplitude images. SAR stereoscopic technique is analogous to the stereo-photogrammetric technique where the optical stereoscopic images are used for DEM generation. While the advantages of the SAR images are their indifference to atmospheric transparency and solar illumination conditions, the side-looking geometry of the SAR increases the complexity in the SAR stereo analysis. The availability of high spatial and temporal resolution SAR data in recent years has facilitated generation of high-resolution DEM with greater vertical accuracy using radargrammetric technique. In the present study, attempt has been made to generate the DEM of Dehra Dun region, India, from the COSMO-Skymed X-band SAR data-pair acquired at 8 days interval through the radargrammetry technique. Here, radargrammetric orientation approach has been adopted to generate the DEM and various issues and processing steps with the radargrammetry technique have been discussed. The DEM was validated with ground measured elevation values using a differential global positioning system and the root-mean-square error of the DEM was found as 7.3 m. The DEM was compared with the reference DEM of the study area generated from the Cartosat-1 stereo data with a model accuracy of 4 m.

Use of Remote Sensing and Geospatial Technique for Pre-feasibility Analysis of Rural Water Pipeline Grids

The article outlines a procedure of pre-feasibility analysis of planned rural water supply pipeline grids in India. Usually, these type of pre feasibility studies prior to actual implementation, is carried out based on ground surveys and is time consuming. In this work, we use thematic spatial data, such as geomorphology and landuse–landcover along with digital elevation model (DEM) to carry out the pre-feasibility assessment of proposed pipeline grids. DEM generated from CartoSat-1 stereo data has been used to understand the possible topographic hindrances along the planned pipeline route and optimise the same. Further, topographic data also indicates the possible routes of gravity assisted flow. The geomorphology thematic data interpreted from Resourcesat-1 LISS III imagery is used to identify possible geomorphologic hindrances along the pipeline route. Similarly, landuse–landcover information derived from Resourcesat-2 LISS III images, was used to assess the land use/cover impact of the planed pipeline corridor. This has been demonstrated, in the current article using a hypothetical pipeline route. The activity can be carried in a specially designed geo-spatial interface in NRSC/ISRO Bhuvan geoportal. This type of assessment can prove to be time saving and cost effective at a pre-feasibility stage.

Development of ‘3D City Models’ using IRS Satellite Data

Urban models are computer-based solutions used for testing theories about spatial location and interaction between land uses and related activities. They also provide digital environments for testing the consequences of physical planning policies on the future form of cities. Earlier, 3D city models were prepared using stereo aerial photography, topographic data and conventional surveying. The geospatial information was extracted using either visual or digital classification techniques. Presently the 3D city models is prepared with the help of ALTM data along with very high resolution imagery, which is costly and time consuming. As alternatives, Cartosat-1 stereo data of the order of 2.5 m resolution, it becomes more practical and economical to generate digital surface model (DSM) with an accuracy of 4 m. Cartosat-II data with 1 m resolution fused with LISS-IV data give high resolution images for building footprint extraction. The availability of high resolution Cartosat-I stereo satellite data assists urban planners and municipal authorities to create a model and visualize the urban space in three dimensions. 3D visualization models have a variety of applications in urban studies. The studies includes urban morphological mapping, disaster management, updation, virtual reality and generation of fly through etc. The primary interest of the planners is not limited towards the extraction of urban features from satellite data. Planners also have interest in creation of 3D models of buildings and terrain surface for detailed urban planning. Therefore, to develop 3D city models 2.5 m Cartosat-1 stereo data fused with 1 m merged product of Cartosat-II and LISS-IV to create DSM and building footprints respectively. Keeping the significance of use of stereo satellite data, an attempt has been made to generate a 3D building model for Ahmedabad and Hyderabad cities. The 3D building model generated by employing geoinformatics techniques with Level of Details (LOD-1). The primary aim of this study was to develop geoinformatics techniques for the extraction of urban features based on object oriented classification techniques with level of details 1 (LOD-1) using photogrammetric DEM. This paper discusses all these techniques and their usefulness in 3D city modeling exercises.

Effect of sensor modelling methods on computation of 3-D coordinates from Cartosat-1 stereo data

The orbital and the rational polynomial coefficients (RPC) models are the two most commonly used models to compute a three-dimensional coordinates from an image stereo-pair. But it is still confusing that with the identical user provided inputs, which one of these two models provides more accurate digital elevation model (DEM), especially for mountainous terrain. This study aimed to find out the answer by evaluating the impact of used models on the vertical accuracy of DEM extracted from Cartosat-1 stereo data. We used high-accuracy photogrammetric DEM as the reference DEM. Apart from general variations in statistics, surprisingly in a few instances, both the DEMs provided contrasting results, thus proving the significance of this study. The computed root mean square errors and linear error at 90% (LE90) were lower in case of RPC DEM for various classes of slope, aspect and land cover, thus suggesting its better relative accuracy.

Automatic Conversion of DSM to DTM by Classification Techniques Using Multi-date Stereo Data from Cartosat-1

Stereoscopic satellite imaging provides directly the digital surface model (DSM) in contrast to the topographic application which needs digital terrain model (DTM). Presently, DTM is generated manually in 3d environment which is a time consuming exercise. To address this problem, the paper proposes DTM generation from Cartosat-1 stereo by adopting automatic classification of mass points similar to LiDAR points by improving its density using multi-date Cartosat-1 stereo data. To illustrate the proposed methodology, two study areas were investigated viz. Dharamshala, Himachal pradesh and Netravathi river,Western ghats, Karnataka in India. The results from the proposed methodology demonstrated that classification techniques when applied to the densified mass points from multi-date stereo data, works well in comparison to mass points generated from a single scene. The study also demonstrated that terrain parameters like slope, drainage pattern and contour derived from the DTM generated by the proposed method were similar to DTM generated by manual methods.

Elicitation of erosional signature of a tropical river basin with high-resolution stereo data

The launch of Cartosat-1 turns into a new era for user communities of remote sensing and mapping. Generation of digital elevation model (DEM) of a particular geographic region of interest is the primary goal and advantage of Cartosat-1 mission. To generate the most accurate DEM from Cartosat-1 stereo data, 34 GCP points were used, and 122 tie points are automatically extracted with the aid of LPS-2011. Here, an attempt has been made to study the quantitative hypsometric analysis of six sub-watersheds of the Kuttiyadi River Basin (676 km2) with a humid tropical setting, using Cartosat-1 DEM. An extension, CalHypso, an add-on tool to ArcGIS 9.2, was utilized to synthesize hypsometric data from Cartosat-1 DEM which reflects the erosional signature of sub-watersheds based on geological stages of development. From hypsometric analysis, it is found that three sub-watersheds are in old stage, and the remaining three are of mature stage.

Generation and Evaluation of DEM from Cartosat-1 Stereo Data Using Ground Control Points from Topographical Maps

Generation and Evaluation of DEM from Cartosat-1 Stereo Data Using Ground Control Points from Topographical Maps Digital Elevation Model (DEM) is a basic input to find out the terrain characteristics and terrain parameters. It is also used for planning of infrastructural facilities of an area. There are several ways to generate a DEM and with the advances in spatial technologies, it becomes easy to generate a DEM from the satellite data. In the present paper, DEM has been generated using Cartosat-1 satellite stereo data with Ground Control Points (GCPs) taken from Survey of India (SOI) topographical map and mass points that are digitized after block triangulation. The generated DEM has been evaluated with elevation values of Survey of India (SOI) topographical map of the study area. The generated DEM has also been compared with the ASTER DEM of the study area and it is observed that Cartosat-1 extracted DEM shows better results when mapping at large scales. From the DEM quality map, it is seen that 86% pixels identified as excellent to good category and only 16% are identified as isolated to suspicious category. From the comparison of DEM prepared from block triangulation and contours, it is seen that 26% pixels have the elevation variation of less than 5 m and 30% pixels have the elevation variation of 5 m to 10 m. Elevation variation of less than 5m is seen for 23% pixels and 5 m to 10 m is seen for the 51% pixels between the ASTER DEM and DEM prepared from contours. DEM extracted from Cartosat-1 satellite data can be used for planning and implementation of infrastructural facilities, as it require more accurate and detailed terrain variations.

Assimilation of DEMs Generated from Optical Stereo and InSAR Pair through Data Fusion

Main objective of this study is to compare and assimilate the digital elevation models (DEMs) generated using C-band Envisat, L-band ALOS PALSAR Interferometric SAR (InSAR) datasets and Cartosat-1 optical stereo data. The study area is Dehradun city and surroundings including lower Shivalik hills i.e. the younger Himalayas in the south and higher Himalayas on the north. The general elevation of the area ranges from 400m to 2000m AMSL. Ground control points (GCPs) collected from Differential Global Positioning System (DGPS) survey, were used for satellite triangulation of optical data & geocoding of InSAR data. RMSE for satellite triangulation for cartosat-1 is 0.745 using 6 ground control points and 3 check points. It is found that when GCP’s are used along with reference DEM (SRTM), the DSM generated by ALOS PALSAR and DSM generated from Cartosat-1 stereo data are well representing the terrain. The fusion of imagery from multiple sensors has been in use in remote sensing for scientific exploration in the past but there is a little work done on data fusion application for generation of topography (DEM) through Optical stereo and SAR interferometry data sources. The defined framework for data fusion uses three fundamental steps in the analysis of the system namely, identification, estimation, and validation for algorithm preparation. The knowledge of the study area, i.e. the field, and the processes involved in the DEM generation of optical and InSAR data are cognitively used for rule-based decision making in the algorithm for mathematical generation of resultant DEM through data fusion implemented at feature level.

DEM generation using Cartosat-1 stereo data: issues and complexities in Himalayan terrain

High-altitude Himalayan terrain exhibits extreme geometric distortion along north-facing (dilation) and south-facing (compression) slopes as observed in satellite stereo data with high look angles. In the present study, Cartosat-1 stereo pairs have been used for generating Digital Elevation Model (DEM) using Differential Global Positioning System based Ground Control Points. DEM quality assessment through stereoscopic visualization revealed distortions especially in E-W oriented steep valleys. The study highlights issues and challenges in DEM generation for Himalayan terrain and articulates density of editing required. Quantitative and qualitative assessment of the DEM produced showed considerable improvements after post processing.

Evaluation of Cartosat-1 Satellite Triangulation & Dsms in Varied Terrain Conditions

Digital surface models (DSMs) and Digital elevation models (DEMs) has become inevitable input for many applications including various types of modeling problems besides photogrammetric product generation such as orthoimages and visualization. Automatically generated DSMs using image matching techniques are an efficient means to extract bare earth DEMs or DTMs for various applications including modeling. This paper highlights and evaluates the accuracy of satellite triangulation, and DEM generated from Cartosat-1 data by using Rational Polynomial Coefficient’s (RPC’s) provided with the Cartosat-1 data along with ground control points (GCPs) collected through differential Global Positioning System (DGPS) surveys. Three study sites were taken for evaluation of DSMs in different topographic conditions, namely, a) Dehradun, Uttarakhand characterized by relatively high undulating terrain comprising of shivalik hills in the south and higher Himalayas on the north, b) Jaipur, Rajasthan having more of urban and plain agriculture area with Aravalli ranges, and c) Kendrapara, Orissa which is having a plain terrain conditions with agriculture fields, river, and sparsely populated area. DGPS surveys were conducted at the three sites to collect ground control points (GCPs) for satellite triangulation & subsequent analysis. The satellite triangulation resulted in RMSE of better than a pixel for all the three sites. The RMSE for DEM is varying from within a pixel for plain area to about four pixels for highly undulating terrain. The paper describes the positional and vertical accuracies achieved for cartosat-1 stereo data through photogrammetric process of satellite triangulation and Digital surface model generation in the three study sites having different topographic conditions.

Validation of Indian National DEM from Cartosat-1 Data

CartoDEM is an Indian National DEM generated from Cartosat-1 stereo data. Cartosat-1, launched in May, 2005, is an along track (aft −5°, Fore +26°) stereo with 2.5 m GSD, give base-height ratio of 0.63 with 27 km swath. The operational procedure of DEM generation comprises stereo strip triangulation of 500 × 27 km segment with 10 m posting along with 2.5 m resolution ortho image and free—access posting of 30 m has been made available (bhuvan.nrsc.gov.in). A multi approach evaluation of CartoDEM comprising (a) absolute accuracy with respect to ground control points for two sites namely Jagatsinghpur -flat and Dharamshala- hilly; second site i.e. Alwar-plain and hilly with high resolution aerial DEM, (b) relative difference between SRTM and ASTERDEM (c) absolute accuracy with ICESat GLAS for two sites namely Jagatsinghpur-plain and Netravathi river, Western Ghats-hilly (d) relative comparison of drainage delineation with respect to ASTERDEM is reported here. The absolute height accuracy in flat terrain was 4.7 m with horizontal accuracy of 7.3 m, while in hilly terrain it was 7 m height with a horizontal accuracy of 14 m. While comparison with ICESat GLAS data absolute height difference of plain and hilly was 5.2 m and 7.9 m respectively. When compared to SRTM over Indian landmass, 90 % of pixels reported were within ±8 m difference. The drainage delineation shows better accuracy and clear demarcation of catchment ridgeline and more reliable flow-path prediction in comparison with ASTER. The results qualify Indian DEM for using it operationally which is equivalent and better than the other publicly available DEMs like SRTM and ASTERDEM.

Cartosat-1 height product and ICESat/GLAS data for digital elevation surface generation

Space born systems like Geoscience Laser Altimeter System (GLAS) onboard collect data for ice, cloud and Land. Elevation satellite (ICESat) collects an unparalleled data set as waveform over terrestrial targets, helps in evaluating the global elevation data. In this study we compared the Digital Elevation Surface (DES) generated by Cartosat-1 point data and DES generated by merging the Cartosat-1 data with ICESat data. Outputs in the form of interpolated surfaces were evaluated with the help of differential global positioning system (DGPS) points collected from study area. The study showed the results that the DES generated from Cartosat — 1 data had less elevation accuracy when compared with the DGPS data. While merging Cartosat-1 point height data with ICESat/GLAS data resulted in better accuracy. On the practical side for processing the interpolation, based on the research the ICESat /GLAS with Cartosat-1 height data can produce better DES compared to the Cartosat-1 stereo data. The DES was generated using geostatistical interpolation methods in which the global polynomial method proved to be the better for generating the surface compare to other interpolation techniques studied in this work. For co-kriging method, the accuracy decreases compare to the kriging interpolation, due to the complexity of parameters that were used for interpolation. On the theory side, based on this research the statement of which interpolation technique is better than the other cannot be mentioned easily, because these are based on the data type, parameters and also on method of interpolation. So research experiment should be more intensely and with more focused.

Evaluation of Cartosat-1 Multi-Scale Digital Surface Modelling Over France

On 5 May 2005, the Indian Space Research Organization launched Cartosat-1, the eleventh satellite of its constellation, dedicated to the stereo viewing of the Earth's surface for terrain modeling and large-scale mapping, from the Satish Dhawan Space Centre (India). In early 2006, the Indian Space Research Organization started the Cartosat-1 Scientific Assessment Programme, jointly established with the International Society for Photogrammetry and Remote Sensing. Within this framework, this study evaluated the capabilities of digital surface modeling from Cartosat-1 stereo data for the French test sites of Mausanne les Alpilles and Salon de Provence. The investigation pointed out that for hilly territories it is possible to produce high-resolution digital surface models with a root mean square error less than 7.1 m and a linear error at 90% confidence level less than 9.5 m. The accuracy of the generated digital surface models also fulfilled the requirements of the French Reference 3D®, so Cartosat-1 data may be used to produce or update such kinds of products.

Extraction and validation of cartosat-1 DEM

CARTOSAT-1 satellite, launched in May, 2005 is a dedicated along track stereo mission providing high quality data for topographic and cartographic applications. The present paper describes the evaluation of the Cartosat-1 stereo data, mainly through the generation and validation of DEM for moderately undulating and hilly areas. Photogrammetric techniques have been used for generation of DEM and Orthoimage for two cases i.e. 1) using RPCs (Rational Polynomial Coefficients) and 2) using RPCs along with ground control points. Root Mean Square Error (RMSE) in elevation values for the moderately undulating (Dehradun) and hilly area (Shimla), are found to be 4.38 and 3.69m respectively.