By Interferometric Synthectic Aperture Radar (InSAR), during the Shuttle Radar Topography Mission (SRTM) height models have been generated, covering the earth surface from 56° south to 60.25°n orth. With the exception of small gaps in steep parts, dry sand deserts and water surfaces, the free available US C-band data cover the earth surface from 56°s outh to 60.25° north completely while the X-band data, distributed by the DLR (German Aerospace Center), cover it only partially. The C-band and Xband radar cannot penetrate the vegetation because of the short wavelength. Therefore, the height Keywords SRTM (Shuttle Radar Topography Mission) . InSAR (Interferometric Synthetic Aperture Radar) . DSM (Digital Surface Model) . DEM (Digital Elevation Model) . Accuracy models are not Digital Elevation Models (DEM) representing bare Earth surface without any details, they are Digital Surface Models (DSM) representing the visible surface including vegetation and buildings. In the area of Zonguldak, Turkey, C-band and X-band DSMs are available and have been analysed in cooperation between Zonguldak Karaelmas University (ZKU) and Leibniz University of Hannover. The digitized contour lines from the 1:25,000 scale topographic maps and also a more precise height model derived directly from large scale photogrammetric mapping are used as reference height models.The terrain inclination influences the accuracy strongly, but also the directions of the inclination in relation to the radar view direction, the aspects, are important. Independent from the aspects, the analysed results do have root mean square differences against the reference data fitting very well to the Koppe formula SZ=a+b*tan α. The analyses are made separately for open and forest areas, with clear 336 J. Indian Soc. Remote Sens. (September 2009) 37:335-349 accuracy differences between both. Also, the analysis of X-band separately for three sub-areas is done and the positive effect of double observation to the accuracy has been clearly determined. The C-band data are only available with a spacing of 3 arcsec, corresponding to 92m × 70m, while the X-band data do have a spacing of 1 arcsec. This is important for the interpolation in the mountainous test area. The accuracy of the height points is approximately the same for the C-and the X-band data. But the C-band data which have three times larger spacing than Xband data, do not include the same morphological information. While C-band data contain very generalised contour lines X-band data have quite more details depending on 1 arcsec point spacing. The differential DEMs have been generated, separately, for displaying the differences between SRTM height models and reference DEMs of the test field.

WorldView-2 (WV-2), whose panchromatic images have a 0Á5 m ground sampling distance (GSD), was launched by DigitalGlobe in 2009. It is the first commercial satellite to offer 8-band multispectral imagery with 1Á8 m resolution. Due to the offnadir sensor rotation of WV-2, it is feasible to obtain stereo coverage. Digital elevation models (DEMs) have been created with three WV-2 stereopairs of northern Istanbul with different land types and one of these is comprehensively analysed in this study. A reference DEM, developed from large-scale aerial photogrammetric mapping, together with a lidar DEM and an overlapping neighbouring WV-2 DEM, are used for validation. The generated WV-2 DEM reached, after filtering and in open areas, a standard deviation in height of approximately 1Á0 GSD. A higher number of discrepancies larger than 4 m exist than would be expected from a normal distribution, influencing the standard deviation more than the normalised median absolute deviation (NMAD). ). Before the development of spaceborne imaging technologies, land surveying techniques and photogrammetry were the only approaches that were available for DEM generation. These techniques yield high accuracy but are time consuming. In addition, in some countries the use of aerial images is restricted. Today, optical satellite images compete with aerial images for mapping applications.The elevation models must conform to predetermined quality standards and user requirements. The quality of the model includes two main components: accuracy and morphologic detail. Accurate elevation information is crucial for mapping products if satellite data are to be used (Li, 1998). Based on optical space images, the accuracy of the generated DEMs is mainly dependent upon the ground resolution, base-to-height ratio, image contrast and terrain roughness (Jacobsen, 2003). IKONOS, QuickBird, OrbView, WorldView-1 (WV-1), GeoEye-1 and WorldView-2 (WV-2) as well as Pleiades were launched sequentially and are capable of providing a ground resolution of up to 0Á5m.The automated DEM generation from WV-2 stereopairs in Istanbul, Turkey, is described and analysed. The next section presents the characteristics of the study area and the applied WV-2 dataset. This is followed by an explanation of the methodology used for DEM generation, including scene orientation and matching, digital surface model (DSM) generation, DSM to DEM conversion by filtering, and gap filling. Next, the DEM evaluation process and results are presented, followed by the conclusions from this research. Study Area and WorldView-2 DatasetThe study area is located north-west of Istanbul, Turkey; it is adjacent to the Black Sea coast with the Bosporus at the eastern limit of the site (Fig. 1). The terrain is flat to undulating, with a few steeper parts (Fig. 2); it includes forests, water bodies, partially worked quarries and gravel pits. The height of the terrain ranges from -43 m, due to opencast mining, to 165 m. Fig. 1 shows an overlay of the three WV-2 pan-sharpened scenes used in this study and ...

Building extraction from high resolution (HR) satellite imagery is one of the most significant issue for remote sensing community. Manual extraction process is onerous and time consuming that's why the improvement of the best automation is a crucial topic for the researchers. In this study, we aimed to expose the significant contribution of normalized digital surface model (nDSM) to the automatic building extraction from mono HR satellite imagery performing two-step application in an appropriate study area which includes various terrain formations. In first step, the buildings were manually and object-based automatically extracted from ortho-rectified pan-sharpened IKONOS and Quickbird HR imagery that have 1 m and 0.6 m ground sampling distances (GSD), respectively. Next, the nDSM was created using available aerial photos to represent the height of individual non-terrain objects and used as an additional channel for segmentation. All of the results were compared with the reference data, produced from aerial photos that have 5 cm GSD. With the contribution of nDSM, the number of extracted buildings was increased and more importantly, the number of falsely extracted buildings occurred by automatic extraction errors was sharply decreased, both are the main components of precision, completeness and overall quality.

Presently, various different methods are I. INTRODUCTION being used for Digital Elevation Model (DEM) generation. DEMs can be generated from topographic maps obtained with terrestrial measurements, As known, Digital Elevation Models (DEM) have big Photogrammetric flight data or Remote Sensing importance for surveying and these are used in large variety of technologies. And also a question can be asked that applications and also lots of different engineering disciplines which method is better than others that's why these are used these models for different aims too. In this reason, the DEM generation techniques have been analysed and accuracy of a Digital Elevation Model becomes considerable. the accuracies of DEMs have been compared in this The important point is required accuracy, for some applications study. the accuracy should not be precise but for some it should be. For example, if 10m accuracy is enough for your study you For Zonguldak test field, three types of DEMs have can use a DEM generated by remote sensing but if you want been used. First DEM has been produced by digitized 10cm accuracy you should use a DEM obtained by contour lines of 1:25000 scale topographic maps, photogrammetric or geodesic methods. second one has been produced by photogrammetric flight project data had been made by Zonguldak Lots of different DEM generation techniques are being used Municipality in 2005 and last one has been derived presently and they have different accuracies and also used for from Shuttle Radar Topography Mission (SRTM) Xdifferent aims. In this study, principle DEM generation band data which has used single-pass Interferometric techniques have been determined and their accuracies have Synthetic Aperture Radar (InSAR) technique for been analysed. Firstly DEMs have been determined briefly DEM generation. then generation techniques have been realized and the comparison of accuracies have been done. In the study, all these DEMs have been compared one by one based on selected reference. The DEM II. DIGITAL ELEVATION MODELS (DEMs) produced with Photogrammetric method has approximately 5.5m better accuracy for open and flat, 6.5m better accuracy for forest areas against the DEM The term Digital Elevation Model (DEM) comprises the generated from 1:25000 scale topographic maps.process of representing the elevation characteristics of the SRTM X-band DEM is 4m less accurate for open, terrain in discreet form in a three-dimensional space of a 4,5m less accurate for forest areas against the DEM surface. However, most often it is used to refer specifically to a produced with Photogrammetric method and 9.5m raster or regular grid of spot heights. A Digital Terrain Model less accurate for open, tlm less accurate for forest or DTM contains also information about object locations and areas against the DEM generated from 1:25000 scale actually be a more generic term for any digital representation topographic maps. And at the result, it has been of a topographic surface. A DEM is the simplest form of digital clearly seen that the...

Global warming threatens ecosystems through rising temperatures, increasing sea levels, drought, and extreme weather conditions. The natural balance of seas and oceans is also at stake with recent outbreaks of mucilage events all over the world. The mucilage phenomenon, which has been frequently observed in the Adriatic and Tyrrhenian seas, has taken place the second time in the Sea of Marmara in Spring 2021. The Sea of Marmara dividing the Asian and European parts of Turkey is an important inland sea with heavy maritime traffic, hosting many industrial zones and surrounded by highly populated cities. This study aims to determine the mucilage formations that were observed intensely all around the Sea of Marmara, focusing on the coasts of Istanbul, Kocaeli, Yalova, and Bursa through classifying Sentinel-2A images dated 19 and 24 May 2021, when the peak period of mucilage bloom, using a new paradigm of object-based image analysis (OBIA) approach. To create representative and homogenous image objects, multi-resolution segmentation was applied, and its result was inputted into a classification process using Random Forest (RF) classifier to generate thematic maps. The produced results were compared with pixel-based classification and a high correlation was estimated. Objectbased classification was found effective for the determination of mucilage-covered areas (> 90% overall accuracy) for both considered dates. More specifically, areas covered with mucilage aggregates were computed as 56.15 km² and 67.51 km² for 19 May and 24 May 2021, respectively, indicating rapid growth in only 5-day period. The resulting thematic maps revealed that mucilage was heavily distributed in the gulfs of Gemlik and Izmit and along the coasts of Darica, Tuzla and Pendik.