G. Büyüksalih

Benchmarking and quality analysis of DEM generated from high and very high resolution optical stereo satellite data

The Working Group 4 of Commission I on “Geometric and Radiometric Modelling of Optical Spaceborne Sensors” will provide on its website several stereo data sets from high and very high resolution spaceborne stereo sensors. Among these are data from the 2.5 meter class like ALOS-PRISM and Cartosat-1 as well as, in near future, data from the highest resolution sensors (0.5 m class) like GeoEye-1 and Worldview-1. The region selected is an area in Catalonia, Spain, including city areas (Terrassa), rural areas and forests in flat and medium undulated terrain as well as steep mountainous terrain. In addition to these data sets, ground truth data like orthoimages from airborne campaigns and Digital Elevation Models (DEM) produced by laser scanning, all data generated by the Institut Cartografic de Catalunya (ICC), are provided as reference for comparison. The goal is to give interested scientists of the ISPRS community the opportunity to test their algorithms on DEM generation, to see how they match with the reference data and to compare their results within the scientific community. A second goal is to develop further methodology for a common DEM quality analysis with qualitative and quantitative measures. Several proposals exist already and the working group is going to publish them on their website. But still there is a need for more standardized methodologies to quantify the quality even in cases where no better reference is available. The data sets, the goal of the benchmarking, the comparison strategy and first very preliminary evaluation results with some data of the selected areas are presented within the paper. The main goal though is to motivate further researchers to join the benchmarking and to discuss pros and cons of the methods as well as to trigger the process of establishing standardized DEM quality figures and procedures.

Semantic analysis of space imagery for mapping purposes

From the area around Zonguldak several space images with different ground sampling distance (GSD) from 30m down to 62cm are available. The semantic information of Landsat images is too poor for the generation of topographic maps, while QuickBird images do allow a mapping in the scale 1:5000. Not only the GSD is determining the possible map scale, also the spectral and radiometric resolution is important. The imaging conditions, especially the sun elevation with the corresponding length of shadows, do lead to quite different results especially in cities with narrow streets. The possibilities and limitations of mapping with the different space images, partially with the same image type taken in different month, has been analysed.

Validation of Sentinel-1A and AW3D30 DSMs for the Metropolitan Area of Istanbul, Turkey

In space-borne remote sensing, one of the most significant tasks is the three-dimensional (3D) surface modelling performance of optical and synthetic aperture radar (SAR) satellite missions. In this study, the quality of Sentinel-1A (S-1A) and Advanced Land Observing Satellite (ALOS) World 3D 30xa0m (AW3D30) Digital Surface Models (DSMs) was comprehensively analysed. In addition, 1xa0arcsec Shuttle Radar Topography Mission (SRTM) C-band DSM was validated for better interpretation of the results. A project area including various land cover classes was selected in Istanbul, where a reference airborne laser scanning DSM is available. Optimal S-1A interferometric wide (IW) swath SAR pairs were determined and a 15xa0m gridded DSM was generated by interferometric processing. AW3D30 and SRTM DSMs were obtained from JAXA and NASA. In the analysis, the absolute and relative vertical accuracies of the DSMs were validated for all land cover classes with a model-to-model comparison to the reference. In addition, the influence of terrain tilt was investigated using a threshold terrain inclination of tan−1u20090.1 (5.7°). Height differences from the reference were visualized by colour-coded height error maps. Vertical profiles and contour lines showed the morphologic character of the DSMs. The results demonstrated that the absolute vertical accuracies and morphologic details of AW3D30 are superior to those of S-1A and SRTM.ZusammenfassungValidierung eines Digitalen Oberflächenmodells von Sentinel-1A und AW3D30 für die Metropolregion Istanbul, Türkei Bei der weltraumgestützten Fernerkundung ist die dreidimensionale (3D) Oberflächenmodellierung aus Daten von Satellitenmissionen mit optischem Aufnahmesystem oder synthetischer Apertur (SAR) eine wichtige Aufgabe. In dieser Studie wurde die Qualität eines digitalen 3D-Oberflächenmodells (DOM) aus Daten des Sentinel-1A (S-1A) und das Advanced Land Observing Satellite (ALOS) World 3D 30xa0m (AW3D30) umfassend analysiert. Darüber hinaus wurde ein 1-Bogensekunden-Shuttle-Radar-Topography-Mission (SRTM) C-Band DSM zur besseren Interpretation der Ergebnisse herangezogen. Als Projektgebiet diente ein Ausschnitt Istanbuls mit verschiedenen Landbedeckungsklassen, in dem ein DOM aus Laserscannerdaten verfügbar war. Optimale S-1A Interferometric Wide (IW) Streifen-SAR-Paare wurden bestimmt, und ein 15xa0m Raster-DOM durch interferometrische Verarbeitung erzeugt. AW3D30- und SRTM-DOM wurden von der JAXA und der NASA bezogen. Die Analyse enthält eine Validierung der absoluten und relativen vertikalen Genauigkeiten der DOM für alle Landbedeckungsklassen, erstellt mit einem Modell-zu-Modell-Vergleich mit der Referenz. Zusätzlich wurde der Einfluss der Geländeneigung mit einem Schwellenwert von tan−1 0.1 (5.7°) untersucht. Höhenunterschiede zur Referenz wurden durch farbcodierte Höhenfehlerkarten visualisiert. Vertikale Profile und Konturlinien zeigten den morphologischen Charakter der DOM. Die Ergebnisse zeigen, dass die absoluten vertikalen Genauigkeiten und morphologischen Details von AW3D30 denjenigen von S-1A und SRTM überlegen sind.