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HIGH RESOLUTION RADARGRAMMETRY WITH COSMO-SKYMED, TERRASAR-X AND RADARSAT-2 IMAGERY: DEVELOPMENT AND IMPLEMENTATIONOF AN IMAGE ORIENTATION MODEL FOR DIGITAL SURFACE MODEL GENERATION
Get PDFDigital Surface and Terrain Models (DSM/DTM) have large relevance in several territorial applications, such as topographic mapping, monitoring engineering, geology, security, land planning and management of Earth's resources. The satellite remote sensing data offer the opportunity to have continuous observation of Earth's surface for territorial application, with short acquisition and revisit times. Meeting these requirements, the SAR (Synthetic Aperture Radar) high resolution satellite imagery could offer night-and-day and all-weather functionality (clouds, haze and rain penetration). Two different methods may be used in order to generate DSMs from SAR data: the interferometric and the radargrammetric approaches. The radargrammetry uses only the intensity information of the SAR images and reconstructs the 3D information starting from a couple of images similarly to photogrammetry. Radargrammetric DSM extraction procedure consists of two basic steps: the stereo pair orientation and the image matching for the automatic detection of homologous points.
The goal of this work is the definition and the implementation of a geometric model in order to orientate SAR imagery in zero Doppler geometry.
The radargrammetric model implemented in SISAR (Software per Immagini Satellitari ad Alta Risoluzione - developed at the Geodesy and Geomatic Division - University of Rome "La Sapienza") is based on the equation of radar target acquisition and zero Doppler focalization
Moreover a tool for the SAR Rational Polynomial Coefficients (RPCs) generation has been implemented in SISAR software, similarly to the one already developed for the optical sensors. The possibility to generate SAR RPCs starting from a radargrammetric model sounds of particular interest since, at present, the most part of SAR imagery is not supplied with RPCs, although the RPFs model is available in several commercial software. Only RADARSAT-2 data are supplied with vendors RPCs.
To test the effectiveness of the implemented RPCs generation tool and the SISAR radargrammetric orientation model the reference results were computed: the stereo pairs were orientated with the two model.
The tests were carried out on several test site using COSMO-SkyMed, TerraSAR-X and RADARSAT-2 data.
Moreover, to evaluate the advantages and the different accuracy between the orientation models computed without GCPs and the orientation model with GCPs a Monte Carlo test was computed.
At last, to define the real effectiveness of radargrammetric technique for DSM extraction and to compare the radrgrammetric tool implemented in a commercial software PCI-Geomatica v. 2012 and SISAR software, the images acquired on Beauport test site were used for DSM extraction. It is important underline that several test were computed. Part of this tests were carried out under the supervision of Prof. Thierry Toutin at CCRS (Canada Centre of Remote Sensing) where the PCI-Geomatica orientation model was developed, in order to check the better parameters solution to extract radargrammetric DSMs.
In conclusion, the results obtained are representative of the geometric potentialities of SAR stereo pairs as regards 3D surface reconstruction
Verifica e validazione di un nuovo software per le trasformazioni di datum planimetrici in ambito nazionale
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
3D mapping potential of COSMO-SkyMed sensor: definition of an image matching strategy
No full textThe topic of this paper is the presentation of an image matching technique suited to generate Digital Surface Models (DSMs) following a radargrammetric approach applied to SpotLight Synthetic Aperture Radar (SAR) stereo pairs collected by the new high amplitude resolution radar sensors COSMO-SkyMed (Italian) and TerraSAR-X (German). At present, thanks to this kind of imagery (GSD up to 1 m), the traditional radargrammetric stereo-mapping approach is likely to become a serious alternative to interferometry for the Digital Surface Models (DSMs) generation from Synthetic Aperture Radar (SAR) imagery. Nonetheless, DSMs accuracy level is strictly related to image orientation and matching strategy. A crucial issue is the definition of an image matching strategy to perform 3D surface reconstruction. Generally we can distinguish two classic techniques to carry out the matching process, the Area Base Matching (ABM) and the Feature Base Matching (FBM): these techniques do not appear suited to manage the strong geometrical deformation and the complex and noisy radiometry of SAR imagery, if separately used. Therefore, here we propose an advanced matching method based on a coarse-to-fine hierarchical solution with an effective combination of geometrical constrains and an Area Base Matching (ABM) algorithm. The suite for radargrammetric approach has been implemented in SISAR (Software per Immagini Satellitari ad Alta Risoluzione), a scientific software developed at the Geodesy and Geomatic Institute of the University of Rome “La Sapienza”. In order to investigate the 3D mapping potential of SpotLight imagery, the implemented radargrammetric tool was ap-plied to a COSMO-SkyMed stereo pair acquired over the area of Merano (Northern Italy), where a quite good LiDAR Digital Elevation Model is available as ground truth. The results are quite en-couraging, with an accuracy of about 2 meters over open areas and a quite dense points cloud even over forested areas, where it is possible to estimate the average canopy height with a mean error of about 4 meters
Fast terrain modeling for hydrogeological risk mapping and emergency management: the contribution of high resolution satellite SAR imagery
No full textGeomatic tools for fast terrain modelling play a relevant role both for hydrogeological risk mapping and for hydrogeological emergency management. Among these tools, Synthetic Aperture Radar (SAR) satellite systems may give important contributions in terms of Digital Surface Models (DSMs) and Digital Elevation Models (DEMs), considering their complete independence from logistic constraints on the ground (as for airborne data collection), illumination (daylight) and weather (clouds) conditions. Here we focus on the present potentialities of high resolution SAR satellite imagery for DSMs generation with the radargrammetric stereo-mapping approach and with the well-known interferometric technique. Therefore, the goal of this paper is just methodological, devoted to illustrate both the fundamental advantages of radargrammetric approach and also its drawbacks respect to the InSAR technique. As regards the pros, it is worth to mention the independence from image coherence (unlike interferometric approach), the parsimony (it can work with just a couple of images), and therefore the short time required for imagery collection (from tens of minutes to few hours) also thanks to the mentioned independence from illumination and weather. Concerning the cons, the well known deformations of SAR imagery (layover and foreshortening) may cause remarkable difficulties with complex morphologies and have to be duly accounted for the acquisition planning. A suite for the DSMs generation through the radargrammetric approach has been implemented in SISAR (Software per Immagini Satellitari ad Alta Risoluzione), a scientific software developed at the Geodesy and Geomatic Division of the University of Rome La Sapienza. In order to demonstrate the radargrammetric mapping potentialities of high resolution SAR satellite imagery, several tests were carried out using data with different features (SpotLight, StripMap) coming from different platforms (COSMO-SkyMed, TerraSAR-X). Here we discuss the results obtained with a COSMO-SkyMed SpotLight stereo-pairs related to the San Francisco area, which is characterized by mixed morphology and land cover; we mainly focused on urban areas and zones covered by bare soil and rocks. Overall, accuracies range from 3 m over bare soil to about 4 m over more complex morphology, whereas they decrease in presence of remarkable image deformations
Matching strategies for DSMs extraction in urban area from High Resolution Satellite Imagery
No full textAt present, thanks to the very high resolution and the good radiometric quality of the imagery ac-quired by very high resolution satellites such as Ikonos, WorldView-1, GeoEye-1, it seems possible to generate Digital Surface Models (DSMs) at a 2-3 meter accuracy level, which are comparable to the one of DSMs derived from middle scale aerial imagery. Nonetheless, DSMs accuracy level is strictly related to image orientation and matching strategy.
Recently a facility for the image matching has been included in the SISAR package developed at Geodesy and Geomatic Area - University of Rome “La Sapienza”; SISAR is a scientific software able to carry out the image orientation with different models for several (very) high resolution sen-sors and to generate the RPCs based on its own physical models.
The new SISAR image matching algorithm is based on affine transformations which drive the Fea-ture Based Matching and the Area Based Matching; several affine transformations are used at dif-ferent heights, estimated starting from some ground points at corresponding heights whose image coordinates are computed from suitably generated RPCs. In such way the image matching has been combined with image orientation in order to increase the accuracy and the reliability of DSMs in urban area.
In order to assess the accuracy of the algorithm some tests were carried out, using a stereo pair of Augusta coastal zone (Siracusa, Sicily) acquired from WorldView-1 and a stereo pair acquired by GeoEye-1 over Rome; as reference data, a DSM obtained from LiDAR surveys and a 3D vector cartography at 1:2000 scale have been employed respectivel
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