High resolution radargrammetry with COSMO-SkyMed, TerraSAR-X and RADARSAT-2 imagery: development and implementation of an image orientation model for Digital Surface Model generation

Digital 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

Protocollo operativo per la validazione geometrica di immagini satellitari ad alta risoluzione

Nel corso degli ultimi anni, la crescente disponibilità di scene acquisite da satelliti ad alta risoluzione spaziale (come GeoEye-1, WorldView-1 e 2 o Pleiades-1A e 1B) ha aperto nuovi scenari di applicazioni realizzabili a scala medio-piccola, avvicinando così il Telerilevamento alla Fotogrammetria

Protocollo operativo per la validazione geometrica di immagini satellitari ad alta risoluzione

Nel corso degli ultimi anni, la crescente disponibilita\u300 di scene acquisite da satelliti ad alta risoluzione spaziale (come GeoEye-1, WorldView-1 e 2 o Pleiades-1A e 1B) ha aperto nuovi scenari di applicazioni realizzabili a scala medio-piccola, avvicinando cosi\u300 il Telerilevamento alla Fotogrammetria

Matching strategies for DSMs extraction in urban area from High Resolution Satellite Imagery

At 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

High resolution SAR radargrammetry. application with COSMO-SkyMed spotlight imagery

The availability of new high resolution radar spaceborne sensors offers new interesting potentialities for the acquisition of data useful for the generation of Digital Surface Models (DSMs). Two different approaches may be used to generate DSMs from Synthetic Aperture Radar (SAR) data: the interferometric and the radargrammetric one. At present, the importance of the radargrammetric approach is rapidly growing due to the new high resolution imagery (up to 1 m GSD) which can be acquired by COSMO-SkyMed, TerraSAR-X and RADARSAT-2 in Spotlight mode. In this respect, it is well known that the two main steps for DSMs generation from SAR imagery according to the radargrammetric approach are the stereo pair orientation and the image matching. In this paper the topics related to image orientation of SAR stereo pairs in zero-Doppler geometry acquired by COSMO-SkyMed sensor in Spotlight mode are investigated. The defined and implemented model performs a 3D orientation based on two range and two zero-Doppler equations, allowing for the least squares estimation of some calibration parameters, related to satellite position and velocity and to the range measure. The model 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”. Starting from this model, based a on geometric reconstruction, also a tool for the Rational Polynomial Coefficients (RPCs) generations has been implemented. To test the effectiveness of the new model, two stereo pairs, acquired by COSMO-SkyMed in Spotlight mode over the test sites of Mausanne (Southern France) and Merano (Northern Italy), have been orientated varying the number of Ground Control Points (GCPs) and independent Check Points (CPs). The results obtained clearly show that the geometric potentialities of COSMOSkymed SpotLight stereo pairs as regards 3D surface reconstruction is at the level of about 3 meter, even with quite few GCPs

3D mapping potential of COSMO-SkyMed sensor: definition of an image matching strategy

The 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

A radargrammetric orientation model and a RPCs generation tool for COSMO-SkyMed and TerraSAR-X high resolution SAR

The topic investigated in this paper is the stereo imagery orientation with regards to the SAR imagery in zero-Doppler geometry acquired by COSMO-SkyMed and TerraSAR-X in Spotlight mode. A rigorous orientation model, based on geometric reconstruction, had been already implemented in the scientific software SISAR; starting from this model, a tool for the Rational Polynomial Coefficients (RPCs) generation has been developed. The results of the orientation tests, performed using both rigorous and RPCs models, clearly show that the generated RPCs exploit the geometric potentialities of SpotLight stereo pairs as regards 3D surface reconstruction at the same accuracy level (about 3 meters) of the rigorous model