Geometric potential of cartosat-1 stereo imagery

Cartosat-1 satellite, launched by Department of Space (DOS), Government of India, is dedicated to stereo viewing for large scale mapping and terrain modelling applications. This stereo capability fills the limited capacity of very high resolution satellites for three-dimensional point determination and enables the generation of detailed digital elevation models (DEMs) not having gaps in mountainous regions like for example the SRTM height model.The Cartosat-1 sensor offers a resolution of 2.5m GSD in panchromatic mode. One CCD-line sensor camera is looking with a nadir angle of 26' in forward direction, the other 5' aft along the track. The Institute "Area di Geodesia e Geomatica"-Sapienza Università di Roma and the Institute of Photogrammetry and Geoinformation, Leibniz University Hannover participated at the ISPRS-ISRO Cartosat-1 Scientific Assessment Programme (CSAP), in order to investigate the generation of Digital Surface Models (DSMs) from Cartosat-1 stereo scenes. The aim of this work concerns the orientation of Cartosat-1 stereo pairs, using the given RPCs improved by control points and the definition of an innovative model based on geometric reconstruction, that is used also for the RPC extraction utilizing a terrain independent approach. These models are implemented in the scientific software (SISAR-Software per Immagini Satellitari ad Alta Risoluzione) developed at Sapienza Università di Roma. In this paper the SISAR model is applied to different stereo pairs (Castelgandolfo and Rome) and to point out the effectiveness of the new model, SISAR results are compared with the corresponding ones obtained by the software OrthoEngine 10.0 (PCI Geomatica).By the University of Hannover a similar general satellite orientation program has been developed and the good results, achieved by bias corrected sensor oriented RPCs, for the test fields Mausanne (France) and Warsaw (Poland) have been described.For some images, digital height models have been generated by automatic image matching with least squares method, analysed in relation to given reference height models. For the comparison with the reference DEMs the horizontal fit of the height models to each other has been checked by adjustment

SVILUPPO ED IMPLEMENTAZIONE DI UN MODELLO RADARGRAMMETRICO IN UN SOFTWARE SCIENTIFICO: APPLICAZIONE A DATI COSMO-SKYMED

L’utilizzo di immagini satellitari ad alta risoluzione per scopi cartografici è un tema di grande interesse, in quanto esse rappresentano una valida alternativa al rilievo fotogrammetrico per la produzione e l’aggiornamento di prodotti cartografici a media scala, e per la generazione di modelli digitali del terreno (Digital Terrain Model - DTMs) o della superficie (Digital Surface Model - DSMs). I DTMs/DSMs sono di fondamentale importanza per il loro utilizzo in diverse applicazioni, come produzione di ortofoto, change detection, analisi spaziali, visualizzazione dei dati. La generazione di modelli digitali 3D a partire da dati radar, acquisiti da sensori SAR (Synthetic Aperture Radar), si basa principalmente su tecniche interferometriche o radargrammetriche. In questo momento è di crescente interesse l’utilizzo della tecnica radargrammetrica, in seguito al lancio dei satelliti SAR di nuovissima generazione che permettono l’acquisizione di immagini ad alta risoluzione. In particolare la costellazione COSMO-SkyMed è dotata di una tecnologia all’avanguardia e pone l’Italia ai vertici dei sistemi di telerilevamento a livello internazionale grazie alla elevata risoluzione raggiungibile in modalità SpotLight (fino ad 1 m). Nel software scientifico SISAR (Software Immagini Satellitari ad Alta Risoluzione), sviluppato dal gruppo di ricerca dell’Area di Geodesia e Geomatica (DICEA), Università di Roma “La Sapienza”, è stato implementato un modello di orientamento basato sul principio della radargrammetria. La radargrammetria, in modo simile alla fotogrammetria, ricava l’informazione altimetrica per via stereoscopica; il modello di orientamento implementato in SISAR è basato sulle due equazioni fondamentali Range-Doppler (RD), che rappresentano il vincolo di distanza piattaforma-bersaglio e il vincolo di proiezione Zero-Doppler (in cui il bersaglio viene acquisito perpendicolarmente al moto del satellite). Inoltre, sulla base del modello rigoroso radargrammetrico, è stato anche sviluppato un algoritmo di generazione di Rational Polynomial Coefficients (RPCs), che permettono di orientare le immagini SAR secondo il modello a Funzioni Polinomiali Razionali (RPFs) raggiungendo lo stesso livello di accuratezza del modello rigoroso. Il modello sviluppato è stato testato su due stereo coppie acquisite dai satelliti COSMOSkyMed in modalità SpotLight sulle zone di Maussane (Francia) e di Merano (Italia).At present, thanks to the very high resolution and the good radiometric quality of the imagery acquired by very high resolution satellites such as Ikonos, WorldView-1, Geo-Eye-1, it seems possible to generate Digital Surface Models (DSMs) at an accuracy level, which is comparable to the one of DSMs derived from middle scale aerial imagery. As regards SAR sensors, 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) following the radargrammetric approach. 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 COSMOSkyMed 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 orientation model is implemented in the software SISAR (Software Immagini Satellitari ad Alta Risoluzione ), developed at the Geodesy and Geomatic Institute of University of Rome “La Sapienza”. 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. 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 over the test sites of Maussane and Merano in SpotLight mode have been orientated

A radargrammetric model for high resolution SAR imagery

Digital Surface and Terrain Models (DSMs/DTMs) have large relevance in some territorial applications, such as topographic mapping, spatial and temporal change detection, feature extraction and data visualization. DSMs/DTMs extraction from satellite stereo pair offers some advantages, among which low cost, speed of data acquisition and processing, surveys of critical areas, easy monitoring of wide areas, availability of several commercial software and algorithms for data processing. In particular, the DSMs generation from Synthetic Aperture Radar (SAR) imagery offers the significant advantage of possible data acquisition during the night and in presence of clouds. The availability of new high resolution SAR spaceborne sensors as COSMO-SkyMed (Italian), TerraSAR-X (German) and RADARSAT-2 (Canadian) offers new interesting potentialities for the acquisition of data useful for the generation of DSMs following the radargrammetric approach, based at least on a couple of images of the same area acquired from two different points of view as for the standard photogrammetry applied to optical imagery. The aim of this work was the development and the implementation of an original rigorous radargrammetric model for the orientation of SAR imagery, suited for the subsequent DSM generation. The model performs a 3D orientation based on two range and two zero-Doppler equations starting from SAR stereo pairs in slant range and zero-Doppler projection, acquired in SpotLight mode, that is at the highest resolution presently available (1 m ground resolution). The model has been implemented in SISAR (Software per Immagini Satellitari ad Alta Risoluzione), a scientific software developed at Geodesy and Geomatic Institute of the University of Rome “La Sapienza”. This software was at first devoted to the orientation of high resolution optical imagery, and in the last year it has been extended also to SAR imagery. 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 RPCs starting from a rigorous model sounds of particular interest since, at present, the most part of SAR imagery is not supplied with RPCs, although the Rational Polynomial Functions (RPFs) model is available in several commercial software. The RPCs can be an useful tool in place of the rigorous model in processes as the image orthorectification/geocoding or the DSMs generation, since the RPFs model is very simple and fast to be applied. The model implemented has been tested on COSMO-SkyMed and on TerraSAR-X SpotLight imagery, showing that a vertical accuracy at level of better than 3 m is achievable even with quite few Ground Control Points

A radargrammetric orientation model for SAR high resolution imagery

Digital Surface and Terrain Models (DSMs/DTMs) have large relevance in some territorial applications, such as topographic mapping, spatial and temporal change detection, feature extraction and data visualization. DSMs/DTMs extraction from satellite stereo pair offers some advantages, among which low cost, speed of data acquisition and processing, surveys of critical areas, easy monitoring of wide areas, availability of several commercial software and algorithms for data processing. In particular, the DSMs generation from SAR data offers the significant advantage of possible data acquisition during the night and in presence of clouds. The availability of new high resolution SAR spaceborne sensors offers new interesting potentialities for the acquisition of data useful for the generation of DSMs. Two different approaches may be used to generate DSMs from SAR data: the interferometric and the radargrammetric one, both using a couple of images of the same area acquired from two different points of view. The aim of this work is the development and the implementation of a rigorous radargrammetric model for the orientation of SAR imagery, suited to the Digital Surface Model generation. The model performs a 3D orientation based on two range and two zero-Doppler equations; the results presented are related to the orientation of SAR stereo pairs in slant range and zero-Doppler projection, acquired in SpotLight mode (1 m ground resolution). The model has been implemented in SISAR (Software per Immagini Satellitari ad Alta Risoluzione), a scientific software developed at Geodesy and Geomatic Institute of the University of Rome La Sapienza. This software was at first devoted to the orientation of high resolution optical imagery, and in the last year it has been extended also to SAR imagery. 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 RPCs starting from a rigorous model sounds of particular interest since, at present, the most part of SAR imagery is not supplied with RPCs, although the Rational Polynomial Functions (RPFs) model is available in several commercial software. The RPCs can be an useful tool in place of the rigorous model in processes as the image orthorectification/geocoding or as the DSMs generation, since the RPFs model is very simple and fast to be applied. The model implemented has been tested on COSMO-SkyMed and on TerraSAR-X images; both satellites are able to acquire imagery in SpotLight mode. The accuracy evaluation shows that the mean vertical accuracy is at 3.0 - 3.5 m; this preliminary results are satisfying, considering the mean accuracy of the available GPs. An investigation using more accurate GPs, for example GPS points, is recommended, although it has to be underlined that also the uncertainty of the GPs collimation on the images (1-3 pixels) could affect the results. As regards the model performance varying the independent sets of GCPs, the software shows a stable behavior and the increase of GCPs number does not improve the results remarkably. The commercial software OrthoEngine provides basically the same level of accuracy of SISAR, whereas a significant difference between the two software is that OrthoEngine needs 8 GCPs at least for the orientation of SAR images, whereas SISAR gets good results also using few points (3 or 5 GCPs). The application of RPCs model to SAR stereo pairs gives good results, absolutely comparable with those derived through the radargrammetric rigorous model, what proves the effectiveness of the RPCs generation tool implemented in SISAR

A radargrammetric orientation model for digital surface models generation from Synthetic Aperture Radar high resolution imagery: applications with Cosmo-SkyMed and TerraSar-X

Digital Surface and Terrain Models (DSMs/DTMs) have large relevance in some territorial applications, such as topographic mapping, spatial and temporal change detection, feature extraction and data visualization. DSMs/DTMs extraction from satellite stereo pair offers some advantages, among which low cost, speed of data acquisition and processing, surveys of critical areas, easy monitoring of wide areas, availability of several commercial software and algorithms for data processing. In particular, the DSMs generation from Synthetic Aperture Radar (SAR) imagery offers the significant advantage of possible data acquisition during the night and in presence of clouds. The availability of new high resolution SAR spaceborne sensors as COSMO-SkyMed (Italian), TerraSAR-X (German) and RADARSAT-2 (Canadian) offers new interesting potentialities for the acquisition of data useful for the generation of DSMs following the radargrammetric approach, based at least on a couple of images of the same area acquired from two different points of view as for the standard photogrammetry applied to optical imagery. The aim of this work was the development and the implementation of an original rigorous radargrammetric model for the orientation of SAR imagery, suited for the subsequent DSM generation. The model performs a 3D orientation based on two range and two zero-Doppler equations starting from SAR stereo pairs in slant range and zero-Doppler projection, acquired in SpotLight mode, that is at the highest resolution presently available (1 m ground resolution). The model has been implemented in SISAR (Software per Immagini Satellitari ad Alta Risoluzione), a scientific software developed at Geodesy and Geomatic Institute of the University of Rome “La Sapienza”. This software was at first devoted to the orientation of high resolution optical imagery, and in the last year it has been extended also to SAR imagery. 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 RPCs starting from a rigorous model sounds of particular interest since, at present, the most part of SAR imagery is not supplied with RPCs, although the Rational Polynomial Functions (RPFs) model is available in several commercial software. The RPCs can be an useful tool in place of the rigorous model in processes as the image orthorectification/geocoding or the DSMs generation, since the RPFs model is very simple and fast to be applied. The model implemented has been tested on COSMO-SkyMed and on TerraSAR-X SpotLight imagery, showing that a vertical accuracy at level of better than 3 m is achievable even with quite few Ground Control Points