Paola Capaldo

High-Resolution SAR Radargrammetry: A First 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 Ground Sample Distance (GSD)] which can be acquired by COSMO-SkyMed, TerraSAR-X and RADARSAT-2 in SpotLight mode. The defined and implemented model is related to COSMO- SkyMed SpotLight imagery in zero-Doppler geometry; it performs a 3-D 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 on a geometric reconstruction, also a tool for the Rational Polynomial Coefficients (RPCs) generations has been implemented. To test the effectiveness of the new model, a stereo pair over the test sites of Merano (Northern Italy) has been orientated using the rigorous model and the RPCs one, and first results of radargrammetric DSM generation are presented; they display the possibility to reach an overall average accuracy of 3.5 m.

Fast terrain modelling for hydrogeological risk mapping and emergency management: the contribution of high-resolution satellite SAR imagery

Geomatic tools fast terrain modelling play a relevant role in hydrogeological risk mapping and emergency management. Given their complete independence from logistic constraints on the ground (as for airborne data collection), illumination (daylight), and weather (clouds) conditions, synthetic aperture radar (SAR) satellite systems may provide important contributions in terms of digital surface models (DSMs) and digital elevation models (DEMs). For this work we focused on the potential of high-resolution SAR satellite imagery for DSM generation using an interferometric (InSAR) technique and using a revitalized radargrammetric stereomapping approach. The goal of this work was just methodological. Our goal was to illustrate both the fundamental advantages and drawbacks of the radargrammetric approach with respect to the InSAR technique for DSM generation, and to outline their possible joint role in hydrogeological risk mapping and emergency management. Here, it is worth mentioning that radargrammetry procedures are independent of image coherence (unlike the interferometric approach) and phase unwrapping, as well as of parsimony (only a few images are necessary). Therefore, a short time is required for image collection (from tens of minutes to a few hours), thanks to the independence from illumination and weather. The most relevant obstacles of the technique are speckle and the lack of texture impact on image matching, as well as the well-known deformations of SAR imagery (layover and foreshortening), which may produce remarkable difficulties with complex morphologies and that must be accounted for during acquisition planning. Here, we discuss results obtained with InSAR and radargrammetry applied to a COSMO-SkyMed SpotLight triplet (two stereopairs suited for radargrammetry and InSAR, sharing one common image) acquired over suburbs of San Francisco (United States), which are characterized by mixed morphology and land cover. We mainly focused on urban areas and zones covered by bare soil and rocks. Image processing was performed using the well-known commercial software SARscape® for InSAR, and the radargrammetric suite implemented in SISAR, software developed at the Geodesy and Geomatic Division of the University of Rome “La Sapienza”. Global accuracies were approximately 5 m using both approaches. However, several differences in terrain morphology reconstruction were determined and are underlined and evaluated here, as well as a possible way to further enhance the results using the integration of InSAR and radargrammetry.

Digital surface models from ZiYuan-3 triplet: performance evaluation and accuracy assessment

At the beginning of 2012, a new optical satellite, called ZiYuan-3 (ZY-3), was launched from the Taiyuan Satellite Launch Centre. This article is aimed at the analysis and the assessment of the digital surface models (DSMs) and orthophotos from a ZY-3 triplet acquired over the city of Bolzano and the surrounding areas. The imagery processing chain was executed with four different software packages. In all cases the Rational Polynomial Functions (RPFs) orientation model was used, with rational polynomial coefficients (RPCs) supplied by the vendors. The accuracies of the extracted DSMs were compared with the public light detection and ranging (lidar) DSM. The DSM extracted with each software package was used to generate the corresponding orthophoto. The orthophoto accuracy was assessed against 1:5000/1:10000 maps. The results obtained show that ZY-3 imagery allow us to generate DSMs with an accuracy, in terms of root mean square error (RMSE), which can reach 1.5–4.2 m in the flat area, 3.9–6.9 in the urban area, and 5.7–8.2 m in the mountain area. These results are better than Shuttle Radar Topography Mission (SRTM). Regarding orthophoto generation, all software packages supply similar results with a significant bias of about 20 m, mainly caused by vendors’ RPC inaccuracy.

DSM generation from very high optical and radar sensors: Problems and potentialities along the road from the 3D geometric modeling to the Surface Model

The availability of new high resolution optical and radar spaceborne sensors offers new interesting potentialities for the acquisition of data useful for the generation of Digital Surface Models (DSMs).

DSM generation from optical and SAR high resolution satellite imagery: Methodology, problems and potentialities

The actual high resolution optical and Synthetic Aperture Radar (SAR) satellite sensors offer interesting potentialities for Digital Surface Models (DSMs) generation. Both optical and SAR imagery are characterized by proper deformations and noise due to the different acquisition geometries and processes, which have to be duly taken into account during the DSM generation procedure in order to fully exploit the aforementioned potentialities. The aim of this work is to evaluate the performances of high resolution optical and SAR imagery for DSMs generation over the same testfield area where a dense network of GCPs and LiDAR DSM are available as ground truth data. The image processing and DSMs generation are carried out with the packages SISAR (Software Immagini Satellitari ad Alta Risoluzione) and SAT-PP (SATellite image Precision Processing) while an additional comparison is performed using PCI Geomatica 2012.

Monitoring ground displacements at centimeter level exploiting TerraSAR-X range measurements

The goal of this work is to exploit the slant-range measurements reaching centimetre accuracies using only the amplitude information of SAR data acquired by TerraSAR-X satellite sensor. The leading idea is to evaluate the positioning accuracy of well identifiable and stable natural and man-made Persistent Scatterers (PSs) along the SAR line of sight. New Earth observation SAR (Synthetic Aperture Radar) satellite sensors, as COSMO-SkyMed, TerraSAR-X and PAZ, acquire imagery on any point of the Earth with high resolutions, in terms of phase and amplitude value. Thanks to this higher amplitude resolution (up to 0.20 m pixel resolution in the Staring SpotLight mode for TerraSAR-X and PAZ) and to the use of on board dual frequency GPS receivers, which allows to determine the satellite orbit with an accuracy at few centimetres level, the SAR images offer the capability to achieve, in a global reference frame, positioning accuracies in the meter range and even better.

Radargrammetric Digital Surface Models Generation from High Resolution Satellite SAR Imagery: Methodology and Case Studies

The goal of this paper is to investigate the potential of high resolution SAR satellite imagery for DSMs generation using the radargrammetric technique. This study is methodological, devoted to illustrate both the fundamental advantages of this approach and also its drawbacks. As for photogrammetry, the achievable accuracy level of a radargrammetric generated DSM is strictly related both to the image orientation and to the image matching procedure. A rigorous orientation model based only on metadata information and an innovative matching strategy have been developed, so that a complete suite for the DSMs generation through radargrammetry has been embedded in SISAR, a scientific software developed at the Geodesy and Geomatic Division of the University of Rome “La Sapienza”. Here we discuss the results coming from two COSMO-SkyMed SpotLight stereo pairs (ascending and descending) acquired over the area of Como (Northern Italy), characterized by a mixed land cover (flat urban area, steep forested mountain slopes). Three DSMs (ascending, descending and merged) have been generated and compared with a LiDAR DSM; the accuracy of the merged product is around 7 m, better than the accuracy of the ascending and descending DSMs (around 8–10 m).

Radargrammetric Generation of DEMs from High Resolution Satellite SAR Imagery: A New tool for Landslide Hazard and Vulnerability Assessment

Spatial information acquisition and analysis tools play a fundamental role to supplying the information necessary to produce landslide inventories, which represent the foundations for quantifying landslide hazard and vulnerability. In this frame, fundamental data are Digital Surface Models (DSMs) and Digital Elevation Models (DEMs).