Mattia Crespi

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.

A Procedure for High Resolution Satellite Imagery Quality Assessment

Data products generated from High Resolution Satellite Imagery (HRSI) are routinely evaluated during the so-called in-orbit test period, in order to verify if their quality fits the desired features and, if necessary, to obtain the image correction parameters to be used at the ground processing center. Nevertheless, it is often useful to have tools to evaluate image quality also at the final user level. Image quality is defined by some parameters, such as the radiometric resolution and its accuracy, represented by the noise level, and the geometric resolution and sharpness, described by the Modulation Transfer Function (MTF). This paper proposes a procedure to evaluate these image quality parameters; the procedure was implemented in a suitable software and tested on high resolution imagery acquired by the QuickBird, WorldView-1 and Cartosat-1 satellites.

GPS Near-Real-Time Coseismic Displacements for the Great Tohoku-oki Earthquake

Here, we present the application to the great Tohoku-oki (Japan) earthquake (United States Geological Survey M = 9.0, March 11, 2011, 05:46:24 Coordinated Universal Time) of a novel approach, named Variometric Approach for Displacements Analysis Stand-Alone Engine, able to estimate accurate coseismic displacements and waveforms in real time, in the global reference frame, just using the standard broadcast products (orbits and clocks) and the high-rate (1 Hz or more) carrier phase observations continuously collected by a stand-alone global-positioning-system receiver. We processed separately the data collected at MIZU (Mizusawa, 140 km from the epicenter) and USUD (Usuda, 430 km from the epicenter) International Global Navigation Satellite System Service sites. A total horizontal displacement of about 2.4 m east-southeast was estimated for the MIZU, with a maximum horizontal oscillation amplitude of about 3.4 m along the same direction. Generally, an overall accuracy better than 10 cm for all the components (east, north, and up) and an average accuracy around 5 cm were assessed over an interval shorter than 5 min, with respect to independent solutions obtained with two different scientific software. The threshold of 5-cm accuracy has been recently indicated as sufficient for real-time fault determination for near-field tsunami forecasting for a major earthquake, like the 2011 Tohoku-oki one.

Reference frames for GNSS positioning services: Some problems and proposed solutions

Abstract Positioning services based on GNSS Permanent Networks (PNs) disseminate the reference frame to users; hence the networks must be adjusted by constraining the ITRF coordinates of some permanent stations (PS), with the satellite orbits and clocks constrained to the values published by the International GNSS Service (IGS). Furthermore, the positioning service provider must use analysis methods, conventions and practices fully consistent with IGS standards. In this framework some problems arise. A first one is that long term solutions for the IGS PS coordinates are not always fully consistent with weekly IGS products, requiring an appropriate use of IGS PS weekly solutions. Moreover, the consistence of the reference frame implied by different positioning services must be checked, to avoid discontinuities between neighbouring networks. Clearly, in order to monitor the PS coordinates, the adjustment of a network needs to be performed on a quasi real time continuous (daily or weekly) basis. However, from a practical point of view, a continuous update of the PS coordinates is neither appropriate nor possible and alternative proposals will be presented. Finally, most users of real-time positioning services need coordinates in another reference frame, perhaps a local one or the national one. In this case the real-time service provider must distribute the transformation between the broadcasted frame and the user required reference frame. In this work some possible solutions of the aforementioned problems are presented, based on experiences obtained during data processing and adjustments of the Piemonte and Lombardia (Northern Italy) networks.

A new rigorous model for high-resolution satellite imagery orientation: Application to EROS A and QuickBird

The correct georeferencing of remote sensing imagery is a fundamental task for orthoimages, digital elevation models (DEMs)/digital surface models (DSMs) generation and 3D feature/object extraction. In this article we focus on the georeferencing of pushbroom sensors imagery, in particular single images collected by EROS A and QuickBird satellites, with a rigorous model that is based on the collinearity equations. The model, implemented in the software SISAR (Software per Immagini Satellitari ad Alta Risoluzione), reconstructs the orbital segment during image acquisition through the Keplerian orbital parameters, the sensor attitude, the internal orientation and additional self-calibration parameters. With respect to the estimation procedure, in order to avoid possible instabilities due to high correlations among some parameters leading to design matrix pseudo-singularity, singular value decomposition (SVD) and QR decomposition are used to select the estimable parameters and finally to solve the extended linearized collinearity equations system in the least square (LS) sense. To test the effectiveness of the new model, SISAR results are compared with the rigorous model implemented in the well-known commercial software OrthoEngine 10.0 (PCI Geomatics, ON, Canada). In this article six images are concerned (two from EROS A and four from QuickBird), showing that SISAR performances are at the level of the OrthoEngine ones.

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.

VII Hotine-Marussi Symposium on Mathematical Geodesy: Proceedings of the Symposium in Rome, 6-10 June, 2009

1. Geodetic sensor systems and sensor networks.- 2. Estimation and filtering theory, inverse problems.- 3. Time series analysis and prediction of multi-dimensional signals in geodesy.- 4. Geodetic boundary value problems and cm-geoid computational methods.- 5. Satellite gravity theory.- 6. Earth oriented space techniques and their benefit for Earth system studies.- 7. Theory, implementation and quality assessment of geodetic reference frames.- 8. Temporal variations of deformation and gravity.

GeoEye-1: Analysis of Radiometric and Geometric Capability

The Geoeye-1 satellite, launched in September 2008, is able to acquire imagery in panchromatic mode, with a spatial resolution of 0.41 m at nadir, offering the most powerful way to obtain detailed imagery actually commercially available.

Global and local reference frames

The goal of this review paper is to recall the concept of geodetic reference frame, showing its intrinsic dependence from all the information and choices related to its realization, and to discuss the still alive distinction between “global” and “local” reference frames, considering the unbreakable link between Geodesy and Geophysics. An up-to-date review of the most relevant presently adopted global and local (in this respect, mainly at European and Italian level) reference frames is presented. Finally, some conclusions and still open problems, related to the current research, are outlined.

Open source tool for DSMs generation from high resolution optical satellite imagery: development and testing of an OSSIM plug-in

ABSTRACT The fully automatic generation of digital surface models (DSMs) is still an open research issue. From recent years, computer vision algorithms have been introduced in photogrammetry in order to exploit their capabilities and efficiency in three-dimensional modelling. In this article, a new tool for fully automatic DSMs generation from high resolution satellite optical imagery is presented. In particular, a new iterative approach in order to obtain the quasi-epipolar images from the original stereopairs has been defined and deployed. This approach is implemented in a new Free and Open Source Software (FOSS) named Digital Automatic Terrain Extractor (DATE) developed at the Geodesy and Geomatics Division, University of Rome ‘La Sapienza’, and conceived as an Open Source Software Image Map (OSSIM) plug-in. DATE key features include: the epipolarity achievement in the object space, thanks to the images ground projection (Ground quasi-Epipolar Imagery (GrEI)) and the coarse-to-fine pyramidal scheme adopted; the use of computer vision algorithms in order to improve the processing efficiency and make the DSMs generation process fully automatic; the free and open source aspect of the developed code. The implemented plug-in was validated through two optical datasets, GeoEye-1 and the newest Pléiades-high resolution (HR) imagery, on Trento (Northern Italy) test site. The DSMs, generated on the basis of the metadata rational polynomial coefficients only, without any ground control point, are compared to a reference lidar in areas with different land use/land cover and morphology. The results obtained thanks to the developed workflow are good in terms of statistical parameters (root mean square error around 5 m for GeoEye-1 and around 4 m for Pléiades-HR imagery) and comparable with the results obtained through different software by other authors on the same test site, whereas in terms of efficiency DATE outperforms most of the available commercial software. These first achievements indicate good potential for the developed plug-in, which in a very near future will be also upgraded for synthetic aperture radar and tri-stereo optical imagery processing.