Tropospheric phase delay in interferometric synthetic aperture radar estimated from meteorological model and multispectral imagery

ENVISAT Medium Resolution Imaging Spectrometer Instrument (MERIS) multispectral data and the mesoscale meteorological model MM5 are used to estimate the tropospheric phase delay in synthetic aperture radar (SAR) interferograms. MERIS images acquired simultaneously with ENVISAT Advanced Synthetic Aperture Radar data provide an estimate of the total water vapor content W limited to cloud-free areas based on spectral bands ratio (accuracy 0.17 g cm^(−2) and ground resolution 300 m). Maps of atmospheric delay, 2 km in ground resolution, are simulated from MM5. A priori pertinent cumulus parameterization and planetary boundary layer options of MM5 yield near-equal phase correction efficiency. Atmospheric delay derived from MM5 is merged with available MERIS W product. Estimates of W measured from MERIS and modeled from MM5 are shown to be consistent and unbiased and differ by ~0.2 g cm^(−2) (RMS). We test the approach on data over the Lebanese ranges where active tectonics might contribute to a measurable SAR signal that is obscured by atmospheric effects. Local low-amplitude (1 rad) atmospheric oscillations with a 2.25 km wavelength on the interferograms are recovered from MERIS with an accuracy of 0.44 rad or 0.03 g cm^(−2). MERIS water product overestimates W in the clouds shadow due to mismodeling of multiple scattering and underestimates W on pixels with undetected semitransparent clouds. The proposed atmospheric filter models dynamic atmospheric signal which cannot be recovered by previous filtering techniques which are based on a static atmospheric correction. Analysis of filter efficiency with spatial wavelength shows that ~43% of the atmospheric signal is removed at all wavelengths

Comparison of Harmonic, Geometric and Arithmetic means for change detection in SAR time series

International audienceThe amplitude distribution in a SAR image can present a heavy tail. Indeed, very high-valued outliers can be observed. In this paper, we propose the usage of the Harmonic, Geometric and Arithmetic temporal means for amplitude statistical studies along time. In general, the arithmetic mean is used to compute the mean amplitude of time series. In this study, we will show that comparing the behaviour of the Harmonic, Geometric and Arithmetic means, enables a change detection method along SAR time series

Application des lois de Meijer à l'imagerie RSO (Radar à Synthèse d'Ouverture) : Calcul d'images "multi-vues géométriques"

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Multi-Link SAR interferograms: Enhancement of a wrapped interferometric database

Ground surface deformation can be monitored from time series of SAR interferograms. Conventional approaches to that problem usually require unwrapping of the interferograms that can be limiting due to decorrelation. We present a method producing denoised wrapped phase time series from a set of differential interferograms. The different paths linking two dates are combined to derive the most likely estimate of wrapped phase difference between these dates. The result is called a Multi-Tink SAR (MuLSAR) interferogram and is shown to have better signal-to-noise ratio than conventional interferogram. The technique also enhances the temporal resolution of an interferometric database as a MuLSAR can be computed for pairs of images for which no interferogram could be produced due to decorrelation. It can be used as a pre-processing to wrapped phase time series exploitation methods. The performance of the technique is demonstrated on a real dataset of ENVISAT images

Correction of tropospheric effects in SAR interferometry: a comparison of ERA-Interim, ERA-5 and HRES Global Atmospheric Models

Since the 1970s, Interferometric Synthetic Aperture Radar is commonly used in Earth Sciences to construct high resolution topographic maps or to study surface displacements. The recent launch of new satellites such as Sentinel-1 constellation allows to routinely derive dense deformation maps with millimetre precision thanks to high revisit frequency and wide swath coverage (300 km wide). However, the accuracy of InSAR is still limited by atmospheric noise, as atmospheric delays may lead to subcentimeter biases in measurements. Global Atmospheric Models (GAMs) allow to compute tropospheric delay maps and correct interferograms from atmospheric delays. In the light of the development of these models over the last ten years, where spatio-temporal resolutions became finer and models more accurate, we propose a quantitative comparison of recent GAMs. We first describe how to correct interferograms from atmospheric delays and present three GAMs used in this paper: ERA-5, ERA-Interim and HRES. We then perform a statistical comparison of the performances of atmospheric corrections. We finally discuss the contribution of the enhanced spatio-temporal resolution of ERA-5, the latest global reanalysis from ECMWF, arguing that improving the spatial resolution is key toward better predictions of atmospheric delays in SAR interferometry

Multi-Link SAR interferograms: Enhancement of a wrapped interferometric database

Ground surface deformation can be monitored from time series of SAR interferograms. Conventional approaches to that problem usually require unwrapping of the interferograms that can be limiting due to decorrelation. We present a method producing denoised wrapped phase time series from a set of differential interferograms. The different paths linking two dates are combined to derive the most likely estimate of wrapped phase difference between these dates. The result is called a Multi-Tink SAR (MuLSAR) interferogram and is shown to have better signal-to-noise ratio than conventional interferogram. The technique also enhances the temporal resolution of an interferometric database as a MuLSAR can be computed for pairs of images for which no interferogram could be produced due to decorrelation. It can be used as a pre-processing to wrapped phase time series exploitation methods. The performance of the technique is demonstrated on a real dataset of ENVISAT images

CorPhU: an algorithm based on phase closure for the correction of unwrapping errors in SAR interferometry

International audienceInterferometric Synthetic Aperture Radar is commonly used in Earth Sciences to study surface displacements or construct high resolution topographic maps. Recent satellites such as those of the Sentinel-1 constellation allow to derive dense deformation maps with millimetric precision with high revisit frequency. However, InSAR is still limited by interferometric coherence. Interferometric phase noise resulting from a loss of coherence, due to changes in scattering properties between repeated SAR acquisitions, may lead to unwrapping errors, which then in turn lead to centimetric errors in time series reconstruction. We present an algorithm based on interferometric phase closure to automatically correct unwrapping errors. We describe the algorithm and highlight its performances with two case studies, in Lebanon with Envisat satellite data and in Central Turkey with Sentinel-1 data. The first dataset is particularly affected by unwrapping errors because of long spatial (500 m) and temporal baseline interferograms (6 years) and decorrelation due, in particular, to vegetation. The second dataset contains unwrapping errors because of temporal changes in the scattering properties of the ground. For these two examples, the algorithm allows the correction of almost all detectable unwrapping errors, without requiring visual inspection or manual deletions. Our algorithm is efficient especially on large datasets, such as with Sentinel-1 constellation, where interferometric phase is redundant and improves eventually the reconstruction of time series

Multi-Link InSAR Time Series: Enhancement of a Wrapped Interferometric Database

Ground surface deformation, in particular of tectonic or volcanic origin, might be monitored from time series of SAR interferograms. Conventional approaches require unwrapping of the interferograms. This is most often a limiting factor because the deformation signal is often obscured by decorrelation noise, baseline and topography compensation residuals and atmospheric effects. We present here a method that produces denoised wrapped phase time series. It can be used as a pre-processing to exploit wrapped phase time series or to facilitate unwrapping. The different paths linking two dates are combined in order to derive the most likely estimate of the phase difference between these dates. The result is called a Multi-Link SAR (MuLSAR) interferogram. We demonstrate the performance of the technique on a synthetic database and on a real database of ENVISAT images. The phase standard deviation is reduced from 0.94 rad to 0.60 rad for the synthetic database and from 1.09 rad to 0.89 rad for the real database. In addition to providing denoised interferograms the technique enhances the temporal resolution of an interferometric database as it is possible to compute a MuLSAR from pairs of images for which no interferogram could be produced due to geometric or temporal decorrelation. The method enhances the exploitation of large database especially when affected by temporal decorrelation

Débruitage multi-modal d'images radar à synthèse d'ouverture par apprentissage profond auto-supervisé

International audience-L'observation de la Terre a été largement facilitée depuis de nombreuses années grâce à l'utilisation des satellites imageurs radar à synthèse d'ouverture (SAR), qui offrent des capacités d'imagerie indépendantes des conditions météorologiques. Toutefois, l'interprétation de ces images SAR est complexe en raison de la présence de bruit inhérent à l'imagerie cohérente. En effet, des fluctuations apparaissent dans les images, notamment là où la réflectivité radar est élevée. Ainsi, de nombreuses méthodes ont été développées pour réduire le bruit présent dans ces images, notamment des méthodes neuronales particulièrement efficaces. Dans cet article, nous proposons d'étudier comment l'ajout d'une donnée auxiliaire comme une image optique peut améliorer la restauration de la réflectivité dans ce cadre