Blar i forfatter "Akbari, Vahid"

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    • Added value of multitemporal polarimetric UAVSAR data for permanent scatterers detection 

      Nikaein, Tina; Akbari, Vahid; Arefi, Hossein (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-11-05)
      In the last decades, differential synthetic aperture radar (SAR) interferometric (InSAR) (DInSAR) techniques have been used to estimate the Earth's surface deformation with high resolution. In this paper, we present an approach for increasing the quantity of permanent scattered pixels. These pixels are selected for DInSAR processing based on polarimetric information prepared by new sensors. The ...

    • Assessment of land subsidence using interferometric synthetic aperture radar time series analysis and artificial neural network in a geospatial information system: Case study of Rafsanjan Plain 

      Bagheri, Mohsen; Dehghani, Maryam; Esmaeily, Ali; Akbari, Vahid (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-12-31)
      Land subsidence resulting from groundwater extraction is a widely recurring phenomenon worldwide. To assess land subsidence, traditional methods such as numerical and finite element methods have limitations due to the complex interactions between the different constructor factors of aquifer in each area. We produced a groundwater-induced subsidence map by applying the geological and hydrogeological ...

    • A change detector for polarimetric SAR data based on the relaxed Wishart distribution 

      Akbari, Vahid; Anfinsen, Stian Normann; Doulgeris, Anthony Paul; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-11-12)
      In this paper, we present an unsupervised change detection method for polarimetric synthetic aperture radar (PolSAR) images based on the relaxed Wishart distribution. Most polarimetric change detectors assume the Gaussian-based complex Wishart model for multilook covariance matrices, which is only satisfied for homogeneous areas with fully developed speckle and no texture. Liu et al. recently proposed ...

    • Estimation of atmospheric temperature and humidity profiles from MODIS data and radiosond data using artificial neural network 

      Akbari, Vahid; Amini, Jalal; Saradjian, Mohammad Reza; Motagh, Mahdi (Journal article; Tidsskriftartikkel; Peer reviewed, 2008)
      The aim of this study is to test the quality of the neural network for retrieving the temperature and humidity by comparison with the radiosond values and a linear regression method. Remote sensed images give useful information about the atmosphere. In this article, MODIS data is used to retrieve temperature and humidity profiles of the atmosphere. Two methods of linear regression and artificial ...

    • The Hotelling-Lawley trace statistic for change detection in polarimetric SAR data under the complex Wishart distribution 

      Akbari, Vahid; Anfinsen, Stian Normann; Doulgeris, Anthony Paul; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2014-01-27)
      In this paper we propose a new test statistic for unsupervised changedetectioninpolarimetricsyntheticapertureradar(PolSAR) data. We work with multilook complex (MLC) covariance matrix data, whose underlying model is assumed to be the scaled complex Wishart distribution. We use the complex kind Hotelling-Lawley (HL) trace statistic for measuring the similarity of two covariance matrices. The sampling ...

    • Iceberg detection in open water and sea ice using C-band radar polarimetry 

      Akbari, Vahid; Brekke, Camilla (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-04)
      Icebergs can cause a significant danger for shipping, offshore oil exploration, and undersea or subsea pipelines and production facilities. Synthetic aperture radar (SAR) is very valuable tool of detecting and monitoring icebergs in the often dark and cloud-covered polar regions. Detection of small icebergs floating in nonhomegeous sea clutter environments is a challenging task in remote sensing. ...

    • A K-Wishart Markov random field model for clustering of polarimetric SAR imagery 

      Akbari, Vahid; Moser, Gabriele; Doulgeris, Anthony Paul; Anfinsen, Stian Normann; Eltoft, Torbjørn; Serpico, Sebastian Bruno (Peer reviewed; Bokkapittel; Bok; Book; Chapter, 2011-10-20)
      A clustering method that combines an advanced statistical distribution with spatial contextual information is proposed for multilook polarimetric synthetic aperture radar (PolSAR) data. It is based on a Markov random field (MRF) model that integrates a K-Wishart distribution for the PolSAR data statistics conditioned to each image cluster and a Potts model for the spatial context. Specifically, the ...

    • A K-Wishart Markov random field model for clustering of polarimetric SAR imagery 

      Moser, Gabriele; Akbari, Vahid; Eltoft, Torbjørn; Doulgeris, Anthony Paul; Anfinsen, Stian Normann; Sebastian, Serpico (Conference object; Konferansebidrag, 2011)

    • Land cover changes detection in polarimetric SAR data using algebra, similarity and distance based methods 

      Najafi, Amir; Hasanlou, Hasan; Akbari, Vahid (Journal article; Tidsskriftartikkel, 2017-09-27)
      Monitoring and surveillance changes around the world need powerful methods, so detection, visualization, and assessment of significant changes are essential for planning and management. Incorporating polarimetric SAR images due to interactions between electromagnetic waves and target and because of the high spatial resolution almost one meter can be used to study changes in the Earth's surface. Full ...

    • Monitoring glacier changes using multitemporal multipolarization SAR images 

      Akbari, Vahid; Doulgeris, Anthony Paul; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2014)

    • Multitemporal Analysis of Multipolarization Synthetic Aperture Radar Images for Robust Surface Change Detection 

      Akbari, Vahid (Doctoral thesis; Doktorgradsavhandling, 2013-06-07)
      This thesis addresses two approaches for change detection from multipolarization, multilooked SAR images: a post-classification comparison and a direct change detection. We consider the complete workflow associated with performing post-classification change detection from time series of multipolarization SAR (PolSAR) images acquired with different imaging geometries and polarimetric configurations. ...

    • Multitemporal Sentinel-1 and Sentinel-2 Images for Characterization and Discrimination of Young Forest Stands Under Regeneration in Norway 

      Akbari, Vahid; Solberg, Svein (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-04-15)
      There is a need for mapping of forest areas with young stands under regeneration in Norway, as a basis for conducting tending, or precommercial thinning (PCT), whenever necessary. The main objective of this article is to show the potential of multitemporal Sentinel-1 (S-1) and Sentinel-2 (S-2) data for characterization and detection of forest stands under regeneration. We identify the most powerful ...

    • Non-gaussian clustering of SAR images for glacier change detection 

      Akbari, Vahid; Doulgeris, Anthony Paul; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel, 2010-12)
      Our aim is to use unsupervised, non-Gaussian clustering of Arctic glaciers for post-classification change detection. Firstly, we demonstrate the consistency of non-Gaussian clustering algorithms for Envisat ASAR images by characterizing the expected random error level for different SAR acquisition conditions (such as incidence angle). This allows us to determine whether an observed variation is ...

    • Non-Gaussian Clustering of SAR images for Glacier Change Detection 

      Akbari, Vahid; Eltoft, Torbjørn; Doulgeris, Anthony Paul (Conference object; Konferansebidrag, 2010)

    • Polarimetric SAR Change Detection with the Complex Hotelling-Lawley Trace Statistic 

      Akbari, Vahid; Anfinsen, Stian Normann; Doulgeris, Anthony Paul; Eltoft, Torbjørn; Moser, Gabriele; Serpico, Sebastian Bruno (Journal article; Tidsskriftartikkel; Peer reviewed, 2016-03-15)
      In this paper, we propose a new test statistic for unsupervised change detection in polarimetric radar images. We work with multilook complex covariance matrix data, whose underlying model is assumed to be the scaled complex Wishart distribution. We use the complex-kind Hotelling-Lawley trace statistic for measuring the similarity of two covariance matrices. The distribution of the Hotelling-Lawley ...

    • Quad-Polarimetric SAR for Detection and Characterization of Icebergs 

      Akbari, Vahid; Brekke, Camilla; Doulgeris, Anthony Paul; Storvold, Rune; Sivertsen, Agnar H. (Conference object; Konferansebidrag, 2016)
      This paper evaluates the performance of fully polarimetric SAR data in iceberg detection and characterization. The study aims to explore the potential of RADARSAT-2 SAR data to detect icebergs and growlers in Svalbard that have broken off from the glaciers nearby. To be able to detect iceberg/growlers in a SAR image, a significant contrast between iceberg and background clutter is required. The ...

    • Subaperture analysis of polarimetric SAR data for iceberg detection 

      Akbari, Vahid; Doulgeris, Anthony Paul; Brekke, Camilla (Konferansebidrag; Conference object, 2016-11-03)
      This paper is focused on investigations of the improved detection of icebergs in open water using spectral analysis of polarimetric SAR data. The objectives of this study are to analyze the behavior of ice objects in open water using the sublook cross-correlation magnitude (SCM). It is shown that there is an improvement of iceberg-sea contrast when the SCM is used instead of multilook intensities ...

    • A Textural–Contextual Model for Unsupervised Segmentation of Multipolarization Synthetic Aperture Radar Images 

      Akbari, Vahid; Doulgeris, Anthony Paul; Gabriele, Moser; Eltoft, Torbjørn; Sebastiano, B. Serpico; Anfinsen, Stian Normann (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      This paper proposes a novel unsupervised, non-Gaussian, and contextual segmentation method that combines an advanced statistical distribution with spatial contextual informa-tion for multilook polarimetric synthetic aperture radar (PolSAR)data. This extends on previous studies that have shown the added value of both non-Gaussian modeling and contextual smoothing individually or for intensity channels ...

    • Time Series Investigation of Land Subsidence Using a Weighted Least Squares Adjustment Based on Image Mode Interferometric Data 

      Akbari, Vahid; Motagh, Mahdi; Rajabi, Mohammad Ali; Yahya, Djamour (Conference object; Konferansebidrag, 2010)
      This study presents the weighted least squares method based on Interferometric Synthetic Aperture Radar (InSAR) images to retrieve spatial-temporal evolution of land subsidence in Mashhad Valley, northeast Iran. Using the analysis of a few interferograms covering the 2003-2005 period, Motagh et al (GJI 2006) presented a preliminary analysis of the subsidence in this area. Here we extend this study ...

    • Validation of SAR Iceberg Detection with Ground-Based Radar and GPS Measurements 

      Akbari, Vahid; Lauknes, Tom Rune; Rouyet, Line; Negrel, Jean; Eltoft, Torbjørn (Peer reviewed; Chapter; Bokkapittel, 2018-11-05)
      Calving of icebergs at the tidewater glacier fronts is a component of the mass loss in Polar regions. Studying the regional distribution of icebergs, their volume, motion, and interaction with the environment is of interest. Here, we present the results from a fieldwork campaign conducted in Kongsfjorden, Svalbard in April 2016, where both satellite and ground-based remote sensing instruments were ...