• An Advanced Non-Gaussian Feature Space Method for POL-SAR Image Segmentation 

      Doulgeris, Anthony Paul; Eltoft, Torbjørn (Conference object; Konferansebidrag, 2013)
      This work extends upon our simple feature-based multichannel SAR segmentation method to incorporate highly desirable statistical properties into a computationally simple approach. The desirable properties include Markov random field contextual smoothing and goodness-of-fit testing to automatically obtain the significant number of classes. To achieve this we need to find an explicit class model to ...
    • Analysis of time series of polarimetric sea ice signatures observed in fast ice it the Belgica Bank area 

      Eltoft, Torbjørn; Johansson, Malin; Lohse, Johannes; Ferro-Famil, Laurent (Journal article; Tidsskriftartikkel, 2023-10-20)
      The CIRFA-Cruise 2022 with <i>RV Kronprins Haakon</i> to the north-eastern coast of Greenland in the period April 22nd to May 9th 2022 was organised to perform measurements and make observations which allow for validation of sea ice remote sensing information and forecast products resulting from work in the Centre for Integrated Remote Sensing and Forecasting for Arctic Operations(CIRFA), a Centre ...
    • Aspects of model-based decompositions in radar polarimetry 

      Doulgeris, Anthony Paul; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-11-12)
      In this paper, we further analyse the problem that polarimetric target decomposition methods in general have more physical parameters than equations, making the decomposition under-determined and hence have no unique solution. The common approach to get around this problem is to make certain assumptions, thus fixing one or more parameters, allowing the other free parameters to be solved from the set ...
    • Assessing ocean ensemble drift predictions by comparison with observed oil slicks 

      Martins de Aguiar, Victor Cesar; Röhrs, Johannes; Johansson, Malin; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-05-16)
      Geophysical models are cornerstone pieces in marine forecasting of floating objects and pollution, such as marine surface oil slicks. Trajectory forecasts of oil spills inherit the uncertainties from the underlying geophysical forcing. In this work we compare the forecast capabilities of an ocean ensemble prediction system (EPS) to those from a higher resolution deterministic model on ...
    • Assessment of Polarimetric Variability by Distance Geometry for Enhanced Classification of Oil Slicks Using SAR 

      Marinoni, Andrea; Espeseth, Martine; Gamba, Paolo; Brekke, Camilla; Eltoft, Torbjørn (Peer reviewed; Chapter; Bokkapittel, 2019-11-14)
      In this paper, we introduce a new approach for investigation of polarimetric Synthetic Aperture Radar (PolSAR) images for oil slick analysis. Our method aims at enhancing discrimination of oil types by exploring the polarimetric features that can be produced by processing PolSAR scenes without dimensionality reduction. Taking advantage of a mixture description of the interactions among classes within ...
    • Automatic Selection of Relevant Attributes for Multi-Sensor Remote Sensing Analysis: A Case Study on Sea Ice Classification 

      Khachatrian, Eduard; Chlaily, Saloua; Eltoft, Torbjørn; Dierking, Wolfgang Fritz Otto; Dinessen, Frode; Marinoni, Andrea (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-07-26)
      It is of considerable benefit to combine information obtained from different satellite sensors to achieve advanced and improved characterization of sea ice conditions. However, it is also true that not all the information is relevant. It may be redundant, corrupted, or unnecessary for the given task, hence decreasing the performance of the algorithms. Therefore, it is crucial to select an optimal ...
    • 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 ...
    • Comparison Between Dielectric Inversion Results From Synthetic Aperture Radar Co- and Quad-Polarimetric Data via a Polarimetric Two-Scale Model 

      Quigley, Cornelius; Brekke, Camilla; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-03)
      In this study, we compare the retrieval results for the dielectric properties of verified oil slick, acquired using airborne multifrequency synthetic aperture radar. A polarimetric two-scale model was used to invert the radar imagery by first employing solely the co-polarization channels, and then by employing the co-polarization channels in conjunction with the cross-polarization channels, and ...
    • Comparison of feature based segmentation of full polarimetric SAR satellite sea ice images with manually drawn ice charts 

      Moen, Mari-Ann; Doulgeris, Anthony Paul; Anfinsen, Stian Normann; Renner, Angelika H.H.; Hughes, Nick; Gerland, Sebastian; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      In this paper we investigate the performance of an algorithm for automatic segmentation of full polarimetric, synthetic aperture radar (SAR) sea ice scenes. The algorithm uses statistical and polarimetric properties of the backscattered radar signals to segment the SAR image into a specified number of classes. This number was determined in advance from visual inspection of the SAR image and by ...
    • Comparison of Machine Learning Methods for Predicting Quad-Polarimetric Parameters from Dual-Polarimetric SAR Data 

      Blix, Katalin; Espeseth, Martine; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-17)
      This paper addresses the problem of up-scaling full polarimetric (quad-pol) parameters from small quad-pol synthetic aperture radar (SAR) scenes to large dual-pol scenes, using a sophisticated Machine Learning (ML) method, namely the Gaussian Process Regression (GPR). The approach is to let the GPR model learn the relationships between the dual-pol input data and the quad-pol parameters on a quad-pol ...
    • Cross-Correlation Between Polarization Channels in SAR Imagery Over Oceanographic Features 

      Brekke, Camilla; Jones, Cathleen; Skrunes, Stine; Holt, Benjamin; Espeseth, Martine; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2016-05-11)
      This letter discusses cross-correlation features de- rived from near-coincident RADARSAT-2 quad-polarimetric and RISAT-1 hybrid-polarity (HP) measurements collected during the NOrwegian Radar oil Spill Experiment in 2015 (NORSE2015). We show that the imaginary part of the cross-correlation between RH and RV is an HP parallel to the real part of the cross-correlation between HH and VV earlier ...
    • Data Augmentation for SAR Sea Ice and Water Classification Based on Per-Class Backscatter Variation With Incidence Angle 

      WANG, QIANG; Lohse, Johannes; Doulgeris, Anthony Paul; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-07-03)
      Monitoring sea ice in polar regions is critical for understanding global climate change and supporting marine navigation. Recently, researchers started to utilize machine/deep learning methodologies to automate the separation of sea ice and open water in synthetic aperture radar imagery. However, this requires a large amount of reliably labeled training data. We here propose an augmentation routine ...
    • Deep Semisupervised Teacher–Student Model Based on Label Propagation for Sea Ice Classification 

      Khaleghian, Salman; Ullah, Habib; Kræmer, Thomas; Eltoft, Torbjørn; Marinoni, Andrea (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-10-14)
      In this article, we propose a novelteacher–student-based label propagation deep semisupervised learning (TSLP-SSL) method for sea ice classification based on Sentinel-1 synthetic aperture radar data. For sea ice classification, labeling the data precisely is very time consuming and requires expert knowledge. Our method efficiently learns sea ice characteristics from a limited number of labeled samples ...
    • Evaluation of feature ranking and regression methods for oceanic chlorophyll-a estimation 

      Blix, Katalin; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-03-22)
      This paper evaluates two alternative regression techniques for oceanic chlorophyll-a (Chl-a) content estimation. One of the investigated methodologies is the recently introduced Gaussian process regression (GPR) model. We explore two feature ranking methods derived for the GPR model, namely sensitivity analysis (SA) and automatic relevance determination (ARD). We also investigate a second ...
    • ExtremeEarth meets satellite data from space 

      Hagos, Desta Haileselassie; Kakantousis, Theofilos; Vlassov, Vladimir; Sheikholeslami, Sina; Wang, Tianze; Dowling, Jim; Paris, Claudia; Marinelli, Daniele; Weikmann, Giulio; Bruzzone, Lorenzo; Khaleghian, Salman; Kræmer, Thomas; Eltoft, Torbjørn; Marinoni, Andrea; Pantazi, Despina-Athanasia; Stamoulis, George; Bilidas, Dimitris; Papadakis, George; Mandilaras, George; Koubarakis, Manolis; Troumpoukis, Antonis; Konstantopoulos, Stasinos; Muerth, Markus; Appel, Florian; Fleming, Andrew; Cziferszky, Andreas (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-08-26)
      Bringing together a number of cutting-edge technologies that range from storing extremely large volumes of data all the way to developing scalable machine learning and deep learning algorithms in a distributed manner and having them operate over the same infrastructure poses unprecedented challenges. One of these challenges is the integration of European Space Agency (ESA)’s Thematic Exploitation ...
    • 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 ...
    • Imaging Sea Ice Structure by Remote Sensing Sensors 

      Eltoft, Torbjørn; Doulgeris, Anthony Paul; Brekke, Camilla; Solbø, Stian; Gerland, Sebastian; Hanssen, Alfred (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-06-14)
      This paper will investigate how new developments in remote sensing and sensor technologies can be applied to image the structure of the sea ice surface. Both segmentation of multipolarimetric synthetic aperture radar images and strategies for the analyses of polarimetric SAR data of sea ice are addressed. The analysis is based on a Radarsat 2 PolSAR scene of from the Fram Strait in September ...
    • Improving Chlorophyll-a Estimation from Sentinel-2 (MSI) in the Barents Sea using Machine Learning 

      Asim, Muhammad; Brekke, Camilla; Mahmood, Arif; Eltoft, Torbjørn; Reigstad, Marit (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-04-22)
      This article addresses methodologies for remote sensing of ocean Chlorophyll-a (Chl-a), with emphasis on the Barents Sea. We aim at improving the monitoring capacity by integrating in situ Chl-a observations and optical remote sensing to locally train machine learning (ML) models. For this purpose, in situ measurements of Chl-a ranging from 0.014–10.81 mg/m <sup>3</sup> , collected for the years ...
    • Inferring the Dielectric Properties of Oil Slick from Multifrequency SAR imagery via a Polarimetric Two-Scale Model 

      Quigley, Cornelius; Brekke, Camilla; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel, 2021-04)
      We apply a polarimetric two-scale model to multifrequency synthetic aperture radar imagery of verified oil slicks measured by DLRs F-SAR instrument, which can acquire high spatial resolution and high signal-to-noise data. The purpose, is to determine the permittivity of the scattering surface via an inversion procedure. The ocean surface is modelled as an ensemble of randomly orientated, tilted ...
    • 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 ...