Are Charles Jensen

• Jensen, Are Charles & Austeng, Andreas (2020). Speckle Reduction Using Adaptive Receive-Side Compounding. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. ISSN 0885-3010. doi: 10.1109/TUFFC.2020.3035031. Fulltekst i vitenarkiv Vis sammendrag

  A typical approach to reduce speckle in coherent imaging systems, is to average same-target images with different speckle realizations. We study settings where such realizations come from applying different transducer-array element-weights at reception, referred to here as receive compounding. An effect of such compounding is reduced spatial resolution, causing smearing of point-like image structures, filling of cysts and expansion of hyperechoic regions. In this paper we study how these unwanted effects can be mitigated by combining the compounding with a small, phase-based, adaptive steering of the array at reception. The adaptivity is based on a criterion akin to that of the Capon beamformer; a minimum-output distortionless response. Here, the distortionless part ensures that however we steer, we have a uniform at-focus response. We have applied this adaptive steering in combination with several receive compounding techniques on simulated Field II, phantom and in vivo data. The results show that all the studied compounding techniques respond to this positively in light of the mentioned unwanted effects. The technique based on Thomson’s multitaper method even surpassed the non-compounded equivalent in reproducing the geometry of structures. The speckle reduction, as measured by the change in the pixel mean to standard deviation ratio, is indeed lower, and there are subtle changes in the spatial speckle patterns when applying steering; however, we believe that in most cases the negative effects are tolerable in light of the benefits gained. The suggested approach is intuitive and easily implemented.

• Waldeland, Anders Ueland; Jensen, Are Charles; Gelius, Leiv-J. & Solberg, Anne H Schistad (2018). Convolutional neural networks for automated seismic interpretation. The Leading Edge. ISSN 1070-485X. 37(7), s. 529–537. doi: 10.1190/tle37070529.1. Vis sammendrag

  Deep-learning methods have proved successful recently for solving problems in image analysis and natural language processing. One of these methods, convolutional neural networks (CNNs), is revolutionizing the field of image analysis and pushing the state of the art. CNNs consist of layers of convolutions with trainable filters. The input to the network is the raw image or seismic amplitudes, removing the need for feature/attribute engineering. During the training phase, the filter coefficients are found by iterative optimization. The network thereby learns how to compute good attributes to solve the given classification task. However, CNNs require large amounts of training data and must be carefully designed and trained to perform well. We look into the intuition behind this method and discuss considerations that must be made in order to make the method reliable. In particular, we discuss how deep learning can be used for automated seismic interpretation. As an example, we show how a CNN can be used for automatic interpretation of salt bodies.

• Austeng, Andreas; Hansen, Roy Edgar & Jensen, Are Charles (2016). Micro-steered multilooking in synthetic aperture sonar imaging. Electronic proceedings (EUSAR). ISSN 2197-4403. 2016, s. 1–5.
• Loog, Marco & Jensen, Are Charles (2015). Semi-supervised nearest mean classification through a constrained log-likelihood. IEEE Transactions on Neural Networks and Learning Systems. ISSN 2162-237X. 26(5), s. 995–1006. doi: 10.1109/TNNLS.2014.2329567.
• Jensen, Are Charles & Austeng, Andreas (2014). The iterative adaptive approach in medical ultrasound imaging. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. ISSN 0885-3010. 61(10), s. 1688–1697 . doi: 10.1109/TUFFC.2014.006478.
• Austeng, Andreas; Jensen, Are Charles; Nilsen, Carl-Inge Colombo; Callow, Hayden John & Hansen, Roy Edgar (2012). Use of the Minimum Variance Beamformer in SAS Imaging, 11th European Conference on Underwater Acoustics 2012 (ECUA 2012). Curran Associates, Inc.. ISSN 978-1-62276-192-0. s. 1908–1915. doi: 10.1121/1.4828823.
• Jensen, Are Charles; Näsholm, Sven Peter; Nilsen, Carl-Inge Colombo; Austeng, Andreas & Holm, Sverre (2012). Applying Thomson's Multitaper Approach to Reduce Speckle in Medical Ultrasound Imaging. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. ISSN 0885-3010. 59(10), s. 2178–2185. doi: 10.1109/TUFFC.2012.2444. Vis sammendrag

  To reduce the variance of speckle in coherent imaging systems, one must average images with different speckle realizations. Traditionally, these images have been formed by observing the target region from slightly different angles (spatial compounding) or by varying the involved temporal frequencies (frequency compounding). In this paper, we investigate a third option based on Thomson's multitaper approach to power spectrum estimation. The tapers are applied spatially, as array weights. Our investigations, based on both recorded ultrasound data and simulations, verify that the multitaper approach can be used for speckle reduction at a rate comparable to that of the more traditional method of spatial compounding. Because of the spectral concentration of the tapers, an added benefit is reduced side lobe levels, which can result in steeper edges and better definition of cyst-like structures.

• Jensen, Are Charles & Austeng, Andreas (2012). An Approach to Multibeam Covariance Matrices for Adaptive Beamforming in Ultrasonography. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. ISSN 0885-3010. 59(6), s. 1139–1148. doi: 10.1109/TUFFC.2012.2304. Vis sammendrag

  Abstract—Medical ultrasound imaging systems are often based on transmitting, and recording the backscatter from, a series of focused broadband beams with overlapping coverage areas. When applying adaptive beamforming, a separate array covariance matrix for each image sample is usually formed. The data used to estimate any one of these covariance matrices is often limited to the recorded backscatter from a single transmitted beam, or that of some adjacent beams through additional focusing at reception. We propose to form, for each radial distance, a single covariance matrix covering all of the beams. The covariance matrix is estimated by combining the array samples after a sequenced time delay and phase shift. The time delay is identical to that performed in conventional delay-and-sum beamforming. The performance of the proposed approach in conjunction with the Capon beamformer is studied on both simulated data of scenes consisting of point targets and recorded ultrasound phantom data from a specially adapted commercial scanner. The results show that the proposed approach is more capable of resolving point targets and gives better defined cyst-like structures in speckle images compared with the conventional delay-and-sum approach. Furthermore, it shows both an increased robustness to noise and an increased ability to resolve point-like targets compared with the more traditional per-beam Capon beamformer.

• Solberg, Anne H Schistad; Jensen, Are Charles & Gelius, Leiv-J. (2012). Robust 2D Hilbert Atributes of Local Amplitude and Phase. I EAGE, 2012 (Red.), 74th EAGE Conference & Exhibition incorporating SPE EUROPEC 2012. European Association of Geoscientists and Engineers (EAGE). ISSN 978-90-73834-27-9. Vis sammendrag

  Instantaneous amplitude and phase are based on the 1D Hilbert transform of seismic traces. We present alternative attributes with improved localization properties by applying a combination of orientationadaptive Hilbert transforms and bandpass filtering. The concept of local amplitude and phase are first explained for the 1D case, before extensions to 2D are given. In the 2D case, the process consists conceptually of two steps: First, the dominant local orientation is estimated, and then the local amplitude and phase are estimated along that orientation. The proposed attributes are compared to the classical instantaneous attributes both for a thin-bed resolution image with a classical wedge model, and for a seismic data set. They show better localization properties for the thin-bed wedge model, and a higher robustness and lateral continuity on the real seismic data.

• Näsholm, Sven Peter; Austeng, Andreas; Jensen, Are Charles; Nilsen, Carl-Inge Colombo & Holm, Sverre (2012). Capon Beamforming Applied to Second-Harmonic Ultrasound Experimental Data. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. s. 2217–2220. doi: 10.1109/ULTSYM.2011.0550. Vis sammendrag

  This paper presents the novelty of adaptive Capon beamforming on received experimental second-harmonic pulse-echo ultrasound imaging channel-data. IQ channel datasets were collected when imaging a tissue-mimicking phantom: two with the transmit frequency 1.7 MHz and the receive band-pass filters centered around 1.7 and 3.4 MHz respectively, as well as one with both the transmit and receive center frequencies being 3.4 MHz. Images are displayed and analyzed for all datasets both using Capon and conventional delay-and-sum beamforming. This work proves the feasibility of Capon beamforming applied to tissue-harmonic imaging.

• Jensen, Are Charles; Nilsen, Carl-Inge Colombo; Austeng, Andreas; Näsholm, Sven Peter & Holm, Sverre (2012). A Multitaper Approach to Speckle Reduction for Medical Ultrasound Imaging. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. s. 397–400. doi: 10.1109/ULTSYM.2011.0095. Vis sammendrag

  A typical approach to reduce unwanted speckle patterns in coherent imaging systems is to average images with different speckle realizations. Traditionally, these images have been formed by observing the target region from slightly different angles (spatial compounding) or by varying the involved frequencies (frequency compounding). In this paper we investigate a third option based on Thomson's multitaper approach to power spectrum estimation applied in the spatial domain. Our investigations, based on both real, measured ultrasound data and data from simulated scenes of point scatterers, verify that the multitaper approach can be used for speckle reduction at a rate compared to that of the more traditional method of spatial compounding. Due to the spectral concentration of the tapers, an added benefit is reduced sidelobe levels, which can yield sharper edges and more defined cyst-like structures.

• Austeng, Andreas; Nilsen, Carl-Inge Colombo; Jensen, Are Charles; Näsholm, Sven Peter & Holm, Sverre (2012). Coherent Plane-Wave Compounding and Minimum Variance Beamforming. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. s. 2448–2451. doi: 10.1109/ULTSYM.2011.0608. Vis sammendrag

  Achieving increased frame rate without compromising the image quality is desirable in medical ultrasound imaging. Coherent plane-wave compounding has recently been suggested as an approach to achieve this. This work proposes to generate coherent compound plane-wave images using a minimum variance adaptive beamformer. Through simulations of point scatterers and cyst phantoms, a threefold increase in frame rate is shown.

• Loog, Marco & Jensen, Are Charles (2012). Constrained Log-Likelihood-Based Semi-supervised Linear Discriminant Analysis. I Gimel'farb, Georgy; Hancock, Edwin; Imiya, Atsushi; Kuijper, Arjan; Kudo, Mineichi; Omachi, Shinichiro; Windeatt, Terry & Yamada, Keiji (Red.), Structural, Syntactic, and Statistical Pattern Recognition. Joint IAPR International Workshop, SSPR&SPR 2012, Hiroshima, Japan, November 7-9, 2012. Proceedings. Springer. ISSN 978-3-642-34165-6. s. 327–335. doi: 10.1007/978-3-642-34166-3_36.
• Jensen, Are Charles & Loog, Marco (2011). Forming different-complexity covariance-model subspaces through piecewise-constant spectra for hyperspectral image classification. I Heyden, Anders & Kahl, Fredrik (Red.), Image Analysis; 17th Scandinavian Conference, SCIA 2011, Ystad, Sweden, May 2011. Proceedings. Springer. ISSN 9783642212260. s. 186–195. doi: 10.1007/978-3-642-21227-7_18.
• Austeng, Andreas; Jensen, Are Fritz Charles; Synnevåg, Johan-Fredrik & Holm, Sverre (2010). Image Amplitude Estimation with the Minimum Variance Beamformer. IEEE International Ultrasonics Symposium Proceedings. ISSN 1051-0117.
• Jensen, Are Fritz Charles; Loog, Marco & Solberg, Anne H S (2010). Using Multiscale Spectra in Regularizing Covariance Matrices for Hyperspectral Image Classification. IEEE Transactions on Geoscience and Remote Sensing. ISSN 0196-2892. 48(4), s. 1851–1859. doi: 10.1109/TGRS.2009.2036842.
• Jensen, Are Fritz Charles; Berge, Asbjørn & Solberg, Anne H S (2008). Regression Approaches to Small Sample Inverse Covariance Matrix Estimation for Hyperspectral Image Classification. IEEE Transactions on Geoscience and Remote Sensing. ISSN 0196-2892. 46(10), s. 2814–2822. doi: 10.1109/TGRS.2008.2001169.
• Solberg, Anne H S; Berge, Asbjørn & Jensen, Are Fritz Charles (2007). Robust classification of hyperspectral images. I Bruzzone, Lorenzo (Red.), Image and Signal Processing for Remote Sensing XIII. SPIE - The International Society for Optics and Photonics. ISSN 9780819469069.
• Jensen, Are Fritz Charles & Solberg, Anne H S (2007). Fast Hyperspectral Feature Reduction Using Piecewise Constant Function Approximations. IEEE Geoscience and Remote Sensing Letters. ISSN 1545-598X. 4(4), s. 547–551. doi: 10.1109/LGRS.2007.896331.
• Berge, Asbjørn; Jensen, Are Fritz Charles & Solberg, Anne H S (2007). Sparse inverse covariance estimates for hyperspectral image classification. IEEE Transactions on Geoscience and Remote Sensing. ISSN 0196-2892. 45. doi: 10.1109/TGRS.2007.892598.

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• Salberg, Arnt-Børre; Liu, Izzie Yi; Jensen, Are Charles; Reksten, Jarle Hamar; Garrett, Joseph Landon & Sample, James Edward [Vis alle 8 forfattere av denne artikkelen] (2023). SeaBee - Norwegian Infrastructure for Drone-based Research, Mapping and Monitoring in the Coastal Zone.
• Jensen, Are Charles (2023). Anecdotes on leveraging SSL in bi-temporal aerial image analysis.
• Jensen, Are Charles (2022). Automatic building-change detection in aerial images.
• Jensen, Are Charles (2022). Self-supervised inspired score values for building-change detection.
• Solberg, Anne H Schistad; Gelius, Leiv-J.; Jensen, Are Charles & Heeremans, Michel (2012). Phase attributes by considering local 3D structure orientation.
• Austeng, Andreas; Jensen, Are Fritz Charles; jetlund, safiye; Hansen, Roy Edgar & Holm, Sverre (2010). Adaptive beamforming in active sonar imaging.
• Jensen, Are Fritz Charles; Berge, Asbjørn & Solberg, Anne H S (2007). Regression Approaches to Small Sample Inverse Covariance Matrix Estimation for Hyperspectral Image Classification.
• Jensen, Are Fritz Charles (2009). Some Approaches to Covariance Regularization and Dimensionality Reduction in Statistical Classification of Hyperspectral Image Data. Unipub forlag. ISSN 1501-7710.

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