Torbjørn Skauli

• Skauli, Torbjørn (2017). Feasibility of a standard for full specification of spectral imager performance. Proceedings of SPIE, the International Society for Optical Engineering.  ISSN 0277-786X.  10213, s 102130H-1- 102130H-12 . doi: 10.1117/12.2262785
• Torkildsen, Hans Erling; Haavardsholm, Trym Vegard; Opsahl, Thomas Olsvik; Datta, Urmila; Skaugen, Atle & Skauli, Torbjørn (2016). Compact multispectral multi-camera imaging system for small UAVs. Proceedings of SPIE, the International Society for Optical Engineering.  ISSN 0277-786X.  9840 . doi: 10.1117/12.2224495
• Rousset-Rouviere, Laurent; Coudrain, Christophe; Fabre, Sophie; Poutier, Laurent; Løke, Trond; Fridman, Andrei; Blaaberg, Søren; Baarstard, Ivar; Skauli, Torbjørn & Mocoeur, Isabelle (2014). SYSIPHE system: A state of the art airborne hyperspectral imaging system. Initial results from the first airborne campaign. Proceedings of SPIE, the International Society for Optical Engineering.  ISSN 0277-786X.  9249 . doi: 10.1117/12.2066643
• Skauli, Torbjørn; Torkildsen, Hans Erling; Nicolas, Stephane; Opsahl, Thomas Olsvik; Haavardsholm, Trym Vegard; Kåsen, Ingebjørg & Rognmo, Atle (2014). Compact camera for multispectral and conventional imaging based on patterned filters. Applied Optics.  ISSN 1559-128X.  (13), s C64- C71 . doi: 10.1364/AO.53.000C64
• Torkildsen, Hans Erling; Hovland, Harald; Opsahl, Thomas Olsvik; Haavardsholm, Trym Vegard; Nicolas, Stephane & Skauli, Torbjørn (2014). Characterization of a compact 6-band multifunctional camera based on patterned spectral filters in the focal plane. Proceedings of SPIE, the International Society for Optical Engineering.  ISSN 0277-786X.  9088 . doi: 10.1117/12.2054477
• Catrysse, Peter B. & Skauli, Torbjørn (2013). Pixel scaling in infrared focal plane arrays. Applied Optics.  ISSN 0003-6935.  52(7), s C72- C77 . doi: 10.1364/AO.52.000C72
• Skauli, Torbjørn (2013). Information capacity as a figure of merit for spectral imagers: the trade-off between resolution and coregistration. Applied Optics.  ISSN 0003-6935.  52(7), s C58- C63 . doi: 10.1364/AO.52.000C58
• Yu, Xiaofang; Skauli, Torbjørn; Skauli, Bjørn; Sandhu, Sunil; Catrysse, Peter B. & Fan, Shanhui (2013). Wireless power transfer in the presence of metallic plates: Experimental results. AIP Advances.  ISSN 2158-3226.  3(6) . doi: 10.1063/1.4809665
• Yu, Zongfu; Sergeant, Nicholas P.; Skauli, Torbjørn; Zhang, Gang; Wang, Hailiang & Fan, Shanhui (2013). Enhancing far-field thermal emission with thermal extraction. Nature Communications.  ISSN 2041-1723.  4 . doi: 10.1038/ncomms2765
• Skauli, Torbjørn (2012). An upper-bound metric for characterizing spectral and spatial coregistration errors in spectral imaging. Optics Express.  ISSN 1094-4087.  20(2), s 918- 933 . doi: 10.1364/OE.20.000918
• Hernandez-Palacios, Julio; Randeberg, Lise Lyngsnes; Haug, Ingvild; Baarstad, I.; Løke, T. & Skauli, Torbjørn (2011). Low-light hyperspectral imager for characterization of biological samples based on an sCMOS image sensor, In Ramesh Raghavachari & Rongguang Liang (ed.),  Design and Quality for Biomedical Technologies IV.  SPIE - International Society for Optical Engineering.  ISBN 9780819484284.  78910V.  s 78910V-1 - 78910V-10
• Skauli, Torbjørn (2011). Quantifying coregistration errors in spectral imaging. Proceedings of SPIE, the International Society for Optical Engineering.  ISSN 0277-786X.  8158 . doi: 10.1117/12.894699
• Skauli, Torbjørn (2011). Sensor noise informed representation of hyperspectral data, with benefits for image storage and processing. Optics Express.  ISSN 1094-4087.  19(14), s 13031- 13046 . doi: 10.1364/OE.19.013031 Vis sammendrag

  Many types of hyperspectral image processing can benefit from knowledge of noise levels in the data, which can be derived from sensor physics. Surprisingly, such information is rarely provided or exploited. Usually, the image data are represented as radiance values, but this representation can lead to suboptimal results, for example in spectral difference metrics. Also, radiance data do not provide an appropriate baseline for calculation of image compression ratios. This paper defines two alternative representations of hyperspectral image data, aiming to make sensor noise accessible to image processing. A "corrected raw data" representation is proportional to the photoelectron count and can be processed like radiance data, while also offering simpler estimation of noise and somewhat more compact storage. A variance-stabilized representation is obtained by square-root transformation of the photodetector signal to make the noise signal-independent and constant across all bands while also reducing data volume by almost a factor 2. Then the data size is comparable to the fundamental information capacity of the sensor, giving a more appropriate measure of uncompressed data size. It is noted that the variance-stabilized representation has parallels in other fields of imaging. The alternative data representations provide an opportunity to reformulate hyperspectral processing algorithms to take actual sensor noise into account. (C) 2011 Optical Society of America

• Hernandez-Palacios, Julio; Randeberg, Lise Lyngsnes; Baarstad, Ivar; Løke, Trond & Skauli, Torbjørn (2010). Hyperspectral low-light camera for imaging of biological samples, In Bin Luo, (ed.),  Hyperspectral Image and Signal Processing: Evolution in Remote Sensing (WHISPERS), 2010 2nd Workshop on.  IEEE Press.  ISBN 978-1-4244-8906-0.  x.  s 1 - 4
• Skauli, Torbjørn; Haavardsholm, Trym Vegard; Kåsen, Ingebjørg; Arisholm, Gunnar; Kavara, Amela; Opsahl, Thomas Olsvik & Skaugen, Atle (2010). An airborne real-time hyperspectral target detection system. Proceedings of SPIE, the International Society for Optical Engineering.  ISSN 0277-786X.  7695 . doi: 10.1117/12.850443 Vis sammendrag

  An airborne system for hyperspectral target detection is described. The main sensor is a HySpex pushbroom hyperspectral imager for the visible and near-infrared spectral range with 1600 pixels across track, supplemented by a panchromatic line imager. An optional third sensor can be added, either a SWIR hyperspectral camera or a thermal camera. In real time, the system performs radiometric calibration and georeferencing of the images, followed by image processing for target detection and visualization. The current version of the system implements only spectral anomaly detection, based on normal mixture models. Image processing runs on a PC with a multicore Intel processor and an Nvidia graphics processing unit (GPU). The processing runs in a software framework optimized for large sustained data rates. The platform is a Cessna 172 aircraft based close to FFI, modified with a camera port in the floor.

• Skauli, Torbjørn (2009). Sensor-informed representation of hyperspectral images. Proceedings of SPIE, the International Society for Optical Engineering.  ISSN 0277-786X.  7334 . doi: 10.1117/12.819491 Vis sammendrag

  Hyperspectral images are customarily stored and transferred as radiance values. Image analysis may benefit from additional sensor-related information such as signal-dependent noise levels. This paper discusses representations of hyperspectral image data in forms which are intermediate between raw data and radiance data. The intermediate-form data can be processed directly, or they can be readily converted into radiance values and estimates of signal-dependent noise. The metadata needed for this data transformation constitutes an informative first-order description of the sensor, as an added benefit for the data user. One of the proposed data formats has already been adopted in commercial hyperspectral sensors. The proposed representations can be stored in a more compact data format than radiance values without loss of information, under reasonable assumptions about the sensor properties. In particular, it will be shown that a square-root transformation of the data leads to a representation which approaches the information-theoretic lower limit for storing light samples. The use of noise estimates derived from sensor physics is likely to be useful in hyperspectral image processing and image compression.

• Tarabalka, Yulija; Haavardsholm, Trym Vegard; Kåsen, Ingebjørg & Skauli, Torbjørn (2009). Real-time anomaly detection in hyperspectral images using multivariate normal mixture models and GPU processing. Journal of Real-Time Image Processing.  ISSN 1861-8200.  4(3), s 287- 300 . doi: 10.1007/s11554-008-0105-x Vis sammendrag

  Hyperspectral imaging, which records a detailed spectrum of light arriving in each pixel, has many potential uses in remote sensing as well as other application areas. Practical applications will typically require real-time processing of large data volumes recorded by a hyperspectral imager. This paper investigates the use of graphics processing units (GPU) for such real-time processing. In particular, the paper studies a hyperspectral anomaly detection algorithm based on normal mixture modelling of the background spectral distribution, a computationally demanding task relevant to military target detection and numerous other applications. The algorithm parts are analysed with respect to complexity and potential for parallellization. The computationally dominating parts are implemented on an Nvidia GeForce 8800 GPU using the Compute Unified Device Architecture programming interface. GPU computing performance is compared to a multicore central processing unit implementation. Overall, the GPU implementation runs significantly faster, particularly for highly data-parallelizable and arithmetically intensive algorithm parts. For the parts related to covariance computation, the speed gain is less pronounced, probably due to a smaller ratio of arithmetic to memory access. Detection results on an actual data set demonstrate that the total speedup provided by the GPU is sufficient to enable real-time anomaly detection with normal mixture models even for an airborne hyperspectral imager with high spatial and spectral resolution.

• Haakenaasen, Randi; Selvig, Espen; Hadzialic, S; Skauli, Torbjørn; Hansen, Vidar; Tibballs, J.E.; Steen, Harald; Foss, S.; Trosdahl-Iversen, Laila; Tafto, Johan; Halsall, M. & Orr, John (2008). Nanowires in the CdHgTe material system. Journal of Electronic Materials.  ISSN 0361-5235.  37(9), s 1311- 1317 Vis sammendrag

  HgTe nanowires have been grown by molecular beam epitaxy (MBE). They are nucleated at Au particles on Si or GaAs substrates and subsequently self-organize and grow laterally on the surface into 20-50 nm wide, 0.5-1 mu m long twisted, but single-crystal, wires. Further growth gives longer, wider, and straighter polycrystalline wires. When unimpeded by Au particles on the surface, the wires become straight and consist of segments of cubic < 111 > HgTe and hexagonal < 001 > Te parallel to the wire. Te nanowires and Au nanowires have also occasionally been formed. All attempts to grow CdHgTe on Si substrates with or without Au particles have resulted in polycrystalline layers. The phase diagrams and diffusion coefficients imply that CdHgTe or HgTe nanowires will not grow by the vapor-liquid-solid technique at the low MBE growth temperatures. SiO2 functions as a mask for selective growth of HgTe, but not for CdHgTe.

• Kåsen, Ingebjørg; Rødningsby, Anders; Haavardsholm, Trym Vegard & Skauli, Torbjørn (2008). Band selection for hyperspectral target-detection based on a multinormal mixture anomaly detection algorithm. Proceedings of SPIE, the International Society for Optical Engineering.  ISSN 0277-786X.  6966 . doi: 10.1117/12.777758
• Laux, E; Genet, C; Skauli, Torbjørn & Ebbesen, T.W. (2008). Plasmonic photon sorters for spectral and polarimetric imaging. Nature Photonics.  ISSN 1749-4885.  2(3), s 161- 164 . doi: 10.1038/nphoton.2008.1
• Selvig, Espen; Tonheim, Celin Russøy; Kongshaug, Kjell Ove; Skauli, Torbjørn; Hemmen, H; Lorentzen, Torgeir & Haakenaasen, Randi (2008). Defects in CdHgTe grown by molecular beam epitaxy on, (211)B-oriented CdZnTe substrates. Journal of Vacuum Science & Technology B.  ISSN 1071-1023.  26(2), s 525- 533 . doi: 10.1116/1.2868782
• Selvig, Espen; Tonheim, Celin Russøy; Lorentzen, Torgeir; Kongshaug, Kjell Ove; Skauli, Torbjørn & Haakenaasen, Randi (2008). Defects in HgTe and CdHgTe grown by molecular beam epitaxy. Journal of Electronic Materials.  ISSN 0361-5235.  37(9), s 1444- 1452 . doi: 10.1007/s11664-008-0447-y Vis sammendrag

  The defect morphology in HgTe and CdHgTe was studied in (211)B-oriented layers grown in a 20 degrees C temperature range around the optimal growth temperature. The density of defects varies strongly with the growth temperature. In HgTe, the shape of the microvoid defects is very sensitive to the growth temperature and can be used to determine the deviation from the optimal growth temperature. Using thermodynamical modeling, the optimal growth temperature for CdHgTe can then be calculated. We describe a mechanism for the formation of microvoids and needles which involves preferential surface diffusion of Te combined with an impurity or defect on the substrate. Microvoids on (111)B-oriented partially twinned HgTe layers were also studied. The microvoids in the twinned parts of the layer were found to be rotated 180 deg relative to the untwinned parts of the layer.

• Selvig, Espen; Tonheim, Celin Russøy; Kongshaug, Kjell Ove; Skauli, Torbjørn; Lorentzen, Torgeir & Haakenaasen, Randi (2007). Defects in HgTe grown by molecular beam epitaxy on (211)B-oriented CdZnTe substrates. Journal of Vacuum Science & Technology B.  ISSN 1071-1023.  25(6), s 1776- 1784 . doi: 10.1116/1.2787876
• Selvig, Espen; Hadzialic, S; Skauli, Torbjørn; Steen, Harald; Hansen, Vidar; Trosdahl-Iversen, L; van Rheenen, Arthur D.; Lorentzen, T & Haakenaasen, Randi (2006). Growth of HgTe nanowires. Physica scripta. Topical Issues.  ISSN 0281-1847.  126, s 115- 120
• Haakenaasen, Randi; Steen, Helge; Selvig, Espen; Rheenen, Arthur Dirk Van; Trosdahl-Iversen, Laila; Hall, D.; Gordon, Neil; Skauli, Torbjørn; Lorentzen, Torgeir & Vaskinn, A (2006). Imaging photovoltaic infrared CdHgTe detectors. Physica Scripta.  ISSN 0031-8949.  T126, s 31- 36 . doi: 10.1088/0031-8949/2006/T126/007

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• Skauli, Torbjørn (2017). Feasibility of a standard for full specification of spectral imager performance. Vis sammendrag

  The current state of the art of specifying spectral imagers falls short of what is needed. Commercial datasheets do not adequately reflect the performance of hyperspectral imagers offered as standard products. In particular, imperfections such as coregistration error, noise performance and stray light are rarely well specified. A standardized way to specify spectral imagers would benefit both developers and users of such instruments. The paper reviews the many different characteristics that are needed to describe various aspects of imager performance, and discusses possible ways to form figures of merit relevant to application performance. In particular, the product of quantum efficiency, optics transmission and nominal throughput (étendue) is shown to be a good figure of merit for radiometric performance. A list of about 30 characteristics is suggested as a standard for a complete specification of spectral imagers. For some characteristics, notably coregistration, it is necessary to establish a standardized measurement methodology.

• Skauli, Torbjørn (2017). Toward Standardization of Performance Characteristics for Spectral Imagers: How to Specify a Hyperspectral Camera?.
• Imai, Francisco Hideki; Von Berg, Dale C. Linne; Skauli, Torbjørn; Tominaga, Shoji & Zalevsky, Zeev (2014). Imaging systems and applications: Introduction to the feature. Applied Optics.  ISSN 0003-6935.  (13), s ISA1- ISA2 . doi: 10.1364/AO.53.00ISA1
• Rousset-Rouviere, Laurent; Coudrain, Christophe; Fabre, Sophie; Poutier, Laurent; Løke, Trond; Fridman, Andrei; Blaaberg, Søren; Baarstad, Ivar; Skauli, Torbjørn & Mocoeur, Isabelle (2014). SYSIPHE system: a state of the art airborne hyperspectral imaging system: initial results from the first airborne campaign.
• Skauli, Torbjørn (2013). How good are your spectral images? Noise, coregistration and information rate in spectral imaging.
• Skauli, Torbjørn & Farrell, Joyce (2013). A collection of hyperspectral images for imaging systems research.
• Skauli, Torbjørn; Torkildsen, Hans Erling; Kåsen, Ingebjørg; Nicolas, Stephane; Haavardsholm, Trym Vegard & Opsahl, Thomas Olsvik (2013). Multispectral and conventional imaging combined in a compact camera by using patterned filters in the focal plane.
• Haavardsholm, Trym Vegard; Kavara, Amela; Kåsen, Ingebjørg & Skauli, Torbjørn (2012). Improving anomaly detection with Multinormal Mixture Models in shadow.
• Skauli, Torbjørn (2012). Optimizing the information rate from spectral imagers in the design tradeoff between resolution and coregistration.
• Denstedt, Martin Anders F.; Haavardsholm, Trym Vegard; Skauli, Torbjørn & Randeberg, Lise Lyngsnes (2011). A hyperspectral imaging system for real-time analysis of skin – capabilities and prospects.
• Rousset-Rouviere, Laurent; Coudrain, Christophe; Fabre, Sophie; Baarstad, Ivar; Fridman, Andrei; Løke, Trond; Blaaberg, Søren & Skauli, Torbjørn (2011). SYSIPHE, an airborne hyperspectral imaging system for the VNIR-SWIR-MWIR-LWIR region.
• Skauli, Torbjørn; Haavardsholm, Trym Vegard; Kåsen, Ingebjørg; Opsahl, Thomas Olsvik; Kavara, Amela & Skaugen, Atle (2011). Hyperspectral imaging technology and systems, exemplified by airborne real-time target detection.
• Haavardsholm, Trym Vegard; Arisholm, Gunnar; Kavara, Amela & Skauli, Torbjørn (2010). Architecture of the real-time target detection processing in an airborne hyperspectral demonstrator system. Vis sammendrag

  An airborne demonstrator for real-time hyperspectral target detection has been developed at FFI. The real-time image processing is challenging, not only due to the computational complexity of the algorithms, but also due to the sustained high data rate. A software framework has been designed in C++ to handle large data flows in a nonlinear pipeline architecture. The cross-platform framework enables full exploitation of multicore processors and graphics processing units (GPU), and even distribution among multiple computers. Object oriented design enables flexible reconfiguration of the pipeline. Tests demonstrate sustained real-time performance of complex anomaly detection processing.

• Hernandez-Palacios, Julio; Randeberg, Lise Lyngsnes; Baarstad, Ivar; Løke, Trond & Skauli, Torbjørn (2010). Hyperspectral low-light camera for imaging of biological samples.
• Hernandez-Palacios, Julio; Randeberg, Lise Lyngsnes; Baarstad, Ivar; Løke, Trond & Skauli, Torbjørn (2010). Hyperspectral low-light camera for imaging of biological samples.
• Hernandez-Palacios, Julio; Randeberg, Lise Lyngsnes; Baarstad, Ivar; Løke, Trond & Skauli, Torbjørn (2010). Hyperspectral low-light camera for imaging of biological samples.
• Hernandez-Palacios, Julio; Randeberg, Lise Lyngsnes; Baarstad, Ivar; Løke, Trond & Skauli, Torbjørn (2010). Hyperspectral low-light camera for macroscopic imaging of biological samples.
• Hernandez-Palacios, Julio; Randeberg, Lise Lyngsnes; Baarstad, Ivar; Løke, Trond & Skauli, Torbjørn (2010). Hyperspectral low-light camera for macroscopic imaging of biological samples.
• Randeberg, Lise Lyngsnes; Haavardsholm, Trym Vegard; Arisholm, Gunnar; Kavara, Amela; Løke, Trond & Skauli, Torbjørn (2010). Rapid hyperspectral characterization of skin.

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