| 1. |
- Alqaysi, Hiba, et al.
(författare)
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Cost Optimized Design of Multi-Camera Domefor Volumetric Surveillance
- 2021
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Ingår i: IEEE Sensors Journal. - 1530-437X .- 1558-1748. ; 21:3, s. 3730-3737
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Tidskriftsartikel (refereegranskat)abstract
- A multi-camera dome consists of number ofcameras arranged in layers to monitor a hemisphere aroundits center. In volumetric surveillance,a 3D space is required tobemonitoredwhich can be achievedby implementing numberof multi-camera domes. A monitoring height is consideredas a constraint to ensure full coverage of the space belowit. Accordingly, the multi-camera dome can be redesignedinto a cylinder such that each of its multiple layers hasdifferent coverage radius. Minimum monitoring constraintsshould be met at all layers. This work is presenting a costoptimized design for the multi-camera dome that maximizesits coverage. The cost per node and number of squaremetersper dollar of multiple configurations are calculated using asearch space of cameras and considering a set of monitoring and coverage constraints. The proposed design is costoptimized per node and provides more coverage as compared to the hemispherical multi-camera dome.
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| 2. |
- An, S., et al.
(författare)
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Characterization of micro pore optics for full-field X-ray fluorescence imaging
- 2023
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 18:1
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Tidskriftsartikel (refereegranskat)abstract
- Elemental mapping images can be achieved through step scanning imaging using pinhole optics or micro pore optics (MPO), or alternatively by full-field X-ray fluorescence imaging (FF-XRF). X-ray optics for FF-XRF can be manufactured with different micro-channel geometries such as square, hexagonal or circular channels. Each optic geometry creates different imaging artefacts. Square-channel MPOs generate a high intensity central spot due to two reflections via orthogonal channel walls inside a single channel, which is the desirable part for image formation, and two perpendicular lines forming a cross due to reflections in one plane only. Thus, we have studied the performance of a square-channel MPO in an FF-XRF imaging system. The setup consists of a commercially available MPO provided by Photonis and a Timepix3 readout chip with a silicon detector. Imaging of fluorescence from small metal particles has been used to obtain the point spread function (PSF) characteristics. The transmission through MPO channels and variation of the critical reflection angle are characterized by measurements of fluorescence from copper and titanium metal fragments. Since the critical angle of reflection is energy dependent, the cross-arm artefacts will affect the resolution differently for different fluorescence energies. It is possible to identify metal fragments due to the form of the PSF function. The PSF function can be further characterized using a Fourier transform to suppress diffuse background signals in the image.
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| 3. |
- Fedorov, Igor, et al.
(författare)
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A two-layer 3D reconstruction method and calibration for multi-camera-based volumetric positioning and characterization
- 2021
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Ingår i: IEEE Transactions on Instrumentation and Measurement. - 0018-9456 .- 1557-9662. ; 70
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Tidskriftsartikel (refereegranskat)abstract
- A three-dimensional (3D) reconstruction method and multi-camera calibration using multiple artificial reference markers have been used for precise volumetric surveillance of fast-flying objects. The method uses a two-layer 3D reconstruction that integrates two multi-camera stereo-nodes. The fields of view of stereo nodes are directed at an acute angles to each other to provide greater coverage with the given constraints and to determine the flight characteristics of objects in 3D. The object’s flight reconstruction includes a “rough” estimation of its positions relative to selected artificial reference points in both stereo nodes separately and subsequent “refinement” of calculated positions. In this paper, we describe the proposed method and calibration technique, using a multi-camera system to measure object characteristics in 3D. The proposed method applies to volumetric surveillance in situations where it is necessary to count, track, and analyze the activities of flying objects, especially birds, using high spatial resolution.
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| 4. |
- Rydblom, Stefani Alita Leona, 1975-, et al.
(författare)
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Measurement of atmospheric icing and droplets
- 2020
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Ingår i: IEEE Transactions on Instrumentation and Measurement. - : Institute of Electrical and Electronics Engineers Inc.. - 0018-9456 .- 1557-9662. ; 69:8, s. 5799-5809
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Tidskriftsartikel (refereegranskat)abstract
- Icing conditions including atmospheric liquid water content (LWC) and size distribution of droplets were recorded close to the top of Mt. Åreskutan, 1260-m above sea level, Sweden, a place known for frequent severe icing. The findings are comparatively analyzed. Combitech IceMonitor was used to measure the ice load, and HoloOptics T41 was used to measure the atmospheric icing rate. A method to translate the digital output from HoloOptics T41 to a value between 0 and 100 is described and used. Two instruments were used for measuring LWC and the median volume diameter (MVD). We created a model of icing intensity based on the k-nearest neighbor (KNN) using wind speed, LWC, and MVD as input. The result indicates that more learning data decrease the error. An heuristic model of erosion/ablation was added to simulate the ice load, and the result was compared with that of the standard Makkonen ice load model. The Makkonen model is suitable for estimating the ice load using a 1-h temporal resolution. With a 1-min temporal resolution, the erosion/ablation needs to be modeled and included. Our observations show that conditions can alternate between icing and erosion/ablation within 1 min during an icing event.
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| 5. |
- Shaikh, Muhammad Saad, et al.
(författare)
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Calibration of a Hyper-Spectral Imaging System Using a Low-Cost Reference
- 2021
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Ingår i: Sensors. - : MDPI. - 1424-8220. ; 21:11
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present a hyper-spectral imaging system and practical calibration procedure using a low-cost calibration reference made of polytetrafluoroethylene. The imaging system includes a hyperspectral camera and an active source of illumination with a variable spectral distribution of intensity. The calibration reference is used to measure the relative reflectance of any material surface independent of the spectral distribution of light and camera sensitivity. Winter road conditions are taken as a test application, and several spectral images of snow, icy asphalt, dry asphalt, and wet asphalt were made at different exposure times using different illumination spectra. Graphs showing measured relative reflectance for different road conditions support the conclusion that measurements are independent of illumination. Principal component analysis of the acquired spectral data for road conditions shows well separated data clusters, demonstrating the system’s suitability for material classification.
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| 6. |
- Shaikh, Muhammad Saad, et al.
(författare)
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Extending Effective Dynamic Range of Hyperspectral Line Cameras for Short Wave Infrared Imaging
- 2022
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Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 22:5
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a multi-exposure method is proposed to increase the dynamic range (DR) of hyperspectral imaging using an InGaAs-based short-wave infrared (SWIR) hyperspectral line camera. Spectral signatures of materials were captured for scenarios in which the DR of a scene was greater than the DR of a line camera. To demonstrate the problem and test the proposed multi-exposure method, plastic detection in food waste and polymer sorting were chosen as the test application cases. The DR of the hyperspectral camera and the test samples were calculated experimentally. A multi-exposure method is proposed to create high-dynamic-range (HDR) images of food waste and plastic samples. Using the proposed method, the DR of SWIR imaging was increased from 43 dB to 73 dB, with the lowest allowable signal-to-noise ratio (SNR) set to 20 dB. Principal Component Analysis (PCA) was performed on both HDR and non-HDR image data from each test case to prepare the training and testing data sets. Finally, two support vector machine (SVM) classifiers were trained for each test case to compare the classification performance of the proposed multi-exposure HDR method against the single-exposure non-HDR method. The HDR method was found to outperform the non-HDR method in both test cases, with the classification accuracies of 98% and 90% respectively, for the food waste classification, and with 95% and 35% for the polymer classification.
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| 7. |
- Shaikh, Muhammad Saad
(författare)
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Hyperspectral imaging for in-situ applications : Methods to improve the classification of materials using hyperspectral imaging
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis addresses several research questions related to in-situ hyperspectral imaging systems, proposes measurement methods for more accurate imaging, and examines the impact of the methods on material classification.First, the thesis investigates the possibility of successfully calibrating a hyperspectral imaging system using a low-cost PTFE reference. A hyperspectral imaging system and practical calibration procedure using an inexpensive calibration reference are introduced. This reference enables accurate measurement of a material’s reflectance spectra independent of lighting and the camera’s spectral distribution of intensity and sensitivity. The study presents experiments conducted on winter roads covered with water, snow, and ice. The results show the robustness of the calibration and the suitability of the system for classifying materials.The thesis further focuses on increasing the dynamic range (DR) of line scanning hyperspectral cameras. A method that relies on the use of multiple exposures is proposed to increase DR, benefiting applications such as plastic detection and polymer sorting. Experiments show that the proposed method can increase the DR for hyperspectral SWIR imaging from 43 dB to 73 dB. Material classification experiments reveal significant accuracy improvements with multiple exposures for large dynamic ranges.The thesis also examines the effect of variations in relative humidity. It shows that even minor changes in humidity can significantly affect measurements. Frequent calibration and pruning of active wavelength bands are proposed as solutions to reduce the classification error rate for polymers from 20% to less than 1%.The thesis also investigates the classification of colored materials by combining visible and infrared imaging. The classification algorithm shows high overall accuracy, close to 99.9% for one test case, which also shows the potential of this approach.Finally, the use of infrared hyperspectral imaging combined with Convolutional Neural Networks (CNN) for the classification of black polymers is evaluated. CNN outperforms all traditional classification algorithms, further demonstrating the potential of the proposed method. Further research on larger and more diversified material samples is recommended.
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| 8. |
- Shaikh, Muhammad Saad, et al.
(författare)
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Impact of water vapour on polymer classification using in situ short-wave infrared hyperspectral imaging
- 2022
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Ingår i: Journal of Spectral Imaging. - : IM Publications Open LLP. - 2040-4565. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Hyperspectral remote sensing is known to suffer from wavelength bands blocked by atmospheric gases. Short-wave infrared hyperspectral imaging at in situ installations is shown to be affected by water vapour even if the pathlength of light through air is only hundreds of centimetres. This impact is especially noticeable with large variations of relative humidity, the coefficient of variation reaching 5 % in our test case. Using repeated calibrations of imaging system at the same relative humidity as in the measurement, we were able to reduce the coefficient of variation to 1 %. The measurement variations are also shown to induce significant error in material classification. Polymer type identification was selected as the test case for material classification. The measurement variations due to the change in relative humidity are shown to result in 20 % classification error at its minimum. With repeated calibrations or by eliminating the most affected wavelength bands from measurements, we were able to reduce the classification error to less than 1 %. Such improvement of measurement and classification precision may be important for industrial applications such as waste sorting, polymer classification etc.
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| 9. |
- Thörnberg, Benny, 1966-
(författare)
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Avbildande materialanalysator samt förfarande för att använda denna
- 2020
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Patent (populärvet., debatt m.m.)abstract
- Avbildande materialanalysator (114), avsedd för klassificering och karakterisering av ytors (101) ingående material, innefattande minst en strålningsavgivande anordning (104,402) samt minst en mottagare (115). Strålningsavgivande anordning (104) avger ljuspulser, som modulerats av minst en modulator (106), mot minst en yta (101) samt att det reflekterade ljuset från ytan (101) registreras av minst en kamera (102) i mottagaren (115). Kameran (102) genererar videosignaler (103) vilka överförs till minst en spektral demodulator (109) som demodulerar de genererade videosignalerna (103) och avger digitala signaler (R1) till (RN) vilka är proportionerliga till intensiteten av det reflekterade ljuset från ytan (101). De strålningsavgivande enheternas (113) avgivna ljus styrs av sinusformade pulsbreddsmodulerade signaler (105) som modulerats av modulatorn (106), samt att modulatorn (106) innefattar en synkroniseringsfunktion som synkroniserar starttiden för de avgivna pulser (105) och ljuspulser från de strålningsavgivande enheterna med starttidpunkterna för kamerans (102) exponeringar. Patentansökan innefattar även ett förfarande för användning av materialanalysatorn.
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| 10. |
- Thörnberg, Benny, 1966-
(författare)
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The Material Imaging Analyzer MIA
- 2022
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Ingår i: 2022 IEEE Sensors Applications Symposium, SAS 2022 - Proceedings. - : IEEE. - 9781665409810
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Konferensbidrag (refereegranskat)abstract
- In this work, Sinewave Pulse Width Modulation (SPWM) of light sources is proposed to be used for spectral imaging and vibrational spectroscopy. Three Light Emitting Diodes (LEDs) transmit SPWM light at different sinewave frequencies and at 1050, 1300 and 1550 nm respectively. A video camera records the active illumination, reflected in the surface to be analyzed and simultaneously for all three LEDs. A similar demodulation method as for lock-in amplifiers is used to demodulate every single pixel into three spectral channels. Experimental results show that this material imaging analyzer, called MIA, can be used for vibrational spectroscopy such that snow, ice, water and plastic are classified from their corresponding spectral signatures at an overall success rate of 92%. Spectral signatures in this particular case are generated from sensing reflection of light at three wavelengths. MIA must thus be configured with LEDs having wavelengths suitable for the particular application. The response of the MIA light sources and the indium gallium arsenide InGaAs detector is close to perfectly linear. Peak signal to noise ratio PSNR was measured to be 54 dB.
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