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- 2015
- Calibration process of OSL detectors
- Iodine-131
- OSL-BeO
- Dosimetry of staff and patients
- Optically Stimulated Luminescence (OSL)
- Akdeniz University
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CALIPSO lidar calibration at 1064 nm: version 4 algorithm
摘要： Radiometric calibration of space-based elastic backscatter lidars is accomplished by comparing the measured backscatter signals to theoretically expected signals computed for some well-characterized calibration target. For any given system and wavelength, the choice of calibration target is dictated by several considerations, including signal-to-noise ratio (SNR) and target availability. This paper describes the newly implemented procedures used to calibrate the 1064 nm measurements acquired by CALIOP (i.e., the Cloud-Aerosol Lidar with Orthogonal Polarization), the two-wavelength (532 and 1064 nm) elastic backscatter lidar currently flying on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission. CALIOP’s 532 nm channel is accurately calibrated by normalizing the molecular backscatter from the uppermost aerosol-free altitudes of the CALIOP measurement region to molecular model data obtained from NASA’s Global Modeling and Assimilation Office. However, because CALIOP’s SNR for molecular backscatter measurements is prohibitively lower at 1064 nm than at 532 nm, the direct high-altitude molecular normalization method is not a viable option at 1064 nm. Instead, CALIOP’s 1064 nm channel is calibrated relative to the 532 nm channel using the backscatter from a carefully selected subset of cirrus cloud measurements. In this paper we deliver a full account of the revised 1064 nm calibration algorithms implemented for the version 4.1 (V4) release of the CALIPSO lidar data products, with particular emphases on the physical basis for the selection of “calibration quality” cirrus clouds and on the new averaging scheme required to characterize intra-orbit calibration variability. The V4 procedures introduce latitudinally varying changes in the 1064 nm calibration coefficients of 25 % or more, relative to previous data releases, and are shown to substantially improve the accuracy of the V4 1064 nm attenuated backscatter coefficients. By evaluating calibration coefficients derived using both water clouds and ocean surfaces as alternate calibration targets, and through comparisons to independent, collocated measurements made by airborne high spectral resolution lidar, we conclude that the CALIOP V4 1064 nm calibration coefficients are accurate to within 3 %.
关键词： calibration,lidar,CALIPSO,version 4 algorithm,cirrus clouds,1064 nm
更新于2025-09-23 15:22:29
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Automatic calibration of an arbitrarily-set near-infrared camera for patient surface respiratory monitoring
摘要： Purpose: A patient’s respiratory monitoring is one of the key techniques in radiotherapy for a moving target. Generally, such monitoring systems are permanently set to a fixed geometry during the installation. This study aims to enable a temporary setup of such a monitoring system by developing a fast method to automatically calibrate the geometrical position by a quick measurement of calibration markers. Methods: One calibration marker was placed on the isocenter and the other six markers were placed at positions 5-cm apart from the isocenter to the left, right, anterior, posterior, superior, and inferior directions. A near-infrared (NIR) camera (NIC) (Kinect v2 (Microsoft Corp.)) was arbitrarily set with ten different angles around the calibration phantom with a fixed tilting-down angle at approximately 45° in a linear accelerator treatment vault. The 3D coordinates in the camera (Cam) coordinate system (CS) (x and y are the horizontal and vertical coordinates of the image, respectively, and z is a coordinate along the NIR time-of-flight) were taken for one minute with 30 frames per second. The data corresponding to the measurement times of 1, 3, 10, 30, and 60 s were created to mimic various measurement times. These data were used to calculate the initial matrix elements, which included six parameters of the pitching, yawing, and rolling angles; horizontal 2D translation in the treatment room; and the source-to-axis distance of NIC, for a conversion from the Cam CS to the treatment-room CS for which the origin was defined at the isocenter (Iso coordinate). The six parameters were then optimized to minimize the displacements of the calculated marker coordinates from the actual positions in the Iso CS. The 3D positional accuracy and angular accuracy of the conversion were evaluated. The random error of the Iso coordinates was analyzed through a relation with the angle of each measurement setup. Results: Three angles of NIC and relative translation vectors were successfully calculated from the measurement data of the calibration markers. The achieved spatial and angular accuracies were 0.02 mm and 1.6°, respectively, after the optimization. Among the mimicked measurement times investigated in this study, both spatial and angular accuracies had no dependence on the measurement time. The average random error of a static marker was 0.46 mm after the optimization. Conclusion: We developed an automatic method to calibrate the 3D patient surface monitoring system. The procedure developed in this study enabled a quick calibration of NIC, which can be easily repeated multiple times for a frequent and quick setup of the monitoring system.
关键词： near-infrared camera,respiratory monitoring,calibration
更新于2025-09-23 15:22:29
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Dual-modality optical projection tomography reconstruction method from fewer views
摘要： In optical projection tomography (OPT), for longitudinal living model studies, multiple measurements of the same sample are required at different time points. It is important to decrease both the total acquisition time and the light dose to the sample. We improved the ordered subsets expectation maximization reconstruction algorithm for OPT, which reduces the acquisition time and number of projections greatly compared with filtered back projection (FBP), and satisfactory reconstructed images are obtained. Using zebrafish, in transmission and fluorescence mode, we demonstrate the capability of the method to reconstruct image from downsampled projection subsets. The result shows that the reconstruction image quality of the proposed method using 30 projections is comparable to that of FBP using 720 projections. The total acquisition procedure can be finished in a few seconds. The method also provides OPT with the remarkable capability to resist noises and artifacts.
关键词： molecular imaging,image reconstruction,dual-modality OPT,preimaging calibration
更新于2025-09-23 15:22:29
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Instrument Calibration of the Interface Region Imaging Spectrograph (IRIS) Mission
摘要： The Interface Region Imaging Spectrograph (IRIS) is a NASA small explorer mission that provides high-resolution spectra and images of the Sun in the 133 – 141 nm and 278 – 283 nm wavelength bands. The IRIS data are archived in calibrated form and made available to the public within seven days of observing. The calibrations applied to the data include dark correction, scattered light and background correction, ?at ?elding, geometric distortion correction, and wavelength calibration. In addition, the IRIS team has calibrated the IRIS absolute throughput as a function of wavelength and has been tracking throughput changes over the course of the mission. As a resource for the IRIS data user, this article describes the details of these calibrations as they have evolved over the ?rst few years of the mission. References to online documentation provide access to additional information and future updates.
关键词： Instrumentation: calibration
更新于2025-09-23 15:22:29
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3D Vehicle Model-based PTZ Camera Auto-calibration for Smart Global Village
摘要： PTZ cameras perform an important part for the surveillance systems in the highway because of their wide field of vision and high flexibility. However, it is difficult to obtain real world physical information accurately by using the image information due to the change in the focal length and angles of the PTZ cameras with the surveillance requirements. Therefore, it is of great value to study off-site auto-calibration method for PTZ cameras in the application of highway surveillance system. This paper proposes a PTZ camera auto-calibration method based on vanishing point constraints and 3D vehicle model constraints to establish an accurate description relationship between image information and real-world physical information. Firstly, the position of vertical vanishing point is estimated accurately using the cascaded Hough Transform voting of the vehicle target motion trajectories. Secondly, the physical size of the 3D vehicle model is used as a constraint, and it is combined with an enumeration strategy to obtain the accurate estimation of the lateral vanishing point. Finally, the calibration parameters of the PTZ camera are calculated with the known camera height. The experiments on numerous sets of highway surveillance scenes show that the proposed auto-calibration method of the PTZ camera is able to satisfy the application requirements of the highway surveillance scenes. Compared with the reference methods, this method has a good performance. Moreover, this method has some value for different application.
关键词： highway,auto-calibration,vanishing point,3D vehicle model,PTZ camera
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE Conference on Antenna Measurements & Applications (CAMA) - Va?ster?s (2018.9.3-2018.9.6)] 2018 IEEE Conference on Antenna Measurements & Applications (CAMA) - UAS-Based Antenna Pattern Measurements and Radar Characterization
摘要： This paper presents an update of the current in-situ antenna characterization and calibration of a radar system using an Unmanned Aircraft System (UAS) developed by the Advanced Radar Research Center (ARRC) at The University of Oklahoma. A large multirotor platform was customized for long endurance (～30 minutes), high positioning accuracy (<3 cm), and high stability, and was integrated with a high precision 3-axis gimbal that holds an antenna array and pulse generator-transmitter. The platform was designed to support measurements from 2 GHz to 10 GHz, however, the current setup described in this article includes an S-band array probe of 3x3 elements. The RF probe beamwidth was optimized to minimize reflections from the UAS frame and to provide accurate antenna measurements in flight conditions.
关键词： In-situ antenna measurements,UAV,dual-polarized radar,radar calibration,DGPS,UAS,antenna measurements,RTK
更新于2025-09-23 15:22:29
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[IEEE 2018 China International SAR Symposium (CISS) - Shanghai (2018.10.10-2018.10.12)] 2018 China International SAR Symposium (CISS) - Range-Variant Channel Errors Calibration Algorithm for Multichannel HRWS SAR Imaging
摘要： Azimuth multichannel SAR system can realize high-resolution and wide-swath (HRWS) SAR imaging, which has attracted interests. The azimuth ambiguities of multichannel SAR can be suppressed by digital beamforming (DBF) techniques. However, the presence of inevitable channel errors deteriorates the performance of ambiguity suppression. In this paper, we focus on the research of range-variant channel phase errors. We analyze the effect of radial position errors by using the second order Taylor series to expand the azimuth phase history. It indicates that the radial position errors can be regarded as range-variant phase errors. We divide the raw data into several blocks along range direction. Then we use the azimuth cross-correlation technique to estimate the phase errors of each block data. Compared with the subspace-based calibration techniques, the azimuth cross-correlation technique does not use the information of azimuth ambiguities. Afterwards, the fitting process is employed to estimate the range-variant channel phase errors. Finally, the experiments on real data processing validate the effectiveness of our proposed method.
关键词： channel error calibration,Range-variant,HRWS,cross-correlation,multichannel SAR
更新于2025-09-23 15:22:29
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A Fuzzy Inference System for Unsupervised Deblurring of Motion Blur in Electron Beam Calibration
摘要： This paper presents a novel method of restoring the electron beam (EB) measurements that are degraded by linear motion blur. This is based on a fuzzy inference system (FIS) and Wiener inverse filter, together providing autonomy, reliability, flexibility, and real-time execution. This system is capable of restoring highly degraded signals without requiring the exact knowledge of EB probe size. The FIS is formed of three inputs, eight fuzzy rules, and one output. The FIS is responsible for monitoring the restoration results, grading their validity, and choosing the one that yields to a better grade. These grades are produced autonomously by analyzing results of a Wiener inverse filter. To benchmark the performance of the system, ground truth signals obtained using an 18 μm wire probe were compared with the restorations. Main aims are therefore: (a) Provide unsupervised deblurring for device independent EB measurement; (b) improve the reliability of the process; and (c) apply deblurring without knowing the probe size. These further facilitate the deployment and manufacturing of EB probes as well as facilitate accurate and probe-independent EB characterization. This paper’s findings also makes restoration of previously collected EB measurements easier where the probe sizes are not known nor recorded.
关键词： electron beam calibration,signal and image processing,fuzzy inference system,fuzzy deblurring,linear motion blur,fuzzy logics
更新于2025-09-23 15:22:29
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3D surface reconstruction of retinal vascular structures
摘要： We propose in this paper, a three-dimensional surface reconstruction of a retinal vascular network from a pair of 2D retinal images. Our approach attempts to address the above challenges by incorporating an epipolar geometry estimation and adaptive surface modelling in a 3D reconstruction, using three steps: segmentation, 3D skeleton reconstruction and 3D surface modelling of vascular structures. The intrinsic calibration matrices are found via the solution of simplified Kruppa equations. A simple essential matrix based on a self-calibration method has been used for the ‘fundus camera-eye’ system. The used method has eventually produced vessel surfaces that could be fit for various applications, such as applications for computational fluid dynamics simulations and applications for real-time virtual interventional.
关键词： Kruppa equations,curvature-dependent subdivision,surface reconstruction,epipolar geometry,segmentation,retinal vascular network,self-calibration
更新于2025-09-23 15:22:29
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A Cyclic TDC using Variable Delay Circuit
摘要： A cyclic TDC can be implemented in a small area with high resolution but it takes long conversion time. To reduce a conversion time, we introduce variable delay circuits that can change a delay time of a pulse. We also introduce calibration techniques, an offset cancellation and delay matching, to improve linearity of the TDC. We confirmed through circuit simulation that the proposed circuit achieves a time resolution of 9.38 ps, dynamic range of 18.7 ns, sampling rate of 2 MS/s, and a power consumption of 11 mW at 1.8 V operation.
关键词： variable delay,Time-to-Digital Converter,calibration,cyclic,Multiple Delay inverter
更新于2025-09-23 15:22:29