Journal articles: 'Flat-field correction'

1

Palmer, Christopher. "Absolute astigmatism correction for flat field spectrographs." Applied Optics 28, no. 9 (May 1, 1989): 1605. http://dx.doi.org/10.1364/ao.28.001605.

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Lee, Meena, Soonmu Kwon, and Kwon Su Chon. "Analysis of Noise Power Spectrum According to Flat-Field Correction in Digital Radiography." Journal of the Korean Society of Radiology 7, no. 3 (June 30, 2013): 227–32. http://dx.doi.org/10.7742/jksr.2013.7.3.227.

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Fugui Yang, Fugui Yang, Qiushi Wang Qiushi Wang, and Ming Li Ming Li. "Light source system for high-precision flat-field correction and the calibration of an array detector." Chinese Optics Letters 13, no. 4 (2015): 040402–40406. http://dx.doi.org/10.3788/col201513.040402.

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Kwan, Alexander L. C., J. Anthony Seibert, and John M. Boone. "An improved method for flat-field correction of flat panel x-ray detector." Medical Physics 33, no. 2 (January 24, 2006): 391–93. http://dx.doi.org/10.1118/1.2163388.

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Ding Yi, 丁毅, 罗海燕 Luo Haiyan, 施海亮 Shi Hailiang, 李志伟 Li Zhiwei, 韩云飞 Han Yunfei, and 熊伟 Xiong Wei. "New Flat-Field Correction Method for Spatial Heterodyne Spectrometer." Acta Optica Sinica 40, no. 19 (2020): 1930002. http://dx.doi.org/10.3788/aos202040.1930002.

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KASK, PEET, KAUPO PALO, CHRIS HINNAH, and THORA POMMERENCKE. "Flat field correction for high‐throughput imaging of fluorescent samples." Journal of Microscopy 263, no. 3 (March 29, 2016): 328–40. http://dx.doi.org/10.1111/jmi.12404.

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KOJIMA, YASUFUMI. "GRAVITATIONAL CORRECTION IN NEUTRINO OSCILLATIONS." Modern Physics Letters A 11, no. 38 (December 14, 1996): 2965–70. http://dx.doi.org/10.1142/s0217732396002939.

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Piccinini, Filippo, and Alessandro Bevilacqua. "Colour Vignetting Correction for Microscopy Image Mosaics Used for Quantitative Analyses." BioMed Research International 2018 (June 7, 2018): 1–15. http://dx.doi.org/10.1155/2018/7082154.

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Image mosaicing permits achieving one high-resolution image, extending the visible area of the sample while keeping the same resolution. However, intensity inhomogeneity of the stitched images can alter measurements and the right perception of the original sample. The problem can be solved by flat-field correcting the images through the vignetting function. Vignetting correction has been widely addressed for grey-level images, but not for colour ones. In this work, a practical solution for the colour vignetting correction in microscopy, also facing the problem of saturated pixels, is described. In order to assess the quality of the proposed approach, five different tonal correction approaches were quantitatively compared using state-of-the-art metrics and seven pairs of partially overlapping images of seven different samples. The results obtained proved that the proposed approach allows obtaining high quality colour flat-field corrected images and seamless mosaics without employing any blending adjustment. In order to give the opportunity to easily obtain seamless mosaics ready for quantitative analysis, the described vignetting correction method has been implemented in an upgraded release of MicroMos (version 3.0), an open-source software specifically designed to automatically obtain mosaics of partially overlapped images.

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Yu, Yongjian, and Jue Wang. "Heel effect adaptive flat field correction of digital x-ray detectors." Medical Physics 40, no. 8 (July 17, 2013): 081913. http://dx.doi.org/10.1118/1.4813303.

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Kong Ningning, 孔宁宁, 李抄 Li Chao, 夏明亮 Xia Mingliang, 齐岳 Qi Yue, 李大禹 Li Dayu, and 宣丽 Xuan Li. "Research on Flat Field Correction Method in Adaptive Optics Retinal Imaging System." Acta Optica Sinica 31, no. 12 (2011): 1211001. http://dx.doi.org/10.3788/aos201131.1211001.

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Davidson, D. W., C. Fröjdh, V. O'Shea, H.-E. Nilsson, and M. Rahman. "Limitations to flat-field correction methods when using an X-ray spectrum." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 509, no. 1-3 (August 2003): 146–50. http://dx.doi.org/10.1016/s0168-9002(03)01563-8.

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Wood, Douglas, Gilbert Feke, Douglas Vizard, and Rao Papineni. "Refining epifluorescence imaging and analysis with automated multiple-band flat-field correction." Nature Methods 5, no. 4 (April 2008): i—ii. http://dx.doi.org/10.1038/nmeth.f.210.

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Moehler, Sabine, Wolfram Freudling, Palle Møller, Ferdinando Patat, Gero Rupprecht, and Kieran O’Brien. "Correction of Field Rotator-Induced Flat-Field Systematics—A Case Study Using Archived VLT-FORS Data." Publications of the Astronomical Society of the Pacific 122, no. 887 (January 2010): 93–102. http://dx.doi.org/10.1086/649963.

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Williams, Timothy C., and Christopher R. Shaddix. "Simultaneous correction of flat field and nonlinearity response of intensified charge-coupled devices." Review of Scientific Instruments 78, no. 12 (December 2007): 123702. http://dx.doi.org/10.1063/1.2821616.

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Yang, Li Jun, Ming Fei Wu, and Yun Hong Zhu. "Quantitative Retrieval of Tidal Flat Moisture Based on TM Images." Applied Mechanics and Materials 448-453 (October 2013): 1066–71. http://dx.doi.org/10.4028/www.scientific.net/amm.448-453.1066.

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Based on spectrometry, the remote sensing inversion researches of the surface tidal flat moisture are conducted in combination with spectral values measured in the field and moisture measured in the laboratory. Firstly, the remote sensing images are preprocessed, including geometric correction, atmospheric correction and image enhancement. Then, the spectral characteristics of typical ground objects are analyzed to partition the whole image and separate the bare tidal flats. At last, TM5 wave band and exponential model are determined to be the best wave band and optimal model for the inversion of the bare tidal flat moisture. The experiment shows: (1)This method can help to improve the accuracy of the surface tidal flat moisture inversion, with the maximum error of moisture inversion is 3%, the relative error is 7.1% and the average relative error is 6.5%. (2)The surface tidal flat moisture is of evident gradient distribution features, which can be used as basis of tidal flat topographic survey.

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Sigernes, F., S. E. Holmen, D. Biles, H. Bjørklund, X. Chen, M. Dyrland, D. A. Lorentzen, et al. "Auroral all-sky camera calibration." Geoscientific Instrumentation, Methods and Data Systems 3, no. 2 (December 10, 2014): 241–45. http://dx.doi.org/10.5194/gi-3-241-2014.

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Abstract. A two-step procedure to calibrate the spectral sensitivity to visible light of auroral all-sky cameras is outlined. Center pixel response is obtained by the use of a Lambertian surface and a standard 45 W tungsten lamp. Screen brightness is regulated by the distance between the lamp and the screen. All-sky flat-field correction is carried out with a 1 m diameter integrating sphere. A transparent Lexan dome at the exit port of the sphere is used to simulate observing conditions at the Kjell Henriksen Observatory (KHO). A certified portable low brightness source from Keo Scientific Ltd was used to test the procedure. Transfer lamp certificates in units of Rayleigh per Ångstrøm (R/Å) are found to be within a relative error of 2%. An all-sky camera flat-field correction method is presented with only 6 required coefficients per channel.

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Sigernes, F., S. E. Holmen, D. Biles, H. Bjørklund, X. Chen, M. Dyrland, D. A. Lorentzen, et al. "Auroral all-sky camera calibration." Geoscientific Instrumentation, Methods and Data Systems Discussions 4, no. 2 (September 1, 2014): 515–31. http://dx.doi.org/10.5194/gid-4-515-2014.

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Abstract. A two-step procedure to calibrate the spectral sensitivity to visible light of auroral all-sky cameras is outlined. Center pixel response is obtained by the use of a Lambertian surface and a standard 45W tungsten lamp. Screen brightness is regulated by the distance between the lamp and the screen. All-sky flat-field correction is carried out with a 1 m diameter integrating sphere. A transparent Lexan dome at the exit port of the sphere is used to simulate observing conditions at the Kjell Henriksen Observatory (KHO). A certified portable low brightness source from Keo Scientific Ltd. was used to test the procedure. Transfer lamp certificates in units of Rayleigh per Ångstrøm (R Å−1) are found to be within a relative error of 2%. An all-sky camera flat-field correction method is presented with only 6 required coefficients per channel.

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Cai, Huaqing, Wen-Chau Lee, Michael M. Bell, Cory A. Wolff, Xiaowen Tang, and Frank Roux. "A Generalized Navigation Correction Method for Airborne Doppler Radar Data." Journal of Atmospheric and Oceanic Technology 35, no. 10 (October 2018): 1999–2017. http://dx.doi.org/10.1175/jtech-d-18-0028.1.

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AbstractUncertainties in aircraft inertial navigation system and radar-pointing angles can have a large impact on the accuracy of airborne dual-Doppler analyses. The Testud et al. (THL) method has been routinely applied to data collected by airborne tail Doppler radars over flat and nonmoving terrain. The navigation correction method proposed in Georgis et al. (GRH) extended the THL method over complex terrain and moving ocean surfaces by using a variational formulation but its capability over ocean has yet to be tested. Recognizing the limitations of the THL method, Bosart et al. (BLW) proposed to derive ground speed, tilt, and drift errors by statistically comparing aircraft in situ wind with dual-Doppler wind at the flight level. When combined with the THL method, the BLW method can retrieve all navigation errors accurately; however, it can be applied only to flat surfaces, and it is rather difficult to automate. This paper presents a generalized navigation correction method (GNCM) based on the GRH method that will serve as a single algorithm for airborne tail Doppler radar navigation correction for all possible surface conditions. The GNCM includes all possible corrections in the cost function and implements a new closure assumption by taking advantage of an accurate aircraft ground speed derived from GPS technology. The GNCM is tested extensively using synthetic airborne Doppler radar data with known navigation errors and published datasets from previous field campaigns. Both tests show the GNCM is able to correct the navigation errors associated with airborne tail Doppler radar data with adequate accuracy.

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WANG, YiRan, XianYong BAI, SiQing LIU, YuanYong DENG, and YueQiang SUN. "Flat-field measuring and correction method for full-disk solar image based on ground glass." Chinese Science Bulletin 62, no. 26 (June 2, 2017): 3057–66. http://dx.doi.org/10.1360/n972016-01477.

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Lee, Hyoung-Koo, Do-Il Kim, Sung-Hyeon Kim, Je-Woong Youn, Dae-Sop Park, Bo-Young Choe, and Tae-Suk Suh. "An iterative method for flat-field correction of digital radiography with arbitrary detector panel position." International Congress Series 1281 (May 2005): 1315. http://dx.doi.org/10.1016/j.ics.2005.03.095.

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21

Giyanani, A., W. Bierbooms, and G. van Bussel. "Lidar uncertainty and beam averaging correction." Advances in Science and Research 12, no. 1 (May 13, 2015): 85–89. http://dx.doi.org/10.5194/asr-12-85-2015.

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Abstract. Remote sensing of the atmospheric variables with the use of Lidar is a relatively new technology field for wind resource assessment in wind energy. A review of the draft version of an international guideline (CD IEC 61400-12-1 Ed.2) used for wind energy purposes is performed and some extra atmospheric variables are taken into account for proper representation of the site. A measurement campaign with two Leosphere vertical scanning WindCube Lidars and metmast measurements is used for comparison of the uncertainty in wind speed measurements using the CD IEC 61400-12-1 Ed.2. The comparison revealed higher but realistic uncertainties. A simple model for Lidar beam averaging correction is demonstrated for understanding deviation in the measurements. It can be further applied for beam averaging uncertainty calculations in flat and complex terrain.

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Iramina, Hiraku, Mitsuhiro Nakamura, Yuki Miyabe, Nobutaka Mukumoto, Tomohiro Ono, Hideaki Hirashima, and Takashi Mizowaki. "Quantification and correction of the scattered X-rays from a megavoltage photon beam to a linac-mounted kilovoltage imaging subsystem." BJR|Open 2, no. 1 (November 2020): 20190048. http://dx.doi.org/10.1259/bjro.20190048.

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Objective: To quantify and correct megavoltage (MV) scattered X-rays (MV-scatter) on an image acquired using a linac-mounted kilovoltage (kV) imaging subsystem. Methods and materials: A linac-mounted flat-panel detector (FPD) was used to acquire an image containing MV-scatter by activating the FPD only during MV beam irradiation. 6-, 10-, and 15 MV with a flattening-filter (FF; 6X-FF, 10X-FF, 15X-FF), and 6- and 10 MV without an FF (6X-FFF, 10X-FFF) were used. The maps were acquired by changing one of the irradiation parameters while the others remained fixed. The mean pixel values of the MV-scatter were normalized to the 6X-FF reference condition (MV-scatter value). An MV-scatter database was constructed using these values. An MV-scatter correction experiment with one full arc image acquisition and two square field sizes (FSs) was conducted. Measurement- and estimation-based corrections were performed using the database. The image contrast was calculated at each angle. Results: The MV-scatter increased with a larger FS and dose rate. The MV-scatter value factor varied substantially depending on the FPD position or collimator rotation. The median relative error ranges of the contrast for the image without, and with the measurement- and estimation-based correction were −10.9 to −2.9, and −1.5 to 4.8 and −7.4 to 2.6, respectively, for an FS of 10.0 × 10.0 cm2. Conclusions: The MV-scatter was strongly dependent on the FS, dose rate, and FPD position. The MV-scatter correction improved the image contrast. Advances in knowledge: The MV-scatters on the TrueBeam linac kV imaging subsystem were quantified with various MV beam parameters, and strongly depended on the fieldsize, dose rate, and flat panel detector position. The MV-scatter correction using the constructed database improved the image quality.

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Lifton, Joseph, and Tong Liu. "Ring artefact reduction via multi-point piecewise linear flat field correction for X-ray computed tomography." Optics Express 27, no. 3 (January 30, 2019): 3217. http://dx.doi.org/10.1364/oe.27.003217.

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Hu, Changmiao, Yang Bai, and Ping Tang. "DENOISING ALGORITHM FOR THE PIXEL-RESPONSE NON-UNIFORMITY CORRECTION OF A SCIENTIFIC CMOS UNDER LOW LIGHT CONDITIONS." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B3 (June 17, 2016): 749–53. http://dx.doi.org/10.5194/isprsarchives-xli-b3-749-2016.

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We present a denoising algorithm for the pixel-response non-uniformity correction of a scientific complementary metal–oxide–semiconductor (CMOS) image sensor, which captures images under extremely low-light conditions. By analyzing the integrating sphere experimental data, we present a pixel-by-pixel flat-field denoising algorithm to remove this fixed pattern noise, which occur in low-light conditions and high pixel response readouts. The response of the CMOS image sensor imaging system to the uniform radiance field shows a high level of spatial uniformity after the denoising algorithm has been applied.

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Hu, Changmiao, Yang Bai, and Ping Tang. "DENOISING ALGORITHM FOR THE PIXEL-RESPONSE NON-UNIFORMITY CORRECTION OF A SCIENTIFIC CMOS UNDER LOW LIGHT CONDITIONS." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B3 (June 17, 2016): 749–53. http://dx.doi.org/10.5194/isprs-archives-xli-b3-749-2016.

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We present a denoising algorithm for the pixel-response non-uniformity correction of a scientific complementary metal–oxide–semiconductor (CMOS) image sensor, which captures images under extremely low-light conditions. By analyzing the integrating sphere experimental data, we present a pixel-by-pixel flat-field denoising algorithm to remove this fixed pattern noise, which occur in low-light conditions and high pixel response readouts. The response of the CMOS image sensor imaging system to the uniform radiance field shows a high level of spatial uniformity after the denoising algorithm has been applied.

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Bartha, Michael C., Paul Allie, and Doug Kokot. "Field Observations of Placement for Large-Panel Flat and Curved Displays for Presbyopic and Prepresbyopic Computer Users." Proceedings of the Human Factors and Ergonomics Society Annual Meeting 64, no. 1 (December 2020): 526–30. http://dx.doi.org/10.1177/1071181320641119.

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Displays with panels larger than 30 inches are being provided to workers in corporate settings at an increasing rate. Additionally, some models are offered that have curved panels. This field study was designed to observe user selected position of 34 inch curved and flat displays and determine if there are positioning, user experience and satisfaction differences between pre-presbyopes and presbyope workers who have multifocal vision correction. The results indicate that participants position larger displays a little farther away than displays with a less than 30 inch diagonal. Newer, larger displays did not reduce reports of eye discomfort, but they did significantly reduce reports of neck and shoulder discomfort. Study participants preferred working with the curved display compared to the large flat display.

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Sharif, Muhammad, and Muhammad Gul. "Dynamics of Anisotropic Cylindrical Collapse in Energy-Momentum Squared Gravity." Physical Sciences Forum 2, no. 1 (March 19, 2021): 40. http://dx.doi.org/10.3390/ecu2021-09513.

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This paper deals with the dynamics of cylindrical collapse with anisotropic matter configuration in the context of energy-momentum squared gravity. This covariant generalization of general relativity allows the presence of T_abT^ab in the action of functional theory. Consequently, the relevant field equations are different from general relativity only in the presence of matter sources. In this theory, there is a maximum energy density and a minimum scale factor of the early universe. This means that there is a bounce at early times which avoids the presence of an early-time singularity. Moreover, this theory possesses a true sequence of cosmological eras. However, the cosmological constant does not play an important role in the early times and becomes important only after the matter-dominated era. In this theory, the “repulsive” nature of the cosmological constant plays a crucial role at early times in resolving the singularity. We formulate the corresponding field equations as well as junction conditions. We construct dynamical equations through the Misner–Sharp technique and examine the impact of energy-momentum squared gravity on the collapse rate. We develop a relation among fluid parameters, correction terms and Weyl scalar and examine the effects of anisotropy, effective matter variables and correction terms on the collapsing phenomenon. Due to the presence of anisotropic pressure, spacetime is no longer considered to be conformally flat. To obtain conformally flat spacetime, we neglect the impact of anisotropy and assume the isotropic matter distribution which yields homogeneity of the energy density and conformally flat spacetime. The hydrodynamical force determines the stability of the system and prevents the collapsing as well as expanding process for the constant energy-momentum squared gravity model. We conclude that positive correction terms and anisotropy provide the anti-gravitational behavior leading to the stability of self-gravitating objects and hence prevent the collapsing process.

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DE LORENCI, V. A., G. MENEZES, and N. F. SVAITER. "LIGHT-CONE FLUCTUATIONS AND THE RENORMALIZED STRESS TENSOR OF A MASSLESS SCALAR FIELD." International Journal of Modern Physics A 28, no. 01 (January 10, 2013): 1350001. http://dx.doi.org/10.1142/s0217751x13500012.

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We investigate the effects of light-cone fluctuations over the renormalized vacuum expectation value of the stress–energy tensor of a real massless minimally coupled scalar field defined in a (d+1)-dimensional flat space–time with topology [Formula: see text]. For modeling the influence of light-cone fluctuations over the quantum field, we consider a random Klein–Gordon equation. We study the case of centered Gaussian processes. After taking into account all the realizations of the random processes, we present the correction caused by random fluctuations. The averaged renormalized vacuum expectation value of the stress–energy associated with the scalar field is presented.

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Chouteau, Michel, and Karl Bouchard. "Two‐dimensional terrain correction in magnetotelluric surveys." GEOPHYSICS 53, no. 6 (June 1988): 854–62. http://dx.doi.org/10.1190/1.1442520.

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Field distortions caused by topography hamper the interpretation of magnetotelluric (MT) data. Topographic features that can be simulated by two‐dimensional models seriously affect the H-polarization results. A technique to reduce those effects in MT data uses a finite‐element program to compute correction coefficients. After correction, the resulting data can be interpreted as if they were obtained over a flat surface and depended only on the subsurface structure. The technique is applied to four examples representative of MT survey targets in high‐relief terrain. Results indicate that terrain correction removes the misleading topographic anomalies and improves the quality of subsurface interpretation in regions where the surface relief is two‐dimensional. The correction technique yields some geometrical distortion of the original subsurface structure, but the distortion is usually of small importance. In practice, telluric dipoles of realistic length do not smooth out topographic effects having wavelengths longer than the telluric dipole. A practical procedure derived from the proposed technique allows terrain correction when the relief is approximately two‐dimensional.

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SUZUKI, NORIKAZU. "DEVIATION FROM THE THERMAL EQUILIBRIUM OF THE ACCELERATED DETEKTOR DUE TO THE FIELD THEORETICAL DIVERGENCE." International Journal of Modern Physics A 17, no. 06n07 (March 20, 2002): 1026–32. http://dx.doi.org/10.1142/s0217751x02010455.

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We investigate the influence of the field-theoretical divergence on the thermal equilibrium property by employing the model of a uniformly accelerated monopole detector nonlinearly coupled to a scalar field in the flat space with the Dirichlet boundary condition. Introducing the Gaussian switching factor to the interaction between the detector and the field, we estimate the correction to the response function coming from this swithing factor. We find that the deviation from the thermal equilibrium of the response of this detector is mostly due to the interplay between the divergence and the existence of the boundary, when the detector is kept switched on during a large but finite amount of time.

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Ren, Yong, Sheng Wu, Mijian Wang, and Zhongjie Cen. "Study on Construction of a Medical X-Ray Direct Digital Radiography System and Hybrid Preprocessing Methods." Computational and Mathematical Methods in Medicine 2014 (2014): 1–7. http://dx.doi.org/10.1155/2014/495729.

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We construct a medical X-ray direct digital radiography (DDR) system based on a CCD (charge-coupled devices) camera. For the original images captured from X-ray exposure, computer first executes image flat-field correction and image gamma correction, and then carries out image contrast enhancement. A hybrid image contrast enhancement algorithm which is based on sharp frequency localization-contourlet transform (SFL-CT) and contrast limited adaptive histogram equalization (CLAHE), is proposed and verified by the clinical DDR images. Experimental results show that, for the medical X-ray DDR images, the proposed comprehensive preprocessing algorithm can not only greatly enhance the contrast and detail information, but also improve the resolution capability of DDR system.

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Kim, D., S. Kim, J. Youn, B. Choe, T. Suh, and H. Lee. "SU-FF-I-23: An Iterative Method for Flat-Field Correction of Digital Radiography with Arbitrary Detector Position." Medical Physics 32, no. 6Part3 (May 26, 2005): 1909. http://dx.doi.org/10.1118/1.1997503.

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Hidayat, Wahyu, and Wrego Seno Giamboro. "Analisis Continuous Wavelet Transform (CWT) Anomali Residual Medan Gravitasi Di Situs Geologi Karangsambung Kebumen Jawa Tengah." Jurnal Mineral, Energi dan Lingkungan 2, no. 2 (February 11, 2019): 61. http://dx.doi.org/10.31315/jmel.v2i2.2368.

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Gravity method is a passive geophysical method that provides information on the distribution of rock density below the surface. The gravity method has a weakness at the level of ambiguity in determining the depth of the anomaly. This study aims to determine the depth of the anomaly using Continuous Wavelet Transform (CWT) analysis to overcome the value of ambiguity, so that the results obtained have a high degree of accuracy. The research method is data survey / acquisition and data analysis. This research was conducted in Karangsambung Kebumen, Central Java with the acquisition of gravitational data as many as 56 measurement points. The results of data acquisition then analyzed included reading to mGal, tool height correction, drift, tides, latitude, free air correction, Bouguer correction, and field correction. The results of this correction obtained Complete Bouguer Anomalies (ABL) values which were then reduced to flat fields and regional-residual anomaly filters. The next step is CWT analysis by making incisions on residual anomaly maps. The results showed that the source of the anomaly was between ± 39.2 - 122.9 meters.

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Held, Dominique P., and Jakob Mann. "Detection of wakes in the inflow of turbines using nacelle lidars." Wind Energy Science 4, no. 3 (July 11, 2019): 407–20. http://dx.doi.org/10.5194/wes-4-407-2019.

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Abstract. Nacelle-mounted lidar systems offer the possibility of remotely sensing the inflow of wind turbines. Due to the limitation of line-of-sight measurements and the limited number of focus positions, assumptions are necessary to derive useful inflow characteristics. Typically, horizontally homogeneous inflow is assumed which is well satisfied in flat, homogeneous terrain and over sufficiently large time averages. However, it is violated if a wake impinges the field of view of one of the beams. In such situations, the turbine yaw misalignment measurements show large biases which require the detection and correction of these observations. Here, a detection algorithm is proposed based on the spectral broadening of the Doppler spectrum due to turbulence within the probe volume. The small-scale turbulence generated within wake flows will typically lead to a significantly larger broadening than in the ambient flow. Thus, by comparing the spectral widths at several measurement locations, situations where a wake is impinging one or more measurement locations can be identified. The correction method is based on an empirical relationship between the difference in turbulence levels at distinct beams and the difference in wind direction derived from the lidar and the real wind direction. The performance of the algorithm is evaluated in a field experiment identifying all wake situations and, thus, correcting the lidar derived wind direction.

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Canfield, Ryan A., Jan Ahrens, Jill Bingham, Barry Fetzer, Thomas Müller-Wirts, Matthew O’Donnell, Gary Georgeson, and Ivan Pelivanov. "Distance and Angle Correction System (DACS) for a kHz A-Scan Rate Pump-Probe Laser-Ultrasound Inspection." Sensors 20, no. 24 (December 18, 2020): 7266. http://dx.doi.org/10.3390/s20247266.

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Non-contact optical detection of ultrasound critically depends on the amount of light collected from the detection surface. Although it can be optimized in multiple ways for an ideal flat polished surface, industrial non-destructive testing and evaluation (NDT&E) usually requires optical detectors to be robust for unpolished material surfaces that are usually rough and curved. Confocal detectors provide the best light collection but must trade off sensitivity with depth of field. Specifically, detection efficiency increases with the numerical aperture (NA) of the detector, but the depth of field drops. Therefore, fast realignment of the detector focal point is critical for in-field applications. Here, we propose an optical distance and angle correction system (DACS) and demonstrate it in a kHz-rate laser-ultrasound inspection system. It incorporates a Sagnac interferometer on receive for the fast scanning of aircraft composites, which minimizes the required initial alignment. We show that DACS performs stably for different composite surfaces while providing ±2° angular and ±2 mm axial automatic correction with a maximum 100 ms realignment time.

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Jahani Poshteh, Mohammad Bagher, and Nematollah Riazi. "A new nonlinear electrodynamics and electrically charged regular black holes." International Journal of Modern Physics D 30, no. 11 (June 28, 2021): 2150079. http://dx.doi.org/10.1142/s0218271821500796.

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A regular static, spherically symmetric electrically charged black hole solution of general relativity coupled to a new theory for nonlinear electrodynamics is presented. This theory has the interesting feature that, at far distances from the black hole, in the weak field limit, the theory reduces to Maxwell Lagrangian with Heisenberg–Euler correction term of quantum electrodynamics. The singular center of the black hole is replaced by flat, de Sitter, or anti de Sitter space, if the spacetime in which the black hole is embedded is asymptotically flat, de Sitter, or anti de Sitter, respectively. Requiring the correspondence to Heisenberg–Euler Lagrangian at large distances, in the weak field limit, we find that (i) a minimum mass is required for the formation of an event horizon for the regular static, spherically symmetric solution of the theory, and, (ii) the mass of the solution must be quantized. We also study the basic thermodynamic properties of the black hole solution and show that they are qualitatively similar to those of Reissner–Nordström black hole.

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Liu, Jing Yuan, and Wen Qiang Cheng. "An Improved Shear Stress Transport(SST) Model for High Speed Flows." Applied Mechanics and Materials 229-231 (November 2012): 625–29. http://dx.doi.org/10.4028/www.scientific.net/amm.229-231.625.

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An improved Shear Stress Transport(SST) model, which allows for the compressible corrections, is proposed in this study. Numerical scheme was established by taking advantage of the improved Total Variation Diminishing (TVD) scheme and by applying implicit scheme to the negative source terms of the turbulence model. Hypersonic flat-plate boundary-layer flows and hypersonic compression ramp flows marked with separation, reattachment and shock/boundary-layer interactions are then computed. The comparisons between the computational results, the experimental results and the semi-empirical formulations show that the compressible correction term of the SST turbulence model is the scalar product of the weighted density average of the turbulent fluctuating velocity and the pressure gradients of the average flow field correlation quantities. In addition, for flow with separation and without separation, calculation results of wall pressures, friction coefficients and wall heat transfer rate distributions using the improved model and established scheme agree better with the experimental results than that using the original SST model.

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Medjoubi, K., and A. Dawiec. "Quantitative evaluation method of the threshold adjustment and the flat field correction performances of hybrid photon counting pixel detectors." Journal of Instrumentation 12, no. 12 (December 18, 2017): P12027. http://dx.doi.org/10.1088/1748-0221/12/12/p12027.

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AMIN, ADNAN, and RICKY SHIU. "PAGE SEGMENTATION AND CLASSIFICATION UTILIZING BOTTOM-UP APPROACH." International Journal of Image and Graphics 01, no. 02 (April 2001): 345–61. http://dx.doi.org/10.1142/s0219467801000219.

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Document image processing has become an increasingly important technology in the automation of office documentation tasks. Automatic document scanners such as text readers and OCR (Optical Character Recognition) systems are an essential component of systems capable of those tasks. One of the problems in this field is that the document to be read is not always placed correctly on a flat-bed scanner. This means that the document may be skewed on the scanner bed, resulting in a skewed image. This skew has a detrimental effect on document analysis, document understanding, and character segmentation and recognition. Consequently, detecting the skew of a document image and correcting it are important issues in realizing a practical document reader. This paper presents the use of analyzing the connected components extracted from the binary image of a document page. Such an analysis provides a lot of useful information, and will be used to perform skew correction, segmentation and classification of the document. Moreover, we describe two new algorithms — one for skew detection and one for skew correction. The new skew correction algorithm we propose has been shown to be fast and accurate, with run times averaging under 1.5 CPU seconds and 30 seconds real time to calculate the angle on a 5000/20 DEC workstation. Experiments on over 100 pages show that the method works well on a wide variety of layouts, including sparse textual regions, mixed fonts, multiple columns, and even for documents with a high graphical content.

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Hanlon, Tara, and David Risk. "Using computational fluid dynamics and field experiments to improve vehicle-based wind measurements for environmental monitoring." Atmospheric Measurement Techniques 13, no. 1 (January 16, 2020): 191–203. http://dx.doi.org/10.5194/amt-13-191-2020.

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Abstract. Vehicle-based measurements of wind speed and direction are presently used for a range of applications, including gas plume detection. Many applications use mobile wind measurements without knowledge of the limitations and accuracy of the mobile measurement system. Our research objective for this field-simulation study was to understand how anemometer placement and the vehicle's external airflow field affect measurement accuracy of vehicle-mounted anemometers. Computational fluid dynamic (CFD) simulations were generated in ANSYS Fluent to model the external flow field of a research truck under varying vehicle speed and wind yaw angle. The CFD simulations provided a quantitative description of fluid flow surrounding the vehicle and demonstrated that the change in wind speed magnitude from the inlet increased as the wind yaw angle between the inlet and the vehicle's longitudinal axis increased. The CFD results were used to develop empirical speed correction factors at specified yaw angles and to derive an aerodynamics-based correction function calibrated for wind yaw angle and anemometer placement. For comparison with CFD, we designed field tests on a square, 12.8 km route in flat, treeless terrain with stationary sonic anemometers positioned at each corner. The route was driven in replicate under varying wind conditions and vehicle speeds. The vehicle-based anemometer measurements were corrected to remove the vehicle speed and course vector. From the field trials, we observed that vehicle-based wind speed measurements differed in average magnitude in each of the upwind, downwind, and crosswind directions. The difference from stationary anemometers increased as the yaw angle between the wind direction and the truck's longitudinal axis increased, confirming the vehicle's impact on the surrounding flow field and validating the trends in CFD. To further explore the accuracy of CFD, we applied the function derived from the simulations to the field data and again compared these with stationary measurements. From this study, we were able to make recommendations for anemometer placement, demonstrate the importance of applying aerodynamics-based correction factors to vehicle-based wind measurements, and identify ways to improve the empirical aerodynamic-based correction factors.

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Beasley, Craig, and Walt Lynn. "The zero‐velocity layer: Migration from irregular surfaces." GEOPHYSICS 57, no. 11 (November 1992): 1435–43. http://dx.doi.org/10.1190/1.1443211.

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Seismic data acquired in areas with irregular topography are usually corrected to a flat datum before migration. A time‐honored technique for handling elevation changes is to time shift the data before application of migration. This simple time shift, or elevation‐static correction, cannot properly represent wide‐angle or dipping reflections as they would have been recorded at the datum. As a result, when elevation varies significantly, accuracy in event positioning may be compromised for migration and other wave‐equation processes, such as dip moveout processing (DMO). Traditionally, such over‐ and under‐migration artifacts have been dealt with by increasing or decreasing the migration velocity. However, simple adjustment of the migration velocity cannot undo the wave‐field distortions induced in seismic data acquired over varying elevations. More sophisticated and accurate solutions such as wave‐equation datuming are too computationally demanding for routine use. Here, we propose an efficient and accurate technique for doing migration from irregular surfaces using conventional migration algorithms. As in elevation‐static corrections, surface‐recorded data are time‐shifted to a horizontal datum; for our process, we choose to have that datum elevation lie at or above the highest elevation in the survey. After migration, the datum elevation can always be adjusted to any other level by means of a bulk time shift. In the migration step, the velocity is set to zero (or some very small value) in the layer between the surface and the datum; below the original surface, the interval velocity represents the best estimate of the subsurface geology. By adding a zero‐velocity layer, the migration algorithm is applied to the data from the flat datum and no lateral propagation is allowed until a nonzero velocity is encountered at the recording surface. Synthetic and field data examples demonstrate that use of the “zero‐velocity layer” significantly improves imaging accuracy relative to conventional migration from a flat datum. Moreover, the geologically derived migration‐velocity field need not be adjusted to compensate for shortcomings in the datum‐static procedure. The technique can be extended to prestack processes such as DMO, shot‐ and receiver‐gather downward extrapolation, and migration and thus suggests a unified approach to processing data from irregular surfaces.

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Mittag, Marco, Alexander Hempelmann, José Nicolás González-Pérez, and Jürgen H. M. M. Schmitt. "The Data Reduction Pipeline of the Hamburg Robotic Telescope." Advances in Astronomy 2010 (2010): 1–6. http://dx.doi.org/10.1155/2010/101502.

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The fully automatic reduction pipeline for the blue channel of the HEROS spectrograph of the Hamburg Robotic Telescope (HRT) is presented. This pipeline is started automatically after finishing the night-time observations and calibrations. The pipeline includes all necessary procedures for a reliable and complete data reduction, that is, Bias, Dark, and Flat Field correction. Also the order definition, wavelength calibration, and data extraction are included. The final output is written in a fits-format and ready to use for the astronomer. The reduction pipeline is implemented in IDL and based on the IDL reduction package REDUCE written by Piskunov and Valenti (2002).

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Kirpanev, A. V., and N. A. Kirpanev. "Methods of antenna and «antenna- radome» system analysis based on amplitude and phase measurements of their far field spherical components." Issues of radio electronics 1, no. 1 (March 13, 2021): 19–25. http://dx.doi.org/10.21778/2218-5453-2021-1-19-25.

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The main principles of electric intensity recovery of electrical field in tested antenna aperture or in the «antenna radome» system radome-close aperture field (false aperture) by amplitude and phase long-range measurements are proposed. Measurements zone means a part of the spherical surface that envelopes analyzed antenna, the boarder of this surface are determined by the kinematic scheme of rotary joint of the scanner. Recovery of amplitude and phase distribution of the field in a flat aperture area or on the plane where array irradiators are located is used in case of wave diagnostics of such type of antennas. It is proposed to use the recovered phase distribution in a false aperture for a phase correction on phased array irradiators in order to compensate phase errors appeared because of the radome. The method of radome dielectric permittivity is discussed.

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Nugayev, R. M. "An Intuitive Understanding of Black-Hole Evaporation by Viewing it in Terms of More Familiar Quantum-Field Effects in Flat Spacetime." Zeitschrift für Naturforschung A 42, no. 7 (July 1, 1987): 657–62. http://dx.doi.org/10.1515/zna-1987-0701.

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The article is aimed at an intuitive understanding of the recently explored deep connections between therm al physics, quantum field theory and general relativity. The physical effects involved in particle creation by a black hole are viewed in terms of more familiar quantum -field effects in flat spacetime. Black hole evaporation is investigated in terms of temperature correction to the Casimir effect. T he application of the Casimir effect results and those for accelerated mirrors reveals that a black hole should produce the blackbody radiation at a temperature that exactly coincides with Hawking’s result. Its blackbody nature is due to the interaction of virtual positive-energy particles with the surface of a “cavity” formed by the Schwarzchild gravitational field potential barrier. The virtual particles are “squeezed out” by the contraction of the potential barrier and appear to an observer at J+ as the real blackbody ones.

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Stanton, M., W. C. Phillips, Y. Li, and K. Kalata. "Correcting spatial distortions and nonuniform response in area detectors." Journal of Applied Crystallography 25, no. 5 (October 1, 1992): 549–58. http://dx.doi.org/10.1107/s0021889892004035.

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Software and hardware methods have been developed to correct images for spatial and intensity distortions produced by optical and electro-optical components in X-ray area detectors. Spatial distortions are divided into two types: gross distortions produced by the inherent properties of the detector components and local distortions formed by irregularities in the components. Intensity distortions are separated into three types: those caused by background nonuniformity; those resulting from pixel-dependent nonuniform intensity response; and those resulting from time-dependent variations in background and incident beam intensity. From background, flat-field, reference and mask images, `forward' and `reverse' interpolation tables are generated to correct for spatial distortions and a lookup table is generated to correct for nonuniform sensitivity. The routines have been used successfully on four different area detectors to correct entire images or to correct intensities of individual Bragg peaks. The spatial-distortion correction is good to within 0.1 pixels and the nonuniformity correction to ≲ 2%.

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Dueñas, J. G., and N. F. Svaiter. "Riemann zeta zeros and zero-point energy." International Journal of Modern Physics A 29, no. 09 (April 8, 2014): 1450051. http://dx.doi.org/10.1142/s0217751x14500511.

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The sequence of nontrivial zeros of the Riemann zeta function is zeta regularizable. Therefore, systems with countably infinite number of degrees of freedom described by self-adjoint operators whose spectra is given by this sequence admit a functional integral formulation. We discuss the consequences of the existence of such self-adjoint operators in field theory framework. We assume that they act on a massive scalar field coupled to a background field in a (d+1)-dimensional flat space–time where the scalar field is confined to the interval [0, a] in one of its dimensions and there are no restrictions in the other dimensions. The renormalized zero-point energy of this system is presented using techniques of dimensional and analytic regularization. In even-dimensional space–time, the series that defines the regularized vacuum energy is finite. For the odd-dimensional case, to obtain a finite vacuum energy per unit area, we are forced to introduce mass counterterms. A Riemann mass appears, which is the correction to the mass of the field generated by the nontrivial zeros of the Riemann zeta function.

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Weitkamp, T., D. Haas, D. Wegrzynek, and A. Rack. "ANKAphase: software for single-distance phase retrieval from inline X-ray phase-contrast radiographs." Journal of Synchrotron Radiation 18, no. 4 (March 16, 2011): 617–29. http://dx.doi.org/10.1107/s0909049511002895.

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A computer program namedANKAphaseis presented that processes X-ray inline phase-contrast radiographs by reconstructing the projected thickness of the object(s) imaged. The program uses a single-distance non-iterative phase-retrieval algorithm described by David Paganinet al.[(2002),J. Microsc.206, 33–40]. Allowing for non-negligible absorption in the sample, this method is strictly valid only for monochromatic illumination and single-material objects but tolerates deviations from these conditions, especially polychromaticity.ANKAphaseis designed to be applied to tomography data (although it does not perform tomographic reconstruction itself). It can process series of images and perform flat-field and dark-field correction. Written in Java,ANKAphasehas an intuitive graphical user interface and can be run either as a stand-alone application or as a plugin toImageJ, a widely used scientific image-processing program. A description ofANKAphaseis given and example applications are shown.

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Lim, Seokbin, and Philipp Baldovi. "Observation of the Velocity Variation of an Explosively-Driven Flat Flyer Depending on the Flyer Width." Applied Sciences 9, no. 1 (December 28, 2018): 97. http://dx.doi.org/10.3390/app9010097.

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Lim proposed a theoretical study on the velocity profile of an explosively-driven flat flyer affected by the rarefaction (or release wave) intrusion during the metal’s projection. This work shows somewhat reasonable agreement in a given range. However, this work is limited only in the early stage of detonation (~3 µs), and the larger scaled flyer projection (or extended time duration) behavior is needed for an engineering perspective. As continued work originating from this investigation, the velocity profile of explosively-driven flyers with different widths is studied based on multiple different approaches which include hydrocode simulation, the Gurney model, and Baum’s side loss correction (or effective charge mass approach), followed by a series of field experiments. In this study, the focus is on the observation of the flat flyer velocity (or terminal velocity) variation, depending on the width of the flyers which vary from 12, 25, 50, and 75 mm (or 100 mm). The terminal velocity profile variation, depending on the flyer width, is observed, and a general trend is identified.

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Hördt, Andreas, and Martin Müller. "Understanding LOTEM data from mountainous terrain." GEOPHYSICS 65, no. 4 (July 2000): 1113–23. http://dx.doi.org/10.1190/1.1444804.

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Long‐offset transient electromagnetic (LOTEM) data from the Vesuvius volcano, in Italy, show that the EM response of the topography is a potential cause of data distortions. A modeling study was carried out to simulate the effect of mountainous terrain on vertical magnetic‐field time derivatives using a 3-D finite‐difference code. The objectives were to assess the importance of topographic effects and to help identify them in existing field data. The total effect of topography on the LOTEM response can be considered as a combination of four distortions of the corresponding responses for a flat terrain. First, the receiver is at some height above the flat surface. Second, the mountain acts as a conductive body displacing air. Third, large loop receivers are nonhorizontal and sense a combination of horizontal and vertical magnetic fields. Finally, the electromagnetic coupling between the mountain and deeper‐lying structure modifies the structure response. Each of the effects can be identified in field data recorded at Mount Vesuvius. The topographic induced distortions for the model used in this study are moderate in the sense that 1-D inversions of the theoretical data still recover the gross conductivity structure, albeit with small deviations from the true parameters. Although this result might imply that topography might be ignored during the first stage of an interpretation, no simple correction method is evident, so topography will have to be included in any 2-D or 3-D inversion attempt.

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Etzold, S., N. Buchmann, and W. Eugster. "Contribution of advection to the carbon budget measured by eddy covariance at a steep mountain slope forest in Switzerland." Biogeosciences 7, no. 8 (August 17, 2010): 2461–75. http://dx.doi.org/10.5194/bg-7-2461-2010.

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Abstract. We calculated the contribution of advection to the C budget measured by the eddy covariance (EC) technique for a steep and forested mountain site (CarboEurope site CH-Lae, Lägeren, Switzerland) during the growing season 2007 (May to August). Thereby we followed two approaches: (1) the physical correction of the EC data for directly measured advection terms and (2) the u∗ filter approach that replaces periods with u∗ below a site-specific threshold with empirically modelled fluxes. We found good agreement between the two approaches in terms of daily (linear regression slope: 0.78 ± 0.04, intercept: 0.68 ± 0.29 μmol m−2 s−1, adj. R2=0.78) and seasonal sums of gross fluxes (difference ≤ 12%), when using a u∗ threshold of 0.3 m s−1 and correcting EC for horizontal advection only. Incorporating also vertical advection into the mass balance equation resulted in unrealistic and highly erratic fluxes. However, on a daily basis vertical advection cancelled out to nearly zero. The u∗ filter seems to account primarily for respiration fluxes, which are mainly affected by horizontal advection. We could confirm our corrections by a cross-validation with independent approaches, such as soil respiration chamber measurements, light curves and energy budget closure. Our results show that flux measurements on steep sites with complex topography are possible. Actually, sloping sites seem to have the advantage over flat sites that advection measurements can be reduced to a simplified two-dimensional measurement approach due to the two-dimensional characteristics of the wind field at those sites.

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Journal articles on the topic 'Flat-field correction'

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