The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Tomochika Matsuyama - One of the best experts on this subject based on the ideXlab platform.
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Coherent Smith-Purcell radiation in the millimeter-wave region from a short-bunch Beam of relativistic electrons
Physical Review E, 1998Co-Authors: Yukio Shibata, S. Hasebe, K. Ishi, Shuichi Ono, Mikihiko Ikezawa, T. Nakazato, Masayuki Oyamada, S. Urasawa, Toshiharu Takahashi, Tomochika MatsuyamaAbstract:Coherent Smith-Purcell radiation, generated by the passage of short-bunched electrons of 150 and 40 MeV above a lamellar-type grating, has been observed in the millimeter-wave region. The intensity of the coherent radiation is proportional to the square of the Beam current, and is enhanced by a factor of $\ensuremath{\sim}{10}^{8}$ in comparison with theoretical intensity of ordinary Smith-Purcell radiation. The enhancement factor is of the same order of magnitude as the number of electrons in a bunch. The intensity decreases with the increase of the Beam Height, or the distance of the Beam from the grating, and the dependence on the Beam Height is expressed approximately by the modified Bessel function of the zeroth order. Owing to a relativistic effect the radiation is emitted in a narrow direction along the plane normal to the grating. The intensity of the radiation varies in a periodic way when the groove depth of the grating was changed. The observed properties of radiation are explained well by a three-dimensional theory of Smith-Purcell radiation, in which the coherence effect due to bunched electrons is taken into account.
Yukio Shibata - One of the best experts on this subject based on the ideXlab platform.
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Coherent Smith-Purcell radiation in the millimeter-wave region from a short-bunch Beam of relativistic electrons
Physical Review E, 1998Co-Authors: Yukio Shibata, S. Hasebe, K. Ishi, Shuichi Ono, Mikihiko Ikezawa, T. Nakazato, Masayuki Oyamada, S. Urasawa, Toshiharu Takahashi, Tomochika MatsuyamaAbstract:Coherent Smith-Purcell radiation, generated by the passage of short-bunched electrons of 150 and 40 MeV above a lamellar-type grating, has been observed in the millimeter-wave region. The intensity of the coherent radiation is proportional to the square of the Beam current, and is enhanced by a factor of $\ensuremath{\sim}{10}^{8}$ in comparison with theoretical intensity of ordinary Smith-Purcell radiation. The enhancement factor is of the same order of magnitude as the number of electrons in a bunch. The intensity decreases with the increase of the Beam Height, or the distance of the Beam from the grating, and the dependence on the Beam Height is expressed approximately by the modified Bessel function of the zeroth order. Owing to a relativistic effect the radiation is emitted in a narrow direction along the plane normal to the grating. The intensity of the radiation varies in a periodic way when the groove depth of the grating was changed. The observed properties of radiation are explained well by a three-dimensional theory of Smith-Purcell radiation, in which the coherence effect due to bunched electrons is taken into account.
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Coherent Smith‐Purcell radiation in the far‐infrared region from a short‐bunched electron Beam
AIP Conference Proceedings, 1996Co-Authors: Yukio Shibata, S. Hasebe, K. Ishi, Mikihiko Ikezawa, T. Nakazato, Masayuki Oyamada, S. Urasawa, Taiki Takahashi, T. Yamakawa, K. TakamiAbstract:Coherent Smith‐Purcell radiation, emitted from short‐bunched electrons passing by a lamellar‐type grating of aluminum, has been observed in the millimeter wave region. The energy of the electrons is either 42 MeV when they are accelerated by an L‐band linear accelerator or 150 MeV accelerated by an S‐band one. The intensity of the radiation is proportional to the square of the Beam current. The radiation is linearly polarized, and the electric vector of the radiation is in the plane defined by the observing point and the Beam trajectory. The intensity decreases with the Beam Height, i.e. the distance of the Beam from the surface of the grating, in accordance with the modified Bessel function of zeroth order.
Harald Kunstmann - One of the best experts on this subject based on the ideXlab platform.
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Joint statistical correction of clutters, spokes and Beam Height for a radar derived precipitation climatology in southern Germany
Hydrology and Earth System Sciences, 2012Co-Authors: A. Wagner, J. Seltmann, Harald KunstmannAbstract:First results of radar derived climatology have emerged over the last years, as datasets of appropriate extent are becoming available. Usually, these statistics are based on time series lasting up to ten years as continuous storage of radar data was often not achieved before. This kind of climatology demands a high level of data quality. Small deviations or minor systematic under- or overestimations in single radar images become a major cause of error in statistical analysis. Extensive corrections of radar data are a crucial prerequisite for radar derived climatology. We present a new statistical post-correction scheme based on a climatological analysis of seven years of radar data of the Munich weather radar (2000–2006) operated by DWD (German Weather Service). Original radar products are used subject only to corrections within the signal processor without any further corrections on single radar images. The aim of this statistical correction is to make up for the average systematic errors caused by clutter, propagation, or measuring effects but to conserve small-scale natural variations in space. The statistical correction is based on a thorough analysis of the different causes of possible errors for the Munich weather radar. This analysis revealed the following basic effects: the decrease of rain amount as a function of Height and distance from the radar, clutter effects such as clutter remnants after filtering, holes by eliminated clutter or shading effects from obstacles near the radar, visible as spokes, as well as the influence of the bright band. The correction algorithm is correspondingly based on these results. It consists of three modules. The first one is an altitude correction which minimises measuring effects. The second module corrects clutter effects and disturbances and the third one realises a mean adjustment to selected rain gauges. Two different sets of radar products are used. The statistical analysis as well as module 1 and module 2 of the correction algorithm are based on frequencies of the six reflectivity levels within the so-called PX product . For correction module 3 and for the validation of the correction algorithm, rain amounts are calculated from the 8-bit so-called DX product . The correction algorithm is created to post-correct climatological or statistical analysis of radar data with a temporal resolution larger than one year. The correction algorithm is used for frequencies of occurrence of radar reflectivities which enables its application even for radar products such as DWD's cell-tracking-product CONRAD. Application (2004–2006) and validation (2007–2009) periods of this correction algorithm with rain gauges show an increased conformity for radar climatology after the statistical correction. In the years 2004 to 2006 the Root-Mean-Square-Error (RMSE) between mean annual rain amounts of rain gauges and corresponding radar pixels decreases from 262 mm to 118 mm excluding those pairs of values where the rain gauges are situated in areas of obviously corrupted radar data. The results for the validation period 2007 to 2009 are based on all pairs of values and show a decline of the RMSE from 322 mm to 174 mm.
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Joint statistical correction of clutters, spokes and Beam Height for a radar climatology in Southern Germany
2012Co-Authors: A. Wagner, J. Seltmann, Harald KunstmannAbstract:Abstract. Extensive corrections of radar data are a crucial prerequisite for radar derived climatology. This kind of climatology demands a high level of data quality. Little deviations or minor systematic underestimations or overestimations in single radar images become a major cause of error in statistical analysis. First results of radar derived climatology have emerged over the last years, as data sets of appropriate extent are becoming available. Usually, these statistics are based on time series lasting up to ten years as storage of radar data was not achieved before. We present a new statistical post-correction scheme, which is based on seven years of radar data of the Munich weather radar (2000–2006) that is operated by DWD (German Weather Service). The typical correction algorithms for single radar images, such as clutter corrections, are used. Then an additional statistical post-correction based on the results of a climatological analysis from radar images follows. The aim of this statistical correction is to correct systematic errors caused by clutter effects or measuring effects but to conserve small-scale natural variations in space. The statistical correction is based on a thorough analysis of the different causes of possible errors for the Munich weather radar. This robust analysis revealed the following basic effects: the decrease of rain rate in relation to Height and distance from the radar, clutter effects such as remaining clutter, eliminated clutter or shading effects from obstacles near the radar, visible as spokes, as well as the influence of the Bright Band. The correction algorithm is correspondingly based on these results. It consists of three modules. The first one is an altitude correction, which minimizes measuring effects. The second module corrects clutter effects and the third one realizes a mean adjustment to selected rain gauges. Two different radar products are used. The statistical analysis as well as module one and module two of the correction algorithm are based on frequencies of occurrence of the so-called PX-product with six reflectivity levels. For correction module 3 and for the validation of the correction algorithm rain rates are calculated from the 8-bit-depth so-called DX-product. An application (2004–2006) and a validation (2007–2009) of this correction algorithm with rain gauges show a much higher conformity for radar climatology after the statistical correction. In the years 2004 to 2006 the Root-Mean-Square-Error (RMSE) decreases from 262 mm to 118 mm excluding those pair of values where the rain gauges are situated in areas of obviously corrupted radar data. The results for the validation period 2007 to 2009 are based on all pairs of values and show a decline of the RMSE from 322 mm to 174 mm.
Masayuki Oyamada - One of the best experts on this subject based on the ideXlab platform.
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Coherent Smith-Purcell radiation in the millimeter-wave region from a short-bunch Beam of relativistic electrons
Physical Review E, 1998Co-Authors: Yukio Shibata, S. Hasebe, K. Ishi, Shuichi Ono, Mikihiko Ikezawa, T. Nakazato, Masayuki Oyamada, S. Urasawa, Toshiharu Takahashi, Tomochika MatsuyamaAbstract:Coherent Smith-Purcell radiation, generated by the passage of short-bunched electrons of 150 and 40 MeV above a lamellar-type grating, has been observed in the millimeter-wave region. The intensity of the coherent radiation is proportional to the square of the Beam current, and is enhanced by a factor of $\ensuremath{\sim}{10}^{8}$ in comparison with theoretical intensity of ordinary Smith-Purcell radiation. The enhancement factor is of the same order of magnitude as the number of electrons in a bunch. The intensity decreases with the increase of the Beam Height, or the distance of the Beam from the grating, and the dependence on the Beam Height is expressed approximately by the modified Bessel function of the zeroth order. Owing to a relativistic effect the radiation is emitted in a narrow direction along the plane normal to the grating. The intensity of the radiation varies in a periodic way when the groove depth of the grating was changed. The observed properties of radiation are explained well by a three-dimensional theory of Smith-Purcell radiation, in which the coherence effect due to bunched electrons is taken into account.
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Coherent Smith‐Purcell radiation in the far‐infrared region from a short‐bunched electron Beam
AIP Conference Proceedings, 1996Co-Authors: Yukio Shibata, S. Hasebe, K. Ishi, Mikihiko Ikezawa, T. Nakazato, Masayuki Oyamada, S. Urasawa, Taiki Takahashi, T. Yamakawa, K. TakamiAbstract:Coherent Smith‐Purcell radiation, emitted from short‐bunched electrons passing by a lamellar‐type grating of aluminum, has been observed in the millimeter wave region. The energy of the electrons is either 42 MeV when they are accelerated by an L‐band linear accelerator or 150 MeV accelerated by an S‐band one. The intensity of the radiation is proportional to the square of the Beam current. The radiation is linearly polarized, and the electric vector of the radiation is in the plane defined by the observing point and the Beam trajectory. The intensity decreases with the Beam Height, i.e. the distance of the Beam from the surface of the grating, in accordance with the modified Bessel function of zeroth order.
K. Ishi - One of the best experts on this subject based on the ideXlab platform.
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Coherent Smith-Purcell radiation in the millimeter-wave region from a short-bunch Beam of relativistic electrons
Physical Review E, 1998Co-Authors: Yukio Shibata, S. Hasebe, K. Ishi, Shuichi Ono, Mikihiko Ikezawa, T. Nakazato, Masayuki Oyamada, S. Urasawa, Toshiharu Takahashi, Tomochika MatsuyamaAbstract:Coherent Smith-Purcell radiation, generated by the passage of short-bunched electrons of 150 and 40 MeV above a lamellar-type grating, has been observed in the millimeter-wave region. The intensity of the coherent radiation is proportional to the square of the Beam current, and is enhanced by a factor of $\ensuremath{\sim}{10}^{8}$ in comparison with theoretical intensity of ordinary Smith-Purcell radiation. The enhancement factor is of the same order of magnitude as the number of electrons in a bunch. The intensity decreases with the increase of the Beam Height, or the distance of the Beam from the grating, and the dependence on the Beam Height is expressed approximately by the modified Bessel function of the zeroth order. Owing to a relativistic effect the radiation is emitted in a narrow direction along the plane normal to the grating. The intensity of the radiation varies in a periodic way when the groove depth of the grating was changed. The observed properties of radiation are explained well by a three-dimensional theory of Smith-Purcell radiation, in which the coherence effect due to bunched electrons is taken into account.
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Coherent Smith‐Purcell radiation in the far‐infrared region from a short‐bunched electron Beam
AIP Conference Proceedings, 1996Co-Authors: Yukio Shibata, S. Hasebe, K. Ishi, Mikihiko Ikezawa, T. Nakazato, Masayuki Oyamada, S. Urasawa, Taiki Takahashi, T. Yamakawa, K. TakamiAbstract:Coherent Smith‐Purcell radiation, emitted from short‐bunched electrons passing by a lamellar‐type grating of aluminum, has been observed in the millimeter wave region. The energy of the electrons is either 42 MeV when they are accelerated by an L‐band linear accelerator or 150 MeV accelerated by an S‐band one. The intensity of the radiation is proportional to the square of the Beam current. The radiation is linearly polarized, and the electric vector of the radiation is in the plane defined by the observing point and the Beam trajectory. The intensity decreases with the Beam Height, i.e. the distance of the Beam from the surface of the grating, in accordance with the modified Bessel function of zeroth order.