The Experts below are selected from a list of 27432 Experts worldwide ranked by ideXlab platform
Xiao Dong - One of the best experts on this subject based on the ideXlab platform.
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Preliminary Significant Wave Height Retrieval from Interferometric Imaging Radar Altimeter Aboard the Chinese Tiangong-2 Space Laboratory
'MDPI AG', 2021Co-Authors: Lin Ren, Xiao Dong, Jingsong Yang, Yongjun Jia, Yunhua ZhangAbstract:The interferometric Imaging Radar altimeter (InIRA) aboard the Chinese Tiangong-2 space laboratory is the first spaceborne Imaging Radar working at low incidence angles. This study focuses on the retrieval of significant wave heights (SWHs) from InIRA data. The retrieved SWHs can be used for correcting the sea state bias of InIRA-derived sea surface heights and can supplement SWH products from other spaceborne sensors. First, we analyzed tilt, range bunching and velocity bunching wave modulations at low incidence angles, and we found clear dependencies between the SWH and two defined factors, range and azimuth integration, for ocean waves in the range and azimuth directions, respectively. These dependencies were further confirmed using InIRA measurements and collocated WaveWatch III (WW3) data. Then, an empirical orthogonal SWH model using the range and azimuth integration factors as model inputs was proposed. The model was segmented by the incidence angle, and the model coefficients were estimated by fitting the collocation at each incidence angle bin. Finally, the SWHs were retrieved from InIRA data using the proposed model. The retrievals were validated using both WW3 and altimeter (JASON2, JASON3, SARAL, and HY2A) SWHs. The validation with WW3 data shows a root mean square error (RMSE) of 0.43 m, while the average RMSE with all traditional altimeter data is 0.48 m. This indicates that the InIRA can be used to measure SWHs
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inverse weighting method for sea surface wind direction retrieval from tiangong 2 interferometric Imaging Radar altimeter imagery
IEEE Asia-Pacific Conference on Synthetic Aperture Radar, 2019Co-Authors: Yunhua Zhang, Xiao DongAbstract:The Interferometric Imaging Radar Altimeter (InIRA) onboard Chinese Tiangong-2 space laboratory is a Ku-band interferometric Radar whose major aim is to measure the wide-swath ocean topography. A large number of observation data of key sea areas and typical land areas have been obtained since the start-up of InIRA. The sea surface wind field plays a major role in marine research, including weather forecasting, ocean-air interactions, and earth climate studies. Therefore, it is of great significance to use InIRA to retrieve the sea surface wind field. The local gradient method is often used for wind direction retrieval in synthetic aperture Radar (SAR). However, the large change of incidence angles of InIRA imposes additional modulation on the gradient of the backscattering coefficient. In this paper, a method of combining Radar backscattering coefficient inverse weighting and local gradient method is used in wind direction retrieval for InIRA. The influence of backscattering coefficient attenuation caused by angle change is analyzed and then the gradient is solved. Experimental results on Tiangong-2 data show better result is obtained using the proposed method than the local gradient method.
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sea surface wind speed retrieval and validation of the interferometric Imaging Radar altimeter aboard the chinese tiangong 2 space laboratory
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2018Co-Authors: Lin Ren, Xiao Dong, Jingsong Yang, Yongjun Jia, Juan Wang, Gang ZhengAbstract:This study focuses on the retrieval and validation of sea-surface wind speeds using data from the interferometric Imaging Radar altimeter (InIRA) aboard the Chinese Tiangong-2 space laboratory. First, an empirical model, KuLMOD2, is proposed, which is a revised version of the former Ku-band low incidence model (KuLMOD) that directly relates the normalized Radar cross section σ 0 to both the wind speed and incidence angle. The revised model extends the ranges of the incidence angle and wind speed and is thus applicable to the new InIRA data. The model coefficients are estimated by fitting precipitation Radar data from the Tropical Rainfall Measuring Mission and collocated wind data from the European Centre for Medium-Range Weather Forecasts. The wind speeds are then retrieved from the InIRA data using KuLMOD2. For more efficient retrieval, a lookup table method is used to find the wind speed solution. Finally, the InIRA wind speeds are validated using collocated Advanced Scatterometer (ASCAT) wind speeds. The validation of the InIRA wind speed data shows that InIRA can capture regional changes and that the data have a bias of 0.02 m/s and a root-mean-square error of 1.58 m/s. This suggests that the InIRA data alone can provide valid wind speeds for future sea state bias correction of InIRA-derived sea-surface heights and that the InIRA data can act as a complement to data from other spaceborne wind sensors.
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Interferometric Imaging Radar Altimeter on Board Chinese Tiangong-2 Space Laboratory
2018 Asia-Pacific Microwave Conference (APMC), 2018Co-Authors: Yunhua Zhang, Xiaojin Shi, Hongjian Wang, Yueyin Tan, Wenshuai Zhai, Xiao Dong, Xueyan Kang, Qingshan Yang, Dong Li, Jingshan JiangAbstract:In this paper, We introduce the Interferometric Imaging Radar Altimeter (InIRA), the first spaceborne wide-swath ocean Radar altimeter on board Chinese Tiangong-2 space laboratory, which was launched on September 15, 2016. The major mission of InIRA is to validate the mechanism and design of new generation ocean Radar altimeter, as well as conduct preliminary application researches. The in-orbit observation results of Tiangong-2 InIRA demonstrate that it is capable of measuring the dynamic sea surface height with wide swath, sea waves of different scales and sea winds, which help us greatly improve the observation and measurement efficiency compared with traditional nadir-looking Radar altimeters. Besides, it can also be used to survey and monitor the inland waters, e.g. lakes and rivers, as well as acquire terrain digital surface model (DSM). Here, we will present some typical observation results over both ocean and land surfaces.
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design and algorithms of the tiangong 2 interferometric Imaging Radar altimeter processor
2017 Progress In Electromagnetics Research Symposium - Spring (PIERS), 2017Co-Authors: Xiao Dong, Yunhua Zhang, Wenshuai ZhaiAbstract:The Interferometric Imaging Radar Altimeter (InIRA) operating at Ku-band (13.58 GHz) was launched on Chinese Tiangong-2 space laboratory on September 15, 2016. The primary goal of Tiangong-2 InIRA is to measure wide-swath sea surface height, sea waves and sea winds. Winds and waves in the observed sea area are retrieved by processing the synthetic aperture Radar (SAR) images. The ocean surface topography and the digital elevation models of land areas are determined using the interferometric SAR (InSAR) technique. The scope of this paper is to present the processing algorithms for the generation of the Tiangong-2 InIRA images from the raw data. The focusing algorithm for generating the single look complex (SLC) image products and the interferometric processing algorithm for generating the surface topography are briefly introduced.
Gang Zheng - One of the best experts on this subject based on the ideXlab platform.
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sea surface wind speed retrieval and validation of the interferometric Imaging Radar altimeter aboard the chinese tiangong 2 space laboratory
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2018Co-Authors: Lin Ren, Xiao Dong, Jingsong Yang, Yongjun Jia, Juan Wang, Gang ZhengAbstract:This study focuses on the retrieval and validation of sea-surface wind speeds using data from the interferometric Imaging Radar altimeter (InIRA) aboard the Chinese Tiangong-2 space laboratory. First, an empirical model, KuLMOD2, is proposed, which is a revised version of the former Ku-band low incidence model (KuLMOD) that directly relates the normalized Radar cross section σ 0 to both the wind speed and incidence angle. The revised model extends the ranges of the incidence angle and wind speed and is thus applicable to the new InIRA data. The model coefficients are estimated by fitting precipitation Radar data from the Tropical Rainfall Measuring Mission and collocated wind data from the European Centre for Medium-Range Weather Forecasts. The wind speeds are then retrieved from the InIRA data using KuLMOD2. For more efficient retrieval, a lookup table method is used to find the wind speed solution. Finally, the InIRA wind speeds are validated using collocated Advanced Scatterometer (ASCAT) wind speeds. The validation of the InIRA wind speed data shows that InIRA can capture regional changes and that the data have a bias of 0.02 m/s and a root-mean-square error of 1.58 m/s. This suggests that the InIRA data alone can provide valid wind speeds for future sea state bias correction of InIRA-derived sea-surface heights and that the InIRA data can act as a complement to data from other spaceborne wind sensors.
Lin Ren - One of the best experts on this subject based on the ideXlab platform.
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Preliminary Significant Wave Height Retrieval from Interferometric Imaging Radar Altimeter Aboard the Chinese Tiangong-2 Space Laboratory
'MDPI AG', 2021Co-Authors: Lin Ren, Xiao Dong, Jingsong Yang, Yongjun Jia, Yunhua ZhangAbstract:The interferometric Imaging Radar altimeter (InIRA) aboard the Chinese Tiangong-2 space laboratory is the first spaceborne Imaging Radar working at low incidence angles. This study focuses on the retrieval of significant wave heights (SWHs) from InIRA data. The retrieved SWHs can be used for correcting the sea state bias of InIRA-derived sea surface heights and can supplement SWH products from other spaceborne sensors. First, we analyzed tilt, range bunching and velocity bunching wave modulations at low incidence angles, and we found clear dependencies between the SWH and two defined factors, range and azimuth integration, for ocean waves in the range and azimuth directions, respectively. These dependencies were further confirmed using InIRA measurements and collocated WaveWatch III (WW3) data. Then, an empirical orthogonal SWH model using the range and azimuth integration factors as model inputs was proposed. The model was segmented by the incidence angle, and the model coefficients were estimated by fitting the collocation at each incidence angle bin. Finally, the SWHs were retrieved from InIRA data using the proposed model. The retrievals were validated using both WW3 and altimeter (JASON2, JASON3, SARAL, and HY2A) SWHs. The validation with WW3 data shows a root mean square error (RMSE) of 0.43 m, while the average RMSE with all traditional altimeter data is 0.48 m. This indicates that the InIRA can be used to measure SWHs
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sea surface wind speed retrieval and validation of the interferometric Imaging Radar altimeter aboard the chinese tiangong 2 space laboratory
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2018Co-Authors: Lin Ren, Xiao Dong, Jingsong Yang, Yongjun Jia, Juan Wang, Gang ZhengAbstract:This study focuses on the retrieval and validation of sea-surface wind speeds using data from the interferometric Imaging Radar altimeter (InIRA) aboard the Chinese Tiangong-2 space laboratory. First, an empirical model, KuLMOD2, is proposed, which is a revised version of the former Ku-band low incidence model (KuLMOD) that directly relates the normalized Radar cross section σ 0 to both the wind speed and incidence angle. The revised model extends the ranges of the incidence angle and wind speed and is thus applicable to the new InIRA data. The model coefficients are estimated by fitting precipitation Radar data from the Tropical Rainfall Measuring Mission and collocated wind data from the European Centre for Medium-Range Weather Forecasts. The wind speeds are then retrieved from the InIRA data using KuLMOD2. For more efficient retrieval, a lookup table method is used to find the wind speed solution. Finally, the InIRA wind speeds are validated using collocated Advanced Scatterometer (ASCAT) wind speeds. The validation of the InIRA wind speed data shows that InIRA can capture regional changes and that the data have a bias of 0.02 m/s and a root-mean-square error of 1.58 m/s. This suggests that the InIRA data alone can provide valid wind speeds for future sea state bias correction of InIRA-derived sea-surface heights and that the InIRA data can act as a complement to data from other spaceborne wind sensors.
Peter H. Siegel - One of the best experts on this subject based on the ideXlab platform.
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thz Imaging Radar for standoff personnel screening
IEEE Transactions on Terahertz Science and Technology, 2011Co-Authors: Ken B Cooper, Goutam Chattopadhyay, Nuria Llombart, R J Dengler, B Thomas, Peter H. SiegelAbstract:A summary of the NASA Jet Propulsion Laboratory's 675 GHz Imaging Radar is presented, with an emphasis on several key design aspects that enable fast, reliable through-clothes Imaging of person-borne concealed objects. Using the frequency-modulated continuous-wave (FMCW) Radar technique with a nearly 30 GHz bandwidth, sub-centimeter range resolution is achieved. To optimize the Radar's range resolution, a reliable software calibration procedure compensates for signal distortion from Radar waveform nonlinearities. Low-noise, high dynamic range detection comes from the Radar's heterodyne RF architecture, low-noise chirp source, and high-performance 675 GHz transceiver. The Radar's optical design permits low-distortion fast beam scanning for single-pixel Imaging, and a real-time Radar image frame rate of 1 Hz is now possible. Still faster speeds are on the horizon as multi-beam THz transceivers are developed.
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time delay multiplexing of two beams in a terahertz Imaging Radar
IEEE Transactions on Microwave Theory and Techniques, 2010Co-Authors: Nuria Llombart, Tomas Bryllert, Goutam Chattopadhyay, Ken B Cooper, R J Dengler, Peter H. SiegelAbstract:We demonstrate a time-delay multiplexing technique that doubles the frame rate of a 660-690-GHz Imaging Radar with minimal additional instrument complexity. This is done by simultaneously projecting two offset, orthogonally polarized Radar beams generated and detected by a common source and receiver. Beam splitting and polarization rotation is accomplished with a custom designed waveguide hybrid coupler and twist. A relative time lag of approximately 2 ns between the beams' waveforms is introduced using a quasi-optical delay line, followed by spatial recombination using a selectively reflective wire grid. This delay is much longer than the approximately 20-ps time-of-flight resolution of the 30-GHz bandwidth Radar, permitting the two beams' reflected signals from a compact target to be easily distinguished in digital post-processing of the single receiver channel.
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A high-resolution Imaging Radar at 580 GHz
IEEE Microwave and Wireless Components Letters, 2008Co-Authors: K. B. Cooper, Eva Schlecht, Imran Mehdi, Robert J. Dengler, Goutam Chattopadhyay, J. Gill, A. Skalare, Peter H. SiegelAbstract:We have developed a high-resolution Imaging Radar at 580 GHz. Coherent illumination in the 576-589 GHz range and phase-sensitive detection are implemented in an all-solid-state design based on Schottky diode sensors and sources. By employing the frequency-modulated continuous wave (FMCW) Radar technique, we achieve centimeter-scale range resolution while utilizing fractional bandwidths of less than 3%. Our high operating frequencies also permit centimeter-scale cross-range resolution at several-meter standoff distances without large apertures. Scanning of a single-pixel transceiver enables targets to be rapidly mapped in three dimensions, and here we apply this technology to the detection of concealed objects on persons.
Yunhua Zhang - One of the best experts on this subject based on the ideXlab platform.
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Preliminary Significant Wave Height Retrieval from Interferometric Imaging Radar Altimeter Aboard the Chinese Tiangong-2 Space Laboratory
'MDPI AG', 2021Co-Authors: Lin Ren, Xiao Dong, Jingsong Yang, Yongjun Jia, Yunhua ZhangAbstract:The interferometric Imaging Radar altimeter (InIRA) aboard the Chinese Tiangong-2 space laboratory is the first spaceborne Imaging Radar working at low incidence angles. This study focuses on the retrieval of significant wave heights (SWHs) from InIRA data. The retrieved SWHs can be used for correcting the sea state bias of InIRA-derived sea surface heights and can supplement SWH products from other spaceborne sensors. First, we analyzed tilt, range bunching and velocity bunching wave modulations at low incidence angles, and we found clear dependencies between the SWH and two defined factors, range and azimuth integration, for ocean waves in the range and azimuth directions, respectively. These dependencies were further confirmed using InIRA measurements and collocated WaveWatch III (WW3) data. Then, an empirical orthogonal SWH model using the range and azimuth integration factors as model inputs was proposed. The model was segmented by the incidence angle, and the model coefficients were estimated by fitting the collocation at each incidence angle bin. Finally, the SWHs were retrieved from InIRA data using the proposed model. The retrievals were validated using both WW3 and altimeter (JASON2, JASON3, SARAL, and HY2A) SWHs. The validation with WW3 data shows a root mean square error (RMSE) of 0.43 m, while the average RMSE with all traditional altimeter data is 0.48 m. This indicates that the InIRA can be used to measure SWHs
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inverse weighting method for sea surface wind direction retrieval from tiangong 2 interferometric Imaging Radar altimeter imagery
IEEE Asia-Pacific Conference on Synthetic Aperture Radar, 2019Co-Authors: Yunhua Zhang, Xiao DongAbstract:The Interferometric Imaging Radar Altimeter (InIRA) onboard Chinese Tiangong-2 space laboratory is a Ku-band interferometric Radar whose major aim is to measure the wide-swath ocean topography. A large number of observation data of key sea areas and typical land areas have been obtained since the start-up of InIRA. The sea surface wind field plays a major role in marine research, including weather forecasting, ocean-air interactions, and earth climate studies. Therefore, it is of great significance to use InIRA to retrieve the sea surface wind field. The local gradient method is often used for wind direction retrieval in synthetic aperture Radar (SAR). However, the large change of incidence angles of InIRA imposes additional modulation on the gradient of the backscattering coefficient. In this paper, a method of combining Radar backscattering coefficient inverse weighting and local gradient method is used in wind direction retrieval for InIRA. The influence of backscattering coefficient attenuation caused by angle change is analyzed and then the gradient is solved. Experimental results on Tiangong-2 data show better result is obtained using the proposed method than the local gradient method.
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Interferometric Imaging Radar Altimeter on Board Chinese Tiangong-2 Space Laboratory
2018 Asia-Pacific Microwave Conference (APMC), 2018Co-Authors: Yunhua Zhang, Xiaojin Shi, Hongjian Wang, Yueyin Tan, Wenshuai Zhai, Xiao Dong, Xueyan Kang, Qingshan Yang, Dong Li, Jingshan JiangAbstract:In this paper, We introduce the Interferometric Imaging Radar Altimeter (InIRA), the first spaceborne wide-swath ocean Radar altimeter on board Chinese Tiangong-2 space laboratory, which was launched on September 15, 2016. The major mission of InIRA is to validate the mechanism and design of new generation ocean Radar altimeter, as well as conduct preliminary application researches. The in-orbit observation results of Tiangong-2 InIRA demonstrate that it is capable of measuring the dynamic sea surface height with wide swath, sea waves of different scales and sea winds, which help us greatly improve the observation and measurement efficiency compared with traditional nadir-looking Radar altimeters. Besides, it can also be used to survey and monitor the inland waters, e.g. lakes and rivers, as well as acquire terrain digital surface model (DSM). Here, we will present some typical observation results over both ocean and land surfaces.
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design and algorithms of the tiangong 2 interferometric Imaging Radar altimeter processor
2017 Progress In Electromagnetics Research Symposium - Spring (PIERS), 2017Co-Authors: Xiao Dong, Yunhua Zhang, Wenshuai ZhaiAbstract:The Interferometric Imaging Radar Altimeter (InIRA) operating at Ku-band (13.58 GHz) was launched on Chinese Tiangong-2 space laboratory on September 15, 2016. The primary goal of Tiangong-2 InIRA is to measure wide-swath sea surface height, sea waves and sea winds. Winds and waves in the observed sea area are retrieved by processing the synthetic aperture Radar (SAR) images. The ocean surface topography and the digital elevation models of land areas are determined using the interferometric SAR (InSAR) technique. The scope of this paper is to present the processing algorithms for the generation of the Tiangong-2 InIRA images from the raw data. The focusing algorithm for generating the single look complex (SLC) image products and the interferometric processing algorithm for generating the surface topography are briefly introduced.