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本文介绍EASE-Grid 3种投影的定义,利用地面实测数据和理论方式开展不同投影下AMSR-E雪水当量(SWE)产品的精度验证对比分析,研究其不同投影导致误差产生的原因。验证对比结果表明,青藏高原地区北半球方位角等积投影和全球圆柱体等积投影对于验证结果具有很大影响。理论分析结果表明,我国青藏高原地区在全球圆柱体等积投影下网格发生的形变较小,更适合采用全球圆柱体等积投影。进一步研究表明,AMSR-E亮温数据轨道采样点落入北半球方位角等积投影和全球圆柱体等积投影对应网格差异较大。雪水当量产品验证结果的误差包含了算法误差和投影带来的误差。在开展大尺度遥感反演时,应根据具体研究区所处的纬度范围及研究目的,选取适合的投影方式以降低投影引起的误差。  相似文献
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This article first reviews the main characteristics of the High-Resolution Hyperspectral Sensor for carbon observation Grating Spectrometer (HRHS-GS) and discusses the impact of spectral resolution on gas absorption lines. The major content of this article is the laboratory calibration of HRHS-GS, the signal-to-noise ratio (SNR), instrument line shape (ILS), and the spectral resolution of each channel were achieved. The SNR results met the mission requirements for the 0.76 µm band, but missed the requirement for the two Carbon dioxide (CO2) bands. To address this problem, the model ‘Multiplex Merging of Spectral Pixels’ was established to improve the SNR by increasing the incident energy of a single spectral channel. This process would lead to spectral broadening; the spectral resolution before and after that process was obtained. The transmittance spectra before and after multiplex merging were compared by the line-by-line radiative transfer model (LBLRTM) to analyse the impact of spectral broadening on gas absorption lines. Next, the results were verified by experiment with a gas absorption cell. The results showed that ‘Multiplex Merging of Spectral Pixels’ could effectively improve the SNR. For the 0.76 µm band, the transmittance spectra before and after multiplex merging were almost the same; for the 1.61 µm band, the peak value of the transmittance spectra decays by about 5%; and for the 2.06 µm band, the attenuation of the transmittance spectra is smaller than 3%. Meanwhile, the spectral resolution after spectral broadening still satisfied the study’s requirement.  相似文献
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The Dunhuang Chinese Radiometric Calibration Site (CRCS), used for the vicarious calibration (VC) of reflective solar bands (RSBs), was determined as the primary radiometric calibration site for Chinese space-borne optical sensors and was also selected in 2008 by the Working Group on Calibration and Validation of the Committee on Earth Observation Satellites as one of the instrumented reference sites. In August 2015, an in situ measurement was carried out at the Dunhuang site to evaluate the RSB radiometric calibration of the Visible Infrared Imaging Radiometer Suite (VIIRS) on Suomi National Polar-orbiting Partnership (NPP) and Moderate Resolution Imaging Spectroradiometer (MODIS) on Aqua based on the reflectance-based method. A portable spectroradiometer was used in the experiment to obtain the surface reflectance, and the atmospheric parameters were obtained by sun photometers and radiosonde. A Dunhuang surface bidirectional reflectance distribution function model obtained during the field missions in 2008 and 2013 was implemented. Two days of in situ measurement data including 2 days of VIIRS data and 1 day of MODIS data were used for this evaluation. The results show that the radiometric calibration accuracy is within ±2% for most NPP/VIIRS and Aqua/MODIS RSBs based on the Dunhuang site. It should be noted that there is a relatively large difference in the NPP/VIIRS day–night band (DNB) and Aqua/MODIS band 7 results at the central wavelength of 2.1 μm, with biases of – 4.78% and – 5.71%, respectively. One factor contributing to the difference is the atmospheric transmittance calculation in these bands using the 6S radiative transfer model. If Moderate Resolution Atmospheric Transmission model is used for atmospheric transmittance correction, part of the bias of the MODIS band 7 and VIIRS DNB can be eliminated. However, the consistency of the VIIRS M11 and MODIS B7 is 3.47%, which is larger than that of the other bands.  相似文献
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Aboveground forest biomass (Bagf) and height of forest canopy (Hfc) are of great significance for the determination of carbon sources and sinks, carbon cycling and global change research. In this paper, Bagf of coniferous and broadleaf forest in the Chinese Three Gorges region is estimated by integrating light detection and ranging (LiDAR) and Landsat derived data. For a better Bagf estimation, a synergetic extrapolation method for regional Hfc is explored based on a specific relationship between LiDAR footprint Hfc and optical data such as vegetation index (VI), leaf area index (LAI) and forest vegetation cover (FVC). Then, an ordinary least squares regression (OLSR) and a back propagation neural network (BP-NN) model for regional Bagf estimation from synergetic LiDAR and optical data are developed and compared. Validation results show that the OLSR can achieve higher accuracy of Hfc estimation for all forest types (R2 = 0.751, Root mean square error (RMSE) = 5.74 m). The OLSR estimated Bagf shows a good agreement with field measurements. The accuracy of regional Bagf estimated by the BP-NN model (RMSE = 12.23 t ha–1) is superior to that estimated by the OLSR method (RMSE = 17.77 t ha–1) especially in areas with complex topography.  相似文献
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张延松  张宇  王珊 《软件学报》2018,29(3):883-895
以MapD为代表的图分析数据库系统通过GPU、Phi等新型众核处理器来支持高性能分析处理,在面向复杂数据模式时连接操作仍然是重要的性能瓶颈.近年来,异构处理器逐渐成为高性能计算的主流平台,内存连接性能的研究从多核CPU平台扩展到新兴的众核处理器,但众多的研究成果并未系统地揭示连接算法性能、连接数据集大小、硬件架构之间的内在联系,难以为未来异构处理器平台的数据库提供连接平台优化选择策略.本文以面向多核CPU、Xeon Phi、GPU处理器平台的内存连接优化技术为目标,通过优化内存哈希表设计,实现以向量映射替代哈希映射操作,消除哈希代价对内存连接算法的影响,从而更加准确地测量内存连接算法在多核CPU的cache大小、Xeon Phi的cache大小、Xeon Phi的并发多线程、GPU的SIMT(单指令多线程)机制等硬件相关因素影响下的性能特征.实验结果表明,缓存与并发多线程机制是提高内存连接算法性能的重要影响因素.缓存机制对于满足cache大小的连接操作具有性能优势,而GPU的并发多线程机制则在较大表的连接操作中具有较高的性能,Xeon Phi则在满足其L2 cache大小的连接操作中具有最高性能.实验结果揭示了内存连接操作性能与异构处理器硬件特性的联系,为未来异构处理器平台内存数据库查询优化器提供了优化策略.  相似文献
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