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91.
??2012??1???????????????????г??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????к?????????????????????????????????--?????????????????????????????? 相似文献
92.
Synthetic aperture radar (SAR) is an important alternative to optical remote sensing due to its ability to acquire data regardless of weather conditions and day/night cycle. The Phased Array type L-band SAR (PALSAR) onboard the Advanced Land Observing Satellite (ALOS) provided new opportunities for vegetation and land cover mapping. Most previous studies employing PALSAR investigated the use of one or two feature types (e.g. intensity, coherence); however, little effort has been devoted to assessing the simultaneous integration of multiple types of features. In this study, we bridged this gap by evaluating the potential of using numerous metrics expressing four feature types: intensity, polarimetric scattering, interferometric coherence and spatial texture. Our case study was conducted in Central New York State, USA using multitemporal PALSAR imagery from 2010. The land cover classification implemented an ensemble learning algorithm, namely random forest. Accuracies of each classified map produced from different combinations of features were assessed on a pixel-by-pixel basis using validation data obtained from a stratified random sample. Among the different combinations of feature types evaluated, intensity was the most indispensable because intensity was included in all of the highest accuracy scenarios. However, relative to using only intensity metrics, combining all four feature types increased overall accuracy by 7%. Producer’s and user’s accuracies of the four vegetation classes improved considerably for the best performing combination of features when compared to classifications using only a single feature type. 相似文献
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从工程实际出发,对岩土工程勘察中钻探、取样、野外地质编录和水文地质观测工作进行了归纳总结,并阐述了岩土工程勘察外业工作的重要性。 相似文献
97.
月球探测对于我国各方面综合实力的提升均具有巨大的推动作用。当前我国各研发机构对月球采样的研发重点集中于采样机具的设计制造上,对采样机具和月壤之间相互作用却研究较少。与地球土壤相比,月壤的形成环境与条件完全不同,从而造就了其较为特殊的物理力学性质。在利用与真实月壤类似的模拟月壤进行的薄壁圆筒贯入试验中,发现存在月壤滞留和月壤附壁现象,从而分析得出在采样机具表面与月壤相互作用的理论分析中,除了传统的摩擦力理论外,还可通过最大抗剪强度进行分析。通过对试验现象和数据对比摩擦力理论和最大抗剪强度理论发现,最大抗剪强度理论更加符合实际情况。故将最大抗剪强度理论引入已有的月球螺旋钻进采样的理论模型中,通过计算得出基于最大抗剪强度理论计算的螺旋临界转速低于基于摩擦力理论计算的临界转速,在一定程度上能够降低采样机具的能耗。 相似文献
98.
Time-Expanded Sampling Approach for Ensemble Kalman Filter:Experiment Assimilation of Simulated Soundings
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In the Ensemble Kalman Filter (EnKF) data assimilation-prediction system, most of the computation
time is spent on the prediction runs of ensemble members. A limited or small ensemble size does reduce the
computational cost, but an excessively small ensemble size usually leads to filter divergence, especially when
there are model errors. In order to improve the efficiency of the EnKF data assimilation-prediction system
and prevent it against filter divergence, a time-expanded sampling approach for EnKF based on the WRF
(Weather Research and Forecasting) model is used to assimilate simulated sounding data. The approach
samples a series of perturbed state vectors from Nb member prediction runs not only at the analysis time
(as the conventional approach does) but also at equally separated time levels (time interval is △t) before
and after the analysis time with M times. All the above sampled state vectors are used to construct the
ensemble and compute the background covariance for the analysis, so the ensemble size is increased from
Nb to Nb+2M£Nb=(1+2M)×Nb) without increasing the number of prediction runs (it is still Nb). This
reduces the computational cost. A series of experiments are conducted to investigate the impact of △t (the
time interval of time-expanded sampling) and M (the maximum sampling times) on the analysis. The results
show that if △t and M are properly selected, the time-expanded sampling approach achieves the similar
effect to that from the conventional approach with an ensemble size of (1+2M)×Nb, but the number of
prediction runs is greatly reduced. 相似文献
99.
随着数字技术的发展,数字信号处理芯片的速度越来越快,这为高速数字滤波的实时实现提供了可能。简要阐述了数字滤波的原理,并对两种数字滤波的实现方法进行了分析;给出了数字滤波较模拟滤波的优势;介绍了数字滤波在射电天文测量中的各种应用。 相似文献
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