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Jun Chen Wenting Quan Zhenhe Wen Tingwei Cui 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
“Clear water” is a scale-dependent concept, so it is more likely to successfully find the “clear water” from images with smaller scale than that with larger scale data. In this study, an optimal spectral relationship of moderate-resolution imaging spectroradiometer (MODIS) 250 m and 1 km resolution data at near-infrared bands (OSRLM) is constructed for converting pseudo “clear water” reflectance at 859 nm to those at 748 and 869 nm. According to scale effects, the satellite-observed pseudo “clear water” reflectance is greater than 5.18%, larger than that derived from OSRLM model. An atmospheric correction model for MODIS 1km data using pseudo “clear water” reflectance of MODIS 250 m data (ACMM) was developed for improving the performance of traditional “clear water” atmospheric correction model (CWAC). The model validation results indicate that ACMM model has a better performance than CWAC model. By comparison, the uncertainty decreases by 19.18% in the use of ACMM model over CWAC model for deriving water-leaving reflectance in Taihu Lake, China. This uncertainty is significantly reduced in water-leaving reflectance estimation due to partial removal of scale effects on “clear water”. These findings imply that satellite-derived aerosol scattering contribution at smaller scale usually has a better performance than that at larger scale. 相似文献
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针对传统捷联惯导算法模型为非线性,需要对姿态、速度和位置分步运算,且高动态下算法精度较低的问题,提出一种地理系下基于伪线性模型的捷联惯导算法。利用伪线性模型及其分析方法,将传统的地理系下捷联惯导方程各部分转换成伪线性形式,定义导航向量并建立其系统模型;再利用高阶数值积分算法提升导航向量更新精度,得到地理系下基于伪线性模型的捷联惯导算法。最后,用仿真评估算法精度,与传统捷联惯导算法相比,大机动条件仿真中伪线性捷联惯导算法的精度提升了两个量级;旋转弹飞行仿真中导航误差不到传统算法的1/5。提出的伪线性捷联惯导算法结构简单,采用一个更新回路即可完成导航向量更新,且在高动态大机动条件下具有更高的算法精度,因此,对于捷联惯导算法研究与工程应用有一定的参考价值。 相似文献
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线性八元树提供一种非常紧凑并适于传统物体处理运算的三维物体体积表示法。它是二维(二值)图象线性四元树表示的一种推广。本文提出一种方法利用体积交技术由物体的正交三轮廓图生成它的线性八元树。这种方法包括两步过程:第一步是将三个给定轮廓图转换成线性四元树;第二步是建造各个线性四元树对应的伪线性八元树,然后通过三个伪线性八元树的交生成物体的线性八元树。 相似文献
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针对深空探测中轨道转移时间长且能量消耗较大的问题,提出基于准流形实现从地球停泊轨道到日地系L3点转移轨道的设计方法。在日地限制性三体问题模型下,在L1点或L2点Halo轨道上施加扰动推力,构造准流形,利用其非线性三体动力学特性,通过霍曼转移轨道与近地轨道进行拼接,使航天器进入准流形后能够无动力滑行到L3点附近区域。在准流形与L3点周期轨道交点,施加速度脉冲,使航天器进入相应周期轨道,从而完成轨道转移。仿真结果表明,利用该方法所得结果与基于不变流形的转移轨道相比,能将速度增量从4398m/s减少为4014m/s,并将转移时间从9年以上缩短到7.3年以内,有效地提高了航天器的工作效率。 相似文献
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设计提出了 1种针对高光谱图像分类任务的 3D-MSCNN模型。在 PCA降维的基础上,利用 3D空谱特征提取网络和 2D多尺度特征提取网络实现高光谱图像特征提取,充分发挥高光谱图像空谱信息价值,增强对不同尺度地表覆盖的表达能力。最后,利用 Softmax分类损失函数实现高光谱图像分类任务。实验结果表明,本文算法在 In. dian Pines和 Pavia University数据集上都取得了较好的分类效果。与 CD-CNN、3D-CNN、SS-Net和 HybirdSN等方法相比,本文算法能够有效提升总体精度、平均精度和 Kappa系数等客观评价指标。 相似文献
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Structural topology optimization subjected to stationary random base acceleration excitations is investigated in this paper. In the random response analysis, the Large Mass Method(LMM) which attributes artificial large mass values at each driven nodal Degree Of Freedom(DOF) to transforming the base acceleration excitations into force excitations is proposed. The Complete Quadratic Combination(CQC) which is commonly used to calculate the random responses in previous optimization has been proven to be computationally expensive especially for large-scale problems. In order to conquer this difficulty, the Pseudo Excitation Method(PEM) and the combined method of PEM and Mode Acceleration Method(MAM) are adopted into the dynamic topology optimization, and random responses are calculated using these two methods to ascertain a high efficiency over the CQC. A density-based topology optimization method minimizing dynamic responses is then formulated based on the integration of LMM and PEM or the combined method of PEM and MAM. Numerical examples are presented to verify the accuracy of the proposed schemes in dynamic response analysis and the quality of the optimized design in improving dynamic performance. 相似文献
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为了评估GPS L1频点信号体制转换前后的空间信号质量,基于高增益天线接收系统采集数据,对相干自适应副载波调制(CASM)调制和QPSK调制信号质量进行对比分析。首先,简要介绍CASM调制模型,利用波形匹配技术求解L1频点授权信号伪码序列。其次,基于星座图分布和极大似然估计分别解决出QPSK和CASM调制信号分量功率分配难题。最后定量地利用相关特性参数中的S曲线过零点偏差(SCB)和相关损失(CL)对比分析L1频点信号体制转换前后各信号分量空间信号质量。该文结果可为不同信号体制下空间信号质量评估对比提供参考。 相似文献
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