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1.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(5):2332-2347
In this study we present an analytical formulation of synthetic-aperture radar (SAR) altimetry signals including narrow banded nonlinear wave fields and conditional statistics between wave elevation displacements, horizontal wave slopes and vertical wave particle velocities. Considering the wave elevation displacements coskewness with respect to horizontal slopes leads to an analytical formulation of the electromagnetic bias within a SAR-mode altimeter stack. This formulation can be either parametrized by the significant wave height (SWH) and mean wave steepness, or in terms of the variance of vertical wave velocities. The effect of conditional vertical wave particle velocity variances with respect to the observed horizontal wave slopes close to nadir incidence angles leads to an effective reduction of the azimuth blurring of SAR-mode stacks. We present here a formulation of this effect by examining JONSWAP ocean wave spectra. In most cases this effect reduces the azimuth blurring by 10% to 30%. Additionally we investigate the effect of a nonlinear wave elevation displacement probability density function (PDF) on estimated geophysical parameters. We were able to show that including an elevation displacement skewness of 0.13 improves significantly the SWH consistency between altimetry and ECMWF Reanalysis v5 ERA5 results.All of these effects are validated with respect to ERA5 model data in the North East Atlantic region and in situ data located in the German Bight and Baltic Sea.The developed model can be used in both SAR and conventional altimetry retrackers. 相似文献
2.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(1):572-585
The overlapping carrier frequencies L1/E1, L5/E5a and B2/E5b from GPS/Galileo/BDS allow inter-system double-differencing of observations, which shows a clear advantage over differencing of the observations of each constellation independently. However, the inter-system biases destroy the integer nature of the inter-system double-differencing ambiguities. Two methods of direct rounding and parameter estimation are used to determine the ISB value. By analyzing data collected from Curtin University from 2015 to 2018, the phase and code inter-system bias (ISB) are related to the receiver type, firmware version and the selected overlapping frequency. Upgrade of receiver firmware version results in changes of ISB values. For example, the upgrade of Javad firmware in Dec, 15, 2017 causes the difference of 0.5 cycles ISB between BDS GEO and non-GEO satellites. By comparing the three dynamic models which include white noise process, random walk process, and random constant in the parameter estimation method, the ISB determined by the random constant model is consistent with the value obtained by the direct rounding method. After the calibration of ISBs, the performances of tightly combined positioning are assessed. The success rate of ambiguity resolution and accuracy of positioning for the tight combination (TC) are significantly improved in comparison with that for the loose combination (LC) over short baselines. For L5/E5a, on which only few satellites can be observed, the maximum increase in success rates of ambiguity resolution can reach 31.7%, i.e., from 54.9% of LC to larger than 86.6% of TC, and the positioning accuracies can even be increased by 0.13 m, i.e., from 0.208 of LC to 0.074 m of TC in East direction for the mix-receiver TRIMBLE NETR9-SEPT POLARX4 in 2018. 相似文献
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4.
刘大云 《南京航空航天大学学报》1988,(3)
本文用Melnikov方法研究高压输电网设计中提出的非线性二阶受迫振动方程的次谐波分枝,分析了系统可能出现次谐解的条件和参数区域,以此为工程应用提供参考。 相似文献
5.
空间等离子体导致高电压太阳阵的电流收集 总被引:3,自引:0,他引:3
给出一种能方便计算空间等离子体引起高电压太阳阵(HVSA)电流收集的理论统计模式,通过对物理过程分析认为空间等离子体致HVSA的功率损耗对HVASA的设计是不应忽视的。 相似文献
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用于航空高压直流电源系统的笼型异步发电机控制策略的研究 总被引:1,自引:2,他引:1
现代电力电子技术的发展使得笼型异步发电机能够适用于航空高压直流系统中。着重对笼型异步电机与电力电子变换器结合构成的发电系统进行了研究,说明了采用直接转矩控制策略可使这种发电系统具有很好的动态特性。介绍了异步发电机直接转矩控制的原理与实现方法,并给出了仿真与实验结果。 相似文献
8.
蒋万青 《中国民航学院学报》2004,22(3):25-28
介绍了一种小功率逆变电源电路的实现方法。对逆变主电路、电压控制电路、驱动电路、SCOTT电路进行了研究。该逆变电源具有工作可靠、波形失真小的特点。 相似文献
9.
本文针对X射线探伤中曝光时间与管电压的关系以及曝光时间在探伤中的实际意义做了详尽分析,并提出了对于不同厚度的零件如何选择曝光时间的原则。 相似文献
10.
杨守环 《中国民航学院学报》1990,(2):19-28
本文在分析现代飞机电源系统所使用的几种过电压保护装置工作原理的基础上,着重对其反延时特性和动作电压进行计算,并就决定和影响过电压保护性能指标的电路参数的调整进行了计算和论述。 相似文献