Snow depth retrieval by using robust estimation algorithm to perform multi-SNR and multi-system fusion in GNSS-IR

Global Navigation Satellite System Interferometric Reflectometry (GNSS-IR) technology provides a new means of snow depth detection. Multi-satellite and multi-Signal-to-Noise Ratio (SNR) provide more data for daily high-precision snow depth retrieval, but also face the problem of data fusion and effective utilization. Therefore, this study proposes a robust estimation algorithm based on multi-satellite and multi-SNR fusion applied to the observations of a GNSS station in Alaska. This study uses four solutions (S_avg, S_med, S_{RE_avg} and S_{RE_med}) to carry out multi-system fusion snow depth inversion and precision comparison research. The S_avg has more obvious disadvantages, which is not suitable for snow depth assessment. The S_{RE_avg} and S_{RE_med} have better snow depth retrieval effects in the snowy periods. The correlation coefficient (R), root mean square error (RMSE) and mean error (ME) of the calculated snow depth using the robust estimation algorithm with respect to the nearest in-situ measurements reached 0.759, 3.7 cm and ?1.4 cm, respectively. Compared with the S_med, the R is increased by 2.0 %, the RMSE corresponds to an improvement of 2.6 %. Moreover, the ME of the snow depth retrievals, as an indicator of the measurement bias, has significantly decreased by 6.7 %. The result also shows that the snow depth inversion by the robust estimation algorithm is more consistent with the in-situ measurements, further extending and advancing the optimal algorithm for snow depth retrieval.     

基于最优机动参数的靶弹变轨研究

在跃升机动、蛇行机动、摆式机动和螺旋机动4种机动的变轨通用控制指令形式基础上,以拦截弹脱靶量的大小作为评判靶弹突防效果的指标,建立了末端机动靶弹突防效果的脱靶量分析模型,并提出了上述4种形式变轨突防最优参数的设计方法。在这些最优参数的作用下,导弹靶弹的机动变轨可实现最佳的突防效果,从而提升防空导弹的实战训练效果。     

X波段在南极地区穿透深度的技术研究

高精度极地数字高程模型(DEM)对于我国极地研究和探索具有重要意义.德国空间局开发的分布式合成孔径雷达干涉(InSAR)测绘卫星TanDEM-X已经被证明是获取大范围高精度DEM的有效工具.X波段在冰雪表面具有一定的穿透性,会导致极地DEM存在偏差.目前国内外针对X波段在极地冰雪表面的穿透研究还很少.本文利用TanDE...     

Study of aerosol anomaly associated with large earthquakes (M>6)

We present the variation of unusual atmospheric phenomena, aerosols, to understand the preseismic irregularities for two major earthquakes in Japan. We consider aerosol optical depth and Angstrom exponent data retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument onboard the Terra satellite to establish possible connections between earthquakes and the generation of aerosols. Variation of the aerosol parameters shows significant changes before the April 15, 2016, Kumamoto earthquake ($M=7.0,h=10$ km) and the November 21, 2016, Fukushima earthquake ($M=6.9$ and $h=9$ km), where M indicates the Richter magnitude and h indicates the focal depth. To identify the source of the aerosol particles, we use the Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT-4). This model uses both Lagrangian and Eulerian approaches to compute trajectories and establish a source-receptor relationship. We compute backward trajectories to check whether the aerosol generated near the epicenter is due to the preseismic processes or is transported from other areas. From our results, we conclude the fine-mode aerosols are generated in the vicinity of the epicenter, 3–7 days before the earthquakes.     

负电子亲和半导体的二次电子发射

根据0.8keV≤Epomax≤5keV的负电子亲和(negative electron affinity,NEA)半导体二次电子发射(secondary electron emission,SEE)的特性，初级电子产额R，现有的次级电子产额δ的通用公式和实验数据，分别推导并实验证明了NEA金刚石的δ在0.5Epomax≤Epo≤10Epomax, GaN在2keV≤Epomax≤5keV, NEA金刚石的δ在08keV≤Epo≤3keV, GaN在08keV≤Epomax≤2keV的特殊公式;其中Epomax为δ达到最大值时的Epo, Epo为初级电子入射能。推导出了08keV≤Epomax≤5keV时NEA半导体的内部二次电子到达发射极表面后逃逸到真空中的概率B。还提出了计算08keV≤Epomax≤5keV NEA半导体1/α的方法;其中1/α为二次电子的平均逃逸深度。分析结果表明，B和1/α的理论研究有助于研究不同样品制备方法对NEA半导体中SEE的定量影响，从而生产出理想的NEA发射体，如NEA金刚石。