UAV-borne interferometric SAR has unique advantages and has attracted the attention of key research institutions in recent years. Baseline is a crucial parameter in InSAR processing, which is directly related to the accuracy of InSAR measurements. Compared with space-borne InSAR, UAV platform is difficult to keep the flight at the same track, and the flight attitude is unstable, which brings great difficulties to the baseline estimation of UAV-borne InSAR. In this paper, an improved baseline estimation method is proposed. This method derives the relationship between the interference phase period, the slant range, the distance between two ground points, and the phase difference through the interference geometric relationship. The distance between the two points is then substituted into the known parameters for baseline estimation using the least squares method. Compared with the original method, the proposed method can fully exploit the potential of the interferogram data by applying the least square method to solve the formula between flight parameters and baseline parameter to achieve baseline estimation. The simulated results and the flight test results of the original method and the proposed method are Compared. The absolute error, RMSE and standard deviation of both methods are calculated. It shows that the accuracy and robustness of the proposed method are significantly improved.
Recently, the low earth orbit（LEO） satellite communication system has received wide attention from academia and industry, due to its global coverage and flexible construction. In the LEO satellite communication system, satellites are connected to a dynamic network through the inter-satellite link（ISL）. How to reduce the communication delay of the network is an urgent research problem to be solved. For the problem of cross seam link-building of the Walker polar orbit constellation, this paper proposes a star cross looping link-building strategy（SCLBS）. SCLBS divides the orbits into multiple cross link-building areas on both sides of cross seam and the transmission delay can be optimized by dynamically established ISL, providing a stable link-building scheme for polar orbit cross seam. SCLBS is applied to actual business scenarios such as the airplane and ship, and the test results show that SCLBS can effectively reduce the transmission delay by 30% to 60% compared with the link-building strategies based on the nearest satellite criterion and the longest visible time criterion, and significantly improve system performance.
The Leggett inequality is a constraint on the bipartite correlation that admits certain types of nonlocalities.Could such constraints be obtained for more parties?Here in search for the answer we found new inequalities for three parties which could be used to check the compatibility between quantum mechanics and nonlocal realism.For certain measurement settings violations are found for GHZ,W and an arbitrary three-qubit pure states.Our inequalities are stronger than the existing inequality in literature(arXiv:1111.4119v1).These experimentally realizable inequalities,generalization to n-parties possible,could better our explanations for nonlocal correlations in multiparty case,along with some applications in cryptographic key distribution beyond the standard quantum key distribution schemes.
以库鲁斯台草原为研究区,基于1990-2020年Landsat数据,选择归一化植被指数(NDVI)及空间异质性作为草地退化的遥感监测指标,对库鲁斯台草地退化状况进行评估.结果表明:1)1990-2020年,研究区中部NDVI呈上升趋势,而边缘区域呈下降趋势;草地空间异质性上升的区域主要集中在研究区中部及西南部地区,北部和南部则以下降为主.2)草地退化的监测表明,约54％的草地出现退化,35％的草地得到了改善,10％的草地植被恢复.3)温度和降水对草地空间异质性的年际变化影响较小,对NDVI影响较大,降水量是影响库鲁斯台草原NDVI时间动态的主要因素.
太阳系外行星大气是系外行星领域迅速发展且最具挑战的课题之一,它依赖于高精度的测光和光谱数据.以WASP-103b的近红外地基望远镜CFHT上WIRCam照相机观测的两次次食数据为例,详细介绍高精度测光对观测的要求,阐述所需的数据处理和分析方法.结果表明,采用本文方法,可以利用地面望远镜实现10-4的超高精度较差测光.
