保形光顺的样条曲线

给出了一种对给定平面上的数据点进行保形的最小二乘逼近的算法,并且得到的逼近曲线是光顺的。本文利用拉格朗日乘数法对带约束条件的参数曲线进行了优化设计。     

偏最小二乘回归在军用飞机价格预测中的应用

由于军用飞机性能要求的不断提高,影响飞机采购价格的费用驱动因子繁多,使得原有的价格预测模型已经不适用于现代军用飞机。分析了军用飞机采购价格样本数据少、费用驱动因子多的特点,考虑到偏最小二乘回归(PLSR)方法在处理小样本多元数据方面的优势,应用PLSR对军用飞机采购价格进行预测。PLSR首先提取第1、第2主成分对采购价格样本的特异点进行剔除;然后进行变量投影重要度分析以筛选费用驱动因子;最后,PLSR对费用驱动因子进行回归建立军用飞机价格预测模型。实例表明,在军用飞机价格预测方面,与原有的预测模型和逐步多元回归模型相比,应用PLSR预测的精度更高,更能体现采购价格与飞机性能参数之间的关系。     

Angular velocity determination of spinning solar sails using only a sun sensor

The direction of the sun is the easiest and most reliable observation vector for a solar sail running in deep space exploration. This paper presents a new method using only raw measurements of the sun direction vector to estimate angular velocity for a spinning solar sail. In cases with a con-stant spin angular velocity, the estimation equation is formed based on the kinematic model for the apparent motion of the sun direction vector;the least-squares solution is then easily calculated. A performance criterion is defined and used to analyze estimation accuracy. In cases with a variable spin angular velocity, the estimation equation is developed based on the kinematic model for the apparent motion of the sun direction vector and the attitude dynamics equation. Simulation results show that the proposed method can quickly yield high-precision angular velocity estimates that are insensitive to certain measurement noises and modeling errors.     

The contribution of local gravimetric geoid models to the calibration of satellite altimetry data and an outlook of the latest GOCE GGM performance in Gavdos

The use of geoid heights has been one of the available methodologies utilized for the independent calibration/validation of altimeters on-board satellites. This methodology has been employed for long in the Gavdos dedicated cal/val facility (Crete, Greece), where calibration results for the Jason satellites have been estimated, both for ascending and descending passes. The present work gives a detailed overview of the methodology followed in order to estimate a high-resolution and accuracy gravimetric geoid model for the wider Gavdos area, in support of the on-going calibration work. To estimate the geoid model, the well-known remove-compute-restore method is used while residual geoid heights are estimated through least-squares collocation so that associated errors are determined as well. It is found that the estimated formal geoid errors from LSC along passes 018 and 109 of Jason satellites, used for the bias estimation, range between ±0.8–1.6 cm. The so-derived geoid heights are employed in the determination of the Jason-2 altimeter bias for all available cycles (cycles 1-114, spanning the period from July 2008 to August 2011) together with the RioMed DOT model. From the results acquired the Jason-2 bias has been estimated to be +196.1 ± 3.2 mm for pass 109 and +161.9 ± 5.1 mm for pass 018. Within the same frame, the GOCE/GRACE-based geopotential model GOCO02s has been used to estimate the mean dynamic ocean topography and the steady-state circulation in the area around Gavdos. The so-derived DOT model was used to estimate the Jason-2 bias in an effort to evaluate the performance of satellite-only geoid models and investigate whether their spatial resolution and accuracy provides some improvement w.r.t. traditional local gravimetric geoids. From the results acquired with geoid heights from GOCO02s, the estimated Jason-2 bias deviates significantly from that of the local gravimetric model, which can be attributed to a possible mean offset and the low resolution of GOCE-based GGMs. On the other hand, when the newly estimated GOCE-based DOT was employed with geoid heights from the local gravimetric geoid model, the Jason-2 bias has been estimated to be +185.1 ± 3.2 mm for pass 109 and +130.2 ± 5.1 mm for pass 018.     

基于光电导航的伪卫星空中基站定位算法

由于具有抗干扰能力强和布置灵活机动的特点,伪卫星在增强卫星系统和独立组网为用户提供更高精度导航定位信息方面具有广阔的应用前景。伪卫星空中基站的精确定位是构建伪卫星区域定位系统的一个关键问题。为此,研究了一种基于光电导航的定位算法,综合利用光电探测成像信息和惯性导航信息,根据伪卫星空中基站的特点建立了相应的误差模型,并采用最小二乘法估计位置误差。计算机仿真结果表明所提算法简单,具有较大的实用价值。     

超声速和高超声速粘性绕流QPNS方程的GLS有限元解

从完全非定常Ｎ－Ｓ方程（ＦＮＳ）中略去流向粘性导数导出拟抛物Ｎ－Ｓ方程（ＱＰＮＳ），ＱＰＮＳ技术结合经典抛物推进和拟时松弛，拟时松弛能有效地抑制解的发散。本文导出的熵变量形式ＱＰＮＳ方程具有对称性和自动满足热力第二定律，这将提高解的稳定性，伽辽金／最小二乘法（ＧＬＳ）被用来构造ＱＰＮＳ的弱解式。对于钝前缘物体，ＱＰＮＳ在前缘区并不适用，本文代之以用ＦＮＳ求解该区，由离散解得到的非对称线性方程组，对     

Dual-frequency carrier smoothed code filtering with dynamical ionospheric delay modeling

In GNSS applications, carrier-smoothed-code is a widely used technique to combine code pseudo-range and carrier phase measurements. A dynamical ionospheric delay modeling method is proposed based on Kalman filter and least-squares theory. The level of the process noise is adaptively tuned along with the real-time KF state estimation, based on the online variance component estimation method. Meanwhile, the correlations of the time differenced carrier phase measurements are considered. This approach avoids overly optimistically evaluating the estimate and improves the transient accuracy of the estimates. A real GPS dataset is employed to check the performance of the proposed method under different conditions. The results show that the new algorithm can model the ionospheric delay variation well with different sampling intervals or even in ionospheric abnormal environment. The positioning accuracy can be confirmed, about 21%, 35% and 16% better are obtained in the N, E, and U direction than raw dataset.     

Joint calibration algorithm for gain-phase and mutual coupling errors in uniform linear array

The effect of gain-phase perturbations and mutual coupling significantly degrades the performance of digital array radar (DAR). This paper investigates array calibration problems in the scenario where the true locations of auxiliary sources deviate from nominal values but the angle intervals are known. A practical algorithm is proposed to jointly calibrate gain-phase errors and mutual coupling errors. Firstly, a simplified model of the distortion matrix is developed based on its special structure in uniform linear array (ULA). Then the model is employed to derive the precise locations of the auxiliary sources by one-dimension search. Finally, the least-squares estimation of the distortion matrix is obtained. The algorithm has the potential of achieving considerable improvement in calibration accuracy due to the reduction of unknown parameters. In addition, the algorithm is feasible for practical applications, since it requires only one auxiliary source with the help of rotation platforms. Simulation results demonstrate the validity, robustness and high per-formance of the proposed algorithm. Experiments were carried out using an S-band DAR test-bed. The results of measured data show that the proposed algorithm is practical and effective in appli-cation.     

Harmonic analysis of the ionospheric electron densities retrieved from FORMOSAT-3/COSMIC radio occultation measurements

In order to investigate the regular variations of the ionosphere, the least-squares harmonic estimation is applied to the time series of ionospheric electron densities derived from about five years of Global Positioning System radio occultation observations by FORMOSAT-3/COSMIC satellites. The analysis is done for different latitudes and altitudes in the region of Iran. The least-squares harmonic estimation is found to be a powerful tool for the frequency analysis of the completely unevenly spaced time series of radio occultation measurements. Although the obtained results are slightly different from the exact expected cycles (i.e. annual and diurnal components with their Fourier decompositions, and the 27-day period) due to the low horizontal resolution of radio occultation measurements, high vertical resolution of the observations enables us to detect not only the total electron content variations but also periodic patterns of electron densities at different altitudes of the ionosphere. The dominant diurnal and annual signals together with their Fourier series decompositions are obtained, which are consistent with the previous analyses on the total electron content. In the equatorial anomaly band, the annual component is weaker than its Fourier decomposition periods. In particular, the semiannual period dominates the annual component, indicating the relationship between the semiannual variation of the electron densities and the ionospheric equatorial anomaly. From detection of the phases of the components, it is revealed that the annual signal generally has its maximum value in summers at high altitudes, and in the winters at low altitudes. This is probably due to the higher [O/N₂] ratios in winter than in the summer in the lower ionosphere. Furthermore, the semiannual component mostly peaks around solstices or about a month before/after them.     

GPS/Galileo组合导航的模糊度搜索空间

为了组合导航的载波相位模糊度固定,将目前在GPS中常用的模糊度固定方法--最小二乘降相关平差（LAMBDA）法直接应用于GPS/Galileo组合模糊度固定,发现其搜索空间的确定方法并不能很好地适应GPS/Galileo组合中模糊度维数较高的情况。通过对常规LAMBDA搜索空间确定方法的分析比较,在传统方法的基础上提出了一种专门针对高维模糊度固定的搜索空间确定方法--修正法确定模糊度搜索空间。通过对修正法进行仿真试验,证明该方法能保证在GPS/Galileo组合定位模式下实际备选模糊度个数基本与预先设定的备选模糊度个数一致,进而能在不降低模糊度固定成功率的基础上有效提高LAMBDA模糊度固定的搜索效率,其性能优于传统的模糊度搜索空间确定方法。