Using cross correlation to estimate Doppler frequency

Doppler frequency estimation with high accuracy is very important for precise orbit determination and scientific studies in deep space exploration. In this paper, we propose a new method which implements cross correlation of only received signals from one single station to estimate Doppler frequency. The algorithm is relatively simple and it can achieve high accuracy even when signal to noise ratio (SNR) is very low. Moreover, the accuracy can be further improved by implementing frequency compensation, especially when the frequency dynamic range is high. Simulations were performed and results proved the validity of this method. X-band observations on MEX (Mars Express) and Juno were performed by a 13 m telescope of Wuhan University, which was equipped by two back ends, i.e. CDAS (Chinese Data Acquisition System) and RSR (Radio Science Receiver). Raw data recorded by the CDAS were processed by using the proposed method, and the estimated frequencies were in good agreement with the real time frequency estimation values by the RSR. What’s more, the accuracy by using cross correlation was higher than the one of RSR.     

Integral inversion of GRAIL inter-satellite gravitational accelerations for regional recovery of the lunar gravitational field

We present an integral-based approach for high-resolution regional recovery of the gravitational field in this article. We derive rigorous remove-compute-restore integral estimators relating the line-of-sight gravitational acceleration to an arbitrary order radial derivative of the gravitational potential. The integral estimators are composed of three terms, i.e., the truncated integration, the low-frequency line-of-sight gravitational acceleration, and the high-frequency truncation error (effect of the distant zones). We test the accuracy of the integral transformations and of the integral estimators in a closed-loop simulation over the Montes Jura region on the nearside of the Moon. In this way, we determine optimal sizes of integration radii and grid discretisation. In addition, we investigate the performance of the regional integral inversion with synthetic and realistic GRAIL observations. We demonstrate that the regional inversion results of the disturbing gravitational potential and its first order radial derivative in the Montes Jura mountain range are less contaminated by high-frequency noise than the global spherical harmonic models.     

曲线轨迹下前视多通道SAR解模糊成像算法

前视合成孔径雷达（SAR）存在左右模糊问题，在直线航迹下，目标关于航线对称模糊，模糊关系不随航线变化，可利用波束形成进行全孔径解模糊处理；但在曲线航迹下，目标的模糊关系具有空变性，不能全孔径解模糊成像。针对这一问题，分析了曲线航迹下目标模糊关系的空变特性，提出一种前视多通道SAR快速后向投影子孔径处理解模糊成像算法。首先进行子孔径划分，在每个子孔径内目标的模糊关系近似不变，每个子孔径分别成像，然后通过波束形成对每幅子图像进行解模糊处理，最后融合子图像得到最终的成像结果。算法有效解决了曲线轨迹下目标模糊关系的空变性对解模糊的影响，仿真实验验证了算法的有效性。     

Application of HF Doppler measurements for the investigation of internal atmospheric waves in the ionosphere

We present results of the spectral analysis of data series of Doppler frequency shifted signals reflected from the ionosphere, using experimental data received at Kazan University, Russia. Spectra of variations with periods from 1 min to 60 days have been calculated and analyzed for different scales of periods. The power spectral density for spring and winter differs by a factor of 3–4. Local maxima of variation amplitude are detected, which are statistically significant. The periods of these amplitude increases range from 6 to 12 min for winter, and from 24 to 48 min for autumn. Properties of spectra for variations with the periods of 1–72 h have been analyzed. The maximum of variation intensity for all seasons and frequencies corresponds to the period of 24 h. Spectra of variations with periods from 3 to 60 days have been calculated. The maxima periods of power spectral density have been detected by the MUSIC method for the high spectral resolution. The detected periods correspond to planetary wave periods. Analysis of spectra for days with different level of geomagnetic activity shows that the intensity of variations for days with a high level of geomagnetic activity is higher.     

在轴流风扇中的流场测量和显示

介绍了利用激光多普勒测速仪(LDA)和激光片光流场显示技术在一轴流风扇转子叶尖附近流场测量得到的结果.试验结果表明,转子叶尖处的通道涡并不是叶尖间隙流卷起造成的,而是由于端壁附面层受到叶尖间隙流的横向冲击后从机匣壁面上脱落形成的.     

多普勒辅助测量IMM-PF机动目标跟踪

针对机动目标跟踪问题,提出了一种辅助多普勒测量的交互多模型粒子滤波算法.该算法利用粒子滤波解决系统观测与目标状态之间的非线性问题,并辅助多普勒测量信息在线估计目标角速率,作为目标转弯模型的参数.采用两个可内部切换的运动模型(常速度/逆时针转弯模型、常速度/顺时针转弯模型)作为交互模型,有效地描述了目标机动并减少了模型个数,进一步提高了算法的效率.对一个以不同角速率多次转弯的机动目标进行跟踪仿真,结果验证了算法的可行性和优越性.     

参考站相对位置对AGNSS接收机卫星信号捕获的影响

AGNSS(Assisted Global Navigation Satellite Service)接收机的性能受辅助信息准确程度的影响.由于参考站位置和终端的真实位置存在偏差,使得接收机获得的参考多普勒频移不准确,将增大弱信号条件下终端对卫星信号频率维搜索的范围.为分析参考站相对位置对AGNSS接收机卫星信号捕获的影响,推导了参考站相对位置偏差引起的多普勒频移分布以及最大频率搜索空间的表达式,并进行了数值仿真和分析,得到了一些有用的结论.     

Argos海洋浮标多普勒定位原理与方法

通过对海洋浮标进行定位,Argos系统在海洋科学方面得到较为广泛的应用。但Argos系统卫星过顶弧段甚短,加之信号发射周期较长,测量资料甚为稀疏,给海洋浮标的定位造成很不利的影响,容易出现矩阵奇异情况,造成定位失败。文章给出了有效的基于多普勒测量的用于数据收集发射平台的定位算法,并利用参考椭球面约束定位目标,从而改进定位算法,计算结果显示如果能有效的使用约束条件,可以使：①原先定位失败的情形成功解算;②原先定位成功的情形定位精度得到改进。文章还给出了针对海洋目标信标运动以及卫星星历误差等因素对定位结果造成的误差影响的统计分析。     

基于角度变化率的机载多普勒直接测距方法

基于角度变化率与多普勒频差之间的关系,提出了一种机载单基线多普勒测距方法,该方法将前置角的正弦变化率引入多普勒频移方程,借助于微分变形所产生的角速度参量就能获得被测目标的距离。模拟分析验证了所导出公式的正确性,同时还分析证明了基于角度变化率的直接测距方法和基于多普勒频移变化率的直接测距方法等效,并基于频率分辨率,给出了...     

高抗干扰性的多普勒频率测量系统

提供一种在噪声背景下可靠测量多普勒频谱信号中心频率值的方法，将锁相理论应用于干扰情况下的多普勒频率测量系统，利用跟踪搜索转换电路，实现了在窄频带内跟踪，宽频带内搜索，使系统具有抗干扰能力强，灵敏度高等优点。实验表明，当系统跟踪多普勒频率信号后，对较强的邻频干扰信号，不产生错误跟踪。