光电探测系统参数与非参数模型运动学标定

为了提高光电探测系统指向精度,提出并对比基于参数模型和非参数模型的运动学标定算法。首先,根据系统组成,全面分析光电探测系统指向误差来源。接着,针对参数模型,运用多体系统理论建立系统指向误差模型,并应用最小二乘法对模型进行标定。然后,针对非参数模型,应用双线性插值算法进行指向误差模型标定。最后,搭建实验平台,获得用于标定和验证的两组实验数据。实验结果表明:经过参数模型标定,指向精度从141.7提高到22.2;经过非参数模型标定,指向精度从141.7提高到27.9。两种方法均能提高光电探测系统指向精度,参数模型标定指向精度略高于非参数模型标定,但是非参数模型运动学标定具有过程简单、计算量小的优势。     

GEO SAR天线波束指向定标中的误差分析

GEO SAR因其超宽测绘带和超长的合成孔径时间,导致低轨SAR波束指向定标方法不再适用,进而采取基于多脉冲分时比幅的波束指向定标方法。本文针对该指向定标方法,结合GEO SAR星地几何关系,对卫星姿态变化、三维系统性误差以及波束指向定标方法中接收机信噪比和通道增益稳定性引入的指向误差进行了详细的推导和仿真分析。仿真结果表明,0.003°的姿态测量误差会引入0.003°的距离向指向误差和0.0033°的方位向指向误差;三维系统性误差是导致天线波束指向变化的主要误差源;当SNR≥35 dB、通道增益稳定性优于1 dB时,GEO SAR波束指向定标方法引入的指向误差小于0.001°。     

增量式光电轴角编码器零点漂移问题解决

介绍了增量式光电轴角编码器的工作原理及其在空间目标测量领域的应用。分析了轴角编码器零点漂移的原因,推导了基于轴系和球谐函数的望远镜系统误差修正模型。提出了采用外复核方法解算望远镜指向精度,即用前两天测星解算出来的系统球谐函数误差模型系数修正并复核当天的测星误差。设计了零点标定实验对轴角编码器零位进行标定,进行了连续11个晴天夜晚的观测实验,在零点标定前后观测在视场内均匀分布的30颗恒星,分别解算得到望远镜指向误差,确认了轴角编码器的零点漂移现象。采集GPS卫星数据进行了精度鉴定,望远镜方位和俯仰的轴系误差均值由13.99、11.50分别降至5.94、-3.49 ,验证了零点标定方法消除零位漂移并提高望远镜测量精度的可行性。     

The pointing calibration of the Haystack antenna

We have applied techniques of optical astronomy to calibrate the pointing of a high-resolution pencil-beam antenna by using radiometric measurements of cosmic radio sources. The Haystack antenna, a 120-ft paraboloidal reflector on an azimuth-elevation mount, was calibrated at a frequency of 15.25 GHz. The beamwidth at this frequency is 36 millidegrees; the rms residual pointing error after calibration was 2.90 millidegrees in azimuth and 3.45 millidegrees in elevation. A total of 172 measurements of pointing error were made on eight sources, and these data were fitted by the method of least squares to determine seven instrumental parameters that take into account axis-alignment errors and gravitational effects on the antenna structure. These techniques are not restricted to antennas used as radio telescopes, and they may be useful in the pointing calibration of other antennas.     

射电望远镜天线的指向精度测量系统设计

指向精度是衡量大口径射电望远镜天线电轴指向准确度的重要指标,如何准确地测量出天线的指向精度对使用者而言尤为重要。针对射电天文望远镜的工作特点,提出了采用射电星作为发射源进行天线指向精度测量的方法,以方位轴为例介绍了测量基本原理,根据测量需要对系统软硬件进行了设计,对实际测量和处理过程进行了描述,给出了测量结果和分析。结果表明该方法可以快捷、准确地测出天线在全天区的指向精度。     

Field Strength Calibration Techniques at the National Bureau of Standards

The techniques and instrumentation utilized by the National Bureau of Standards to calibrate field strength meters and standards in terms of absolute field strength at frequencies from 10 kHz to 1 GHz are described. Two basic techniques are used: (1) the standard-field method for loop antennas at frequencies from 30 kHz to 30 MHz and (2) the standard-antenna method for horizontally-polarized dipole antennas at frequencies from 30 to 1000 MHz. The accuracy and the limitations of each technique are discussed. Present loop antenna calibration uncertainties vary from 3 to 5 percent depending on the frequency. Dipole antenna uncertainties are presently 12 percent. Various other antenna calibration techniques that have been studied are mentioned, pointing out their limitations. The instrumentation used to calibrate the field strength receiver characteristics is described. These measurements include the calibration of the signal attenuators, calibration of the overall linearity of the receiver, and calibration of the receiver as a two-terminal rf voltmeter. Future plans of the National Bureau of Standards field strength and noise calibration services are discussed. Improved uncertainties and extended services are planned for antennas from 30 Hz to 1000 MHz. New noise calibration services are planned; these include the calibration of random noise generators at selected frequencies from 30 to 1000 MHz, and the calibration of impulse generators in terms of their spectral density.     

单脉冲跟踪接收机相位自动校正的研究

在单通道单脉冲自跟踪系统的基础上,说明了交叉耦合产生的原因,讨论了导致交叉耦合恶化的各种因素及解决方法,分析目前存在的几种相位校正方法的局限性,从工程应用的角度提出一种新的相位自动校正方案。该方案对天线平台的稳定性没有要求,校相过程中无需对准卫星,同时还可以实现跟踪接收机的自检,快速实现故障定位。试验表明,该方案校相精度高,适用范围广,具有很高的应用价值。     

基于立体方向图和十字跟踪扫描法校准天线指向

针对明安图射电频谱日像仪（Mingantu spectral radioheliograph，MUSER）天线高指向精度动态跟踪要求，同时为降低非理想因素对复杂系统天线指向测量影响，提出校准天线指向的组合方法.先用网格法测量天线的双圆极化多频率通道立体方向图定性评估系统测量链路状态，后对太阳运行轨道进行十字跟踪扫描测量天线指向偏差，再用最小二乘法拟合获得天线指向模型的8个参数.国家天文台明安图观测基地的2台20 m地平式天线将在MUSER系统观测和校准中起重要作用.对20 m天线跟踪指向进行了校准，指向偏差均方根从12'改善到4.4'，验证了方法的可行性，为类似复杂系统的相关工作提供了借鉴和参考.     

一种用于高精确度双框架伺服系统的标定方法

为实现对空间动态目标的稳定跟踪，介绍了一种高精确度双框架结构伺服系统，通过标定提高了其指向精确度。利用旋转变压器作为角度位置传感器，通过激光测距机和相机实现远场目标的稳定跟踪。利用高精确度单轴转台、激光测距机和平面反射镜对伺服系统双框架指向精确度进行标定实验测量。针对伺服系统几何误差，对获得的采样数据进行分段直线拟合，并写入控制程序。对测量数据进行分段检索定位，通过拟合直线参数对数据进行修正。实验结果表明，标定后的双框架伺服系统指向精确度优于16"，可有效提高伺服系统指向精确度。     

Accurate measurements of pressure-broadened linewidths in a transversely excited CO2discharge

A novel technique is used to measure He-dominated pressure-broadening coefficients in the 10μm band of CO2. Gain measurements in a pulsed transversely excited CO2discharge are made at line center using a CW CO2laser as a probe, and at a known offset frequency using a CW N2O laser. By measuring this gain ratio as a function of discharge pressure, we determine the linewidth with an accuracy of ∼ 2 percent. Linewidths are measured for nine different transitions in the 10 μmP-branch, and theJ-dependence of the CO2-He pressure-broadening coefficient is determined and compared to theory. In addition, we examine the temperature dependence of the linewidth under conditions of constant number density and find that the linewidth increases asT^{0.42 pm 0.06}. This agrees well with a recent theoretical prediction of T^0.38(R. T. Pack, "Pressure broadening of the dipole and Raman lines of CO2by He and Ar. Temperature dependence," J. Chem. Phys., vol. 70, pp. 3424-3433, 1979). To our knowledge, these experiments represent the first direct linewidth measurements in a transversely excited CO2discharge.     

某型地基相控阵天线指向系统性误差分析

相控阵天线的指向精度决定着雷达系统对目标的探测精度,甚至会影响跟踪、截获目标的成败。以一种地基相控阵天线为例,详细分析了机电混合扫描天线的指向系统性误差来源：1)热形变导致的单元间距误差,2)空气折射,3)伺服机械转动误差,4)天线内部温度场变化等。从理论上分析了上述因素对天线指向精度的影响,并提出了完整的远场误差校准方法和误差修正流程。试验结果表明,误差来源分析准确,所提出的校准方法可以明显改善天线指向精度,从而提高雷达系统跟踪精度和威力,对于地基乃至移动平台相控阵天线的设计与应用具有重要的参考价值。     

Analysis and improvement of tipping calibration for ground-basedmicrowave radiometers

The tipping-curve calibration method has been an important calibration technique for ground-based microwave radiometers that measure atmospheric emission at low optical depth. The method calibrates a radiometer system using data taken by the radiometer at two or more viewing angles in the atmosphere. In this method, the relationship between atmospheric opacity and viewing angle is used as a constraint for deriving the system calibration response. Because this method couples the system with radiative transfer theory and atmospheric conditions, evaluations of its performance have been difficult. In this paper, first a data-simulation approach is taken to isolate and analyze those influential factors in the calibration process and effective techniques are developed to reduce calibration uncertainties. Then, these techniques are applied to experimental data. The influential factors include radiometer antenna beam width, radiometer pointing error, mean radiating temperature error, and horizontal inhomogeneity in the atmosphere, as well as some other factors of minor importance. It is demonstrated that calibration uncertainties from these error sources can be large and unacceptable. Fortunately, it was found that by using the techniques reported, the calibration uncertainties can be largely reduced or avoided. With the suggested corrections, the tipping calibration method can provide absolute accuracy of about or better than 0.5 K     

An adaptive calibration and beamforming technique for a GEO satellite data relay

High throughput data links from low Earth orbit satellites through a geostationary orbit satellite data relay have been proposed to increase the available contact times to ground stations. Accurate antenna beam pointing and tracking of moving targets are key requirements for the relay satellite. In this work, we propose an adaptive calibration and beamforming methodology on the basis of least mean squares, which is suitable for a geostationary orbit data relay. The target system consists of the combination of a high gain reflector fed by a digitally steerable patch antenna array. The proposed method is first presented by numerical cosimulation of the antenna and the calibration algorithm. The results are then validated in an outdoor experimental setup with all digital signal processing implemented in a field‐programmable gate array. We demonstrate the tracking ability and pointing performance of the digitally enhanced reflector antenna with gain fluctuations smaller than 3 dB over a field of view of at least 2,5°. The demonstrated performance shows that the digitally enhanced reflector antenna is a suitable candidate for long‐distance space communications.     

夜间遥感场地替代定标的微光光谱仪设计与试验分析

针对目前传统的地物光谱仪对光信号强度要求较高,只能白天使用,无法在夜间使用而导致夜间遥感在轨辐射定标不确定度较高的问题,提出一种将传统光谱仪的CCD(Charge-Coupled Device)探测器与像增强器直接耦合提升光谱仪低照度条件下信息获取能力的技术方案。基于该技术方案的光谱仪可有效实现地面目标光谱信息的夜间测量。相关测试试验结果表明:在入射光源只有月光和星光的条件下,该微光光谱仪可有效实现对地面目标光谱信息的测量,且性能良好稳定,未来可应用于夜间遥感定标、夜间目标光谱信息获取等应用领域,为夜间遥感在轨定标精度的提升奠定技术基础。     

超连续激光单色仪系统级光谱响应度定标比对验证

细分光谱扫描定标技术是实现遥感器高精度光谱辐射定标的重要方式,基于超连续激光单色仪的定标装置是实现遥感器细分扫描定标的新选择。为验证所建立的超连续激光单色仪装置的系统级定标能力,利用硅辐亮度计和滤光片辐射计,分别采用超连续激光单色仪定标装置和可调谐激光定标装置对其进行了系统级绝对光谱响应度定标比对验证。实验结果表明:在所验证波段范围内,两种定标装置获得的硅辐亮度计绝对光谱响应度系统级定标结果最大偏差为0.6%。通道式滤光片辐射计的带内绝对光谱响应度定标结果最大偏差优于0.4%,带内积分响应度最大偏差约0.1%。文中的研究验证了超连续激光单色仪定标装置具有良好的系统级定标能力,能够获得较高的定标精度,在遥感器的绝对光谱响应度定标中具有重要应用前景。     

Measuring process capability based on CPK with gauge measurement errors

The well-known process capability index C_PK has been popularly used in the manufacturing industry for measuring process reproduction capability. Existing research papers related to C_PK have assumed with no gauge measurement errors. Unfortunately, such assumption does not reflect real situations accurately even with highly sophisticated advanced measuring instruments. Conclusions drawn from process capability analysis are hence unreliable. In this paper, we consider estimating and testing C_PK with presence of gauge measurement errors. The results show that the estimator using the sample data contaminated by the measurement errors severely underestimates the capability, resulting imperceptible power of capability testing. To obtain the true process capability, modified confidence bounds and critical values are presented to practitioners for their factory applications.     

机载光电跟踪系统的模糊PID控制

为了提高机载光电跟踪系统的控制性能,提出了一种模糊自适应PID控制算法。首先,针对机载光电跟踪控制系统的特点,建立了被控对象的模型。接着,对机载光电跟踪系统模糊PID控制器的设计进行了详细介绍。最后,利用经典PID控制、模糊控制、模糊PID控制3种算法对机载光电稳定跟踪系统进行仿真比较。仿真结果表明模糊PID控制算法较之前两种算法具有响应快、超调量小、抗干扰能力强、稳态性能好等优点,对机载光电跟踪系统具有较好的控制能力。     

基于地面红外探测器的星载激光测高仪在轨几何定标

高精度在轨几何定标是星载激光测高仪有效应用的基础,在参考国外冰、云和陆地高程卫星（Ice,cloud and land Elevation Satellite,ICESat）卫星搭载的地球科学激光测高系统（Geo-science Laser Altimeter System,GLAS）几何定标的基础上,提出了一种基于地面红外探测器的星载激光测高仪几何定标方法。采用资源三号02星上搭载的国内首台试验性对地观测激光测高仪的真实数据开展了实验验证。实验结果表明:地面红外探测器能有效捕捉到激光测高仪对地发射的激光信号,几何定标方法能有效消除指向角的系统误差项,标定后平面绝对精度可提高到15.0 m左右,而华北某地高精度地形数据验证表明其绝对高程精度可提高到1.09 m,少量点高程误差小于0.5 m。虽然精度水平离国外GLAS还有一定差距,但相关结论能为后续国产激光测高卫星的优化设计、数据处理与应用提供参考。     

适用于TIADC的高精度时间失配误差校准算法

设计了一种适用于TIADC的高精度时间失配误差校准算法。基于相邻通道信号互相关原理,对相邻通道的输出信号作相关运算来估计时间失配误差,再利用基于泰勒级数展开的高阶误差校准方法进行误差校正。误差估计模块与校准模块构成一个反馈环路,可以实现误差的实时跟踪和校正。校准算法行为级仿真结果表明,在12位1 GHz四通道的TIADC中,当输入信号归一化频率f_in/f_s=0.477 1时,校准后系统的ENOB提高到11.85位,SNR提高了43 dB以上,校准效果明显。相比已有的校准算法,该校准算法具有更高的校准精度,不受通道数的限制,结构更简单,且在整个奈奎斯特频率范围内都适用,非常适合工程应用。     

阵列天线因随机振动引起的测向误差分析及校准

针对阵列天线受舰船甲板低频机械随机振动引发振子位移变化导致的测向误差问题,建立了天线振子随机振动误差模型,仿真分析了天线阵列3个轴向随机振动模式对测角接收信号的影响,提出了一种基于多个接收机在不同位置同时测量的测角误差校正方法.该方法采用最小二乘法得到多个误差校准矢量,通过调用天线波束指向扇区内校准矢量的方法进行误差补偿,解决了低频随机振动模式下阵列天线测角误差的校准问题.该方法已应用到舰载微波着舰引导系统数据解算中.