On-orbit Geometric Calibration and Preliminary Accuracy Evaluation of GF-14 Satellite

GF-14 satellite is a new generation of sub-meter stereo surveying and mapping satellite in China,carrying dual-line array stereo mapping cameras to achieve 1∶10000 scale topographic mapping without Ground Control Points(GCPs).In fact,space-based high-precision mapping without GCPs is a challenging task that depends on the close cooperation of several payloads and links,of which on-orbit geometric calibration is one of the most critical links.In this paper,the on-orbit geometric calibration of the dual-line array cameras of GF-14 satellite was performed using the control points collected in the high-precision digital calibration field,and the calibration parameters of the dual-line array cameras were solved as a whole by alternate iterations of forward and backward intersection.On this basis,the location accuracy of the stereo images using the calibration parameters was preliminarily evaluated by using several test fields around the world.The evaluation result shows that the direct forward intersection accuracy of GF-14 satellite images without GCPs after on-orbit geometric calibration reaches 2.34 meters(RMS)in plane and 1.97 meters(RMS)in elevation.

GYRO BIAS ON-ORBIT CALIBRATION FOR MICRO SATELLITES

According to gyro application in micro-satellites, a new gyro bias real-time on-orbit calibration technology is presented and it is independent of any other sensors. The approach relies on gyro on-orbit measurements restricted by satellite attitude dynamics and estimates the gyro bias generated when the gyro is electrified. Observability of the calibration model is analyzed and applicable conditions of the technology are derived. Simulation results indicate that the calibration algorithm is accurate and robust at gyro sampling rate, and its convergence speed is fast. Within the given attitude dynamics model error, the convergence time is less than 100 s and the convergence accuracy is about 1.0 （°）/h. Calibration performance can meet requirements of spacecraft operations.

GF-5 VIMI On-Orbit Calibration Instrument and Performance

The Visible and Infrared Multispectral Imager (VIMI) is one of the main payloads of the GF-5 satellite. It has 12 spectral bands covering the wavelength from visible light to thermal infrared. The imager designed life is 8 years. In order to monitor and correct the radiometric performance of the imager for a long time and meet the user’s demand for the quantitative remote sensing application, the expandable diffuser used for calibration in full FOV and full optical path method is designed. The solar diffuser is installed on the front side of the optical system and does not affect the normal imaging of VIMI. When VIMI need calibration, the diffuser is expand to the front of optical system via the driving mechanism. According to the characteristics of the GF-5 satellite orbit, the requirement of the calibration energy and the installation matrix of the imager relative to the satellite, the expansion angle of the diffuser is 39 degrees. The 430 mm × 430 mm large-size PTEE diffuser is manufactured to ensure full FOV and full optical path calibration. The diffuser’s directional hemispherical reflectance is higher than 95% from 420 nm to 2400 nm and variation of BRDF in the direction of imager observation is better than 2.5%. The diffuser stability monitoring radiometer is designed to monitor the on-orbit attenuation performance of the diffuser. Results of ground simulation experiments and preliminary on-board calibration experiments were introduced.

On-orbit Geometric Calibration of Linear Push-broom Optical Satellite Based on Sparse GCPs

The paper presents a geometric calibration method based on the sparse ground control points (GCPs), aiming to the linear push-broom optical satellite. This method can achieve the optimal estimate of internal and external parameters with two overlapped image pair along the charge-coupled device (CCD), and sparse GCPs in the image region, further get rid of the dependence on the expensive calibration site data. With the calibrated parameters, the line of sight (LOS) of all CCD detectors can be recovered. This paper firstly establishes the rigorous imaging model of linear push-broom optical satellite based on its imaging mechanism. And then the calibration model is constructed by improving the internal sensor model with a viewing-angle model after an analysis on systematic errors existing in the imaging model is performed. A step-wise solution is applied aiming to the optimal estimate of external and internal parameters. At last, we conduct a set of experiments on the ZY-3 NAD camera and verify the accuracy and effectiveness of the presented method by comparison.

Calibration chain design based on integrating sphere transfer radiometer for SI-traceable on-orbit spectral radiometric calibration and its uncertainty analysis

In order to satisfy the requirement of SI-traceable on-orbit absolute radiation calibration transfer with high accuracy for satellite remote sensors,a transfer chain consisting of a fiber coupling monochromator（FBM） and an integrating sphere transfer radiometer（ISTR） was designed in this paper.Depending on the Sun,this chain based on detectors provides precise spectral radiometric calibration and measurement to spectrometers in the reflective solar band（RSB） covering 300–2500 nm with a spectral bandwidth of 0.5–6 nm.It shortens the traditional chain based on lamp source and reduces the calibration uncertainty from 5% to 0.5% by using the cryogenic radiometer in space as a radiometric benchmark and trap detectors as secondary standard.This paper also gives a detailed uncertainty budget with reasonable distribution of each impact factor,including the weak spectral signal measurement with uncertainty of 0.28%.According to the peculiar design and comprehensive uncertainty analysis,it illustrates that the spectral radiance measurement uncertainty of the ISTR system can reach to 0.48%.The result satisfies the requirements of SI-traceable on-orbit calibration and has wider significance for expanding the application of the remote sensing data with high-quality.

Calibration Method of Magnetometer Based on BP Neural Network

Due to the influence of processing technology and environmental factors, there are errors in attitude measurement with the three-axis magnetometer, and the change of parameters during the operation of the magnetometer in orbit will have a great impact on the measurement accuracy. This paper studies the calibration method of magnetometer based on BP neural network, which reduces the influence of model error on calibration accuracy. Firstly, the error model of the magnetometer and the structural characteristics of the BP neural network are analyzed. Secondly, the number of hidden layers and hidden nodes is optimized. To avoid the problem of slow convergence and low accuracy of basic BP algorithm, this paper uses the Levenberg Marquardt backpropagation training method to improve the training speed and prediction accuracy and realizes the on-orbit calibration of magnetometer through online training of the neural network. Finally, the effectiveness of the method is verified by numerical simulation. The results show that the neural network designed in this paper can effectively reduce the measurement error of magnetometer, while the online training can effectively reduce the error caused by the change of magnetometer parameters, and reduce the measurement error of magnetometer to less than 10 nT.

面向全自主智能机器人的无标定图像视觉伺服控制研究

在利用全自主智能机器人检测、搬运目标物的过程中,为了提高主机元件对机器人的伺服控制效果,设计了一种无标定图像视觉伺服控制方法;首先,根据机器人轨迹的无标定估计结果,计量目标物的位姿点,推导出机器人无标定图像中的目标物检测与追踪条件;按需连接视觉伺服控制器,通过求解机器人无标定运动内积的方式,计算图像视觉特征的伺服选择标准,实现对机器人无标定图像视觉特征的伺服选择;然后,在无标定图像中定义雅克比矩阵,根据图像视觉分割原则,完成机器人图像角点的伺服匹配处理,再通过确定强化控制参数的取值范围,实现无标定图像的视觉伺服控制;根据实验可知,应用该方法可以解决智能机器人难以运动至标定区域的问题,为提高伺服控制指令的执行有效性提供了保障。

非接触三点内径测量法中角度安装误差的校准方法研究

由于操作简便,非接触三点内径测量法常用于工业现场测量。为提高工件内径测量精度,对在安装中无法避免的位移传感器角度安装误差进行分析建模,提出了一个新的考虑角度安装误差的非接触内径测量模型及一种基于多观测位置联立方程的误差校准方法。通过仿真分析了模型中观测位置数、工件内径尺寸与其他参数的设置对校准结果的影响,确认了在观测位置数大于4时即可实现对误差的校准。最终,使用激光位移传感器构建内径测量系统并开展实验,验证了角度安装误差校准方法的有效性,圆工件的内径测量的绝对精度与重复性精度分别在0.6μm与0.4μm以下。

A review of structures,verification,and calibration technologies of space robotic systems for on-orbit servicing

Recently,with the rapid development of aerospace technology,an increasing number of spacecraft is being launched into space.Additionally,the demands for on-orbit servicing(OOS)missions are rapidly increasing.Space robotics is one of the most promising approaches for various OOS missions;thus,research on space robotics technologies for OOS has attracted increased attention from space agencies and universities worldwide.In this paper,we review the structures,ground verification,and onorbit kinematics calibration technologies of space robotic systems for OOS.First,we systematically summarize the development of space robotic systems and OOS programs based on space robotics.Then,according to the structures and applications,these systems are divided into three categories:large space manipulators,humanoid space robots,and small space manipulators.According to the capture mechanisms adopted,the end-effectors are systematically analyzed.Furthermore,the ground verification facilities used to simulate a microgravity environment are summarized and compared.Additionally,the on-orbit kinematics calibration technologies are discussed and analyzed compared with the kinematics calibration technologies of industrial manipulators with regard to four aspects.Finally,the development trends of the structures,verification,and calibration technologies are discussed to extend this review work.

基于持续时空注意力网络的人脸微表情识别

人脸微表情具有持续时间短,运动幅度小,只发生在面部局部区域的特点,给微表情的准确识别带来了极大的挑战。针对上述问题,提出一种基于持续时空注意力网络(Continuous Spatiotemporal Attention Network,CSTN)的人脸微表情识别算法。该算法由主、副两个通道组成,主通道为持续时空注意力模块,副通道为位置校准模块。首先主通道进行离散采样,等间隔抽取原始视频帧组成一个新的视频序列,利用帧间差分法提取各帧之间的运动差异,再将其输入到持续时空网络,提取面部肌肉运动的时空特征;其次利用副通道提取的面部位置信息对主通道信息进行位置校准,最后将融合信息输入到Softmax分类器对微表情进行分类。实验表明在3个公开微表情数据集CASMEⅡ,SAMM,MMEW上该算法识别的平均准确度分别达到了89.96%,86.73%,89.76%,优于现有其他算法。

Method study and uncertainty analysis of calibration coefficients validation based on the Inner Mongolia test site

Calibration coefficients validation is the foundation for ascertaining the sensor performance and carrying out the quantitative application.Based on the analysis of the differences between the calibration and validation,two calibration coefficients validation methods were introduced in this paper.Taking the HJ-1A satellite CCD1 camera as an example,the uncertainties of calibration coefficients validation were analyzed.The calibration coefficients validation errors were simulated based on the measured data at an Inner Mongolia test site.The result showed that in the large view angle,the ground directional reflectance variation and the atmospheric path variation were the main error sources in calibration coefficients validation.The ground directional reflectance correction and atmospheric observation angle normalization should be carried out to improve the validation accuracy of calibration coefficients.

应用内外定标修正实现红外测量系统辐射定标

由于现有的大口径短波红外测量系统的辐射定标需要制备大口径红外平行光管,不仅机动性差且成本较高,故提出了一种基于内、外定标修正的辐射定标新方法。该方法将一个中、高温腔型黑体置于红外系统内部,通过切换反射镜,将中、高温腔型黑体辐射引入红外光学系统,并对部分光路进行中、高温段的内定标。然后,使用大面源黑体对全系统进行中温段的外定标;提取并处理公共温度范围的内、外定标数据以获取内、外定标之间的修正系数。最后,对中、高温段的内定标数据进行修正从而获取全系统的辐射定标数据。使用该方法对某Φ400mm口径的红外测量系统进行了辐射定标,并根据定标结果反演了黑体的辐射亮度和温度。结果显示:辐射亮度反演的最大误差为1.67%,温度反演的最大误差为1.02℃。实验结果证明了该方法可以准确、有效地对大口径短波红外测量系统进行辐射定标。

测绘一号卫星相机的光谱和辐射定标

对测绘一号卫星相机的各个光谱通道进行了光谱定标和辐射定标以验证其光谱辐射性能是否达到设计指标要求。进行光谱定标时,利用单色仪分光谱扫描波长提供准直单色辐射照明,同时同步采集定标图像数据;然后将图像灰度值与已经过校准的参考标准探测器的输出进行比对和数据处理,得到相机各个谱段的相对光谱响应函数曲线,从而进一步获得各项光谱特性参量。辐射定标时,采用近距离面源法充满相机的孔径和视场进行端对端的绝对和相对辐射定标。星上内定标则采用经老炼和筛选过的发光二极管(LED)作为星上定标光源,对焦平面阵列探测器及其成像电路的状态和辐射响应性能变化进行在轨监测,在必要的情况下予以校正。定标结果显示:测绘一号卫星相机的各项光谱和辐射性能均达到了设计指标要求,经过相对辐射校正后响应非均匀性由1.93%下降到0.22%,相机全色谱段信噪比超过90倍,多光谱各通道信噪比优于180倍;发射后在轨星上内定标数据与发射前实验室测试结果的比对显示相机的辐射响应性能未发生明显变化,暂时无须校正。

三线阵CCD相机亚像元精度几何标定方法研究

为了解决三线阵CCD立体测绘相机内方位元素的几何标定问题,提出了一种实现相机亚像元精度内方位元素和交会角标定的方法。该方法利用光学高精度角度发生器和CCD细分测量相结合的检测方法,由最小二乘回归分析,实现相机内方位元素的标定,并通过扫描星点图像标定交会角。校飞实验的数据处理结果验证了该方法的有效性。

借助于星点标定相机的内方位元素

为满足单个或一批次测绘相机的标定,提出了一种利用已知坐标值的星点对测绘相机进行标定的方法。介绍了该方法的原理以及计算步骤,给出了实验过程。该方法建立在小孔成像的基础上,通过各个坐标系的相互转换,建立起星点坐标和像素坐标之间的联系,以此求解相机内方位元素。与基于平行光管和精密转台的精密测角法相比,该方法不需要昂贵的实验设备,且简化了标定步骤。最后,对标定精度进行了分析,讨论了噪声扰动和已知内方位元素误差对标定结果的影响。分析结果表明,采用该标定方法,相机的主点精度优于3μm(1/3pixel),主距精度优于7μm(小于1pix-el),满足标定精度要求。

大面阵数字航测相机的精密几何标定

通过将大面阵数字航测相机固定在二维内方位仪的高低轴内部,转动测量机架,使平行光管的点像目标依次成像在被测相机的CCD靶面上,结合相应的计算公式和测控软件,得出了大面阵数字航测相机的内方位元素及畸变值,解决了大面阵数字航测相机视场大、不易标定的问题.实践证明该方法是可行的。

36维Kalman滤波的激光陀螺捷联惯导系统级标定方法

分析了系统级标定的研究现状,建立了惯导系统误差模型。额外考虑加速度计二次项误差系数与内杆臂参数对系统的影响,提出了一种36维Kalman滤波系统级标定方法。设计了合适的标定路径,建立了Kalman滤波模型。仿真及实验结果表明,激光陀螺和加速度计零偏估计精度分别优于0.001(°)/h和9μg,标度因数误差估计精度分别优于3 ppm(1 ppm=10-6)和2 ppm,安装误差角估计精度分别优于1″和3″,二次项误差系数估计精度优于4×10-10 s2/m,内杆臂参数估计精度优于3 mm,满足高精度惯导系统的标定要求。

风云二号卫星在轨辐射定标技术进展

在轨辐射定标性能是影响风云二号(FY-2)卫星定量化应用的关键因素。本文在简要回顾FY-2卫星在轨辐射定标技术发展的基础上,着重介绍了最新引进的高光谱交叉定标,以及自主研发的基于月球辐射校正的内黑体定标(CIBLE)等方法的技术特点。分析表明:以月球定标和内黑体定标为核心的CIBLE方法,从机理上解决了FY-2卫星红外波段随环境温度场频繁变化的辐射响应的高精度标定难题,实现了我国静止气象卫星在轨辐射定标技术的重大突破,并已于2012年7月、2013年3月和2013年5月分别在FY-2F、FY-2E和FY-2D星中实现业务运行。最后,对未来气象卫星在轨辐射定标技术的发展进行了初步探讨。

光学式轴孔内径在线测量方法研究与误差分析

轴孔内径尺寸测量是发动机箱体检测中的一项关键技术,是提升发动机性能和质量的必要手段。为提高轴孔内径在线测量水平,同时克服现有方法的局限性,提出一种新型光学式多方向轴孔内径测量方法。该方法借鉴气动量仪的布局,均匀分布激光位移传感器于测棒截面,并根据发动机箱体轴孔的结构特点,匹配测棒长度和测量截面层数。为评价装配误差和测量随机误差对测量精度的影响,利用遗传算法分析内径测量数学模型,寻找影响最终测量误差的关键因素,并以此作为指导测量的依据。结合校准过程,通过比较轴孔内径的测量值和已知检定值,证明该方法内径测量误差优于5μm。试验结果表明该方法可以用于轴孔内径的高精度自动化在线测量。

数码相机检校和摄像测量的部分问题探讨

介绍了数码相机检校的概念 ,阐述数码相机的检校内容和误差来源 ,内方位元素的计算和镜头畸变差校正 ;控制场的建立和影像获取方法 ,直接使用现有摄影测量软件Australis并使检校过程简化 ,指出并分析了实验过程中存在的问题及其原因 .