Ground calibration of the Mars orbiter magnetometer onboard Tianwen-1

Ground calibration experiments of the Mars orbiter magnetometer(MOMAG)onboard the orbiter of Tianwen-1 were performed to determine the sensitivity,misalignment angle,and offset of the sensors.The linearity of the applied calibrated magnetic fields and the output from the sensors were confirmed to be better than 10^(-4),and the sensor axes were orthogonal to each other within 0.5 degrees.The temperature dependencies of the sensitivity and misalignment angle were examined,but no clear signatures of temperature dependencies could be seen.Sensor offset and the stability of sensor offset drift with a temperature change were also determined by the rotation method.The stability of the sensor offset drift was less than 0.01 nT/℃.The ground calibration of MOMAG determines all the calibration parameters of the sensors for accurate magnetic field measurements in orbit with the appropriate corrections.

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.

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.

GOCE kinematic orbit adjustment for EGM validation and accelerometer calibration

The main principle and mathematical model of GOCE kinematic orbit adjustment for Earth gravity field model （EGM） validation and accelerometer calibration are presented. Based on 60 days GOCE kinematic orbits with 1-2 cm accuracy and accelerometer data from 2009-11-02 to 2009-12-31, the RMS-of-fit （ROF） of them using EGM2008, EIGEN-SC, ITG- GRACE2010S and GOCO01S up to 120, 150 and 180 degree and order （d/o） are evaluated and compared. The scale factors and biases of GOCE accelerometer data are calibrated and the energy balance method （EBM） is performed to test the accuracy of accelerometer calibration. The results show that GOCE orbits are also sensitive to EGM from 120 to 150 d/o. The ROFs of EGMs with 150 and 180 d/o are obviously better than those of EGMs with 120 d/o. The ROFs of GOCO01S and ITG-GRACE2010S are almost the same up to 120 and 150 d/o, which are about 3.3 cm and 1.8 cm, respectively. They are far better than those of EGM2008 and EIGEN-SC with the same d/o. The ROF of GOCO01S with 180 d/o is about 1.6 em, which is the best one among those EGMs. The accelerometer calibration accuracies （ACAs） of ITG-GRACE2010S and GOCO01S are obviously higher that those of EGM2008 and EIGEN-SC. The ACA of GOCO01S with 180 d/o is far higher than that of EGMs with 120 d/o, and a little higher than that of ITG-GRACE2010S with 150 d/o. I t is suggested that the newest released EGM such as GOCO01S or GOCO02S till at least 150 d/o should be chosen in GOCE precise orbit determination （POD） and accelerometer calibration.

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.

红外高光谱大气探测仪(FY-3E/HIRAS-Ⅱ)在轨数据非线性校正方法

风云三号E星(FY-3E)搭载的高光谱大气探测仪(HIRAS-Ⅱ)能够实现大气的垂直探测,具有高光谱、高灵敏度、高精度的特点。仪器在轨之后由于仪器衰减和环境变化的原因产生非线性响应,影响在轨定标精度。针对非线性响应的问题,提出了一种基于带内光谱的非线性校正方法。首先基于带外低频光谱的非线性特征求解非线性校正系数,将此系数作为初值输入到辐射定标模型中,以星上测量的黑体带内光谱与理想光谱的偏差为目标函数,通过迭代优化非线性校正系数。通过辐射定标实验得出,校正后的黑体亮温偏差明显低于未校正和基于带外光谱的校正方法。将HIRAS-Ⅱ的观测数据与IASI进行交叉比对并计算平均亮温偏差和偏差绝对值,经过带内校正法非线性校正后的亮温平均偏差为-0.13 K,优于带外校正方法。

敦煌戈壁地表反射率光谱的旋翼无人机测量及定标评估

利用敦煌中国遥感卫星辐射校正场的星地同步观测试验,实现对我国在轨气象、海洋、陆地资源、环境减灾、测绘地震、高分、军事等系列卫星光学成像载荷太阳反射波段的绝对辐射定标,是目前的重要手段之一。然而,中国遥感卫星辐射校正场传统的地表反射率光谱星地同步测量方法是基于汽车跑场观测,不仅耗费较大的人力物力、容易造成场地破坏,而且获取的测量数据缺乏区域代表性。鉴于此,自2016年起,在敦煌星地同步观测试验中以旋翼无人机低空同步测量为主,跑场测量为辅,完成从航线设计、航高选择、仪器参数配置、采样策略、航空数据处理的全链路摸底测试。多次飞行试验表明,采用多旋翼无人机低空飞行来代替汽车跑场同步测量,不仅提高了地表反射特性测量的空间一致性和代表性,还提高了地表反射率光谱的测量效率,也对宝贵的中国遥感卫星辐射校正场敦煌戈壁场区地表进行了有效保护,极大的节约了人力物力成本。通过传统跑场测量和航飞测量的地表反射率光谱数据对比分析,发现多次测量数据的均值一致性较好,并且航飞测量的数据标准差更小。利用TERRA MODIS的同步观测来对无人机测量数据开展辐射定标评估,结果表明航飞数据的相对偏差均在5%以内,可以代替跑场数据完成定标,精度满足要求。随着无人机性能的进一步优化和提高,在不久的将来必将得到更加广泛和深入的应用,在外场定标试验领域也将发挥更大更重要的作用。

高精度地形星载激光测高仪在轨几何标定方法

激光测高仪数字化标定方法由于标定频次高、人力物力消耗少等突出性优点越来越受到关注。本文提出了一种两步法的激光测高仪数字化标定方法,针对线性体制激光测高仪的几何定位模型,构建了关于翻滚角、俯仰角和测距系统误差的几何标定模型,并使用公开参考地形数据SRTM与高精度机载LiDAR点云进行了标定试验。与GF-14实际外场面探测器试验标定的数据比较分析。结果显示,本文提出的几何标定方法与地面探测器标定参数测角差异在0.5角秒以内,测距差异在0.2 m以内。通过独立数据验证标定结果的高程精度,本文提出的数字化标定方法和探测器标定方法的足印高程偏差表现出良好的一致性,两种方法标定所获取的足印高程与高精度机载点云高程的RMSE均优于0.3 m。本文方法在保证精度的同时,减少了人力物力的消耗,为星载激光测高仪在轨常态化标定提供了新的思路和方法。

附加距离约束的导航相机快速标定方法

针对在轨条件下因观测条件匮乏导致巡视器导航相机标定精度受限的问题,提出了一种基于直线特征的导航相机快速在轨自标定方法。首先,利用SAM(segment anything model)对导航影像太阳能板区域进行图像分割,并对太阳能板OCR(optical control room)直线特征进行提取;然后,构建附加距离约束的导航相机自检校模型;最后,利用Levenberg-Marquardt方法对标定模型进行求解。开展了模拟实验及在轨实验。分析结果表明,相比光束法自标定、CAHVOR及Vanishing Points等标定方法,所提出方法标定参数重建的坐标精度平均值分别提升了20.60%、30.82%和35.92%,对太阳能板OCR距离恢复距离偏差范围在-1.4~1.5 mm之间。该方法可为巡视器导航相机在轨标定技术提供一定的价值参考。

低轨卫星激光载荷配置及快速建链方法的研究

为了适应未来低轨卫星轻量化和低成本的发展趋势,满足星间激光快速建链的使用需求,对星间激光配置原则进行了分析,采用转台式激光载荷和固定式激光载荷相结合的载荷配置方式,分别用于异轨道面间和同轨道面内的星间建链,设计了基于在轨恒星标校、信标光辅助建链和光轴一致性的激光载荷快速星间建链方案,并介绍了全流程。结果表明,星间激光载荷建链时间小于30 s,可实现长时间的星间激光稳定跟踪通信。该研究结果有助于推动星间激光通信的发展和大规模在轨应用。

大视场相机最优投影模型识别及星光标定方法

针对在轨摄影测量中近距离大尺寸测量需求,提出利用星光约束的大视场角摄影测量相机最优投影模型识别及标定方法。首先,构建了具备调节系数的星光几何投影分段函数模型。随后,针对分段星光投影模型开发多站位自标定光束平差算法。通过将光束平差算法与北方苍鹰寻优策略相结合,对投影模型调节系数、相机内方位参数、相机外方位参数及镜头畸变系数同步优化,直到星点像面重投影均方根误差达到全局最小,得到最优投影模型及其参数。实测实验表明,大视场角相机星光标定后,星点像面坐标的重投影均方根误差为1/9 pixel。在连续帧星光标定实验中,通过卡尔曼滤波算法对相机参数随机误差进行了有效消除。该方法可在相机星光标定过程中识别最优投影模型并标定全部成像参数,具备连续帧标定及参数校准能力。

光轴位置测量数据辅助立体影像无控定位技术

在卫星摄影测量中,相机参数经过在轨标定后,仍有随时间变化的低频误差,在无地面控制点情况下,这类低频误差影响卫星影像的定位精度。基于光学自准直原理的光轴位置测量设备可以在轨实时监测相机参数的变化情况,对于全球实时或准实时影像处理,可以使用该测量数据削弱低频误差对立体影像定位精度的影响。本文基于光轴位置测量设备的工作原理,建立了光轴位置测量数据辅助立体影像定位的模型和算法,并利用高分十四号卫星数据进行了试验验证。试验结果表明,利用光轴位置测量数据辅助立体影像定位,无须频繁地进行相机参数在轨标定,也无须地面控制点支持,即可实现卫星影像高精度定位,且全球范围内影像无地面控制点定位精度基本一致,平面精度约为1.87 m,高程精度约为0.73 m。

基于高光谱自动化观测设备的高分二号卫星在轨定标应用与验证

为验证高光谱自动化野外观测设备的地表反射率数据的应用效果,基于反射率基法开展了高分二号(GF-2)卫星遥感器的在轨定标数据应用及验证。首先系统介绍了设备安装定标场的状况及多种自动化观测设备的工作方式及性能指标,并给出了仪器的观测数据及地表反射率数据的计算方式。随后结合GF-2卫星遥感器定标的需求并利用卫星大气数据产品和GF-2遥感器的同步过顶观测影像,完成了GF-2多光谱相机(PMS)遥感器的在轨定标。最后根据获得的定标系数,利用不同时段的遥感器影像数据进行了验证。两种不同地表的应用验证表明,卫星表观辐亮度的数据整体相对偏差优于2%,验证了高光谱设备在卫星遥感器在轨定标上的可行性。

Application of camera calibrating model to space manipulator with multi-objective genetic algorithm

The multi-objective genetic algorithm(MOGA) is proposed to calibrate the non-linear camera model of a space manipulator to improve its locational accuracy. This algorithm can optimize the camera model by dynamic balancing its model weight and multi-parametric distributions to the required accuracy. A novel measuring instrument of space manipulator is designed to orbital simulative motion and locational accuracy test. The camera system of space manipulator, calibrated by MOGA algorithm, is used to locational accuracy test in this measuring instrument. The experimental result shows that the absolute errors are [0.07, 1.75] mm for MOGA calibrating model, [2.88, 5.95] mm for MN method, and [1.19, 4.83] mm for LM method. Besides, the composite errors both of LM method and MN method are approximately seven times higher that of MOGA calibrating model. It is suggested that the MOGA calibrating model is superior both to LM method and MN method.

一种星载相对测量设备的在轨标定方法

受主动段振动、在轨力热变形等因素影响,星载相对测量设备的测量坐标系相对于设备基准坐标系会产生一定偏移,引入测量误差,从而影响卫星的相对导航精度。为解决该问题,提出了一种基于全球卫星导航系统(global navigation satellite system,GNSS)差分定位数据的星载相对测量设备在轨标定方法,通过分析确定了影响其在轨标定精度的主要因素和其可达到的在轨标定精度水平,并结合在轨数据验证了该方法的正确性和有效性。

高分十四号卫星双线阵相机高精度在轨几何标定

在轨几何标定是卫星实现高精度定位的关键环节。本文基于宁夏1∶2000数字化定标场采用前方交会与后方交会交替迭代的方式对双线阵相机标定参数进行整体解算,实现了高分十四号卫星双线阵相机高精度在轨几何标定,并利用全球多处检测场对标定结果进行了检测试验。试验结果表明,通过高精度在轨几何标定后,高分十四号卫星影像无地面控制条件下直接前方交会精度达到平面2.34 m(RMS),高程1.97 m(RMS)。

黑体与恒星相结合的短波红外遥感器在轨辐射定标简析

为满足气象水文、天文观测等领域对短波红外遥感器高精度探测需求,近年来对短波红外探测定量化应用的需求越来越高。本文针对高轨面阵短波红外遥感器在轨各种因素引起的非均匀性变化情况,基于面源黑体定标结合恒星定标的在轨绝对辐射定标设计方案,结合某遥感器任务研制过程的具体实际,分析了定标精度主要影响因素及优化措施,包括星上定标方案优化、星上黑体温度控制优化、恒星提取算法优化等。通过实验室测试对在轨辐射定标方法进行了验证,并对在轨绝对辐射定标不确定度进行预估,评估结果表明定标不确定度能够满足应用要求。

高分十四号激光测量系统在轨几何定标与初步精度验证

高分十四号卫星搭载了一台三波束激光测距系统,用于辅助双线阵光学相机开展全球1∶10000无地面控制点立体测图。由于振动及环境等因素变化,激光测高仪的几何参数相比实验室测量参数会发生改变,必须开展高精度在轨几何定标。针对高分十四号激光载荷的特点,构建了激光测高严格几何模型,在大气改正、潮汐改正的基础上,利用地面探测器阵列捕获的激光光斑开展激光器在轨几何定标与精度验证。实验结果表明:高分十四号激光测量系统标定后3个波束的高程精度(1σ)分别优于0.190,0.256和0.220 m,达到设计指标,可作为高程控制点开展业务化生产。

GF5B热红外通道星上定标与验证

以GF5B卫星发射前实验室定标为基础,采用星上0级黑体定标数据,建立了适用于GF5B热红外通道的星上绝对辐射定标模型。通过对2022年01月12日星上黑体定标数据进行处理,获得成像仪热红外通道的绝对辐射定标系数。对星上定标系统精度进行分析,并采用地面同步烟台浮标数据对定标结果进行精度验证,结果表明,在轨后星上定标系统的绝对定标精度为0.9 K;星地验证结果显示B11和B12通道亮温的偏差分别为0.33、0.77 K。说明基于星上黑体的定标方法具有较好的精度,定标结果可靠,可满足遥感数据定量化应用的需要,为实时准确获取热红外通道定标系数提供了方法借鉴。

分析型光压模型在北斗导航卫星精密定轨中的应用

太阳辐射压摄动是导航卫星受到的最大非保守力,是精密定轨的主要误差源,目前一般使用扩展经验光压模型(ECOM)等经验模型应用于卫星的精密定轨,分析型光压模型物理背景清晰,更加适合在轨初期的精密定轨。文章分析了分析型光压模型在我国北斗高轨导航卫星中的应用。选取了约1个月的北斗地球静止轨道-6(GEO-6)和倾斜地球同步轨道-5(IGSO-5)卫星数据进行分析,其太阳辐射压摄动加速度在轨道的径向(R)、横向(T)和法向(N)3个方向分别约为10-7、10-7和10-8m/s2量级,将分析型光压模型和精密定轨输出的太阳辐射压加速度进行比较,GEO-6卫星径向和横向的差异在10-8m/s2量级,法向方向在10-9m/s2量级,相对误差在10%左右,对IGSO-5卫星,差异要小1/2左右,约为5%。以多模GNSS系统试验网络(MGEX)的轨道作为参考,直接使用分析型光压模型,GEO-6位置误差约为2.5 m, IGSO-5位置误差约为1.5 m,增加偏差和尺度因子标校参数后,位置精度分别提高到约0.5 m和0.1 m。结果表明:利用分析型光压模型,可以实现北斗GEO和IGSO卫星分米级的定轨精度。