Knowledge Resource Center for Ecological Environment in Arid Area
| 高精度可溯源SI在轨绝对光谱辐亮度定标传递链路研究 | |
| 其他题名 | Research on Transfer Chain for SI-traceable Absolute Spectral Radiance Calibration On-orbit with High Accuracy |
| 赵维宁 | |
| 出版年 | 2016 |
| 学位类型 | 博士 |
| 导师 | 方伟 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 摘要遥感技术是人们获取地球环境信息的最主要手段，遥感数据的精度直接决定了人们对自身生存环境的认识的准确程度。对遥感器进行精确的辐射定标是其定量化的基础，辐射定标的精度决定了遥感数据的质量及其应用领域。目前，遥感器在轨辐射定标主要采用星载标准灯、太阳漫射板或交互定标方法，由于受到发射状态和空间环境的影响，其定标传递链断裂，溯源性差，定标精度只能达到10-2量级，不能满足气候监测等领域对遥感数据精度达到10-3量级的要求。为适应该精度量级的需求，本文提出了一种可溯源SI的高精度在轨绝对光谱辐亮度定标传递的方法，设计了由光纤耦合单色仪（FBM）配合积分球传递辐射计（ISTR）组成的ISTR系统，建立了以太阳为定标光源，以在轨低温辐射计为初级基准，以ISTR系统为工作标准的高精度定标传递链，实现了功率基准向亮度标准的转换，缩短了基准传递过程，最终对太阳漫反射板（SDP）反射辐亮度的在轨测量不确定度达到了0.5%水平。配合交互定标方法，可完成对成像光谱仪等光学载荷的持续可溯源SI的高精度在轨光谱辐射定标。为了满足ISTR系统高精度基准定标传递的要求，FBM采用双级联双通道光栅分光的同光路结构，利用离轴抛物反射镜配合一二级光谱完成了太阳反射谱段（0.3~2.5μm）的覆盖；通过线性编码器配合步进电机控制光栅的角度选择，实现了岀射波长精度高、带宽1~2nm的性能要求；通过前置抛物聚光镜参数与入射狭缝尺寸的协调设计，配合过渡狭缝的引入，实现了出射光谱功率1μW~50μW，带外杂光为10-6，满足了低温辐射计动态测量范围以及SDP反射光谱量级的需求。推导了使用出射狭缝高度及系统焦距对单色仪出射光谱变化进行计算的解析模型，更适合光谱辐射定标的应用。再配合坐标变换矢量方程，建立了典型光线岀射光谱变化计算的矢量追迹模型，并由此提出了对由装调误差及光栅转动偏差导致的FBM波长精度和带宽精度评估的创新方法。结合Zemax和Tracepro的模拟仿真结果，得出了FBM实际波长精度和带宽精度在0.04%左右，满足ISTR系统高精度定标对其的性能要求。ISTR采用了集成一体式设计，利用积分球朗伯性的特点，将陷阱探测器二级标准溯源至低温辐射计基准的过程和二级标准定标滤光片辐射计（FR）光谱工作标准的过程在一个定标光路下完成，缩短了整体定标传递链，减少了测量不确定度的误差源。ISTR系统选择了RSB内15个典型的光谱通道进行定标，利用光学斩光调制器配合数字相敏检波技术，实现了极弱太阳光谱信号的高精度测量，完成辐射功率基准向辐亮度标准的转换。通过对ISTR系统基准定标传递中各溯源环节的物理过程对应的测量方程进行了准确的建模，包括二级标准溯源至低温辐射计基准、二级标准定标FR光谱辐射标准以及FR测量SDP涉及的光源不匹配性漂移，对整体定标传递过程涉及的A类和B类不确定度来源进行了准确的理论分析及实验测量。影响因素包括基准转换影响、FBM岀射功率传输、探测器增益及响应空间非均匀性和非线性、弱光检测测量精度、光谱稳定性及带宽匹配对响应度定标的影响、积分球岀射光朗伯性以及各装置装调不匹配带入的对比误差。通过有效波长响应度替代通道响应度的方法，准确分析了光谱带宽和不匹配性引入的各级标准的定标精度影响，并提出了评估定标光源与测量光源差异所引起的测量精度漂移的方法。最终配合高精度的离散激光定标数据及统计拟合修正算法，得到ISTR系统各级标准光谱响应度定标合成不确定度为0.25%，整体辐亮度测量不确定度为0.45%，满足预期要求。最后，本文利用FORTRAN语言完成了基于低纬度沙漠靶场进行中低轨卫星遥感器SNO-x交互定标方法的算法实现，以TERRA/MODIS为参考仪器首次对FY3C/MERSI进行了RSB通道响应定标。通过利用SGP4轨道算法筛选定标区域、像元匹配分析设计条件阈值、独特的光谱通道匹配方法、星下点环境均匀性和响应异常过滤以及两卫星匹配样本的拟合修正，实现了高精度的遥感器在轨定标传递。通过MERSI和MODIS不同带宽匹配形式的对应通道的交互定标结果比较，说明了在MODIS通道带宽包含MERSI通道带宽时定标精度最高且最终精度受参考仪器自身精度的影响最大，验证了SNO-x方法实现以ISTR系统为参考仪器进行遥感器可溯源SI在轨光谱辐射定标精度达到1%的可行性。本文所研究的以ISTR系统为核心的在轨辐射定标新技术是目前国际上公认的唯一可以实现卫星遥感器在轨溯源SI光谱辐射定标的途径，具有高光谱分辨率和高精度标准传递等特点，可满足多数卫星遥感载荷的可溯源SI绝对辐射定标需求，为我国未来对地观测和大气监测等遥感领域高质量应用数据的获取奠定了理论和技术基础。 |
| 英文摘要 | AbstractRemote sensing technology is the main means for human to get access to information on the Earth's environment, and the precision of remote sensing data directly determines the depth of our recognition to the survival environment. Accurate radiometric calibration for remote sensors is the basis of its quantification and the accuracy of radiometric calibration determines the quality of the data acquired by remote sensors. At present, remote sensors radiometric calibration is based-on on-board standard source and solar diffuser plate or intercalibration method. Due to the influence of launch state and rigorous environment in space, the calibration transfer chain fracture and traceability is not good. Thus the calibration accuracy can only reach to 10-2 scale but not meet the requirements of the accuracy up to 10-3 scale for climate monitoring field. In order to acquire high precision data, this paper proposes a method for absolute spectral radiance calibration transfer traceable to SI reference benchmark on-orbit with high precision. The ISTR system consisted of a fiber coupled monochromator (FBM) and an integral sphere transfer radiometer (ISTR) is designed. This paper builds on the high-accuracy calibration transfer chain through setting the sun as the calibration source, the cryogenic radiometer on-orbit as the benchmark and ISTR system as the working standard, thus realizing conversing the power benchmark to the radiance standard and shortening the calibration transfer process. Ultimately, it makes the uncertainty of measuring the radiance reflected from the solar diffuser plate (SDP) on-orbit reach to 0.5% level, which can complete the on-orbit SI-traceable spectral radiometric calibration of optical loads like imaging spectrometers with high precision through the intercalibration method.In order to meet the requirements of achieving the calibration transfer of ISTR system with high precision, FBM adopts the dispersing structure of dual-channel with double gratings in the same light path and completes covering the Reflected Solar Bands (RSB: 0.3~2.5μm) by using off-axis parabolic mirrors cooperated with primary and secondary spectrum. It achieves the performance index of high wavelength accuracy and the bandwidth of 1~2nm through rotating gratings with high precision which is controlled by a linear encoder and a stepper motor. Through the parameters design of the front parabolic mirror and the entrance slit size, the output spectral power ranges from 1uW to 50uW with the stray light level of 10-6 realized by the addition of the transitional slit, which meet the cryogenic radiometer measuring range and the spectral power scale of the SDP. This paper derived a novel analytic former to calculate accurately the export spectrum changes only by the exit slit height and system focal length, which is more suitable in spectral radiation calibration. Cooperated with the coordinate transformation vector equation, a vector tracing model for calculating the export spectrum changes of several typical light paths is build. Through this model, an innovation method to estimate the accuracy of the FBM’s output central wavelength and the bandwidth, which is caused by the alignment error and grating rotation bias, is proposed. Finally combined with the simulation results of Zemax and Tracepro software, it is concluded that the actual wavelength accuracy and bandwidth accuracy of FBM is about 0.04%, which meets the requirements put forward by the ISTR system with high precision.ISTR adopts integrated design and combines the traceability of the trap detector secondary standard to the cryogenic radiometer benchmark with the process of the filter radiometer (FR) spectral work standards calibrated by the secondary standards in the same calibration light path depending on Lambertian characteristics of the integrating sphere. It shortens the overall calibration transfer chain and reduces the error sources of the measurement uncertainty. ISTR system choose 15 typical spectral channels in the RSB for calibration, and realizes the high-accuracy measurement of extreme weak solar spectral signal to achieve the conversion between the power benchmark and the radiance standard through an optical chopping light modulator and digital phase sensitive detection technique. This paper proposes the accurate analysis mathematic models for the measurement equations corresponding to each calibration links in the whole traceability transfer process of the ISTR system, including secondary standard tracing to cryogenic radiometer benchmark, secondary standard calibrating FR spectral standard and the mismatch drift of different sources along FR measuring SDP. Then the type A and type B uncertainty sources of the calibration transfer were acquired accurately by theory analysis or experimental measurements and the influence factors include standard conversion, the FBM export power transmission, the gain and response non=uniformity and nonlinearity of detectors, weak signal detection accuracy, the effects of spectrum stability and the bandwidth matching on the responsivity calibration, the spatial uniformity of the integrating sphere and the alignment match error among each device. Using the response of the effective wavelength to substitute the channel average response, the influences caused by the size and mismatch of spectral bandwidth on the calibration accuracy of secondary standard and FR standard were analyzed exactly, and the method for evaluating the measuring accuracy drift caused by the difference between the calibration source and the measured source was carried out. Eventually cooperating with the high-precision calibration data obtained by the discrete laser sources and the statistical fitting corrected algorithm, the calibration uncertainty of the spectral responsivity for each standard in ISTR system is 0.25% and the overall measurement uncertainty of the radiance is 0.45%, which meet the expected requirements.Finally, this paper realized the algorithm for the SNO-x method based-on the low latitude desert used to the intercalibration among Leo satellite remote sensors, and for the first time achieved the intercalibration for the responsivity of the RSB channels in FY3C/MERSI taken TERRA/MODIS as the reference instrument. Through using SGP4 orbit algorithm to select the calibration area, pixel matching analysis to set condition thresholds, special method to match the correlative spectral channels, the filtering of substellar point environment uniformity and abnormal response, and the correction fitting for the two satellites’ matching sample data, it realizes on-orbit calibration transfer for remote sensors with high accuracy. Through the comparison among the intercalibration results of different corresponding channel groups with different bandwidth matching forms between MERSI and MODIS, it explained that the highest precision is acquired when MODIS channel bandwidth contains MERSI channel bandwidth and that the final accuracy is mainly affected by the precision of the reference instrument itself. The SNO-x method is proved to achieve the feasibility of making the SI-traceable spectral radiance calibration on-orbit for remote sensors reach 1% scale through taking ISTR system as the reference instrument.The original method for the on-orbit radiation calibration, which takes the ISTR system as the core and investigated in this paper, is the only way recognized internationally to realize the SI-traceable spectral radiance calibration on-orbit for satellite remote sensors. It has the characteristics of high spectral resolution and high precision standard transfer, which can meet the needs of SI-traceable absolute radiometric calibration for most satellite remote sensing payloads. It eventually laid the theoretical and technical basis for acquiring the high-quality remote sensing data on the Earth observation and atmospheric monitoring field for China in the future. |
| 中文关键词 | 可溯源SI基准传递 ; ISTR系统 ; FBM单色光源 ; 不确定度分析 ; 交互定标 |
| 英文关键词 | SI-traceable standard transfer ISTR system FBM monochromatic source Uncertainty analysis Intercalibration |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 光学工程 |
| 来源机构 | 中国科学院长春光学精密机械与物理研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287817 |
| 推荐引用方式 GB/T 7714 | 赵维宁. 高精度可溯源SI在轨绝对光谱辐亮度定标传递链路研究[D]. 中国科学院大学,2016. |
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