基于冷空观测单元的综合孔径微波辐射计幅度定标方法
doi: 10.11728/cjss2024.05.2023-0131 cstr: 32142.14.cjss2024.05.2023-0131
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仝星 男, 1998年出生于河南省南阳市, 现为中国科学院国家空间科学中心硕士研究生, 主要研究方向为综合孔径微波辐射计的定标等. E-mail: tongxing20@mails.ucas.ac.cn -
刘浩 男, 1978年出生于江西九江, 研究员, 主要研究方向为干涉式被动微波、毫米波/太赫兹成像技术及其在定量遥感、目标探测与环境感知等方面的应用. E-mail: liuhao@mirslab.cn
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Amplitude Calibration Method for Synthetic Aperture Radiometer Based on Cold-sky Observation Unit
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摘要: 微波辐射计通过定标获取目标准确的亮温, 是数据定量化应用的必要手段. 综合孔径微波辐射计由多个辐射计单元组成, 定标需求从单一接收机扩展至所有接收单元. 噪声注入是包括综合孔径微波辐射计在内的固定波束指向辐射计所常用的定标方法. 作为定标参考的噪声二极管在轨会受到温度影响发生短期波动, 并受器件老化影响发生长期漂移, 从而导致系统定标精度恶化. 针对上述问题, 提出一种基于冷空观测单元的综合孔径辐射计幅度定标方法. 通过设计专门的冷空观测辐射计通道, 对综合孔径辐射计的公共噪声源进行实时标定, 减小其噪声温度不确定性对综合孔径辐射计系统所有观测通道幅度定标的影响. 结合中国海洋盐度探测卫星主被动探测仪中K波段一维综合孔径辐射计的实际系统方案, 建立了辐射计系统模型及定标模型, 开展了数值仿真及样机定标实验验证. 仿真及实验结果验证了方法的有效性.Abstract: Microwave radiometers obtain the accurate brightness temperature of the target scene through calibration, which is a necessary means for quantitative data application. The synthetic aperture microwave radiometer consists of multiple radiometer units, and the calibration requirement extends from a single receiver to all units. Noise injection is a calibration method for fixed antenna beam radiometers, including synthetic aperture microwave radiometers. However, the noise diode used as the calibration reference encounters issues such as short-term fluctuation caused by temperature and long-term drift resulting from the aging of the device, leading to the deterioration of the system's calibration accuracy. To address the aforementioned problems, this paper proposes a method of amplitude calibration for synthetic aperture radiometers based on a special cold-sky observation unit. By designing a dedicated cold-sky observation radiometer channel, the common noise source of the synthetic aperture radiometer is calibrated in real-time, reducing the influence of noise temperature uncertainty on the amplitude calibration of all observation channels in the synthetic aperture radiometer system. Based on the system scheme of the K-band one-dimensional synthetic aperture radiometer in the Microwave Imager Combined Active and Passive of China’s Ocean Salinity Detection Satellite, the radiometer system model and calibration model are established, and numerical simulations and prototype calibration experiments are carried out. Simulation and experimental results validate the effectiveness of the proposed method.
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图 1 基于冷空观测单元定标系统的结构
Figure 1. System structure block diagram based on cold-sky observation unit calibration
图 5 非线性差异对目标亮温的影响
Figure 5. Influence of different nonlinear on the target brightness temperature
图 6 公共噪声修正系数定标误差对幅度定标的影响
Figure 6. Influence of common noise correction factor calibration error on amplitude calibration
图 7 公共噪声变化曲线(a)与目标亮温误差(b)
Figure 7. Common noise variation curve (a) and target brightness temperature error (b)
图 8 公共噪声修正系数定标实验
Figure 8. Schematic diagram of common noise correction coefficient calibration experiment
图 9 高亮温场景(黑体墙)定标实验
Figure 9. Schematic diagram of calibration experiment for high brightness temperature scene (Blackbody wall)
图 10 高亮温场景定标实验过程中天线及接收机物理温度变化
Figure 10. Physical temperature change of antenna and receiver during calibration experiment of high brightness temperature scene
图 11 冷空定标单元实时定标所获取的公共噪声源噪声温度变化. (a)高公共噪声, (b)低公共噪声, (c)公共噪声温度差
Figure 11. Noise temperature change of common noise source obtained by real-time calibration of cold-sky calibration unit. (a) High common noise, (b) low common noise, (c) difference of high and low
图 12 高亮温场景定标实验结果. (a)观测单元接收机增益, (b)目标亮温结果, (c)背景温度与亮温对比, (d)公共噪声修正的效果
Figure 12. Calibration experiment result of high brightness temperature scene. (a) Observation unit receiver gain, (b) result of target brightness temperature, (c) contrast between background temperature and brightness temperature, (d) effect of common noise correction
图 13 低亮温场景(黑体墙背景下的液氮定标源)定标实验
Figure 13. Schematic diagram of calibration experiment for low brightness temperature scene (Liquid nitrogen calibration source under blackbody wall background)
图 14 低温目标观测实验场景图. (a)低温目标与天线的位置关系(侧视图), (b)低温目标与天线的位置关系(俯视图)
Figure 14. Cold target observation experiment scene. (a)Positional relationship between the cold target and the antenna (side view), (b) position relationship between cold target and antenna (top view)
图 15 低亮温场景定标实验过程中辐射计天线及接收机物理温度变化
Figure 15. Physical temperature change of antenna and receiver during calibration experiment of low brightness temperature scene
图 16 低亮温场景定标实验结果. (a)目标亮温, (b)背景温度与亮温对比, (c)公共噪声修正的效果
Figure 16. Calibration experiment result of low brightness temperature scene. (a) Target brightness temperature, (b) contrast between background temperature and brightness temperature, (c) the effect of corrected common
表 1 公共噪声网络修正系数定标误差仿真参数
Table 1. Common noise network correction coefficient calibration error simulation parameters
参数 数值 公共噪声至冷空观测单元
路径损耗/dB16.502 公共噪声至综合孔径单元
路径损耗/dB18.52 公共噪声温度差/K 330～380 定标参数误差/(%) ±4 目标亮温/K 100～320 接收机非线性 0.9999 
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表 2 公共噪声漂移仿真设置参数
Table 2. Common noise drift simulation set parameters
参数 数值 公共噪声路径损耗/dB 16.502 公共噪声漂移/(%) 1 高公共噪声温度/K 674 低公共噪声温度/K 350 目标亮温/K 100～320 接收机非线性 0.9999
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