FY-3A MERSI短波红外通道图像增益突跳自动识别和归一

Identification and Normalization of Image Gain of FY-3A MERSI Shortwave Infrared Bands

搭载于我国第二代极轨气象卫星风云三号A星(FY-3A)上的中分辨率光谱成像仪(MERSI),肩负着获取全球图像和辐射资料的作用。然而,太空环境影响等因素,导致短波红外通道发生在轨增益突跳现象,大大限制了数据的定量应用。通过对冷空、星上定标器和黑体等MERSI星上观测目标的分析,选择冷空作为增益突跳识别的指征目标。提出自动识别、增益归档和档位归一化方法,采用日识别和天内精检测的方法获取增益突跳时空信息,采用分类统计突跳数据的方法获取突跳的在轨增益档位,并利用星上定标源目标和对地观测图像进行归一化效果验证,实现了对1.64μm和2.13μm两通道整个生命期91次和18次突跳事件的精确定位,获得了8个在轨增益档位和全部突跳事件的档位信息,并得到了理想的归一化效果验证。研究结果同样显示,增益突跳事件大多发生在对地目标扫描过程,而且每个探元增益突跳的时间不尽相同。由于地球目标的复杂性,基于物理方法很难实现对突跳帧图像的归一。该研究成果不仅有助于FY-3A MERSI图像质量的提升,而且对历史数据再处理也有重要支撑作用。

Medium-resolution spectral imager （MERSI） obtains global image and radiation data from the second generation polar-orbiting meteorological satellite, FY-3A, launched by China. However, the on-orbit gain levels of imager in shortwave infrared bands occasionally jump due to the unpredictability of space environment and other factors. Such phenomena limit the quantitative application of the data. The space view is selected to identify gain jumps based on the analysis of MERSI observation targets, such as space view, visible onboard calibrator, and blackbody. Automatic identification, gain classification, and level normalization are proposed as methods. The daily identification and intraday precision detection methods are combined to obtain the time and space of gain jumps, and the classified statistical method contraposing the data of gain jumps is used to obtain the on-orbit gain levels. In addition, the onboard calibration source targets and Earth view images are used to verify the normalized effect. The 91 gain jumps of 1.64 μm and 18 gain jumps of 2.13 μm are accurately positioned during the lifetime. In addition, the eight on-orbit gain levels and the levels of all gain jumps are obtained. The results revealed that the normalized effect is ideal. Further, the most gain jumps occur during the Earth view scanning process and the gain jump time varied between the detectors. Because of the complexity of the Earth view targets, it is difficult to realize the normalization of the image of the jumping frame based on the physical methods. These results contribute to the improvement of FY-3A MERSI image quality and play an important role in reprocessing historical data.