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对于深入了解地球大气成分(例如臭氧、氯氟碳化物)的动态及其长期特性变化,可进行全球监测的星载仪器提供了最好的信息。为了研究在一个甚长时间周期内的大气趋势,这些仪器必须以非常精确的方式相对太阳而得到标准化的定标。此外,在仪器的寿命期间,定标的精度必须得到保持。 本文同时涉及地球观测仪器在地面上和飞行中的辐射度定标问题。某些有关问题将通过在TPD接受定标的两台特殊仪器来举例说明,这两台仪器分别是于1995年4月发射的ERS-2卫星的全球臭氧监测实验(GOME)仪器和即将在2000年前后发射的Envisat卫星的大气绘图扫描成像吸收光谱仪(SCIAMACHY)。 我们将区别太阳标准化定标和绝对辐射度定标。在这两种情况下,仪器对偏振的灵敏度是一个复杂的因素。将要涉及的其它因素包括地面定标过程中的湿度影响和标准具效应。这些都需要先进的定标方法和完全合适的辐射度定标设备。 经过地面定标之后,仪器可能会发生变化或者退化。因此,GOME和SCIAMACHY都包含有一块经过精确定标的漫射体,它能提供精确的反射率标准。然而,由于沾污和辐射效应,漫射体本身也会随着时间的推移而退化。因此,必须遵循一种飞行中监测原理。本文将利用SCIAMACHY的例子来阐明所涉及到的定标状况。
The best information available is the on-board instruments that can be used for global monitoring to gain insight into the dynamics of the Earth’s atmosphere components (such as ozone, chlorofluorocarbons) and their long-term property changes. In order to study the atmospheric trends over a long period of time, these instruments must be calibrated to the sun in a very precise way against the sun. In addition, the calibration accuracy must be maintained during the life of the instrument. This article also addresses the issue of calibration of radiometric degrees of Earth observation instruments on the ground and in flight. Some related issues will be exemplified by two special instruments calibrated at the TPD, the Global Ozone Monitoring Experiment (GOME) instrument for the ERS-2 satellite launched in April 1995 and the forthcoming The Atmospheric Mapping Scanning Imaging Absorption Spectrometer (SCIAMACHY) for the Envisat satellite launched years ago. We will differentiate between solar normalization and absolute radiometric scaling. In both cases, the sensitivity of the instrument to polarization is a complex one. Other factors to be covered include the effects of humidity and etalon effects during surface calibration. These require advanced calibration methods and fully suitable radiometric calibration equipment. After calibration on the ground, the instrument may change or degrade. Therefore, both GOME and SCIAMACHY include a precisely calibrated diffuser that provides accurate reflectivity standards. However, the diffuser itself degenerates over time due to contamination and radiation effects. Therefore, an in-flight monitoring principle must be followed. This article will use the SCIAMACHY example to illustrate the calibration involved.