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The water- leaving radiance (Lw) and remote sensing reflectance (Rrs)are not only the main apparent optic properties (AOPs) of water but also the basic parameters of ocean water color remote sensing. In order to realize the measurement of water- leaving radiance and remote sensing reflectance in the spectrum with the range from 300 nm to 900 nm, the high precision of the sea-surface radiance, the sky radiance and the sea-surface incident irradiance should be first obtained. The radiometer is composed of the measurement unit, control unit and tracking unit. The measurement unit is the core of the radiometer. Comparing with the previous tunnel radiometer, the measurement unit of the automatic observation radiometer is designed. In order to collect the spectral images of the incident slit into a plane, the radiometer uses flat-field concave grating for diffraction spectroscopy. And the linear array detector can detect the intensity signals of each spectrum simultaneously on the same plane. At the same time, in order to guarantee 10° field of view, the radiometer is equipped with the lens. It is also required to ensure the spectral observation principal plane make 135° with the principal plane so that it can avoid the influence of solar flares. In addition, the instrument shell adopts multi-layer coating treatment to avoid the erosion of the instrument structure parts by sea water and foggy sea atmosphere. After the spectrometer is installed, spectral calibration is done in the laboratory. The full width at half maximum of the radiometer is less than 4nm and the spectrum completely covers from 300nm to 900nm. The development of radiometer fills the gap of the automatic measurement of water- leaving radiance in China. It can inspect and correct satellite data and remote sensing products, and provide continuous and reliable on-site observation data for satellite remote sensing radiation calibration and product authenticity inspection.
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