Satellite - Ocean Colour - NOAA20 - 1 day - Diffuse attenuation coefficient (k490)

The NOAA20 satellite platform carries a VIIRS sensor that observes sunlight reflected from within the ocean surface layer at multiple wavelengths. These multi-spectral measurements are used to infer the diffuse attenuation coefficient (Kd) at 490nm wavelength which provides information on how light is attenuated in the water column. It is defined as the scaling length of the exponential decrease of the downwelling irradiance, and has units (m^-1). The VIIRS K490 product estimates Kd at 490nm wavelength, using a semi-empirical model based on the ratio of water leaving radiances at 490nm and 555...NOAA20卫星平台搭载了VIIRS传感器（Visible Infrared Imaging Radiometer Suite），该传感器可在多个波段捕捉海洋表层反射的太阳光。上述多光谱测量数据可用于反演490nm波长处的漫衰减系数（diffuse attenuation coefficient, Kd(490)），该系数可表征光在水柱中的衰减规律。其被定义为下行辐照度指数衰减的尺度长度，单位为m⁻¹。VIIRS K490产品基于490nm与555nm处的离水辐亮度比值，通过半经验模型估算490nm波长处的Kd值。