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

The SNPP 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 555nm...SNPP卫星平台搭载可见光红外成像辐射仪（Visible Infrared Imaging Radiometer Suite，VIIRS）传感器，该传感器可在多个波段下观测海洋表层内反射的太阳光。此类多光谱测量数据被用于反演490nm波长处的漫衰减系数（diffuse attenuation coefficient，Kd），该参数可反映光在水柱中的衰减规律。漫衰减系数被定义为下行辐照度（downwelling irradiance）指数衰减的尺度长度，单位为m⁻¹。VIIRS K490产品基于490nm与555nm波段的离水辐亮度（water leaving radiances）比值，采用半经验模型估算490nm波长处的Kd值。