Atmospheric Correction and Aerosol Models

The total water leaving radiance measured by the satellite is composed of 10% ocean signal and 90% atmosphere signal. The atmospheric and ocean surface scattering effects need to be accurately modelled and removed from the total radiance measurement to provide the information needed to understand the oceanic component. This is accomplished with the atmospheric correction. The variables involved in the atmospheric correction equation (and the equation itself) are demonstrated in this diagram:

Here is a flow diagram of how each component in the above equation is defined (from Gordon and Wang):

The concentration of the aerosols and their optical properties need to be determined in order to solve the

term. This can be estimated in the NIR (bands 15 and 16), and then extrapolated to the visible wavelengths using the aerosol models (adapted from Shettle and Fenn 1979) in the table below. Then the aerosol radiance contribution is known and can be removed.

There are three primary models with variable amounts of relative humidity. The coastal model is a mix of Shettle and Fenn's (1979) rural and maritime models, while the oceanic model is an extreme oceanic case. It is important to have models at each of the listed humidity levels because with increasing humidity, the sizes of the aerosol particles increase. This changes the light-scattering effects of the aerosols (Shettle and Fenn 1979), and invokes the need for separate models to represent the conditions at a given relative humidity.

Curator: OceanColor Webmaster

Authorized by: gene carl feldman