Ocean and land products use completely different algorithms. For any dark target retrieval algorithm we must accurately account for surface effects and build correct models of the aerosols. Due to the complexities of the land surface it is more difficult for the land retrieval to account for surface effects. In addition aerosol models are fixed for the land product based on season and location. The ocean product selects coarse and fine mode models dynamically.
These two factors account for several differences in the two products.
1) The greater error of the AOD in land product
2) AOD values for land are available at 0.47, 0.55, 0.67 and 2.1 µm
AOD values for ocean are available at 0.47, 0.55, 0.67,0.87,1.2, 1.6 and 2.1 µm
3) In collection 5 and 6 the ocean product contains parameters which report fine and coarse mode AOD separately and the fine mode fraction. Over land we do not have the ability to retrieve these parameters accurately. These parameters are reported over land in Collection 5, but we do not recommend their use. In Collection 6, only fine mode fraction is reported but it is a diagnostic of how the retrieval is operating and not a representative value of the actual fine mode fraction.
For additional information see the presentations on the ocean and land algorithms in the education and reference materials section.