OMI Radiative Cloud Fraction

The reflectivity calculated for OMI is the Lambertian equivalent reflectivity. That is, it is the diffuse reflectivity that would need to be at the bottom of the atmosphere to explain the 331 nm radiance that OMI measures at the top of the atmosphere. The reflectivity calculated depends on the height of the reflecting layer. For low reflectivities it is assumed that the ground is observed and a terrain height is used. For higher reflectivity it is assumed that clouds are being observed and a cloud height climatology is used. Errors in assumed cloud height are likely the biggest source of error in the reflectivity. It is possible to get reflectivity greater than 100% if there is specular (mirror-like) reflection or unusually high clouds. It is possible to get reflectivity less than zero if there is light absorbing dust in the atmosphere. This is because the reference is the scattering that is expected from a clear atmosphere.

The OMI reflectivity data are in the form of grid averaged values written in ASCII format. This is the same format that was used for all previous TOMS CD-ROMS and the products offered on the TOMS website. Software written to read TOMS Level 3 files may be used to read all OMI Level 3 data files by changing filename and date entries. For each 1 degree latitude by 1 degree longitude grid cell, all the OMI measurements in the cell have been averaged.

Refelectivity is calculated as part of generating the ozone product, which is why that product is included below.