Hi,

it's a bit unclear, what you are looking for. Do you search for the first one who uses the term 'aerosol optical depth' of for an explanation. The expression is quite common and used extensive. In general, the optical depth (or thickness) is just the integrated extinction along a path and is a measure for the likelihood of interaction between radiatiion and matter. If not stated differently, it is usually defined for a wavelength of 0.55 microns (in atmospheric science).

Hope that helps

Rolle

Thanks.