Earthdata Forum

Not sure I like this new interface. Can someone point me to a reference that discusses the choice of Kd490 as a standard product?

Hello,

There are references at the bottom of the KD algorithm description page: https://oceancolor.gsfc.nasa.gov/atbd/kd_490/

Hi - Thanks. I've got those and have read them. They generally talk about how to estimate kd490, but not why one would want to. I am interested in finding out why that particular wavelength was selected as the standard.

The diffuse attenuation coefficient is useful for estimating light penetration depth (which in turn is useful in productivity models, and radiative heating estimates, as well as other applications). Early estimates of water absorption (e.g. Hale and Querry, 1973) put the minimum absorption around 490nm. Although later efforts shifted that a wee bit lower to ~420nm, (Pope and Fry aw well as Sogandares and Fry, both in 1997), the ship had sailed and 490 was king.

Sean

Thanks, Sean. This is helpful. It sounds as if the choice of 490 was based on the expectation that light at (or near) that wavelength would penetrate deepest into the water. The specific choice of 490 is, in some sense, historical - that's what we picked first and even though there have been refinements since that choice, we stick with with. I can work with that. I appreciate your help.

Barry

There is some history of early measurements of material properties being revised when more "pure" materials became available. In some cases earlier measurements were more useful for practical purposes because the material used in for original measurements more closely resembled the material found in "real-world" applications.