Hi there,

I need to study the diffuse attenuation coefficient "K(490)" derived from Lee's semi-analytical algorithm. Two questions regarding to this matter:
1) Is K(490) suitable for detecting the water clarity?
2) I have tried to process MODIS image L1A using SeaDAS 5.1.6 to L1B to L2 (Using MSL12,4) in order to obtain K(490). When I opened product selection window I could not find Kd_lee(490). What I found was kd_lee(488) at the very end of this window. My question: Is Kd_lee(490)= Kd_lee(488)?
As I know, the mid point of MODIS band 3 is 488 nm, which is equivalent to SeaWiFS bans 3 (490 nm). I am wondering if this is also the case with Kd_lee.

Regards,
Mohammad Alsahli

On item 1, I suggest you search the literature.

On 2, yes Kd_lee(490)= Kd_lee(488).  We traditionally output any spectral quantities at the sensor center wavelengths.  It's just a convention.  I suppose that if you are really concerned about the 2-nm difference, you could interpolate (from Kd_lee_488 and Kd_lee_531), but I suspect any difference is well within the algorithm uncertainties. 

-- bryan

Thanks Bryan. I appreciate you response.