This result is obtained in the 10-14 m depth range. Kblue/Kgreen=0.59 is a nice statement, knowing that
these pixels are genuine NotSmoothed DNs
system noise is high in TM data
waters in this heavily developped residential area might not be quite as homogeneous as assumed
Image_B without any smoothing : @-Smooth/5/Smart+ White circles show the location of the BPL pixels in the Blue/Green pair The 4SM Extraction process picks up isolated bright bottomed BPL pixels, which are located in small sized clearances in vegetated bottoms. No hand-picking of arguably bright bottoms at various depths , Lyzenga style, could have achieved that remarkable result!
Such small patches are smoothed out by the Smoothing process, even though a "smart" one.