Reflectances are dimensionless ratios.
Through the visible spectrum:
Reflectance of bright coral sand
increases steadily from 0.28 to 0.65
Reflectance of dark red algae Sargassum
is stable at 0.02 from 400 to 500 nm
then peaks at 0.05 at 600 nm
then decreases to 0.02 at 670 nm
then rises sharply to 0.25 at 750 nm
Reflectance of terrigeneous sand at Mahares is ~1/3 that of coral sand
Reflectance of deep water exceeds that of dark seagrasses and algae below ~525 nm:
the negative bottom contrast case
Normalized reflectances in 4SM
dots: raw reflectances r in % plain: normalized reflectances
At all wavelengths in 4SM:
at the base of the atmosphere,
Color composite: through the normalization process,
we typically want to enhance
the remote sensing image
so that beach sands display as
shades of grey in any color composite.
Soil Line: then for all pairs of bandsthe slope of the Soil Line is 1.
Distortion: Because the reflectance of the reference-sand increases steadily through the visible spectrum, this normalization distorts ("morphs") the spectrum of spectrally contrasted bottom signatures. This might have consequences on the water column correction process in 4SM.