CSIR NET June 2016 Q68: Physical Oceanography
Remote sensing estimation of chlorophyll-a from ocean colour is degraded mainly by coloured dissolved organic matter (CDOM), which absorbs strongly in the same blue wavelengths used for chlorophyll retrieval.
CDOM (gelbstoff/yellow substance) absorbs blue light in a spectral region that overlaps with chlorophyll absorption, causing standard blue/green band-ratio ocean-colour algorithms to overestimate or misattribute chlorophyll concentration, especially in coastal and case-2 waters. It is considered the most significant optically active interferent for remote chlorophyll estimation. Option 3 is correct.
1) Suspended detrital (mineral) particles scatter/absorb light but are a secondary interferent compared to CDOM in most formulations. 2) 'Dissolved organic matter' broadly is vague; it is specifically its coloured (light-absorbing) fraction that matters. 3) Correct — CDOM's spectral overlap with chlorophyll absorption is the dominant confounding factor. 4) Water itself has a well-characterized, correctable absorption and is not the main confounding variable.