Ocean optics — scattering, colour, and reflectance ratio Which consolidated statement correctly describes short-wavelength scattering in seawater and a standard reflectance definition?

Introduction / Context:
Why the open ocean looks blue—and how we quantify the light field—are fundamental topics in marine optics. The balance between molecular/small-particle scattering and absorption sets the water colour, while radiometric ratios standardize how we compare optical states across sites and times.

Given Data / Assumptions:

• Clear oceanic water with low suspended sediment and CDOM.
• Standard definitions of upwelling and downwelling irradiance.
• Shorter wavelength means violet–blue bands of visible light.

Concept / Approach:

Rayleigh-like scattering by water molecules and small ions increases as wavelength decreases, so blue light is scattered/backscattered more effectively than red. In clear waters, absorption is low in blue, so enhanced backscatter yields the characteristic deep blue appearance. The irradiance reflectance is defined as R = Eu(0−)/Ed(0+), i.e., upwelling irradiance just below the surface divided by downwelling irradiance just above the surface, a common metric in ocean color research.

Step-by-Step Solution:

Verification / Alternative check:

Textbook spectral curves show minimal absorption in the blue for pure water and increasing absorption toward red/IR, supporting the colour mechanism and the usefulness of blue-band reflectance metrics.

Why Other Options Are Wrong:

• Each of (a)–(c) is correct; hence the combined correct choice is “All of these”.

Common Pitfalls:

• Confusing irradiance reflectance with remote-sensing reflectance R_rs, which uses radiance rather than irradiance.
• Ignoring CDOM/sediment effects that can shift colour toward green/brown.

Final Answer:

All of these.