Final answer:
Span loss is used to determine channel losses in CWDM and DWDM systems, accounting for attenuation across a fiber optic transmission system including fiber, splices, and connectors.
Step-by-step explanation:
The measurement used to determine CWDM (Coarse Wavelength Division Multiplexing) and DWDM (Dense Wavelength Division Multiplexing) channel losses is C: Span loss. Span loss refers to the attenuation or reduction in optical power across a fiber optic transmission span. This encompasses the cumulative loss due to the fiber itself, any splices, and connectors over a given distance. Testing and measuring span loss are crucial in network design and maintenance to ensure signal integrity and proper system performance.