Which statement concerning Inmarsat-B and Inmarsat-C terminals is correct?

The correct statement indicates that both Inmarsat-B and Inmarsat-C units are indeed subject to shadowing effects, and it highlights that Inmarsat-B units utilize directional antennas. Shadowing effects occur when physical obstructions block the line of sight between the terminal and the satellite, which can happen with any satellite communication system.

Inmarsat-B terminals generally use directional antennas, which require precise alignment with the satellite for optimal communication. Because these antennas are more focused, they can experience more pronounced shadowing effects when compared to omni-directional antennas, which are typically used in Inmarsat-C terminals. This directional nature of Inmarsat-B antennas means they have a narrower beamwidth, making them more susceptible to interruptions from obstacles in their path.

Conversely, while Inmarsat-C terminals can also experience shadowing, they primarily use omni-directional antennas that are less dependent on alignment with satellites. Therefore, the specific mention of Inmarsat-B using directional antennas accurately reflects how shadowing affects system performance differently between these two types of terminals.