In fog conditions at a range of 100m, which position reference system is not usable?

In fog conditions, visibility is significantly reduced, making it challenging to use visual position reference systems. Hydroacoustic systems rely on sound waves transmitted through the water to measure distance to the seafloor or underwater structures. These systems are generally used in situations where the underwater profile needs to be monitored or when precise positioning relative to the seabed is required.

However, in dense fog, if the hydroacoustic system depends on line-of-sight features or on specific signal interactions that may be negatively impacted by the environmental conditions, its utility could be compromised compared to other systems that do not depend on visual input. The hydroacoustic system may still function in terms of measuring depth or distance to underwater objects, but its effectiveness as a position reference system is limited when other systems can provide clear positional information regardless of visibility.

In contrast, GPS utilizes satellites to determine geographic position and operates effectively under fog conditions, as long as there is a clear line of sight to enough satellites. Laser systems, while they may be impacted by fog, can still function in some capacities, and gyrocompasses provide orientation data independent of atmospheric conditions. Therefore, hydroacoustic systems are less favorable as a reliable position reference in fog compared to these other navigational tools.