What is the primary function of an Inertial Reference Unit (IRU)?

The primary function of an Inertial Reference Unit (IRU) is to navigate without external references. An IRU utilizes a series of accelerometers and gyroscopes to detect changes in speed and orientation, allowing for precise calculations of position, velocity, and attitude. This self-contained navigation capability is critical, especially in environments where GPS or other external navigation aids may not be reliable or available, such as underwater or in space.

The use of accelerometers helps measure linear movement, while gyroscopes provide information about rotational movement. Together, these sensors work to track a vehicle's movements from a known starting point, allowing for continuous navigation based solely on the unit's internal calculations. This is crucial for maintaining situational awareness and navigation fidelity in various situations.

In contrast, the other options pertain to functions that fall outside the primary purpose of an IRU. Providing visual navigation aids involves different types of navigation systems, calculating position based on gravitational forces is more related to geodesy or satellites, and monitoring weather conditions does not connect to the navigation functions of an IRU. Thus, the correct answer highlights the unique capability of an IRU to function autonomously for navigation purposes.