Which instrument accurately measures the force of acceleration in one direction in an inertial navigation system?

The instrument that accurately measures the force of acceleration in one direction in an inertial navigation system is the accelerometer. Accelerometers are devices that can detect changes in velocity and orientation by measuring the forces acting upon them due to acceleration. In an inertial navigation system, which relies on dead-reckoning to track the position and velocity of an aircraft or vehicle, accelerometers help to calculate the current speed and direction of movement by measuring acceleration along one or more axes.

While gyroscopes are crucial for determining orientation and maintaining stability in navigation systems, they do not measure linear acceleration directly. Instead, gyroscopes track rotational movement. An altimeter measures altitude above a reference point, typically using atmospheric pressure, and a barometer measures air pressure. Neither of these instruments provides information related to linear acceleration. Thus, the accelerometer is specifically designed for the task of measuring acceleration directly, making it the correct choice for this question.