SDI-161 north seeker is composed of high-precision fiber optic gyroscope, mechanical rotating device and signal solving circuit. The rotation axis of the gyroscope maintains the same orientation relative to the inertial space, and the earth rotates around the polar axis relative to the inertial space at its rotational angular velocity. If the earth is used as a reference, the rotation axis of the gyroscope will be seen to rotate relative to the earth, so the gyroscope can Track and measure the angular velocity of the Earth’s rotation. Calculate the earth’s rotation angular rate signal to calculate the angle between the main axis of the gyroscope and the true north of the earth, and provide azimuth information for the carrier.