The intensity and frequency variation due to retroscatter in a ring laser gyroscope are determined and used to correct the gyro scale factor. The orthogonal types of scatter due to dielectric variation and due to height variation, which lead to common mode phase delays of 0 and Ï€/2 respectively are taken into account in calculating the correction to the scale factor. The scale factor errors are determined in terms of observable quantities. Scale factor error control is accomplished by extracting a portion of both of the two counterpropagating light beams and measuring their respective intensities at 50, 52, creating intensity modulation indices representative of the sum and difference intensities, using closed loop control of the real-time difference between the intensities of the beam in the ring laser gyro to reduce scale factor variation using pushâ€”pull mirror control of at least two mirrors 18, 21. The residual error after pushâ€”pull mirror control minimization is output for use by a navigation system computer.
Ring laser gyroscope scale factor error control apparatus and method