Method for estimating scattering coefficients of a laser gyro in operation and associated gyroscopic system

A method of determining an angular rotation (Δθ) of a laser gyro in operation, the method comprising:

• implementing a real time iterative method for determining scattering coefficients (m, ξ) of the cavity of a laser gyro in operation supporting two counter-propagating modes, comprising steps of:
• determining a set of variables dependent on characteristic physical quantities of the laser gyro,
• the characteristic physical quantities comprising a first and second light intensity corresponding to the first and second counter-propagating modes, respectively, and a phase difference (φ) between said modes,
• said variables being determined so that they are related to one another by at least a first and a second dependency relationships (R1 (u, {dot over (u)}, cos φ), R2 (v, {dot over (v)}, sin φ)) modelling the behaviour of the laser gyro and using a plurality of coefficients, said coefficients depending on parameters of the laser cavity including said scattering coefficients, the first dependency relationship relating variables, referred to as the first set of variables, to one another, and the second dependency relationship relating variables, referred to as the second set of variables, to one another, the first and second dependency relationships being such that one variable of a set is equal to a linear combination of the other variables of the same set;
• one reference variable ({dot over (u)}, {dot over (v)}) per dependency relationship being selected from the variables;
• measuring values of the characteristic physical quantities of the laser gyro in operation;
• determining measured values of the variables, deduced from the measured values of the characteristic physical quantities and from the first and second dependency relationships;
• estimating, via an iterative method, estimated values of the coefficients ({circumflex over (F)}) minimising a discrepancy between the measured values ({dot over (u)}, {dot over (v)}) of the reference variables and estimated values ({dot over (û)}, {dot over ({circumflex over (v)})}) of the reference variables, which are estimated from the values of the coefficients, the measured values of the variables (u, cos φ v, sin φ) other than the reference variables and from the first and second dependency relationships;
• determining estimated values of the scattering coefficients ({circumflex over (m)}, {circumflex over (ξ)}) from the estimated values ({circumflex over (F)}) of the coefficients;
• and
• determining the angular rotation (Δθ) of the laser gyro from the estimated values of the scattering coefficients ({circumflex over (m)}, {circumflex over (ξ)}).