  To obtain a high-accuracy position with SINS(Strapdown Inertial Navigation
System), initial alignment needs to determine initial attitude rapidly and
accurately. High-accuracy grade IMU(Inertial Measurement Uint) can obtain the
initial attitude indenpendently, however, the low-accuracy grade gyroscope
doesn't adapt to determine the heading angle, hence the initial attitude matrix
will not be obtained. If using large misalignment angle model to estiamting
heading angle, the convergence time will become much longer. For solving these
two problems, a novel alignment algorithm combined backtracking algorithm and
reverse navigation updating method with GNSS(Global Navigation Satellite
System) aiding is proposed herein. The simulation and land vehicle test were
finished to evaluate the alignment accuracy of the proposed algorithm. The
horizontal misalignment is less than 2.3 arcmin and the heading misalignment is
less than 10.1 arcmin in test. The proposed algorithm is a feasible and
practical alignment method for low-cost IMU to obtain initial attitude in short
term and large misalignment condition aided by GNSS.
