| Summary: | This paper derives an improved multistage in-motion attitude determination alignment (IMADA) for strapdown inertial navigation system, which integrates the traditional IMADA and the designed dual velocity-modeling IMADA, as well as the multiple repeated alignment process, to address the principled model errors and the calculation errors of traditional <inline-formula> <math display="inline"> <semantics> <mrow> <msup> <mi>V</mi> <mi>b</mi> </msup> </mrow> </semantics> </math> </inline-formula>-aided IMADA. With the proposed algorithm, not only the designed drawbacks of traditional <inline-formula> <math display="inline"> <semantics> <mrow> <msup> <mi>V</mi> <mi>b</mi> </msup> </mrow> </semantics> </math> </inline-formula>-based IMADA can be solved, but also the degradation phenomenon of high-level alignment for multistage IMADA would be largely less. Moreover, the degradation of the alignment accuracy with the vehicle velocity is also removed. Finally, the 30 groups of car-mounted experiments and the Monte Carlo simulation experiments with the navigation-grade SINS are carried out to demonstrate the validity of the proposed algorithm. The results show that the number of the heading degradation of the second-level alignment is reduced to 10 as compared the traditional number 20. Moreover, the alignment accuracy of heading is improved by 23%. Even with the different speeds of 20 m/s, 60 m/s, 80 m/s, the heading alignment accuracies are 1.3063°, 1.3102°, 1.3564° and are still almost the same.
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