## 6 Conclusions  
An integrated navigation scheme of SINS/DVL/MCP/PS for AUVs is presented in this paper, and the error propagation models and data fusion schemes are studied. The analysis indicates that under submarine conditions, the position accuracy is mainly determined by the accuracy of the DVL because of the shortness of the external reference level position information. The negative effects caused by the random noise and sudden change in the measurements of the DVL velocity are investigated. The analysis shows the random noise in the DVL causes random oscillation in the level attitude and velocity and decreases their accuracy. In addition, the sudden change caused by seafloor gullies and fish populations generate sudden changes in the level position that cannot be corrected and significantly decrease the accuracy of the level position.  
To solve these problems, the characteristics of the AUV when sailing for a long time and a long distance are analyzed, and it is concluded that the AUV always sails at a constant and economic velocity or changes slowly. The acceleration along the axes of the body frame can be assumed to be as zero or nearly zero. Then, a velocity tracing algorithm based on a constant velocity motion model is designed to restrain the random noise in the velocity from the DVL, in which the velocity disturbance caused by the wave is considered as system noise. Then, the fault diagnosis based on \(\chi^{2}\) rules is  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Statistical Items** & **Pitch** & **Roll** & **Yaw** & **East Velocity** & **East Velocity** & **East Velocity** & **Height** \\ \hline \multirow{2}{*}{Scheme 1} & Mean & \(-0.2208\) & \(0.0935\) & \(-0.3450\) & \(0\) & \(0.0015\) & \(-0.0012\) & \(-0.4873\) \\  & Std & \(1.0416\) & \(1.0835\) & \(3.9327\) & \(0.0406\) & \(0.0418\) & \(0.0073\) & \(0.2589\) \\ \hline \multirow{2}{*}{Scheme 2} & Mean & \(-0.2232\) & \(0.1092\) & \(-0.3507\) & \(0\) & \(0.0020\) & \(-0.0015\) & \(-0.4907\) \\  & Std & \(0.6773\) & \(0.5885\) & \(4.0719\) & \(0.0056\) & \(0.0231\) & \(0.0061\) & \(0.2540\) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Statistic results of the navigation errors.  
introduced to judge the sudden change, and the time update velocity in the model is used to perform data fusion instead of the velocity from the DVL when the sudden change occurs.  
Simulation results based on the straight line trajectory indicate that with this velocity tracing algorithm, the random noise and sudden change in DVL can be effectively restrained, the standard variance in the level attitude and velocity can be decreased, and the level position accuracy can be ensured.  
This work has been supported in part by the National Natural Science Foundation of China (61273056, 61101163) and the Nature Science Foundation of Jiangsu Province of China (No. BK2012739, BK20130628).  
All authors discussed the contents of the manuscript. [PERSON] contributed to the research idea and the framework of this study. [PERSON], [PERSON], and [PERSON] performed the experimental work. [PERSON] wrote the manuscript. [PERSON] revised and polished the manuscript.  
The authors declare no conflicts of interest.