**3.1. Data processing of 11-DOF sensing module**

The 10-DOF sensing module including the 9-DOF IMU (three accelerometers, three gyroscopes, three magnetometers), barometer, and thermometer integrated with a microcontroller (Arduino Mega2560). The six-axis inertial sensor (MPU6050), which is a complete triple-axis gyroscope and triple-axis accelerometer inertial sensing system, is the most suitable sensor for stabilization and attitude measurement. MPU6050 contains the digital motion processor (DMP) which performs the motion processing algorithm itself. However, the horizontal attitude (yaw) is not a possible measurement. We used a magnetometer (HMC5883L) with fusion algorithm accordingly for eliminating the gyroscope offset to recognize the AUV activity context more reliably. The barometer (BMP180) is used in AIRS to detect the depth of the AUV and control the pressure of the airbag for supplying the perfect buoyancy. In addition, BMP180 also includes a temperature sensor, which does not only measure the underwater temperature but also thermal compensation for the MPU6050. Although the development of the MEMS technology has made a great progress, the IMUs are still difficult to collect precise data in the presence of various errors. Calibration is the process of comparing the measurement outputs with known reference data and determining the coefficients that drive the output to agree with the reference data over a range of output. We calibrated the sensor in terms of its thermal noise, bias, and scale factor.
