Citation: Frutuoso, A.; Silva, F.O.; de
Barros, E.A. Influence of Integration
Schemes and Maneuvers on the
Initial Alignment and Calibration of
AUVs: Observability and Degree of
Observability Analyses. Sensors 2022,
22, 3287. https://doi.org/10.3390/
s22093287
Academic Editors: Luis Payá, Oscar
Reinoso García and Helder Jesus
Araújo
Received: 15 March 2022
Accepted: 1 April 2022
Published: 25 April 2022
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Article
Influence of Integration Schemes and Maneuvers on the Initial
Alignment and Calibration of AUVs: Observability and Degree
of Observability Analyses
Adriano Frutuoso
1,
*, Felipe O. Silva
2
and Ettore A. de Barros
1
1
Unmanned Vehicles Laboratory, Department of Mechatronics Engineering, University of Sao Paulo,
Avenida Professor Mello Moraes, 2231, Sao Paulo 05508-030, Brazil; eabarros@usp.br
2
Department of Automatics, Federal University of Lavras, Lavras 37200-900, Brazil; felipe.oliveira@ufla.br
* Correspondence: adriano.frutuoso@usp.br
Abstract:
The use of autonomous underwater vehicles (AUV) has increased in a wide range of
sectors, including the oil and gas industry, military, and marine research. The AUV capabilities to
operate without a direct human operator and untethered to a support vessel are features that have
aroused interest in the marine environment. The localization of AUV is significantly affected by the
initial alignment and the calibration of the navigation sensors. In this sense, this paper proposes a
thorough observability analysis applied to the latter problem. The observability analysis is carried
out considering three types of sensor fusion integration and a set of maneuvers, and the results are
validated through numerical simulations. As main contribution of this paper, it is shown how the
addition of position errors in the observation vector can decouple some gyro and accelerometer
biases from the latitude and altitude errors, particularly in the stationary observability analysis. The
influence of oscillations in the diving plane and typical AUV maneuvers are analyzed, showing their
relative impacts on the degree of observability of the inertial measurement unit (IMU)/Doppler
velocity log (DVL) misalignment and DVL scale factor error. Finally, the state’s estimation accuracy
is also analyzed, showing the limitation of the degree of observability as an assessment tool for the
estimability of the states.
Keywords: AUV; observability analysis; degree of observability
1. Introduction
Technological advances in recent years have promoted the development of autonomous
vehicles for a wide variety of sectors, including aerial, aquatic, and terrestrial applications.
Internet of Things and smart cities [
1
,
2
] inspection of oil and gas pipelines [
3
], swarm of
underwater robots [
4
], and autonomous cars [
5
] are some examples of recent applications
of autonomous vehicles.
Unlike terrestrial and aerial mobile robots, autonomous underwater vehicles (AUV)
should deal with particular boundaries related to the limited transmission of electromag-
netic signals underwater. Those limits consist of the absence of the localization measures
provided by satellite-based systems, and the absence of a high band and long range com-
munication with the human user who is at the surface. The first kind of limitation has an
impact at AUV self-localization, which is the subject of this work.
The initial alignment, which consists of determining the initial orientation of the
vehicle, and the calibration of the navigation sensors are key factors that significantly
influence the performance of AUV navigation.
The inertial measurement unit (IMU), Doppler velocity log (DVL), pressure sensor
(PS), and global positioning system (GPS) are navigation sensors widely used in AUVs [
6
].
Therefore, the proper estimation of the navigation sensor errors, e.g., inertial sensors biases,
Sensors 2022, 22, 3287. https://doi.org/10.3390/s22093287 https://www.mdpi.com/journal/sensors
